SUGARS Sugar is used extensively in cookery, in the preparation of processed fruit products, flavoured syrups, non-alcoholic beverages, confectionery etc. In addition to pure sugar, crude sugar(brown sugar and jaggery), corn syrup and honey are also used. Types of sugar Type Characteristics Uses Castor Fine white crystals Bakery Granulate d Crystals of medium size General sweetening agent Cube Crystals compressed to cubes Tea service Icing Fine white powder with or without starch Cake icings Golden syrup Processed to a yellow syrup Cooking and baking confectionery Molasses Dark – by – product of sugar Cooking and confectionery Diamond sugar Small rectangular crystals Used with beetle nuts, confectionery Rock sugar Big slabs Used on festive occasions Brown sugar Contain molasses, glucose and fructose pleasing and distinctive flavour Baked products Sugar powder Pulverized granulated sugar Dough nuts, hard puris Sugar and sugar related products Pure sugar Pure sugar is commonly manufactured from sugar cane or beet root. It contains 99.8% sucrose.
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SUGARS
Sugar is used extensively in cookery, in the preparation of processed fruit products, flavoured syrups, non-alcoholic beverages, confectionery etc. In addition to pure sugar, crude sugar(brown sugar and jaggery), corn syrup and honey are also used.
Types of sugar
Type Characteristics UsesCastor Fine white crystals Bakery Granulated Crystals of medium size General sweetening
agent Cube Crystals compressed to cubes Tea service Icing Fine white powder with or without
starch Cake icings
Golden syrup
Processed to a yellow syrup Cooking and baking confectionery
Molasses Dark – by – product of sugar Cooking and confectionery
Diamond sugar
Small rectangular crystals Used with beetle nuts, confectionery
Rock sugar
Big slabs Used on festive occasions
Brown sugar
Contain molasses, glucose and fructose pleasing and distinctive flavour
Baked products
Sugar powder
Pulverized granulated sugar Dough nuts, hard puris
Sugar and sugar related products
Pure sugar
Pure sugar is commonly manufactured from sugar cane or beet root. It contains 99.8% sucrose.
Brown sugar
Brown sugar is manufactured from sugar cane. It contains about 92% sucrose and 3.7% of invert sugar.
Jaggery
Jaggery is mainly obtained from sugar cane though it can also be prepared from palm, date palm and coconut. Jaggery obtained from sugar cane juice contains about 90.0% sucrose and 5.2% invert sugar. It is used in the preparation of peanut candy, puffed rice balls, chick pea candies etc. in India. Jaggery is preferred to sugar because it is rich in iron, gives colour has a typical flavour, gives body or thickness and it is less expensive.
Corn syrup
Corn syrup (liquid glucose) is prepared by the hydrolysis of corn starch. It is extensively used in the preparation of confectionery products.
Honey
Honey contains about 17% water and 82.5% carbohydrate with small amounts of minerals and vitamins and enzymes. The carbohydrate portion of honey includes invert sugar (glucose and fructose), maltose and sucrose.
Properties
1. Solubility
In the natural state of foods, sugars are in solution. Crystallization of sugar occurs from a sufficiently concentrated sugar solution, and use of this is made in the commercial production of sugar from sugarcane and beets. The most soluble sugar is fructose, followed by sucrose and lactose. The sugar that is the most difficult to crystallise than that the least soluble sugar, lactose.
2. Absorption of moisture
Sugars are hygroscopic. Fructose is more hygroscopic than the other sugars. Cakes made with honey, molasses remain moist for a long time.
3. Fermentation
Most sugars, except lactose may be fermented by yeasts to produce CO2 gas and alcohol. This is an important reaction in making bread and other baked products. The CO2 leavens the product and the alcohol volatilizes during baking.
4. Acid hydrolysis
Sucrose is easily hydrolysed by acid but maltose and lactose are slowly acted on. The end products of sucrose hydrolysis are a mixture of glucose and fructose. This mixture is commonly called invert sugar. The monosaccharides are not appreciably affected by acids. Heat accelerates the action of acid.
5. Enzyme hydrolysis
The enzyme sucrose also called invertase is used in the candy industry to hydrolyze some of the sucrose in cream fondant to fructose and glucose. This is done to produce soft, semi fluid centres in chocolates. The enzyme is commonly added to the fondant layer around the fruit in chocolate coated cherries.
6. Melting point and decomposition by heat
Caramelization: With the application of sufficient dry heat, sugar melts or changes to a liquid state. Heating beyond the melting point brings about a number of decomposition changes. As sucrose melts around 160C, a clear liquid forms that gradually changes to a brown colour with continued heating. At about 170C, caramelization occur with the development of a characteristic caramel flavour along with the brown colour.
Caramelisation is a complex reaction, involving the removal of water and eventual polymerization. Caramel has a pungent taste, is often bitter, is much less sweet than the original sugar from which it is produced, and is non crystalline. It is soluble in water. Fructose caramelizes at 110C and maltose caramelizes at about 180C, galactose at 170C.
Granulated sugar, when heated in a heavy pan, caramelizes. When hot liquid is added, the caramelized sugar dissolves and can be used to flavour puddings, custards, ice creams, cakes and sauces. Caramel is also produced in making peanut brittle and caramel candy.
7. Decomposition by alkalies
The monosaccharides are markedly decomposed by alkalies and flavour may become strong and bitter. Sucrose is least affected by alkalies.
8. Sweetness
Of the sugars, lactose is the least sweet, followed by maltose, galactose, glucose and sucrose with fructose being the most sweet. A maximum sweetness from fructose is most likely to be achieved when it is used with likely to be achieved when it is used with slightly acid, cold foods and in beverages.
Crystallization
A crystal is composed of closely packed molecules arranged in a pattern. Crystallization occurs only if the solution is super saturated. The size of the crystals produced will depend on the rate of the formation of nuclei about which the crystals grow and the rate of growth of crystals around the nuclei. If only one or two nuclei are formed, the size of the crystals produced will be large but if the rate of formation of nuclei is very rapid, many small crystals will form. Both the rate of crystallization and the rate of nuclei formation are modified by many factors.
Factors affecting the crystallization of sugar
In the preparation of fondant, fudge, etc., from super-saturated sugar solutions, crystallization of sugar occurs. The factors affecting the rate of crystallization of sugar and the size of crystals are as follows: (1) Formation of nuclei, (2) Seeding, (3) Concentration of the solution, (4) Temperature, (5) Agitation and (6) Presence of other sugars.
Formation of nuclei: Nuclei can only form from a super-saturated solution. Nuclei form spontaneously in various places in the solution and crystallization begins from these nuclei. The rate of nuclei formation may be favoured by specks of dust present in the solution. When only a few nuclei develop in the solution, the crystals grow to a large size.
Seeding: When crystals of the same material are added to the solution to start crystallization, the process is called seeding. These crystals serve as nuclei for crystal formation.
Concentration of the solution: A more super-saturated solution favours the formation of nuclei and crystals. A fondant syrup boiling at 114oC contains more sugar and less water than one boiling at 111oC. Nuclei will form more readily from the more concentration syrup, i.e., the syrup, boiling at 114oC.
Temperature: If crystallization is allowed to occur at high temperature, then coarser crystals are formed. The most favourable temperature for crystal growth in a sugar syrup boiling at 112oC is between 70oC and 90oC. Further, lowering the temperature at 30oC, increases the viscosity of the syrup and retards crystallization. Larger size crystals are formed at higher temperature, while super-saturation and low temperature are conductive for formation of small crystals.
Agitation: Agitation or stirring of the super-saturated sugar solution accelerates the formation of nuclei and helps in the formation of small crystals. Continuous agitation is necessary, till crystallization is complete if a fine textured product is desired.
Presence of other sugars: When glucose or fructose is added to sucrose syrup, crystallization of sucrose is slow. The mixture has a higher solubility and glucose and fructose crystallize less readily than sucrose. A mixture of sucrose, glucose and fructose is formed when sucrose is cooked with acid or acid salts such as citric acid or acid potassium tartrate. Syrups containing 30-45 per cent invert sugar will not crystallize, those containing 16-23 per cent form semi-fluid mass of crystals and those with 6-15 per cent give a plastic mouldable product. Fondants containing 7 per cent invert sugar have a fine texture.
STAGES OF SUGAR COOKERY
Product Temperature (oC)
Stage Description Test
Syrup 110-112 Thread When syrup is dropped from a spoon syrup spins a 5 cm thread
Barfi, fondant fudge
112-115 Soft ball Forms a soft ball when syrup is dropped into cold water; Flattens on removal from H2O
Caramels 118-120 Firm ball
Forms a firm ball when syrup is dropped into cold water; does not flatten on removal from water
Divinity, LaduMarshmellow
120-130 Hard Ball
Forms a ball hard enough to hold its shape when syrup is dropped into cold water.
Butterscotch Toffees
132-143 Soft crack
Forms threads which are hard but not brittle when syrup is
dropped into cold waterBrittle, glaze
150-154 Hard crack
Forms thread which are brittle when syrup is dropped
Barley sugar
160 Clear liquid
Sugar melts`
Caramel 170 Brown liquid
Sugar melts and browns
SUGAR-BOILED CONFECTIONERY
From boiled sugar solution, two types of confectionery are prepared – crystalline and noncrystalline. The temperature of boiling sugar solution, the ingredients used and the method of handling the supercooled sugar solution determine the nature of the end product.
Crystalline candies (Nonamorphous candies)
Crystalline candies are chewed easily and they may be cut with a knife. Sugar is present in the form of very small crystals. Fondant and fudge are two types of crystalline candies. Crystallization is ensured by adjusting (1) the consistency of sugar syrup to enable the sugar to crystallize (2) to induce crystallization by seeding or agitation and (3) addition of small amounts of other materials which will prevent formation of large crystals.
In the case of fondant, small amounts of corn syrup (or) cream of tartar are used, while in the case of fudge, a mixture of corn syrup and cream (or) corn syrup, milk and butter are used. Such substances prevent the crystal formation.
Fondant : Fondant is prepared from sucrose syrup boiling at 113-115oC . A good fondant should be snowy white in colour, the crystals soft enough to be plastic and velvetty, but not gritty when tasted.
Fondant can be prepared with the addition of cream of tartar or corn syrup to sugar. The ingredients are sugar – 400 gm, cream of tartar 0.5 gm (or) corn syrup (30 gm), tap water – 200 gm.
The first step in the preparation of fondant is to dissolve the amount of sugar used completely by adding sufficient water. The candy mixture in solution is next concentrated by boiling until it reaches the appropriate doneness. Slow heating resulted in excess acid hydrolysis and many produce too soft a product. The doneness of the candy mixture is determined by measuring the temperature of the
boiling solution. For fondant, it should be 113-115oC. Another method of measuring doneness in the making of candies is by dropping a small portion of boiling syrup into very cold water, allowing the syrup to cool and evaluating its consistency. In the case of fondant it is the softball shape.
In the preparation of fondant, at the appropriate stage, the boiled solution is poured on a smooth flat surface and allowed to cool to 40oC. Then it is beaten continuously until it becomes a creamy mass. At first, the mixture becomes cloudy from the air beaten into it and then sets into a stiff mass. A 24 hours ripening period in a tightly covered container softens the crystalline candy slightly and promotes smoothness.
Fondants are used in confectionery for numerous purposes. They are used to make mints. In this case, the supersaturated sugar mixture in the boiling kettle is cooled to about 71oC and flavoured with mint. The mint quickly solidifies on further cooling. Softened fondant is used in coating fruit and nut mixtures that are moulded and sliced. Fondants are largely used as cream centers of chocolate confectionery.
Fudge : Fudge is generally prepared from brown sugar. As brown sugar contains a higher percentage of invert sugar than white sugar, sucrose crystallizes less readily. Fudge ripens during storage and becomes soft and velvetty after 24 hr storage.
The ingredients required for the preparation of fudge is sugar – 200 gm, milk – 120 gm, butter – 14 gm and chocolate – 21 gm. The procedure is as follows : 1) add the chocolate and butter to cooking pan and heat it on a steam bath till the chocolate and butter have melted add sugar. Mix the chocolate and butter well with sugar (2) Then add milk and heat till the sugar dissolves completely (3) Cook the syrup to a soft ball stage (112oC) (4) Allow it to cool to about 70oC and transfer to a greased moulding pan (5) Cut the candy when it is cool and wrap in butter or foil and store in an air-tight container.
Non-crystalline candies (Amorphons candies)
Amorphous candies in contrast, have a heterogenous structure and crack into pieces rather than be cut with a knife (eg. toffee and brittles). Caramels, the softest of the amorphous candies, however, may be cut.
In amorphous candies, sugar is not present in the form of crystals and crystallization of sugar should be prevented by (1) cooking the syrup to a high temperature so that the finished product hardens
quickly before crystals can be formed and (2) adding large amounts of materials like corn syrup, cream, butter etc. which prevent crystallization and make the product plastic and chewy. Amorphous candies are caramels, toffees, brittles and butterscotch. These confections owe their character mainly to the presence of milk, butter and certain vegetable fats.
Milk solids, when heated in the presence of water and sugars, develop a characteristic flavour due to the reaction between the milk proteins and the reducing sugars. This is known as malliard reaction. Caramelization of a different type also occurs in sugar, glucose and invert sugar when syrups are boiled to temperature of 149 to 157oC. A stronger type of caramelization with yet another flavour is obtained by alkaline treatment, for example, by the reaction of NaHCO3 with boiling syrup at about149oC.
The action of ammonia on certain reducing sugars also gives ‘caramel colour’. Butter when added to high boiled syrup is subject to some decomposition and gives a characteristic and attractive flavour. Brown sugars, golden syrup and molasses have a flavour that goes well with caramelized milk and these sugars are used a great deal in caramel recipes.
The flavour produced by heating milk solids with sugars is related to the method and time of cooking. Sweetened condensed milk is mostly used for the preparation of caramel. Vegetable fats with suitable emulsifiers (glycerol mono sterate) can be used in place of milk fat (butter) for preparing caramels.
Caramels: Caramels are hard type (or) hard boiled candy, which are not crystalline. To prevent crystallization of sucrose, larger amounts of invert sugar (or) corn syrup are added to sucrose. The temperature at which the syrup should be cooked for obtaining a product of proper texture will depend on the quantity of corn syrup, molasses (or) invert sugar present in the syrup. Addition of milk improves the colour and flavour of caramels. The temperature for caramel preparation is 118-120C.
The ingredients required for the preparation of caramels are water 750 gm, sugar, white granulated – 1125 gm, sugar brown – 1125 gm, glucose syrup – 1925 gm, sweetened condensed milk 2050 gm, hardened vegetable fat 900 gm, glycerol monosterate – 57 gm and salt – 36 gm.
All the ingredients are placed in the pan and the mixer set in motion. The gas fire is lighted and heating continued on a low flame
until the sugar is dissolved and the ingredients are completely mixed. Any sugar or other solids that may have accumulated on the sides of the pan above the liquid level are removed. Heating and mixing proceed with the heat increased and the mixture boiling steadily. The level of heating will be obtained by experience, fierce heat will produce scorching on the pan surface and cause dark particles to appear in the mixture. The degree of boil is determined by hand thermometer, which should be kept in hot water before use. The heat is lowered, the mixture stopped, and the thermometer moved quickly through the caramel until the temperature is constant. Boiling is continued and the testing repeated until the thermometer registers 118oC. The fire is turned off, mixing continued for a few minutes, and then the caramel is discharged on a cooling table.
Toffee : Toffees are harder than caramels and therefore are made from syrups cooked at higher temperature. Invert sugar or corn sirup or molasses are added to prevent crystallization of sucrose. Taffies appear white, due to air bubbles present in them. The temperature required is 132-143C. The manufacture of toffee can be divided into four stages (1) preparation of the raw materials (2) cooking to the desired consistency (3) cooling and cutting into shapes (4) packing. For preparation of the raw materials all the ingredients are mixed in a mixing machine. The chief function of this stage is to bring about emulsification of the fat. Formulation for a quality toffee is sugar – 12 lbs, liquid glucose -8 lbs, salt-1 tsp, water-1½ qt, hardened coconut – 4 oz, butter -1lb malted milk extract – 1 tablespoonful.
The mixer used for this purpose generally consists of a horizontal cylindrical vessel, inside which rotates a number of arms fixed along the length of a horizontal axis. Babbles re fixed to break the flow. For loading there is a lid on the top, and for unloading a large diameter hole in the bottom fitted with a closing plate. In some case, raw materials are prepared in the boiling pan prior to cooking.
In the boiling pan the mixture is cooked rapidly. The temperature of cooking is adjusted between (260-280oF). The stem pressure required for toffee boiling is upwards of 90 lb.
The toffee from the pans is cooled by pitching on to rectangular cast-iron tables through which cold water can be circulated. Its treatment on the tables varies according to the method of cutting to be adopted. In many cases the toffee is passed through rollers or by “leveling” the still liquid toffee on the tables. If it is to be made into slab toffee, steel frames are forced into the cooling mass and removed when the toffee has set.
The toffee can be brought to the correct thickness by the use of rollers. The machine used is called a ‘break’. The toffee is poured onto the tubes, not leveled, but allowed to cool until plastic, then passed through the ‘break’ and treated exactly as leveled toffee.
In the case of roll pieces, they are put into automatic cut and wrap machines which produce 400 pieces of toffee a minute, wrapped in over strip-aluminum foil laminated with waxed paper, cellulose film or waxed paper.
Brittles: Brittles are much harder than caramels or toffees. Since the syrup is cooked to a higher temperature than that require for caramels or toffees, slight caramelization of the sugar takes place to impart a characteristic flavour. Sodium bicarbonate is added in small amounts to syrup to liberate Co2 which gives a porous structure and glassy appearance to the product (150-154oC). Peanut and cashew nut brittle are commercially prepared and sold in the market. The ingredients required for the preparation of peanut brittle is sugar – 375 gm, corn sirup (light) – 125 ml, water – 125 ml, Butter – 45 ml, soda – 2 gm, roasted peanut – 375 gm and vanilla essence – 2 gm.
First combine the water, corn sirup and sugar in a pan. Heat the sugar mixture rapidly to 138oC. Stir as little as possible to keep mixture from scorching, when the syrup reaches 138oC, add the peanuts and the butter. Stir the mixture continuously and heat to 152oC. Remove pan from heat immediately. Add the soda and the vanilla; stir these ingredients as quickly as possible. Pour the mass on the greased plate, cool it and cut it into desired sizes.
Butter scotch
Butter scotch has a chewy consistency. It is prepared by boiling a mixture of sugar and corn syrup in the ratio of 4:1 with water till the syrup attains a temperature of 146C. Butter and flavour are then added to the mixture. The ingredients required for the preparation of butter scotch are as follows:. sugar- 500 g, corn sirup – 125gm, water-150 ml, butter -20 gm, salt- 1.0 gm, oil of lemon -1.0 gm. The method is: Dissolve sugar in water and bring to 146C.Add the butter in small pieces. Add oil of lemon and salt ,while the material is still plastic. Cut it into pieces using a frame cutter. Wrap in waxed foil or paper.
PULSES
Pulses are the edible fruits or seeds of pod bearing plants belonging to the family of Leguminous. The major pulses which find an important place in our dietaries are red gram dhal, bengal gram dhal black gram dhal, green gram dhal and masoor dhal. Some are used as whole grams. Cowpea, rajmah and dry peas also comes under leguminous family.
Composition and nutritive value Principal nutritional characteristics of food legumes1. Positive factors High protein content High lysine content Excellent supplementary protein to cereal grains2. Limiting factors Sulphur amino acid deficiency Low protein digestibility Antiphysiological substances
Trypsin inhibitors Haemagglutinins Polyphenolic compounds Flatulence factors Energy: Pulses give 340 calories per 100 gm which is almost similar to cereal calorie value.Protein: In a vegetarian diet, pulses are important sources of protein. They give double the amount of protein compared to cereals. They contain chiefly globulins. Albumins can also be seen in pulses. The protein of pulses are of low quality since they are deficient in methionine and red gram is deficient in tryptophan also. Bengal gram contains higher amounts of arginine and sufficient amount of tyrosine. However pulses are rich in lysine. Hence they can supplement cereal protein. A mixture of cereals and pulses is superior to that of the either one. Legumes are better than cereals as a source of the essential amino acids like isoleucine, leucine, phenylalanine, threonine and valine. Carbohydrates : Pulses contain 55 to 60 per cent starch. Soluble sugars, fibre and unavailable carbohydrates are also present. The unavailable sugars in pulses include substantial levels of oligosaccharides of the raffinose family (Raffinose, verbascose and stachiose) which produce flatulence in man. These sugars escape digestion due to lack of -galactosidase activity and digested by the microflora of the lower intestinal tract resulting in the production of large amount of CO2, hydrogen and small amount of methane. Fermentation, germination, cooking, soaking and autoclaving reduce considerable amount of oligosaccharides. Lipids: Pulses contain 1.5 per cent lipids on moisture free basis. They contain high amounts of polyunsaturated fatty acids. Along with cereals they meet the requirements of essential fatty acids for an adult. Apart from linoleic acid most legume seed oils contain high proportion of linolenic acid. They undergo oxidative rancidity during storage resulting in loss of protein solubility, off flavour development and loss of nutritive quality, oleic, stearic and palmitic acids are also present. Minerals : They contain calcium, magnesium, zinc iron, potassium and phosphorus. 80 per cent phosphorus is present as phytate phosphorus. Phytin complexes with proteins and minerals and renders them biologically unavailable to human beings and animals. Processing such as cooking, soaking, germination and fermentation can reduce or eliminate appreciable amounts of phytin.
Vitamins: Legume seeds are excellent source of B complex vitamins particularly thiamine, folic acid and pantothenic acid. Like cereals, they do not contain any vitamin A or C but germinated legumes contain some vitamin C. Pulse cookery Mostly pulses are cooked and consumed and they take longer time to cook than cereals. The cooking process softens that hard seed by improving the plasticity of the cell wall, thus facilitating cell expansion and reduction of intercellular adhesion. Cell cementing material – pectin is altered during cooking so that the cells of the beans separate with comparative ease. Effect of cooking1. Antinutritional factors: Uncooked legume seeds contain
antinutritional factors that can be toxic if large amounts are consumed. Trypsin inhibitors and haemagglutinins disappear at about 90 minutes however, polyphenolic compounds although decreasing with time are still found in the cooked material. Relatively high amounts are found in the cooking liquid.
2. Protein quality: Heating increases protein quality by destroying antinutritional factors, increase digestibility and availability of amino acids. Excess heat reduces the quality of the bean protein.
3. Vitamins: Loss of thiamine may occur due to the heat applied.
4. Colour: Sodium metabisulphite is found to be effective in maintaining colour of lentils, other seeds acquired in darker colour processing.
Factors affecting cooking quality The hardness is of two types, hard shell and sclerema. Hard shell is described as a physical condition in which the seed fails to absorb water. Sclerema takes place in the cotyledons and is induced by various factors:1. Inherent character: Some varieties are hard-to-cook
inherently. 2. Storage condition: Cooking quality is influenced by time,
temperature and relative humidity during storage. Cooking time for the some hardness increases with storage time. Moisture content during storage is above 10 per cent may cause deterioration in the cooking quality.
3. Seed maturity : Cooking time decreases with the increase in seed maturity. The very hard mature seeds take long time to cook.
4. Dehulling: This reduces the cooking time and increases digestibility.
5. Pre cooking: The cooking time for pre cooked lentil seeds is less compared to untreated ones. Precooking is done by cooking, treating with enzymes and dehydrating in controlled conditions.
6. Phytin content : High available phosphorus in the soil contribute to high phytin content in the seed and consequently to good cooking. Phytin has a softening action on peas during cooking by acting as a calcium absorbent, consequently preventing the formation of insoluble calcium pectate.
It is suggested that the softening of peas during cooking takes place through a reaction between sodium/potassium phytate and insoluble calcium/magnesium pectate that converts the latter into the soluble sodium / potassium pectate. Thus cooking quality is related to levels of monvalent elements and to some extent to the ratio of monovalent to divalent elements. No direct relationship is found between phytic acid content in the seed and the cooking quality. 7. Calcium and magnesium: Large amounts of insoluble
calcium and magnesium pectates are formed in the middle lamella of the cell walls when the seed is high in calcium and magnesium or when the cooking water is high in these elements. When legumes are cooked in hard water, they take long time to get cooked. Hard water contains chlorides and sulphates of calcium and magnesium salts. They appear to react with pectic substances and phytates and harden the cellulose and delay the cooking of pulses.
8. Cellulose: The thickness of the palisade layer and the contents of lignin and alpha cellulose in the seed coats are probably important factors in the cooking quality of pulses. Sodium bi carbonate softens the cellulose and hastens cooking.
It has been proposed that polymerization of polyphenolic compounds in the seed coat where these substances are found and changes in the micro chemical structure of the cotyledons involving carbohydrates-pectic substances. Phytic acid and potassium, calcium and magnesium ions, affect cooking quality.Effect of soaking in water: Dry legumes have to absorb water before they can be cooked. If legumes are soaked in cold water overnight or in warm water (60-700C) for 4 to 5 hours prior to
cooking, they absorb enough water and can be cooked easily in about 30 to 40 minutes. Germination (or) sprouting Whole grains are soaked overnight and water should be drained away and the seeds should be tied in a loosely woven cotton cloth and hung. Water should be sprinkled twice or thrice a day. In a day or two germination takes place. Moisture and warmth are essential for germination. Green gram can be germinated in a shorter time. In summer germination process is faster than in winter. Bengal gram, dry beans and dry peas can also be germinated. Advantages:1. (a). During sprouting dormant enzymes get activated and digestibility and availability of nutrients is improved. Starches and proteins are converted to simpler substances. As germination proceeds, the ratio of essential to non essential amino acids changes providing more of essential amino acids. Sprouting reduces trypsin inhibiting factors due to the release of enzymes. Germinated seeds have more of maltose. The action of cytases and pectinases are released during sprouting and the cell walls are broken down and the availability of nutrients increases.
b) During sprouting minerals like calcium, zinc and iron are released from bound form. Phytic acid amount is reduced so the availability of proteins and minerals are increased.
c) Riboflavin, niacin, folic acid, choline and biotin content are increased.
d) Vitamin C is synthesized during germination hence germinated pulses can be substituted for fruits. The increase in Vitamin C is around 7-20 mg per 100 gm of pulses. Vitamin C content is maximal after about 30 hours of germination.2. Sprouting decreases cooking time. The thick outer coat bursts
open the grain and the grain becomes soft making it easier for the cooking water to penetrate the grain.
3. Dehusking is easier when the grains are sprouted and dried.4. Germination decreases the mucus inducing property of
legumes. 5. Thickening power of starch is reduced due to conversion of
starch to sugars.6. Germination metabolises oligosaccharides and hence do not
produce gas or flatulence.
7. Germination improves taste and texture and without much cooking also sprouts like green gram can be consumed.
8. Germinated pulses add variety to diet. Antinutritional factors in legumes Some pulses used in food contain chemical constituents having toxic properties. 1. Trypsin inhibitor Trypsin inhibitors are proteins that inhibit the activity of trypsin in the gut and interfere with digestibility of dietary proteins and reduce their utilization. They are generally heat labile. Autoclaving at 1200C for 15-30 minutes inactivates almost all trypsin inhibitors. Trypsin inhibitors are easily inactivated from dhals but more drastic heat treatment is necessary to inactivate trypsin inhibitors of soyabean and kidney bean. 2. Lathyrism Lathyrism is a nervous disease that cripples man. This is entirely preventable. The disease is now known to result from an excessive consumption of the pulse Lathyrus sativus (Khesari dhal). It affects young men between the ages of 15 and 45 years. Lathyrus sativus is grown in dry districts of MadhyaPradesh, Uttarpradesh, Bihar, Bengal, Maharashtra, Mysore and Andhrapradesh. Throughout the country, it is known by the common name “ Khesari dhal”. The dehusked seeds resemble Bengal gram dhal or red gram dhal. Hence sometimes khesari dhal is used as adulterant in other dhals. When it is eaten in small quantities lathyrus seeds are valuable as food since it contains 28 per cent protein. But if they are the main source of energy providing more than 50 per cent a severe disease of spinal cord may result. The neurotoxin responsible for lathyrism is -N-Oxalyl-L-, diamino propionic acid. Toxin can be removed by steeping or parboiling. Steeping process1. Four times the quantity of seeds is first brought to boil.2. Seeds are soaked in hot water for two hours.3. Water should be drained off.4. The seeds are washed with cold fresh water and sun dried.5. 80 to 90% of the toxin is removed by this method. Parboiling process
1. The seeds are soaked in cold water for 12 hours. 2. Then the seeds are steamed for 20 to 30 minutes. 3. Again seeds are soaked for one hour and dried. 4. 80 to 90% of toxin leach out by this process.3. Favism Favism is a disease characterized by haemolytic anaemia that occurs when individual who are deficient in glucose-6-phophate dehydrogenase consume faba beans or broad beans. In susceptible individuals the level of glutathione in the erythrocytes is also reduced. Three different compounds present in faba beans have been implicated as playing a causative role in the disease. Two of these are glycosides known as Vicine and Covicine and the third is an amino acid derivative known as dihydroxy phenyl alanine- DOPA. These are present only in the cotyledons of the beans, the hulls being essentially free. Germinating and boiling reduce these toxic substances. 4. Haemagglutinins: These are proteins in nature and sometimes referred to as phytoagglutins or lectins. They occur widely in leguminous seeds. Haemagglutinins reduce the food intake and resulting in poor growth. Haemagglutinins are heat labile. Haemagglutinins combine with the cells lining the intestinal wall, in almost the same way as it combines with red blood cells thus causing an impairment with the absorption of amino acids. 5. Cyanogenic glycoside: Cyanogenic glycosides yield hydro-cyanic acid upon hydrolysis by an enzyme present in the foodstuff. This causes cyanide poisoning by interferring with tissue respiration. On hydrolysis of the glycoside of the enzyme -glycosidase hydrogen cyanide is liberated. Cyanide content in the range of 10-20 mg/100g of pulse is considered safe. Many legumes except lima bean contain cyanide within this limit. 6. Saponins: Saponins produce lather or foam when shaken with water. These are glycosides of high molecular weight. They are present in soyabeans. Saponins cause nausea and vomiting. These toxins can be eliminated by soaking prior to cooking. 7. Goitrogens : These substances interfere with iodine uptake by thyroid gland. Thiocyanate, isothiocyanates and their derivatives are present in soyabean, groundnuts and lentils. Excessive intake of these foods in the face of marginal intake of iodine from foods and water may lead to precipitation of goitre.
8. Tannins: Tannins are condensed polyphenolic compounds. They are present in high amounts in seed coat of most legumes. Tannins bind with iron irreversibly and therefore interfere with iron absorption. Removal of seed coat of legumes reduce the tannin content. Tannins also bind proteins and reduce their availability. White coat beans have negligible quantity of tannins whereas black and red varieties have higher content of tannins.
NUTS AND OIL SEEDS
Nuts and oilseeds are seeds or fruits consisting of an edible fat containing kernel and surrounded by a hard or a brittle shell. The nuts and oilseeds are almond, cashewnut, coconut, groundnut, gingelly seeds, mustard seeds, soyabean, walnut pistachio nut, safflower seeds and sunflower seeds.
Nutritive value
Like pulses, oil seeds and nuts are rich in protein and in addition they contain a high level of fat. Hence they are not only good sources of protein but are concentrated source of energy. They do not contain
an appreciable amount of carbohydrate but contain high level of B-vitamins. Groundnuts are particularly rich in thiamine and nicotinic acid. Since they are concentrated in fat and protein and also expensive, usually they are not used as main ingredient in cooking and hence may not contribute substantially to the nutrient intake.
Role of nuts and oilseeds in cookerya. Nuts are used fresh, raw, roasted or boiled or salted forms and
also fried forms. b. Nuts are used as thickening agents. Coconut, poppy seeds and
cashewnuts are used as thickening agents in the preparation of gravy.
c. Chutneys can be made and used from nuts e.g. groundnut and coconut.
d. Sweets are made from nuts, e.g. chikki, burfi, kozhukattai, chashewnut cake.
e. Oil is used as cooking media for frying and seasoning. Oil is also used as preservative in pickles.
f. Powders made out of nuts like ground nut and coconut are used as chutneys and salad dressing.
g. Nuts are also used in ice creams, cakes, pastries, payasams and confectionery (chocolate).
h. Nuts are also used in beverages. E.g. badam kheer.i. Peanut butter is used as a topping on the bread or as a side dish
along with chapathis. j. Oil seed cakes are used as weaning food or as thickening agents
in vegetables like capsicum. k. Nuts are used as garnishing material – raw, roasted, salted (or)
boiled forms.
Fats and oils Physical properties 1. Melting point: All food fats are mixtures of triglycerides and therefore do not have sharp melting point, but melt over a range of temperatures.
2. Creaming of fats: Solid fats like butter and margarine can be creamed or made soft and fluffy by the incorporation of air. Fat and sugar are usually creamed together in the preparation of cakes.
3. Plasticity of fats: Fats are mouldable and can be creamed to exhibit plasticity. Such fats do not have the ability to flow at room temperature and are thus solid fats. The spreading quality of butter is the result of its plastic nature. Plastic fats are composed of a mixture of triglycerides and not of one kind of a molecule. They
therefore do not have a sharp melting point and are plastic over a fairly wide range of temperature.
4. Emulsification: The specific gravity of oils and fats is about 0.9, which indicates that they are lighter than water. Though insoluble in water, they can form an emulsion with water when beaten up with it to form tiny globules in the presence of suitable emulsifying agent. Butter is an emulsion, so also is cream. The presence of minute amounts of milk protein helps to stabilize these emulsions. Lecithin, a phospholipid from egg yolk helps to stabilize mayonnaise, a salad dressing made from vegetable oil. Emulsification of fats is a necessary step in a number of products such as cakes, ice cream and other frozen desserts.
5. Smoke point: When fats and oils are heated to a high temperature, decomposition occurs and finally a point is reached at which visible fumes are given off. This is called the smoke point. Fats and oils with low molecular weight fatty acids (those with a short chain length) have low smoke point. If oils with low smoke points are used for deep fat frying purposes, then the food stuff is fried at a lower temperature and thus will take a longer time to acquire the stage of doneness. The factors affect the smoking point of fats and oils are (1) the quantity of free fatty acids present (2) they surface area of oil exposed while heating and (3) the presence of suspended matter (i.e.) repeated use of same sample of oil for frying results in a decrease in its smoke point ultimately in its decomposition. The smoke point of a fat is partly a matter of its natural composition and partly a matter of the processing it has received. Soyabean, cotton seed, peanut and corn have smoke points at about 230oC. Hydrogenated fats smoke at 221oC to 232oC. Shortening containing monoglyceride as a emulsifier smoke at a lower temperature about 176oC. First, smoke is given off by the emulsifier and later the smoke point may raise from 190o to 193oC.
6. Hydrogenation: By this process, liquid fats can be converted into semi solid and solid fats (e.g. Dalda) and to increase the stability of the oils to prevent spoilage from oxidation, which results in undesirable rancid flavour and odours. Plant oils contain a large percentage of unsaturated fatty acids. These unsaturated glycerides in the oil can be converted to more saturated glycerides by addition of hydrogen. This process is known as hydrogenation. Hydrogenated fat is manufactured from vegetable oils by the addition of molecular hydrogen to the double bonds in the unsaturated fatty acids in the presence of nickel, platinum or palladium catalysts under pressure at 300-370oF for a period of 1-3 hours. During hydrogenation, the double bonds present in unsaturated fatty acids taken up hydrogen
and saturated fatty acids result. This hydrogenated fat used as shortening in the preparation of bakery products. They hydrogenated fat has very good keeping quality. They are colourless and odourless.
Chemical properties of fats: The chemical properties of fats such as iodine value, acid number, and saponification number are useful in that they have been widely used in the identification of different kinds of fats and oils, and in the detection of adulteration of refined oils with other oils that are cheaper and of poorer quality.
Uses/Functions of fats and oils in cookery
In addition to their nutritional function, oils and fats have other uses which derive principally from their distinct physical properties. They contribute to the tenderness, flavour, colour and texture of food products. They also serve as chief ingredients in preparing foods that form emulsions and as cooking media.
1. Tenderness : One of the most important function of oils and fats is to tenderize baked products. Large quantities of them find use in the preparation of baked products, such as breads, cakes, biscuits cookies etc. Their function is particularly important in pastry and bread which have little or no sugar to contribute to tenderness. Butter, margarine a blend of vegetable and animal fats, and hydrogenated fats or oils are used as shortening agents.
Fats also contribute to the incorporation and retention of air in the form of small bubbles in the batter. Carbondioxide and steam diffuse into these air cells during baking. Thus, fats contribute to the grain and volume of the baked products.
2. Flavour: Some fats influence the flavour of the food. Fats that are used for seasonings, table use and salad dressings, possess distinctly pleasing flavours. Ghee and buter when used in the recipe improve the flavour. The ability of fats to take up or dissolve certain aromatic flavour substance is frequently used in food preparation. Onion, ginger, garlic, peppers and other flavourful foods are cooked in oil so initially flavour fruit and other flavours are also by fat. Butter, margarine, pecan fat and olive oil are commonly used for salad dressings. Cotton seed oil, corn oil, groundnut oil and soyabean oil lack flavour and are used for salad dressing when a bland flavour is required.
3. Texture : Fats have texture effects in foods. They affect the smoothness of crystalline candies and frozen desserts through the retardation of crystallization and the gelatinization of starch
in starch –thickened mixtures. They contribute to the juiciness of meats and the foam structure of whipped cream.
4. Emulsion: Fats constitute one of the essential constituents in food emulsions. Prominent among the natural food emulsions are milk, cream and egg yolk. In most food emulsions, oil is the dispersed or discontinuous phase and water is the dispersion medium or continuous phase. For the stabilization of the emulsion, an emulsifying agent is required. Various substances commonly used as emulsifiers are egg yolk, whole eggs, gelatin, starch paste. Vegetable gum, casein and fine powders such as those of paprika and mustard. Salad dressings such as mayonnaise, French dressings and cooked salad dressings are permanent or semipermanent emulsions of oil-in-water.
5. Fat/oil used as medium of cooking: Fat is used in shallow and deep fat frying. Cooking oil is a better heat transfer medium than air or water in that it heats up very quickly because of its greater specific heat, and its operating temperature of about 200oC is considerably higher than that of water.
Pan frying is used to cook dosas, chapathis, omelettes, cutlets and tikkis. In pan frying, the amount of fat used can be limited.
Deep fat frying method is used in preparing pooris, vadas, cutlets, bajjis and pakodas. In deep fat frying, there is direct transfer of heat from the hot fat to the cold food that continues until the food is cooked. Water is lost from the exterior surface of the food as it is converted the steam. The steam carries of energy from the surface of the food and prevents charring.
Changes in fats due to heat during cooking: Several changes occur in fats and oils during frying of
foods. Some of the changes are (a) increasing in free fatty acids (b) decrease in iodine value (c) increase in peroxide value and carbonyl, (d) reduction in the content of polyunsaturated fatty acids (e) formation of polymers (f) increase in viscosity.
Free fatty acids: The free fatty acids content increases during heating. Moisture present in the food material fried tends to hydrolyse the fat and increase the free fatty acid content.
Iodine value: The iodine value decreases as a result of heat treatment. The decrease is due to the formation of dimers, polymers and epoxides at the double bond.
Peroxides and carbonyls:The peroxide formed are unstable and yield volatile aldehydes, ketones alcohols and acids.
Polymerisation of unsaturated fatty acids: During the thermal oxidation of fats, there is considerable isomerisation of double bonds. Epoxides are formed and cleavage products of fatty acids are formed. Some of the cleavage products are not volatile and are called monomers. Hydroxy fatty acids are formed. Cyclic compounds having benzene nucleus are also formed. More complicated compounds known as dimers and polymers are also formed. The content of polyunsaturated fatty acids decreases as a part of it undergoes polymerization.
Increase in viscosity : The viscosity of heated oil increases due to the formation of cyclic compounds and polymerized products.
Factors affecting amount of fat absorbed during frying
The chief factors influencing the amount of fat absorbed by fried foods are (1) the temperature and time of cooking (2) the total surface area of the food (3) the moisture content of the food (4) the protein, carbohydrate and fat contents of the food and (5) smoking temperature of the fat.
1. Temperature and time of cooking : When doughnuts were fried at 170oC, 185oC and 200oC the time required for frying at 170oC was greater than at 200oC. Consequently, the amount of fat absorbed was also greater.
2. Total surface area: Studies with frying of doughnuts have shown that doughnuts having a greater surface area absorbed more fat than doughnuts with smaller surface area.
3. Moisture content of the dough: Studies with frying poories and vadas have shown that if the moisture content of the material is highest, the fat absorption is also greater than the control.
4. Protein, fat and carbohydrate contents: Studies with doughnuts showed that if doughnuts are made of hard wheat flour having more protein, they absorbed less fat than doughnuts made out of soft wheat flours containing less protein. Foods containing more fat, e.g. pork chops absorb less fat than lean fish during frying.
5. Smoking temperature of fat: Studies with doughnuts showed that fat absorption was greater when doughnuts were fried in fats
having lower smoking temperature and containing higher amounts of free fatty acids.
Rancidity in fats
The development of off-flavours in fats is known as rancidity. There are three main types of rancidity. (a) Hydrolytic (b) oxidative and (c) ketonic.
a. Hydrolytic rancidity: Hydrolysis of fat by lipase need not always produce off-flavours. Incase of butter fat and coconut oil, butyric acid and other low molecular weight fatty acids are set free by hydrolysis by lipase. The odours of these acids contribute largely to the smell of rancid butter. The higher fatty acids such as palmitic and stearic acids have little odour.
b. Oxidative rancidity : This is the common type of rancidity observed in all fats and oils. The oxidation takes place at the unsaturated linkage. Certain metals, e.g. copper, hasten the onset of oxidative rancidity. The addition of oxygen to the unsaturated linkage results in the formation of peroxide value, which on decomposition, yields aldehydes and ketones having pronounced off-flavour.
c. Ketonic rancidity : This type is most frequently encountered as a result of action of fungi such as Aspergillus niger, pencillium glaucum on coconut or other oil seeds. They tallowy odour developed may be due to aldehydes and ketones formed by the action of the enzymes present in the fungi on oils.
Factors affecting the development of rancidity
The rate at which oxidation occurrs varies with the degree of unsaturation and the conditions of storage. The other factors which influence the rates of oxidation are certain metals (e.g., copper), light, temperature of storage, moisture content and presence of lipoxidases.
Metals: Certain metals e.g. copper, even when present in traces (2 ppm) accelerates the development of rancidity. Lead, iron and zinc are moderately active while tin and aluminium are the least active of the metals studied. Copper is 20 times as active as iron as a pro-oxidant.
Lipoxidase: These enzymes are present in some food stuffs., e.g., oilseeds, cereals etc. and they accelerate the oxidation of fatty acids containing 1-4 pentadiene system.
Light: Light accelerates the development of rancidity when the fat is exposed to light as such or in white transparent bottles.
Moisture: The moisture content of the product may affect the rate of development of oxidative rancidity. For example, biscuits with 2% moisture content develop oxidative rancidity more rapidly than biscuits with 3-5% moisture content.
Temperature: Rancidity develops more rapidly with increase in the temperature of storage e.g. products stored at 37oC develop rancidity more rapidly than products stored at 10oC.
Prevention of rancidity
Fats can be protected against the rapid development of rancidity by controlling the conditions of storage.
1. Storage at refrigerator temperature prevent rancidity. 2. Rays of light catalyse the oxidation of fats. By the use of
coloured glass containers that absorb the active rays, fats can be protected against spoilage. Certain shades of green bottles and wrappers and yellow transparent cellophane wrappers are effective in preventing rancidity.
3. Vacuum packaging also helps to retard the development of rancidity by excluding oxygen.
4. Antioxidants naturally present in the food such as vitamin C, beta carotene and vitamin E protect against rancidity.
5. Antioxidants can also be added like butylated hydroxy anisole (BHA), butylated hydroxy toluene (BHT), tertiary butyl hydroquinone (TBHQ) and propyl gallate.
6. Substances like citric acid may be used along with antioxidants in foods as synergists. A synergist increases the effectiveness of an antioxidant but is not as effective an agent when used alone. Some synergists may be effective because of their ability to bind or chelate the metals and prevent them catalyzing the oxidation process. Chealting agents are sometimes called sequestering agents.
MILK
Composition of milk:
Milk from different sources, regardless of breed or even species, will contain the same classes of constituents. They are milk fat (3-6%), protein (3-4 %), milk sugar (5%) and ash (0.7%). Water accounts for the balance of 85.5-88.5%. All the solids in milk are referred to as ‘ total solids’ (11.4 – 14.5%) and the total solids without fat is known as ‘milk solids – non fat’ (MSNF) or ‘ solids – not-fat’. The composition of milk from various sources include Buffalo, Cow, Goat, Human and Ass. The yield of milk and its composition, from the same source, vary depending upon many factors. These include the breed of the animal, its age, the stage of lactation, time of milking, time interval between milking, season of the year, feed of the animal condition of the animal and so on.
Milk fat
Milk fat or butter fat is of great economical and nutritive value. The flavour of milk is due to milk fat. It exists in milk in the form of minute globules in a true emulsion of oil-in-water type, the globules being the dispersed phase. The fat globules are invisible to the naked eye, but are readily seen under a microscope. Each globule of fat is surrounded by a very thin layer of protein, phospholipids and neutral lipids.
Fat globules vary widely in size from 2 to 10 m, and in numbers 3 x 109/ml. Milk fat is a mixture of several different glycerides. Other lipid materials present in milk are phospholipids, sterols, free fatty acids, carotenoids and fat soluble vitamins. Carotenes are responsible for the yellow colour of milk fat.
Milk proteins
Casein : Casein constitutes 80% of the total nitrogen in milk. It is precipitated on the acidification of milk to pH 4.6 at 20oC. The remaining whey protein constitutes lactoglobulin and lactalbumen. Milk protein contains proteoses, peptones and milk enzymes.
Casein is also a glycoprotein. The calcium content of whole casein is about 8.2%, carbohydrates are present to the extent of 5.7% in casein. Glutamic acid is the predomiant one in casein. Proline, aspartic, leucine, lysine and valine are also present. Casein is a good source of essential amino acids.
Casein can also be separated from the milk by the addition of rennin an enzyme secreted by the young calves.
Why proteins: Whey protein constitutes lactoglobulin and lactalbumin. These are not precipitated by acid or rennin, they can be coagulated by heat. Whey also contains small amounts of lactoferrin and serum transferrin.
Milk sugar: The chief carbohydrate present in milk is lactose or milk sugar is a disaccharide, although trace amounts of glucose, galactose and other sugars are present. Lactose gives on hydrolysis glucose and galactose. Lactose has only one sixth the sweetness of sucrose and one third – one fourth of its solubility in water. When milk is heated lactose reacts with protein and develops a brown colour. The development of brown colour is due to non-enzymatic browning. It is called Maillard reaction. Reducing sugar reacts with the amino acid lysine and brown colour develops. As the amino acid lysine is involved the quality of protein is decreased. The brown colour in condensed milk, khoa, basundi and gulabjamun is due to maillard reaction.
Lactose is acted upon by bacteria to produce lactic acid. The acid produced by the action of intestinal microorganisms on lactose checks the growth of undesirable putrefactive bacteria and promotes absorption of minerals. The acid fermentation is used in making butter, cheese and curd.
Ash and salts: Milk ash is a white residue remaining after incineration of milk at 600oC. It consists of oxides of sodium, potassium, calcium, magnesium, iron, phosphorus and sulphur, plus some chloride. In addition to these, milk contains many trace elements like copper, zinc, aluminium ,molybdenum, iodine etc., depending upon the feed of the animal.
The salts of milk are phosphates, chlorides, and citrates of sodium, potassium, calcium and magnesium. Milk is a rich source of calcium. The calcium, phosphorus ratio (1:2:1) in milk is regarded as most favourable for bone development. In addition, dairy products contain other nutrients such as vitamin D and lactose which favour calcium absorption. The calcium requirement cannot be met easily without taking milk.
Enzymes: The enzymes present in milk is alkaline phosphatase, lipase, xanthin oxidase, catalase and lactoperoxidase.
Vitamins: Thiamine occurs in only fair concentration in milk, but is relatively constant in amount. Riboflavin is present in a higher concentration in milk than the other B-vitamins and its stability to heat makes milk a dependable source of this vitamins. Milk is not a good source of niacin but it is an excellent source of tryptophan. Milk is very
poor source of vitamin C. The amount of fat soluble vitamins depend on the feed of the animal.
Colour: The yellowish colour of milk is due to the presence of carotene and riboflavin. The fat soluble carotenes are found in the milk fat; the riboflavin is water soluble which can be visible clearly in whey water.
Use/Role of milk and milk products in cookery
1. It contributes to the nutritive value of the diet., e.g. milk shakes, plain milk, flavoured milk, cheese toast.
2. Milk adds taste and flavour to the product e.g. payasam, tea, butter to toast.
3. It acts as a thickening agent along with starch, e.g., white sauce or cream soups.
4. Milk is also used in desserts., e.g. ice cream, puddings.5. Curd or butter milk is used as a leavening agent and to
improve the texture e.g. dhokla, bhatura. 6. Curd is used as a marinating agent, e.g. maintaining chicken
and meat.7. Cur is used as a souring agent, e.g. rava dosa, dry curd
chillies.8. Khoa is used as a binding agent, e.g. carrot halwa.9. Milk and curd increases shelf life poories preserve better when
the dough is mixed with milk / curd. 10. To prevent browning in vegetables, e.g. butter milk is used for
preventing browning when plantain stem is cut.11. Variety to the diet., e.g. butter milk sambar, avial and butter
paneer.12. Cheese is used as garnishing agent.13. Milk is used as clarifying agent in sugar syrup.14. Salted buttermilk is used for quenching thirst.
Points to be remembered in using milk and milk products in cookery
1. Prevention of scorching: Too thin vessels and too high a temperature can scorch the milk at the bottom of the vessel . Use double boiler or stir constantly and continuously.
2. Prevention of curdling in fruit milk beverages: Fruit and milk are cooled thoroughly as high temperature favour curdling. Raw pineapple contain pomelin and may lead to curdling of milk.
3. Prevention of curdling in fruit custard: This can be done by adding ripe (or) canned fruits. Some fruits like grapes and pineapples may curdle custard.
4. Prevention of scum formation can be achieved by covering the pan, stirring, using milk cooker, or by adding whipped cream.
5. Prevention of curdling in tomato soups: This can be done by adding tomato juice to the white sauce.
Enzymatic browning
Browning can be observed on the cut surfaces of light coloured fruits and vegetables such as apples, banana, potatoes and brinjal due to enzymatic action is known as enzymatic browning. Normally, the natural phenolic compounds present in intact tissues do not come in contact with the phenol oxidase present in some tissues. When the tissue is injured or cut and the cut surfaces is exposed to air. Phenol oxidase enzymes released at the surface act on the polyphenols present oxidizing them to Orthoquinones. The orthoquinones rapidly polymerize to form brown pigments. Tyrosine, Chlorogenic acid, the various catechins and several mono and dihydroxy phenols are among the many compounds that can serve as substrates for oxidation by polyphenoloxidase to cause browning or other discolouration in these foods.
• Developing flavor in tea (here the reaction is incorrectly called fermentation)
• Developing color and flavor in dried fruit such as figs and raisins.
Enzymic browning is detrimental to
• Fresh fruit and vegetables, in particular apples and potatoes
• Seafood such as shrimp
Prevention of enzymatic browning
The methods commonly used for the prevention of enzymatic browning are the following:
1. Thermal in activation of polyphenolase: The most commonly used method is blanching i.e. heating in live steam. The enzyme is fairly heat-stable and requires to be heated at 100oC for 2 to 10 min. for complete inactivation. This may not be possible in practice as cooking for long periods will affect the flavour and texture of the fruit or vegetable. Further, blanching breaks the cellular structure and brings about the contact of the enzyme with the substrate. If the thermal destruction is not complete or rapid, the high temperature may accelerate browning.
2. Changes of pH using acids: The optimal pH for polyphenolase activity is between 6.0 and 7.0. Lowering of the pH to 4.0 by the addition of citric acid inhibits the phenolase activity. It is also possible citric acid reacts with the copper present in the enzyme. Malic acid also has been found to be effective.
3. Use of antioxidants: Ascorbic acid retards browning by virtue of its reducing power. It reduces 0-quinones formed to the parent o-diphenols. Ascorbic acid is used along with citric acid to prevent browning in fruit products. SO2, sulphites and bisulphites inhibit effectively browning.
4. Prevention of contact with oxygen: a)Using controlled / modified atmosphere packaging for the processed foods i.e. packaging the product under nitrogen prevents surface browning effectively. b)Contact with oxygen can be reduced by immersing the fruits in water or liquids like milk, curd, fruit juice or honey or sugar solution or sodium chloride solution after cutting or by covering with a wet cloth.
Inhibitors of enzymatic browning :
Category Example of inhibitor Mode of action
Reducing agents
sulphiting agentsascorbic acid and analogscysteineglutathione
Removal of oxygen
Chelating agents
phosphates EDTA organic acids
Removal of metals (most PPO enzymes contain metal atoms)
The formation of brown discolouration in foods during heat processing and storage is known as nonenzymatic browning. Four mechanisms are involved in non-enzymatic browning in foods.
1. Maillard reaction involving interaction between reducing sugars, amino acids and proteins
2. Reaction of oxidation products of ascorbic acid with proteins or amino acids.
3. Reaction of oxidation products of polyunsaturated fatty acids with amino acid and proteins and
4. Caramelization of sugars.
1. Reaction between reducing sugars and amino acids (or) proteins
The steps involved in the maillard reaction between reducing sugars and amino acids (or) proteins are as follows :- a) Condensation of the aldehyde or ketone group with the amino group. b) rearrangement of condensation products. c) dehydration of rearrangement products d) further degradation and e) polymerization to brown pigments. The monosaccharides, ie. glucose, fructose etc., react faster with aminoacids than the disaccharides – maltose and lactose. Sucrose does not react by itself as it has no reacting group but
the hydrolytic products of sucrose ie., glucose and fructose react with amino acids.
2. Reaction of oxidation products of ascorbic acid with amino acids (or) proteins
Ascorbic acids is responsible for the development of browning reactions in fruit juices, and concentrates and in canned vegetables. Mixtures of ascorbic acid and amino acids develop brown colour more rapidly than mixtures of reducing sugars and amino acids. Dehydroascorbic acid is highly reactive and can react with amino acids. In the decomposition of ascorbic acid or dehydro ascorbic acid, the following products which are highly reactive are formed; a) Furfural and b) ozone of L-xylose.
3. Reaction between oxidation products of polyunsaturated fatty acids and amino acids.
When polyunsaturated fatty acids undergo oxidation, the hydroperoxides formed are broken down to aldehydes and ketones. One of the main products of autoxidised polyunsaturated fatty acids is malonaldehyde. This reacts with amino acids and proteins yielding coloured products. Malonaldehyde and other aldehydes and ketones formed by the degradation of polyunsaturated fatty acids react with the end amino group of lysine in the protein leading to the development of brown colour.
4. Browning due to caramelization of sugars
Sugars can undergo browning in the absence of amino acids by the process of caramelization but this reaction requires a high temperature of over 160C.
Conditions for the browning reactions
The factors affecting the reaction of reducing sugars or oxidation products of ascorbic acid (or) polyunsaturated fatty acids with proteins (or) amino acids are : 1) pH of the medium 2) Temperture and 3) Moisture content.
pH
The maillard reaction occurs in neutral or slightly acid or alkaline pH. The reaction is faster in neutral or slightly alkaline medium than in slight acid medium.
Temperature
The reaction does not takes place at very low temperature (0C). As the temperature is raised, the reaction velocity increases, a linear relationship exists between the rate of reaction and temperature over a range of 30 – 90C.
Moisture
The reaction does not take place at low moisture levels ie., 3 to 4% moisture. The optimal moisture levels for the reaction range from 10 to 15% in a dehydrated product.
Prevention of non-enymatic browning
The browning reactions can be prevented or retarded by the following procedures: a) storing the material at low temperature 0-5C. 2) keeping the moisture content of dry products below 4-0%. 3) excluding oxygen in the case of products containing ascorbic acid and fat to prevent their oxidation and 4) addition of SO2 or bisulphite in the case of dehydrated vegetables and fruits.
Effect on nutritional quality
The development of browning reaction in protein – rich foods such as skim milk powder, fish meal, egg powder etc., lead to the loss of available lysine due to the reaction of the end amino group of lysine with the reducing sugars. The reduction in the available lysine content will lower the nutritive value of the proteins. Good correlation has been found between the available lysine content and protein efficiency ratio of the proteins in processed foods.
MILK
Composition of milk
Milk from different sources, regardless of breed or even species, will
contain the same classes of constituents. They are milk fat (3-6%), protein (3-4
%), milk sugar (5%) and ash (0.7%). Water accounts for the balance of 85.5-
88.5%. All the solids in milk are referred to as ‘ total solids’ (11.4 – 14.5%) and
the total solids without fat is known as ‘milk solids – non fat’ (MSNF) or ‘ solids –
not-fat’. The composition of milk from various sources include Buffalo, Cow,
Goat, Human and Ass. The yield of milk and its composition, from the same
source, vary depending upon many factors. These include the breed of the
animal, its age, the stage of lactation, time of milking, time interval between
milking, season of the year, feed of the animal condition of the animal and so on.
Milk fat
Milk fat or butter fat is of great economical and nutritive value. The flavour
of milk is due to milk fat. It exists in milk in the form of minute globules in a true
emulsion of oil-in-water type, the globules being the dispersed phase. The fat
globules are invisible to the naked eye, but are readily seen under a microscope.
Each globule of fat is surrounded by a very thin layer of protein, phospholipids
and neutral lipids.
Fat globules vary widely in size from 2 to 10 m, and in numbers 3 x
109/ml. Milk fat is a mixture of several different glycerides. Other lipid materials
present in milk are phospholipids, sterols, free fatty acids, carotenoids and fat
soluble vitamins. Carotenes are responsible for the yellow colour of milk fat.
Milk proteins
Casein : Casein constitutes 80% of the total nitrogen in milk. It is precipitated on
the acidification of milk to pH 4.6 at 20oC. The remaining whey protein constitutes
lactoglobulin and lactalbumen. Milk protein contains proteoses, peptones and
milk enzymes.
Casein is also a glycoprotein. The calcium content of whole casein is about
8.2%, carbohydrates are present to the extent of 5.7% in casein. Glutamic acid is
the predomiant one in casein. Proline, aspartic, leucine, lysine and valine are
also present. Casein is a good source of essential amino acids.
Casein can also be separated from the milk by the addition of rennin an
enzyme secreted by the young calves.
Why proteins: Whey protein constitutes lactoglobulin and lactalbumin. These
are not precipitated by acid or rennin, they can be coagulated by heat. Whey also
contains small amounts of lactoferrin and serum transferrin.
Milk sugar: The chief carbohydrate present in milk is lactose or milk sugar is a
disaccharide, although trace amounts of glucose, galactose and other sugars are
present. Lactose gives on hydrolysis glucose and galactose. Lactose has only
one sixth the sweetness of sucrose and one third – one fourth of its solubility in
water. When milk is heated lactose reacts with protein and develops a brown
colour. The development of brown colour is due to non-enzymatic browning. It is
called Maillard reaction. Reducing sugar reacts with the amino acid lysine and
brown colour develops. As the amino acid lysine is involved the quality of protein
is decreased. The brown colour in condensed milk, khoa, basundi and
gulabjamun is due to maillard reaction.
Lactose is acted upon by bacteria to produce lactic acid. The acid
produced by the action of intestinal microorganisms on lactose checks the growth
of undesirable putrefactive bacteria and promotes absorption of minerals. The
acid fermentation is used in making butter, cheese and curd.
Ash and salts: Milk ash is a white residue remaining after incineration of milk at
600oC. It consists of oxides of sodium, potassium, calcium, magnesium, iron,
phosphorus and sulphur, plus some chloride. In addition to these, milk contains
many trace elements like copper, zinc, aluminium ,molybdenum, iodine etc.,
depending upon the feed of the animal.
The salts of milk are phosphates, chlorides, and citrates of sodium,
potassium, calcium and magnesium. Milk is a rich source of calcium. The
calcium, phosphorus ratio (1:2:1) in milk is regarded as most favourable for bone
development. In addition, dairy products contain other nutrients such as vitamin
D and lactose which favour calcium absorption. The calcium requirement cannot
be met easily without taking milk.
Enzymes: The enzymes present in milk is alkaline phosphatase, lipase, xanthin
oxidase, catalase and lactoperoxidase.
Vitamins: Thiamine occurs in only fair concentration in milk, but is relatively
constant in amount. Riboflavin is present in a higher concentration in milk than
the other B-vitamins and its stability to heat makes milk a dependable source of
this vitamins. Milk is not a good source of niacin but it is an excellent source of
tryptophan. Milk is very poor source of vitamin C. The amount of fat soluble
vitamins depend on the feed of the animal.
Colour: The yellowish colour of milk is due to the presence of carotene and
riboflavin. The fat soluble carotenes are found in the milk fat; the riboflavin is
water soluble which can be visible clearly in whey water.
Use/Role of milk and milk products in cookery
1. It contributes to the nutritive value of the diet., e.g. milk shakes, plain
milk, flavoured milk, cheese toast.
2. Milk adds taste and flavour to the product e.g. payasam, tea, butter to
toast.
3. It acts as a thickening agent along with starch, e.g., white sauce or
cream soups.
4. Milk is also used in desserts., e.g. ice cream, puddings.
5. Curd or butter milk is used as a leavening agent and to improve the
texture e.g. dhokla, bhatura.
6. Curd is used as a marinating agent, e.g. maintaining chicken and meat.
7. Cur is used as a souring agent, e.g. rava dosa, dry curd chillies.
8. Khoa is used as a binding agent, e.g. carrot halwa.
9. Milk and curd increases shelf life poories preserve better when the
dough is mixed with milk / curd.
10. To prevent browning in vegetables, e.g. butter milk is used for preventing
browning when plantain stem is cut.
11. Variety to the diet., e.g. butter milk sambar, avial and butter paneer.
12. Cheese is used as garnishing agent.
13. Milk is used as clarifying agent in sugar syrup.
14. Salted buttermilk is used for quenching thirst.
Points to be remembered in using milk and milk products in cookery
1. Prevention of scorching: Too thin vessels and too high a temperature
can scorch the milk at the bottom of the vessel . Use double boiler or stir
constantly and continuously.
2. Prevention of curdling in fruit milk beverages: Fruit and milk are cooled
thoroughly as high temperature favour curdling. Raw pineapple contain
pomelin and may lead to curdling of milk.
3. Prevention of curdling in fruit custard: This can be done by adding ripe
(or) canned fruits. Some fruits like grapes and pineapples may curdle
custard.
4. Prevention of scum formation can be achieved by covering the pan,
stirring, using milk cooker, or by adding whipped cream.
5. Prevention of curdling in tomato soups: This can be done by adding
tomato juice to the white sauce.
VEGETABLES
Classification
Vegetables are classified on the basis of the parts consumed of plants,
such as roots, stems, leaves, flowers etc. This is not satisfactory as some parts
of plants may be grouped under more than one heading. Vegetables can be
divided into two main groups: winter or rabi vegetables and summer or kharif
vegetables according to their growing seasons. They are further sub divided into
groups based on their cultural requirements. On this basis, the commonly used