PowerPoint Presentation · PPT file · Web view · 2006-12-05Starter Cultures The primary function of lactic starters is the production ... and alcohol production Production of

Fermented Foods• Foods that have been subjected to the action of micro-

organisms or enzymes, in order to bring about a desirable change.

• Numerous food products owe their production and characteristics to the fermentative activities of microorganisms.

• Fermented foods originated many thousands of years ago when presumably micro-organism contaminated local foods.

Fermented Foods• Micro-organisms cause changes in the foods which:

– Help to preserve the food,– Extend shelf-life considerably over that of the

raw materials from which they are made,– Improve aroma and flavour characteristics,– Increase its vitamin content or its digestibility

compared to the raw materials.

Table 1 History and origins of some fermented foods

Food Approximate yearof introduction

Region

MushroomsSoy sauceWineFermented milkCheeseBeerBread Fermented MeatsSourdough breadFish saucePickled vegetablesTea

4000 BC3000 BC3000 BC3000 BC2000 BC2000 BC1500 BC1500 BC1000 BC1000 BC1000 BC 200 BC

ChinaChina, Korea, JapanNorth Africa, EuropeMiddle EastMiddle EastNorth Africa, ChinaEgypt, EuropeMiddle EastEuropeSoutheast Asia, North AfricaChina, EuropeChina

Fermented Foods• The term “biological ennoblement” has

been used to describe the nutritional benefits of fermented foods.

• Fermented foods comprise about one-third of the world wide consumption of food and 20- 40 % (by weight) of individual diets.

Table 2 Worldwide production of some fermented foods

Food Quantity (t) Beverage Quantity (hl)

Cheese

Yoghurt

Mushrooms

Fish sauce

Dried stockfish

15 million

3 million

1.5 million

300 000

250 000

Beer

Wine

1000 million

350 million

Table 3 Individual consumption of some fermented foods: average per person per year

Food Country Annualconsumption

Beer (I)Wine (I)

Yoghurt (I)

Kimchi (kg)Tempeh (kg)Soy sauce (I)Cheese (kg)Miso (kg)

GermanyItaly, PortugalArgentinaFinlandNetherlandsKoreaIndonesiaJapanUKJapan

130

90

70

40

25

2218

10

10

7

Table 4 Benefits of fermentation

Benefit Rawmaterial

Fermentedfood

Preservation Milk(Most materials)

Yoghurt, cheese

Enhancement of safetyAcid productionAcid and alcohol production

Production of bacteriocinsRemoval of toxic components

FruitBarleyGrapesMeatCassavaSoybean

VinegarBeerWineSalamiGari, polviho azedoSoy sauce

Enhancement of nutritional valueImproved digestibilityRetention of micronutrientsIncreased fibre contentSynthesis of probiotic compounds

WheatLeafy veges.CoconutMilk

BreadKimchi, sauerkrautNata de cocoBifidus milk, Yakult, Acidophilus yoghurt

Improvement of flavour Coffee beansGrapes

CoffeeWine

Cassava• Fresh cassava contains cyanhydric acid (HCN) that

should be eliminated from any product originating from cassava to render it fit for human consumption. Depending on the production method (particularly traditional methods) gari could contains up to 20 mg / kg of HCN - against 43 mg / kg for fresh peeled cassava.

• Gari is a fermented, gelled and dehydrated food produced from fresh cassava. It is a popular diet in Nigeria, Benin, Togo, Ghana and in other West Africa's countries. The consumption area even expands to Central Africa: Gabon, Cameroon, Congo Brazzaville and Angola.

• Polvilho is a fine tapioca/manioc/cassava flour. it can be found at latino markets in california as "sour starch" (polvilho azedo) or "sweet starch" (polvilho doce)

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Nata de Coco

• A high fiber, zero fat Philippino dessert.• A chewy, translucent, jelly-like food product

produced by the bacterial fermentation of coconut milk.

• Commonly sweetened as a candy or dessert, and can accompany many things including pickles, drinks, ice cream, and fruit mixes.

• Highly regarded for its high dietary fiber, and its zero fat and cholesterol content.

• It is produced through a series of steps ranging from milk extraction, mixing, fermentation, separating, cleaning, cutting to packaging.

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Lactic Acid Bacteria

• Major group of Fermentative organisms.

• This group is comprised of 11 genera of gram-positive bacteria:

• Carnobacterium, Oenococcus, Enterococcus, Pediococcus, Lactococcus, Streptococcus, Lactobacillus, Vagococcus, Lactosphaera, Weissells and Lecconostoc

• Related to this group are genera such as Aerococcus, Microbacterium, and Propionbacterium.

Lactic Acid Bacteria

• While this is a loosely defined group with no precise boundaries all members share the property of producing lactic acid from hexoses.

• As fermenting organisms, they lack functional heme-linked electron transport systems or cytochromes, they do not have a functional Krebs cycle.

• Energy is obtained by substrate-level phosphorylation while oxidising carbohydrates.

Lactic Acid Bacteria• The lactic acid bacteria can be divided into two groups based on

the end products of glucose metabolism.

• Those that produce lactic acid as the major or sole product of glucose fermentation are designated homofermentative.

• Those that produce equal amounts of lactic acid, ethanol and CO2 are termed heterofermentative.

• The homolactics are able to extract about twice as much energy from a given quantity of glucose as the heterolactics.

Lactic Acid Bacteria• All members of Pediococcus, Lactococcus, Streptococcus,

Vagococcus, along with some lactobacilli are homofermenters.

• Carnobacterium, Oenococcus, Enterococcus, Lactosphaera, Weissells and Lecconostoc and some Lactobacilli are heterofermenters

• The heterolactics are more important than the homolactics in producing flavour and aroma components such as acetylaldehyde and diacetyl.

Lactic Acid Bacteria - Growth

• The lactic acid bacteria are mesophiles:– they generally grow over a temperature range

of about 10 to 40oC, – an optimum between 25 and 35oC. – Some can grow below 5 and as high as 45 oC.

• Most can grow in the pH range from 4 to 8. Though some as low as 3.2 and as high as 9.6.

Starter Cultures• Traditionally the fermenting organisms came from the natural

microflora or a portion of the previous fermentation.

• In many cases the natural microflora is either inefficient, uncontrollable, and unpredictable, or is destroyed during preparation of the sample prior to fermentation (eg pasteurisation).

• A starter culture can provide particular characteristics in a more controlled and predictable fermentation.

Starter Cultures

• Lactic starters always include bacteria that convert sugars to lactic acid, usually:– Lactococcus lactis subsp. lactis, – Lactococcus lactis subsp. cremoris or – Lactococccus lactis subsp. lactis biovar diacetylactis.

• Where flavour and aroma compounds such as diacetyl are desired the lactic acid starter will include heterofermentative organisms such as:– Leuconostoc citrovorum or – Leuconostoc dextranicum.

Starter Cultures

• The primary function of lactic starters is the production of lactic acid from sugars

• Other functions of starter cultures may include the following:

• flavour, aroma, and alcohol production • proteolytic and lipolytic activities• inhibition of undesirable organisms

A good starter CULTURE will:

• Convert most of the sugars to lactic acid

• Increase the lactic acid concentration to 0.8 to 1.2 % (Titratable acidity)

• Drop the pH to between 4.3 to 4.5

A single bacterial colony

• Food scientists frequently use the ability of bacterial cells to grow and form colonies on solid media to:– isolate bacteria from foods, – to determine what types and – how many bacteria are present.

• Streak plates

The streak plate technique

• Bacteria are “streaked”over the surface of an agar plate so as to obtain single colonies.

• Obtaining single colonies is important as it enables;– the size, – shape and – colour of the individual colonies to be examined. – It can also highlight the presence of contaminating

micro-organisms

The Streak Plate Technique

When conditions are right bacteria can double in number every 20 minutes

Microscopic examination• Can provide information on the size

and shape of the bacteria– Rods (1)– Cocci (2)– Spiral (3)

• It cannot provide enough information to enable bacteria to be identified

Microscopic views of stained bacteria

Lactobacillus spp.

Lactococcus spp.