Spoilage of Milk

Milk & Milk products Spoilage

Milk: Unique flavor and textureMilk: Unique flavor and textureRejected if off flavor or other Rejected if off flavor or other

defectsdefectsSpoilage occur by Biochemical Spoilage occur by Biochemical

reactions of contaminating reactions of contaminating bacteria (initiated after milking)bacteria (initiated after milking)

Manifestations of spoilageManifestations of spoilage

Lactic acid production/ Lactic acid production/ souringsouring

ProteolysisProteolysisLipolysisLipolysisSweet curdling Sweet curdling

Spoilage ProcessSpoilage Process

Fermentation-milk constituents by microbesNormal fermentation: curdling Abnormal fermentations: Gassiness,

ropiness, proteolysis, sweet curdling, lipolysis

Mixed fermentation: two or more fermentations occur simultaneously e.g. acid and gas (coliforms)

Associative actionAssociative action

Combined action (two or more-species Combined action (two or more-species or genera)or genera)

Desirable or undesirableDesirable or undesirableChanges not possible by single Changes not possible by single

microbemicrobeThree typesThree types

SynergismSynergismMetabiosisMetabiosisAntibiosis.Antibiosis.

SynergismSynergism

Changes brought by two microbes (not Changes brought by two microbes (not single one)single one)

Mixed starter (Mixed starter (Streptococcus lactis &Streptococcus lactis & Leuconostoc Leuconostoc spp.)spp.)

Leuconostocs convert citrate to volatile Leuconostocs convert citrate to volatile compounds (only at low pH)& produce compounds (only at low pH)& produce flavourflavour

Lowering of pH due to lactic acid Lowering of pH due to lactic acid production S. production S. lactis.lactis.

SynergismSynergism

Blue discoloration: Blue discoloration: Pseudomonas Pseudomonas syncyaneasyncyanea only in association with only in association with S. S. lactis lactis

Lactic acid bacteria required for 'yeasty Lactic acid bacteria required for 'yeasty creamy' defect creamy' defect (Candida (Candida pseudotropicalis, Torulopsis sphaerica) pseudotropicalis, Torulopsis sphaerica) in creamin cream

Coagulation of milk & foaming for Coagulation of milk & foaming for subsequent gas production by yeastssubsequent gas production by yeasts

Metabiosis

Food chain is formedFood chain is formedMetabolic end products of one are Metabolic end products of one are

utilized as food by other for utilized as food by other for producing final changeproducing final change

Swiss cheese: lactose to lactic Swiss cheese: lactose to lactic acid (bacteria), utilized by acid (bacteria), utilized by propionibacteria to produce propionibacteria to produce propionic acid (flavour)propionic acid (flavour)

Metabiosis

Spoilage of Raw milk at room temp.Curdling of milk by S. lactis

(precipitation of casein) up to 1 % acidity

Lactobacilli (L. casei) convert rest of lactose to lactic acid 2% lactic acid

Molds (Geotrichum candidum) growth on surface and reduce acidity by oxidizing lactic acid to C02 and H20.

Cont..Cont..

Reduced acidity, proteolytic spore Reduced acidity, proteolytic spore formers (formers (Bacillus Bacillus spp.) degrade spp.) degrade casein fractioncasein fraction

Sub sequently lipolytic bacteria Sub sequently lipolytic bacteria develop and utilize fat fractiondevelop and utilize fat fraction

Decomposed mass-water, inorganic Decomposed mass-water, inorganic substances, C0substances, C022, NH, NH33, H, H22S etc.S etc.

Antibiosis

One organism inhibits/suppressesgrowth of the others

Lactic acid -bacteria causes the inhibition of proteolytic organisms (spore formers)

Starter cultures do not propagate well in reconstituted milk-certain preformed substances inhibitory to starter bacteria are elaborated in milk and get carried over to the product during subsequent drying

Natural souring/curdling

Raw milk held at ambient Raw milk held at ambient conditionsconditions

Immediate effect is souring Immediate effect is souring followed by curdling (due to followed by curdling (due to acidity-lactic acid) by bacteria acidity-lactic acid) by bacteria already present in raw milkalready present in raw milk

Fresh milk normal acidity (0.14 to Fresh milk normal acidity (0.14 to 0.19%)0.19%)

Cont..Cont..

Milk sours (0.20 to 0.25%)Milk sours (0.20 to 0.25%)Milk curdles (0.50-0.65%)Milk curdles (0.50-0.65%)COB test positive (0.30 to 0.45%)COB test positive (0.30 to 0.45%)Acidity increase even after coagulation Acidity increase even after coagulation

of casein till lactic acid producing flora of casein till lactic acid producing flora inhibited or till whole of lactose is inhibited or till whole of lactose is exhausted (acid tolerant organisms exhausted (acid tolerant organisms predominate)predominate)

Acid coagulationAcid coagulation

Interaction of lactic acid with calcium Interaction of lactic acid with calcium bound to casein-precipitation of casein-bound to casein-precipitation of casein-curd (pH range 4.64 to 4.78)curd (pH range 4.64 to 4.78)

Lactic streptococci - Lactic streptococci - S. S. lactis, lactis, S. S. cremoriscremoris (room temperature) (room temperature)Gets inhibited at 1% Gets inhibited at 1%

Lactobacilli-Lactobacilli- L. L. casei casei (at room (at room temperature), L. temperature), L. acidophilus acidophilus and and L. L. bulgaricus bulgaricus (optimally at around 40°C).(optimally at around 40°C).Gets inhibited beyond 2% level of Gets inhibited beyond 2% level of

lactic acidlactic acid

Cont..Cont..

Leuconostocs. Leuco. dextranicum Leuconostocs. Leuco. dextranicum and and Leuco. citrovorum-Leuco. citrovorum-responsible for flavour responsible for flavour development and lower level of lactic aciddevelopment and lower level of lactic acid

Other streptococciOther streptococciS. S. thermophilusthermophilus at around 45 C though at around 45 C though

it is produced slowly even at lower it is produced slowly even at lower temperature range. This organism is temperature range. This organism is also capable of surviving higher heat also capable of surviving higher heat treatments such as pasteurization.treatments such as pasteurization.

S. S. liquefaciens liquefaciens at about 31C. Milk is at about 31C. Milk is rapidly coagulated followed by rapidly coagulated followed by proteolysis (causes the curd to shrink proteolysis (causes the curd to shrink from the walls of the container and from the walls of the container and separation of whey).separation of whey).

Cont..Cont..

Bacillus coagulalls Bacillus coagulalls -aerobic spore former--aerobic spore former-survive heating and multiply and produce survive heating and multiply and produce lactic acid at 31to 55°C.lactic acid at 31to 55°C.

Coliforms-Coliforms- E. coli E. coli and and Enterobacter Enterobacter aerogenes aerogenes Produces acid & gas (37°C) Produces acid & gas (37°C)

The coagulum formed by lactic The coagulum formed by lactic streptococci, S. streptococci, S. themrophilus themrophilus and and lactobacilli is smooth and with typical clean lactobacilli is smooth and with typical clean sour flavour (used as starter culture for sour flavour (used as starter culture for desirable fermentations) desirable fermentations)

Cont..Cont..

S. S. liquefacienls, B. coagulans liquefacienls, B. coagulans and and coliforms produce a coagulum with coliforms produce a coagulum with undesirable flavours due to liberation of undesirable flavours due to liberation of certain volatile flavour substances from certain volatile flavour substances from lactose, proteins and milklactose, proteins and milk

Organisms present in raw milk varies and Organisms present in raw milk varies and produce coagulum which varies with the produce coagulum which varies with the composition of the causative microflora.composition of the causative microflora.

Sources of floraSources of flora

At the farm level fromAt the farm level fromUtensilsUtensilsCoat of the cowCoat of the cowFeed (silage, grains etc.)Feed (silage, grains etc.)Faecal matter Faecal matter EnvironmentEnvironment

MalpracticesMalpractices

Neutralization with caustic soda to mask Neutralization with caustic soda to mask the developed acidity and escape the the developed acidity and escape the rejection of milkrejection of milk

Control measuresControl measures Practiced under hygienic conditions to Practiced under hygienic conditions to

minimize entry of acid-producing organismsminimize entry of acid-producing organisms Immediate chilling of raw milk Immediate chilling of raw milk Clean/ Sanitized Utensils and equipments Clean/ Sanitized Utensils and equipments

involved in milk production, collection and involved in milk production, collection and transportation stransportation s

Holding of milk needs to be minimizedHolding of milk needs to be minimized Adequate pasteurization of milk followed by Adequate pasteurization of milk followed by

coolingcooling Household levels heated immediately and Household levels heated immediately and

stored in refrigerator.stored in refrigerator.

Gas productionGas production

Cream: production of gas (mainly COCream: production of gas (mainly CO22) by ) by micro-organisms responsible for defect micro-organisms responsible for defect called 'gassiness‘called 'gassiness‘

Foaming as the gas escapes the partially Foaming as the gas escapes the partially coagulated mass-defect frothiness coagulated mass-defect frothiness

Frothiness-associative action of acid Frothiness-associative action of acid producing bacteria & gas producing producing bacteria & gas producing yeasts. yeasts.

Gassy cream- accompanied by yeasty Gassy cream- accompanied by yeasty odour called yeasty cream odour called yeasty cream

Cont..Cont.. Gas production in canned dairy products-Gas production in canned dairy products-

bulging of cans/blowing of cans bulging of cans/blowing of cans Lactose fermenting yeasts-Candida Lactose fermenting yeasts-Candida

pseudotropicalis, Torulopsis sphaericapseudotropicalis, Torulopsis sphaerica produce C02 and ethyl alcohol in milk, cream, produce C02 and ethyl alcohol in milk, cream, whey at or below whey at or below 31C31CAcid tolerant-grow under acidic conditions Acid tolerant-grow under acidic conditions

(as in sour cream) (as in sour cream) Coliforms: Coliforms: Escherichia coli, Enterobacter Escherichia coli, Enterobacter

aerogenes aerogenes ferment lactose into gas and acid ferment lactose into gas and acid Gas escapes before coagulation of casein-Gas escapes before coagulation of casein-

no frothiness unlike that in yeast no frothiness unlike that in yeast fermentation. fermentation.

Anaerobic spore forming bacteria Cl. Anaerobic spore forming bacteria Cl. butyricum, butyricum, Cl. pCl. pasteurianum Cl. asteurianum Cl. Sporogenes-Sporogenes-produce gas anaerobic produce gas anaerobic conditionsconditions

Grow well if acid producers are destroyed Grow well if acid producers are destroyed by heating and the product has anaerobic by heating and the product has anaerobic atmosphere e.g. in canned dairy productsatmosphere e.g. in canned dairy products

Sources of gas producing organismSources of gas producing organism

Soil, manure, feed or utensilsSoil, manure, feed or utensilsColiforms mainly associated with Coliforms mainly associated with

faecal contaminationfaecal contaminationClostridia through feed (silage) and Clostridia through feed (silage) and

manuremanure

Control measuresControl measures

Avoid excessive contamination of milk/cream from potent Avoid excessive contamination of milk/cream from potent sources at the farm level sources at the farm level

Milch animal be cleaned/washed before milking Milch animal be cleaned/washed before milking Feed or manure particles should not be allowed to fall in Feed or manure particles should not be allowed to fall in

milkmilk Milk - utensils should be cleaned properlyMilk - utensils should be cleaned properly Holding of milk and cream under ambient conditions Holding of milk and cream under ambient conditions

should be minimizedshould be minimized The heat treatment given to the product should be The heat treatment given to the product should be

adequate (kill heat-sensitive gas producers-coliforms)adequate (kill heat-sensitive gas producers-coliforms)

Ropiness/sliminessRopiness/sliminess

Growth of bacteria leading to change in Growth of bacteria leading to change in consistency that forms threads or viscous consistency that forms threads or viscous masses when pouredmasses when poured

Ropy material may be tough and doughy Ropy material may be tough and doughy due to acid-producing bacteria. Causative due to acid-producing bacteria. Causative organismsorganisms

Lipolytic/ Hydrolytic rancidity Lipolytic/ Hydrolytic rancidity Rancidity from hydrolysis of milkfatRancidity from hydrolysis of milkfatCaused by enzyme lipoprotein lipase (LPL)Caused by enzyme lipoprotein lipase (LPL)Flavour-short chain fatty acidssuch as Flavour-short chain fatty acidssuch as butyric acidbutyric acidLPL indigenous or bacterialLPL indigenous or bacterialActive at the fat/water interface (ineffective Active at the fat/water interface (ineffective unless the fat globule membrane is damaged- unless the fat globule membrane is damaged- agitation, foaming, and pumping.agitation, foaming, and pumping.

•Homogenized milk-rapid lipolysis Homogenized milk-rapid lipolysis unless lipase is destroyed by heating unless lipase is destroyed by heating (enzyme denatured at 55-60(enzyme denatured at 55-60˚ C)˚ C)Homogenize milk immediately Homogenize milk immediately before or after pasteurization and before or after pasteurization and avoid mixing new milk because it avoid mixing new milk because it leads to rapid rancidity.leads to rapid rancidity.

•Some cows can produce spontaneous Some cows can produce spontaneous lipolysis from reacting to something lipolysis from reacting to something

indigenous to the milk.indigenous to the milk. Late lactation, mastitis, hay and grain Late lactation, mastitis, hay and grain ration diets (more so than fresh forage ration diets (more so than fresh forage or silage), and low yielding cows are or silage), and low yielding cows are

more suseptible. more suseptible.

Lipolysis can be detected by measuring the Lipolysis can be detected by measuring the acid degree value which determines the acid degree value which determines the

presence of free fatty acids. presence of free fatty acids.