Defects and spoilage of fermented dairy products Submitted to:- Dr. Navneet Submitted by:- Ramveer Singh

Type Of fermented Milk: Mesophilic Fermentation Cultured Buttermilk Sour Cream Thermophilic Fermentation Yogurt Bulgarian Buttermilk Yeast-Lactic Fermentation Kefir Kumiss

Microbial Defect Several microorganism present In Fermented Milk products which cause flavour and/or texture defects. Coliform Bacteria Butyric Acid Bacteria Lactobacilli Heat-Resistant Streptococci Propionic Acid Bacteria

Coliform Bacteria Coliform bacteria rarely cause defects in cheese made from pasteurized milk Coliforms can only grow as long as sugar is available, since they cannot ferment lactic acid Prevention - (a)Using a fast-souring starter (b)sodium or potassium nitrate (saltpeter). Fermentation by coliforms has little effect on the pH of the cheese. e.g. Escherichia coli, Enterobacter aerogenes

BUTYRIC ACID BACTERIA Clostridium spp. (i.e., anaerobic spore-forming bacteria) can grow in cheese and ferment lactic acid; these are called butyric acid bacteria. The pH of the cheese is increased by the fermentation. The main breakdown products are butyric acid, CO2, and H2: 2 CH3–CHOH–CO2H → CH3–CH2–CH2–CO2H + 2 CO2 + 2 H2 This butyric acid fermentation leads to texture and flavor defects. In serious cases, cracks or large spherical holes are formed in the cheese, as are very bad off-flavors. Because of this, growth of butyric acid bacteria in cheese is considered a serious defect. e.g. Clostridium tyrobutyricum, C. butyricum

PROPIONIC ACID BACTERIA LACTOBACILLI Growth of mesophilic lactobacilli may induce texture and flavor defects. The organisms involved are called nonstarter lactic acid bacteria and they occur in many cheese types as an adventitious flora, especially in raw milk cheeses. e.g. Lactobacillus casei HEAT-RESISTANT STREPTOCOCCI S. thermophilus is used as starter in the case of cheeses made with thermophilic cultures, some strains can cause defects in cheeses made with mesophilic starters. PROPIONIC ACID BACTERIA Growth of propionic acid bacteria is desirable in certain varieties of cheese to achieve a satisfactory quality; the bacteria are added to the cheese milk. In other cheeses, excessive growth of these bacteria causes defects

Sources of Spoilage Microorganisms Contamination of Raw Milk The stresses placed on the cow’s teats and mammary glands by the very large amounts of milk produced and the actions of the milking machine cause teat canals to become more open and teat ends to become misshapen as time passes. These stresses may open the teat canal for the entry of bacteria capable of infecting the glands. The highly nutritious nature of dairy products makes them especially good media for the growth of microorganisms. e.g. Pseudomonas spp, C. butyricum, Bacillus spp. (mainly B.cereus and B. polymyxa)

Sources of Spoilage Microorganisms Contamination of Dairy Products Washed curd types of cheeses are especially susceptible to growth of coliforms Bacteria. A high incidence of contamination of brine-salted cheeses by yeasts Fungi causing a “thread mold” defect in Cheddar cheeses were found in the cheese factory environment Ascospores of B. nivea and other heat-resistant species shown to be able to survive pasteurization, such as Talaromyces avellaneus, Neosartorya fischeri , and Eupenicillium brefeldianum, have also been found in raw milk

Butter (Spoilage & defects) Many of the defects of butter originate in the cream from which it is made Flavor Defects

Butter (Color Defects) Some Color defects not caused by Microorganism

Cheese (Spoilage & Defects) Factors that determine the rates of spoilage of cheeses are water activity, pH, salt to moisture ratio, temperature, characteristics of the lactic starter culture, types and viability of contaminating microorganisms, and characteristics and quantities of residual enzymes. fresh, raw milk pasta filata cheeses, Melilli et al. (2004) determined that low initial salt and higher brining temperature (18◦C) allowed for greater growth of coliforms, which caused gas formation in the cheese. Fungal growth in packaged cheeses was found. Coliform bacteria rarely cause defects in cheese made from pasteurized milk. Fermentation by coliforms has little effect on the pH of the cheese. e.g. Enterobacter aerogenes This butyric acid fermentation leads to texture and flavor defects in Cheese. e.g. Clostridium tyrobutyricum, C. butyricum

Gassy Swiss cheese BY Clostridium tyrobutyricum Spoilage and Defects of Cheese

Yogurt (FLAVOR DEFECTS & SHELF LIFE ) A main quality problem with yogurt is that souring tends to go on after delivery Yogurt may become bitter due to excessive proteolysis. The off-flavors may be characterized as yeasty, fruity, musty, cheesy, or bitter. Other defects may be caused by yeasts and molds.

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