Spoilage of Milk and Dairy Products. Doç. Dr. Arzu Çağrı Mehmetoğlu

Transcription

1 Spoilage of Milk and Dairy Products Doç. Dr. Arzu Çağrı Mehmetoğlu

2 Dairy processing Preservation methods: Pasteurization, 72C for 15 sec destroy natural inhibitor-(lactoperoxidase, antibodies) Increase available nitrogen content by hydrolysis of protein and breaking down sulfidril compounds encaurage thermoduric spoilage m.o Heat sterilization Fermentation Dehydration Refrigeration Freezing

3 Composition of milk Nutrition: free amino acids, proteins Lactose (4.8%) Minerals ph-6.4

4 Contamination Milk contain only few bacteria when it leaves the udder of a healthy animal Micrococci and streptococci Milk contaminated by the animal, feces, air, utensils, hands, milking machines Lactic acid bacteria, Streptoccocci, coliforms, psychotrophic Gram negative rods, thermodurics (bacilli, micrococci, enterococci) and brevibacterium

5 Spoilage in Milk Some microoganisims have advantage in milk spoilage How? If they have lactose hydrolysing enzyme (lactase or Betagalactosides), they can metabolise lactose and grow

6 Raw mik is rapidly cooled after collection Kept cold until pasteurized After pasteurization, the milk kept cold until comsumption Shelf-life days at 4C Psychrotrophic bacteria can grow

7 Raw milk Gram (-) aerobic psychrotrophic rods Alcaligenes, Flavobacterium, Pseudomonas and coliforms They are generally proteolitic, lipolytic and phospholipolytic Pseudomonas produce protease (heat stable) and lipase Bitter, fruit by lipolysis putrit, unclean flavor and coagulate milk by proteoliysis They cannot utilize lactose

8 Souring Acid producing fermentative bacteria Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Pediococcus and Streptococcus If storage temperature is high enough Psychrotrophic bacteri cannot grow Or the presence of inhibitory compounds to Gr(-) bacteria

9 Lactic acid- clean pleasant acid flavor Acetic acid and propiyonic acid- unpleasand acid flavor and taste of spoiled milk some coliforms can be lactose positive Produce lactic acid, acetic and formic acid, Also CO2 and H2 Curdling, foaming abd souring This is very rare problem

10 Spoiled defects Heat stable proteases Off flavor-bitterness Off odor-ammonia, amines and sulfides Heat resistant lipases Malty flavor (burn ad caramel)- Lactobacillus maltigenes Fruity flavor- P. Fragi Soapy flavor- fatty acids (high moleculer) Cardboardy flavor- ketones, aldehydes

11 Ropiness and sliminess Some bacteria produce extracellular polymers İncrease viscosity, rope defect Surface roppiness Alcaligenes viscolactis and Micrococcus freundenreichii Near the surface E. Aerogonas Throughout the milk Klebsialla Bottom of the milk Lb. Bulgaricus, Lb. Casei, Lactococcus lactis, Bacilli

12 Pasteurized milk Pasterurization kils most activ acid forming bacteria But not heat-resistant thermoduric bacteria Micrococcus, Enterococcus, Lactobacillus, Streptococcus, Corynobacterium and spores of Bacillus and Clostridium They usually spoil pasteurized milk Utilize lactose to reduce ph to around 4.0 Curdling occurs

13 Bitty Bacillus can also survive and grow They produce lectinase Hydrolyses phospholipids of the fat globules Causing agregation of the fat globules Adhere to the container surfaces

14 Sweet Curdling B. Cereus, Proteus, Alcaligenes Produce rennin-like enzyme Break down casein Decrease stability Coagulation and Can cause sweet curdling of milk at higher ph Bitterness can be observed

15 Butter spoilage The main source of contamination: Cream, milk, equipments and water Cream is heated at 71C for 30 min or 87 to 93C for few sec

16 Bacteria can cause 4 types of spoilage in butter:

17 Bacteria can cause 4 types of spoilage in butter: 4. Discoloration Dark, smoky or greenish areas-alterneria, CladosporiumSmall black spots- Stemphyleium Green color-penicillum Brown areas- Phoma and Alternaria Bright reddish-pink areas-fusarium culmorum Pink color-yeast Black discolorations- P. nigrifiacans

18 Cheese spoilage Lactic acid bacteria Heterofermantative produce gas and off-flavor Lactobacillus brevis, Lactobacillus pseudoplantarum L. casei produce soft body defect Pink spots-propionibacterium, Lb. bularicus, yeast, White crystaline deposit on the surface Facultatively Heterofermentative Lactobacillus Lactic acid production-insoluble Calcium lactate Phenolic flavor- horse urine, 2-6 months of aging L. casei subsp. alactosus, L. casei subsp. rhamnosus

19 Coliform bacteria Early Gassy defects (early blowing) in cheese Coliforms growth during cheese manifacture or during the few days of storage When it happens? Lactic acid fermentation fails- ph not low enough When higly contaminated raw milk is used 10 7 CFU coliform per g needs

20 Spore Forming bacteria Late Gas formation (Late blowing) After several weeks of aging Clostridium tyrobutyricum Fermentation of lactate to butyric acid, acetic acid, CO 2 and H 2 When it happens High ph High moisture Low interior salt Milk is contamineted from silage

21 Yeast and Molds They are very common Can grow at low ph Yeast spoilage fruity or yeasty odor and/or gas formation Candida, Rhodotorula, Torulospora Mold growth on surface-main problem Penicillum, Aspergillus, Alterneria, Fusarium, Clodosporium, Geotrichum, Mucor