Milk microbiologystandards for milk and milk productShivnam RanaMsc. Microbiology (PAU)L -2011- BS -251 – M
Introduction• Complete food – Carbohydrates(Lactase),Protein(Casein), Fats, Minerals• due to: Complex biochemical compositionHigh water activity• Excellent culture medium for the growth andmultiplication of microorganisms
Factors that influence survival and growth ofmicroorganismsIntrinsic• Nutrient availability• pH• Water availabilityExtrinsic• Temperature• Atmosphere
Origin of microorganism in milk• Commensal micro flora- teat skin, epithelial lining of the teatcanal, duct that conveys the milk from the mammary gland tothe teat orifice.Staphylococcus, Streptococcus,Bacillus, Micrococcus,Corynebacterium, coliforms• Environmental contamination- soil, water equipment, dairyfarm area are reservoir for many food borne pathogensSalmonella species,L. monocytogenes
• Diseased animalMastitis- Staphylococcus (S.agalactiae) andStreptococcus species
Lactobacillus• Obligate homofermentative lactobacillus –hexoses ferment lactic acid• Growth at 45°C but not at 15°C• Lactobacillus delbrueckii, lactobacillus helveticus,lactobacillus salivarius and L. Acidophilus
• Facultative homofermentative lactobacillus-hexoses ferment lactic acid orglucoselimitation acetic acid, ethanol,formic acid• Grow at 15°C and show variable growth at45°C• Lactobacilluscasei,lactobacilluscurvatus,lactobacillussakeiandlactobacillusplantarum.
Benefit• Resist weak acids of ph 3.5 to 4.5 resulting toa yield of 90% lactic acid.• Starter culture.• Preservative for the production of cheese andyoghurt.
Lactobacillus acidophilus• Absorb B vitamins, vitamin K, fatty acids andcalcium.• Reduce lactose intolerance.• Increases the production of anti-allergycytokines, chemical messengers released bycells of the immune system.
Lactobacillus bulgaricus• Helps reduce symptoms of lactose intolerance.• Provides the stomach and intestine with theenzyme bacterial lactase that helps digest thelactose in milk.
Enterococci• Ubiquitous gram-positive, catalase-negative• Ability to survive extreme ph, temperatures,and salinity.• Psychrotrophic nature, heat resistance andadaptability to different substrates and growthconditions
• Enterococci also occur in natural milk (orwhey) starter cultures• Made by incubating it at 42–44 °C for 12–15 h• Used for manufacturing of cheese ( artisan)
• Strains E. Faecalis and E. Faecium producingenterocins• Activity against listeria monocytogenes,staphylococcus aureus, clostridium spp.,Including clostridium botulinum andclostridium perfringens, and vibrio cholerae
Bifidobacterium bifidum• Optimum growth ph 6- 7.0• Optimum growth temperature 37- 41°C,maximum 43- 45°C, minimum 25- 28°C• Produce acetic acid, lactic acid- 3:2• Helping in digestion• Strengthens the immune system• To eliminate harmful bacteria
Lactobacillus rhamnosus• Lactose-intolerant people to reduce theinflammatory response that occurs when theyconsume milk.• Helps the immune system by stimulating theproduction of antibodies and combatingpathogenic bacteria.
Lactose and galactose utilization by different lactic acid bacteria
Lactobacillus curd• Milk is heated to a temperature of 30-40 °C• Complex and heterogenous flora - L. Lactis , L.Lactis subsp cremoris , S. Thermophilus , L.Debrueckii subsp bulgaricus , L. Plantarum andlactose fermenting yeast.• Anaerobic respiration
Special attribute of Curd• Dysentery and other gastrointestinaldisorders.• Improve appetite , vitality and increasedigestibility.
yogurt• Mixed starter culture – S. Thermophilus and lactobacillus delbrueckii orlactobacillus bulgaricus.• Ratio 1:1• Fermentation :- lactose content of milk to yield lactic acid, CO2, aceticacid, diacetyl, acetaldehyde• Ph reduces :- around 6.5 to 4.5 due to the production of organic acids• Initially streptococcus thermophilus ferments the lactose• Lactobacillus bulgaricus, which is more acid tolerant, continues to fermentthe remaining lactose.LactaseLactose glucose + galactoseHydrolyzes
Benefit• Easier digestibility,• The ingested organismsenhance bioavailabilityof nutrients• Ensure gastrointestinal balance,• Promoting colon health• Accelerates the healing of gastrointestinaltract disorder• Reduction in cholesterol level.
Different cheese using differentstrains• Swiss cheese formation involves a latepropionic acid fermentation with ripeningdone by Propioni bacteria shermanii.• Blue cheeses are produced by Penicillium spp.• Roquefort cheese is produced by using P.roqueforti• Camembert and Brie by using P. camembertiand P. candidum.
Pathway for Citrate – positive strain of lactococcus and leuconostoc species
Gas production:• Fermentation occurs at faster rate, then rawmilk present a foamy layer on the uppersurface• Air bubbles becomes entrapped and gasbecomes saturated throughout the body ofthe milk• Colliforms, clostridium and bacillus species.
Proteolysis• Acid Proteolysis:Milk whey separated, Milk taste will be soured, Micrococcus sp.• Alkaline Proteolysis:Milk whey separated and pH >6.9 (towards neutral and alkaline). Milk taste will be bitter• Sweet curdling:Bacillus cerus – it release enzymes “protease” which targets the casein. Bacteria use lactoseand convert into acids and aldehyde components. Milk is sweet in taste• Slow Proteolysis:Release of endogenous proteases in the milk, cause slow proteolysis of the milk.• Proteolysis due to Anaerobic Bacteria:Bacillus and clostridial species are heat resistant.result into specific kind of smell names as butyrine smell
• Roppiness or sliminess:Milk viscosity is increased, rope like structure is formedAlcaligenes viscolactis• Change in the color of milk:Blue color ------------------------ pseudomonas syncianiRed color ------------------------- brubibacteriumerythrogenes,sarcinia marcenseYellow color --------------------- pseudomonas synxanthaBrown color --------------------- pseudomonas putrificiansGreen color ---------------------- pseudomonas aurogenosa
Changes in Milk Fat• Oxidation of unsaturated fatty acids:Milk fat oxidation aldehydes + ketones + acids• Oxidation imparts tallowy odors• Hydrolysis of overall milk fat:lipaseFatty acids glycerols + free fatty acidsHydrolysis• Gives rise to putrefied odor (rotten egg like smell)• Combined hydrolysis and oxidationeg:- Proteus, Alcaligenes, Micrococcus
Change in the Flavor of MilkSour Flavour:It is due to acidic changes in the milks:Clean: Low contents of acids, Streptococcus lactisAromatic: streptococci and aroma- forming Leuconostoc sp. ,moderated type of acidic components.Sharp: coliform bacteria, clostridium species, volatile fatty acids,high acidic contents• Bitter Flavour:It is due to alkaline changes in the milk.• Potato-like Flavour:Pseudomonas mucidolense• Fishiness:Acromian hydrophila, It is due to formation of tri-methyl amine
Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE)
Prevention method• Pasteurization• Ultra-High Temperature- 138 °C to 150 °C for 4 to 15 seconds• Steam under pressure- 115 to 118°C for 14 to 18 min, caned milk• Radiation- gamma, UV rays• Preservatives- sorbic acid, propionic acid, sugar, salt,hydrogen peroxide• Modified atmosphere packaging• Refrigeration - 10 °C or low temperature• Freezing- -17 to -18 °C
HACCPPrinciple 1: Conduct a hazard analysis.Principle 2: Determine the Critical Control Points(CCPs).Principle 3: Establish critical limit(s).Principle 4: Establish a system to monitor controlof the CCP.
Principle 5: Establish the corrective action to betaken when monitoring indicates that aparticular CCP is not under control.Principle 6: Establish procedures for verificationto confirm that the HACCP system is workingeffectively.Principle 7: Establish documentation concerningall procedures and records appropriate tothese principles and their application.
New bacteria discovered in raw milk• Chryseobacterium oranimense, which cangrow at cold temperatures(7°C) and secretesenzymes that have the potential to spoil milk.“• C. haifense and C. bovis
laws• Milk and milk product order, 1992• Milk and milk product amendment regulation,2009
Precautions• The animal should be healthy and free from diseases.• A healthy person should milk the animals. He should avoid sneezing, coughing,etc., and must wear clean clothes.• Milking vessels should be cleaned properly with chemicals or detergents that arenot injurious to health.• Arrangements must be made in advance to immediately cool the milk to 4 ºCwithin an hour of milking.• The ingredients and cleaning agents used must be of the desired quality.• There should be a provision for checking the quality, sampling and testing of milk.
Reference• Beresford T P, Fitzsimons N A, Brennan N L and Cogan T M (2001) Recent advancesin cheese microbiology. International Dairy Journal 11 259–74.• Ledenbach L H and Marshall R T 2009 Microbiological Spoilage of Dairy Products.Compendium of the Microbiological Spoilage of Foods and Beverages 1-4419• Nwamaka N T and Chike A E (2010) Bacteria population of some commerciallyprepared Yoghurt sold in Enugu State, Eastern Nigeria. African Journal ofMicrobiology Research 4 (10) 984-88.• Papademas P and Bintsis T (2010) Food safety management systems (FSMS) in thedairy industry: A review International Journal of Dairy Technology 63 14-07.• Varga L (2007) Microbiological quality of commercial dairy products.Communicating Current Research and Educational Topics and Trends in AppliedMicrobiology