Milk microbiology- standards of milk and milk product

Milk microbiology
standards for milk and milk product
Shivnam Rana
Msc. Microbiology (PAU)
L -2011- BS -251 – M
• Complete food – Carbohydrates(Lactase),
Protein(Casein), Fats, Minerals
• due to: Complex biochemical composition
High water activity
• Excellent culture medium for the growth and
multiplication of microorganisms
Factors that influence survival and growth of
• Nutrient availability
• pH
• Water availability
• Temperature
• Atmosphere
Origin of microorganism in milk
• Commensal micro flora- teat skin, epithelial lining of the teat
canal, duct that conveys the milk from the mammary gland to
the teat orifice.
Staphylococcus, Streptococcus,Bacillus, Micrococcus,
Corynebacterium, coliforms
• Environmental contamination- soil, water equipment, dairy
farm area are reservoir for many food borne pathogens
Salmonella species,
L. monocytogenes
• Diseased animal
Mastitis- Staphylococcus (S.agalactiae) and
Streptococcus species
• Obligate homofermentative lactobacillus –
lactic acid
• Growth at 45°C but not at 15°C
• Lactobacillus delbrueckii, lactobacillus helveticus,
lactobacillus salivarius and L. Acidophilus
• Facultative homofermentative lactobacillushexoses
lactic acid or
glucose limitation acetic acid, ethanol,
formic acid
• Grow at 15°C and show variable growth at
• Lactobacillus casei, lactobacillus curvatus,
lactobacillus sakei and lactobacillus plantarum.
• Obligate heterofermentative lactobacillusHexoses ferment
lactic acid+ acetic acid+
ethanol+ CO2
pentoses ferment lactic acid + acetic acid
• Lactobacillus fermentum, lactobacillus brevis and
lactobacillus keferi.
• Resist weak acids of ph 3.5 to 4.5 resulting to
a yield of 90% lactic acid.
• Starter culture.
• Preservative for the production of cheese and
Lactobacillus acidophilus
• Absorb B vitamins, vitamin K, fatty acids and
• Reduce lactose intolerance.
• Increases the production of anti-allergy
cytokines, chemical messengers released by
cells of the immune system.
Lactobacillus bulgaricus
• Helps reduce symptoms of lactose intolerance.
• Provides the stomach and intestine with the
enzyme bacterial lactase that helps digest the
lactose in milk.
• Ubiquitous gram-positive, catalase-negative
• Ability to survive extreme ph, temperatures,
and salinity.
• Psychrotrophic nature, heat resistance and
adaptability to different substrates and growth
• Enterococci also occur in natural milk (or
whey) 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 producing
• Activity against listeria monocytogenes,
staphylococcus aureus, clostridium spp.,
Including clostridium botulinum and
clostridium 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 the
inflammatory response that occurs when they
consume milk.
• Helps the immune system by stimulating the
production of antibodies and combating
pathogenic 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 and
lactose fermenting yeast.
• Anaerobic respiration
Special attribute of Curd
• Dysentery and other gastrointestinal
• Improve appetite , vitality and increase
• Mixed starter culture – S. Thermophilus and lactobacillus delbrueckii or
lactobacillus bulgaricus.
• Ratio 1:1
• Fermentation :- lactose content of milk to yield lactic acid, CO2, acetic
acid, 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 ferment
the remaining lactose.
glucose + galactose
• Easier digestibility,
• The ingested organisms
enhance bioavailability
of nutrients
• Ensure gastrointestinal balance,
• Promoting colon health
• Accelerates the healing of gastrointestinal
tract disorder
• Reduction in cholesterol level.
Different cheese using different
• Swiss cheese formation involves a late
propionic acid fermentation with ripening
done by Propioni bacteria shermanii.
• Blue cheeses are produced by Penicillium spp.
• Roquefort cheese is produced by using P.
• Camembert and Brie by using P. camemberti
and P. candidum.
Pathway for Citrate – positive strain of lactococcus and leuconostoc species
Changes in milk by
Gas production:
• Fermentation occurs at faster rate, then raw
milk present a foamy layer on the upper
• Air bubbles becomes entrapped and gas
becomes saturated throughout the body of
the milk
• Colliforms, clostridium and bacillus species.
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 lactose
and 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 formed
Alcaligenes viscolactis
• Change in the color of milk:
Blue color ------------------------ pseudomonas synciani
Red color ------------------------- brubibacterium
sarcinia marcense
Yellow color --------------------- pseudomonas synxantha
Brown color --------------------- pseudomonas putrificians
Green color ---------------------- pseudomonas aurogenosa
Changes in Milk Fat
Oxidation of unsaturated fatty acids:
Milk fat
aldehydes + ketones + acids
Oxidation imparts tallowy odors
Hydrolysis of overall milk fat:
Fatty acids
glycerols + free fatty acids
Gives rise to putrefied odor (rotten egg like smell)
Combined hydrolysis and oxidation
eg:- Proteus, Alcaligenes, Micrococcus
Change in the Flavor of Milk
Sour Flavour:
It is due to acidic changes in the milks:
Clean: Low contents of acids, Streptococcus lactis
Aromatic: 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)
Fluorescent in situ hybridization(FISH)
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
Principle 1: Conduct a hazard analysis.
Principle 2: Determine the Critical Control Points
Principle 3: Establish critical limit(s).
Principle 4: Establish a system to monitor control
of the CCP.
Principle 5: Establish the corrective action to be
taken when monitoring indicates that a
particular CCP is not under control.
Principle 6: Establish procedures for verification
to confirm that the HACCP system is working
Principle 7: Establish documentation concerning
all procedures and records appropriate to
these principles and their application.
New bacteria discovered in raw milk
• Chryseobacterium oranimense, which can
grow at cold temperatures(7°C) and secretes
enzymes that have the potential to spoil milk.“
• C. haifense and C. bovis
• Milk and milk product order, 1992
• Milk and milk product amendment regulation,
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 are
not injurious to health.
Arrangements must be made in advance to immediately cool the milk to 4 ºC
within 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.
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Nwamaka N T and Chike A E (2010) Bacteria population of some commercially
prepared Yoghurt sold in Enugu State, Eastern Nigeria. African Journal of
Microbiology Research 4 (10) 984-88.
Papademas P and Bintsis T (2010) Food safety management systems (FSMS) in the
dairy industry: A review International Journal of Dairy Technology 63 14-07.
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Communicating Current Research and Educational Topics and Trends in Applied

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