Milk microbiologystandards for milk and milk product

Shivnam RanaMsc. Microbiology (PAU)

L -2011- BS -251 – M

Introduction

• 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 ofmicroorganisms

Intrinsic • Nutrient availability • pH • Water availability Extrinsic • 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

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 or

glucose limitation acetic acid, ethanol,

formic acid• Grow at 15°C and show variable growth at

45°C• Lactobacillus casei, lactobacillus curvatus,

lactobacillus sakei and lactobacillus plantarum.

• Obligate heterofermentative lactobacillus- Hexoses ferment lactic acid+ acetic acid+

ethanol+ CO2 pentoses ferment lactic acid + acetic acid • Lactobacillus fermentum, lactobacillus brevis and

lactobacillus keferi.

Benefit

• 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

yoghurt.

Lactobacillus acidophilus

• Absorb B vitamins, vitamin K, fatty acids and calcium.

• 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.

Enterococci

• Ubiquitous gram-positive, catalase-negative• Ability to survive extreme ph, temperatures,

and salinity.• Psychrotrophic nature, heat resistance and

adaptability to different substrates and growth conditions

• 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 enterocins

• 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 disorders.

• Improve appetite , vitality and increase digestibility.

yogurt• 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.

Lactase Lactose glucose + galactose Hydrolyzes

Benefit • 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.

Cheese

Different cheese using different

strains• 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.

roqueforti • Camembert and Brie by using P. camemberti

and P. candidum.

Pathway for Citrate – positive strain of lactococcus and leuconostoc species

Changes in milk by microorganism

Gas production:

• Fermentation occurs at faster rate, then raw milk present a foamy layer on the upper surface

• Air bubbles becomes entrapped and gas becomes saturated throughout the body of the 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 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 syncianiRed color ------------------------- brubibacterium erythrogenes,

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: lipase

Fatty acids glycerols + free fatty acids Hydrolysis

• 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

Detection of microorganism

Polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE)

Fluorescent in situ hybridization(FISH)

ELISA

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 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 effectively.

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

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 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.

Reference • Beresford T P, Fitzsimons N A, Brennan N L and Cogan T M (2001) Recent advances in

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 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.

• Varga L (2007) Microbiological quality of commercial dairy products. Communicating Current Research and Educational Topics and Trends in Applied Microbiology