Food Microbiology Milk Fermentation

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Food MicrobiologyMilk Fermentation

• 2009. 5. 26

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Food Microbiology

• Fermented Foods
• Ethanol Fermentation
• Alcoholic beverages
• Breads
• Lactic Acid Fermentation
• Kimchi
• Yoghurt and other fermented milks
• Pickles
• Others
• Cheese
• Butter

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Diversity of Milk Composition

• Composition can vary according to
• Species
• Strain or breed of animal
• Stage of Lactation
• Stage of milk removal
• Milk fat is the most variable component.
• Lactose is the least variable component.

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Composition of Milk

• Milk fat
• the most variable component of milk.
• It ranges from a little over 1 to greater than
  50 .
• Aquatic mammals typically have high milk fat
  percentage.
• Lactose
• ranges from only a trace to less than 7.
• Some species have very little lactose in milk,
  such as the bear and kangaroo.
• Milk protein
• Ranges from 1 to about 14.
• Generally milk protein percentage is positively
  correlated with milk fat percentage.

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Lactose Intolerance

• Lactase
• Hydrolyzes lactose into galactose and glucose
• associated with the intestinal brush border
  membrane.
• disappears after weaning.
• Lactose malabsorption (lactose nondigestion)
• genetic defects
• normally associated with advancing age
• Lactose intolerance
• Diarrhea, abdominal pain, and gaseous
  accumulation in the intestine
• Osmotic effect of the undigested lactose results
  in fluid being drawn into the intestinal lumen.

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Microorganisms in Milk

• Milk is sterile at secretion in the udder
• Contaminated by bacteria even before it leaves
  the udder.
• Except in the case of mastitis, the bacteria at
  this point are harmless and few in number.
• Further infection of the milk by microorganisms
  can take place during milking, handling, storage,
  and other pre-processing activities.

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Mastitis
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Lactic acid bacteria

• Ferment lactose to lactic acid.
• Normally present in the milk and are also used as
  starter cultures in the production of cultured
  dairy products such as yogurt.
• Lactococci
• L. delbrueckii subsp. lactis (Streptococcus
  lactis )
• Lactococcus lactis subsp. cremoris (Streptococcus
  cremoris )
• Lactobacilli
• Lactobacillus casei
• L.delbrueckii subsp. lactis (L. lactis )
• L. delbrueckii subsp. bulgaricus (Lactobacillus
  bulgaricus )
• Leuconostoc

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Coliforms

• Indicator organisms
• Closely associated with the presence of pathogens
  but not necessarily pathogenic themselves.
• Can cause rapid spoilage of milk because they are
  able to ferment lactose with the production of
  acid and gas, and are able to degrade milk
  proteins.
• Killed by HTST treatment, therefore, their
  presence after treatment is indicative of
  contamination.
• Escherichia coli is an example belonging to this
  group.

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Pathogenic Microorganisms in Milk

• Milkborne diseases
• tuberculosis, brucellosis, listeriosis, and
  typhoid fever.
• Bacillus cereus
• Listeria monocytogenes
• Yersinia enterocolitica
• Salmonella spp.
• Escherichia coli O157H7
• Campylobacter jejuni

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Pasteurization

• 74C for 15 seconds (low pasteurization)
• kills most organisms and inactivates some enzymes
• does not alter the milk.
• 90C for 15 seconds (high pasteurization)
• kills all vegetative microorganisms
• inactivates most enzymes
• renders some whey proteins insoluble.
• 118C for 20 seconds
• sterilizes the milk
• inactivates all enzymes
• causes changes to the milk such as the browning
  reaction
• Ultra-high temperature (UHT) pasteurization
• 145C for a few seconds
• sterilizes milk while minimizing the chemical
  changes.
• UHT milk which is properly stored has a long
  shelf life, even at room temperature.

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Starter Cultures

• Used in the production of cultured dairy products
  such as yogurt and cheese.
• Can provide particular characteristics in a more
  controlled and predictable fermentation.
• The natural microflora of the milk is either
  inefficient, uncontrollable, and unpredictable
• Functions
• The primary function production of lactic acid
  from lactose
• Other functions flavour, aroma, and alcohol
  production, and inhibition of undesirable
  organisms

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Starter Cultures

• simple or defined
• single strain, or more than one in which the
  number is known
• mixed or compound
• more than one strain each providing its own
  specific characteristics

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Starter cultures
                                                
                                                  
    

• Mesophilic
• Lactococcus lactis subsp. cremoris
• L. delbrueckii subsp. lactis
• L. lactis subsp. lactis biovar diacetylactis
• Leuconostoc mesenteroides subsp. cremoris
• Thermophilic
• Streptococcus salivarius subsp. thermophilus
  (S.thermophilus)
• Lactobacillus delbrueckii subsp. bulgaricus
• L. delbrueckii subsp. lactis
• L. casei
• L. helveticus
• L. plantarum

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