Starter Cultures (II)

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Starter Cultures (II)
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Strain Identification

• Using biochemical scheme to classify dairy
  streptococci
• 16S rRNA gene sequence analysis
• Essential for proper labeling
• Important for proper cultivation

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Starter Culture Math

• Ensures consistent and predictable fermentation
• Use enough cells to inoculate in large scale
  fermentation
• Initiate fermentation promptly and rapidly
• Short lag phase
• Scale up cultures
• A plant receiving 1 million L milk/day needs
  10,000 L of culture
• Make intermediate and mother (fully grown bulk
  for inoculation) cultures

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Culture Types

• Bulk cultures
• Including intermediate and final fully-grown bulk
  culture, can be used to inoculate the vat
• Direct-to-vat set cultures
• Can or packaged cultures from culture company,
  ready to be used as inocula
• Eliminating bulk cultures
• Minimize bacterial phage attack incidence
• Labor, equipment and facility savings

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Culture Composition

• Mixed or undefined cultures
• Defined cultures
• Single strain or blend of tow or more strains
• Metabolic complementation
• PHAGE RESISTANCE
• Culture compatibility
• No inhibition to other strains (such as
  bacteriocin production, etc)

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Manufacture of Starter Cultures

• Fig. 3-1
• To achieve high cell density, maximize biomass
  production and cell viability
• Neutralize pH
• Remove inhibitory metabolic end-products

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Culture Usage

• Bulk Culture
• Media buffer capacity
• Optimal growth
• Incubation conditions
• Direct-to-vat
• Fig. 3-2

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Bacteriophages and Their Control

• Major problem in cheese manufacture
• Mesophilic L. lactis
• Also becomes an issue in yogurt fermentation
• Thermophilic cultures such as S. thermophilus and
  Lb. helveticus

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Bacteriophage life cycle
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Major problem in dairy industry

• Fermentation conducted in non-sterile
  environment, including milk and the facility
• Processing efficiency easily disrupted with
  stringent manufacturing schedules
• Limited number and diversity of dairy starter
  cultures due to increasing reliance on
  specialized strains
• Continuous use of defined culture more
  susceptible to phage attach

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Host defense system

• Interference with phage adsorption
• Restriction/modification
• Host DNA protected from phage attach by
  endonuclease/methylase enzyme modification
• Anti-restriction mechanisms in phage
• Abortive infection
• Infectious cycle inhibited even through
  adsorption, DNA entry, initial viral gene
  expression are normal
• Novel phage defense mechanisms
• Anti-sense RNA

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Practices to minimize phage infection

• Strain with resistant mechanisms
• Adsorption, R/M, abortive infection
• Combination of multiple defense systems
• Bioengineering strains with new approaches
• Phage-encoded resistance
• antisense
• Strain rotation
• Chelating agents
• Table 3.5

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The US LAB Family

• L. L. McKay
• Created the field of LAB genetics
• Addressed plasmid biology in LAB
• Loss of Lactose utilization (Lac-) and Proteolyic
  activity (Prt-)
• Phage resistance
• Metabolic pathways
• Bacteriocin production

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The LAB Family
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Cheese

• Of 75 billion Kg of milk produced in the US in
  2001, more than 1/3 used to make cheese (3.7
  billion Kg)
• About ¼ of the cheese used to make processed
  cheese
• US cheese consumption increased from 8 Kg in 1980
  to 14 Kg in 2003 per person/year
• American style (Cheddar, Colby) 41.5, Italian
  (Mozzarella and pizza cheese) 40.6
• Greece (26 Kg/person, year), France (24), Italy
  (21)