Starter Cultures

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Starter Cultures
Starter culture A concentrated preparation of
live cells that is added to a raw material to
initiate fermentation rapidly
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Starter Cultures
References Kosikowski, F.V. and V.V. Mistry 1997
. Cheese and fermented milk foods. Frank
Kosikowski, Brooktondale, N. Y. Chapter 3,
Cultures and starters, pp. 26 38. Marth, E.H.
and J.L. Steele. (eds.). 1998. Applied Dairy
Microbiology. Marcel Dekker, Inc., New York,
NY. Chapter 6, Starter cultures and their use.
pp. 131-172
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Criteria for strain selection
Product Flavor and texture Acid production
rate Reliability ex. bacteriophage resistance
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Classification of Dairy Starter Cultures
Based on .. Growth temperature Number of
strains in culture Culture preservation
method Inoculation method
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Classification based on growth temperature Thermop
hilic vs. mesophilic
Thermophilic dairy starter cultures
Optimum growth temperature 92110 ?F (3343
?C) S. thermophilus Lb. delbrueckii subsp.
bulgaricus Lb. helveticus

Yogurt, Italian cheeses, Swiss cheese, others
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Classification based on growth temperature Thermop
hilic vs. mesophilic
Mesophilic dairy starter cultures
Optimum growth temperature 7090 ?F (2132
?C) Lc. lactis subsp. lactis Lc. lactis subsp.
cremoris
Cheddar, Camembert, others
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Classification based on growth temperature Thermop
hilic vs. mesophilic
Mesophilic aromatic dairy starter cultures
Optimum growth temperature 7090 ?F (2132
?C) Lc. lactis subsp. lactis biovar.
diacetylactis Leuc. mesenteroides subsp.
cremoris Leuc. lactis
Buttermilk, sour cream, cottage cheese, other
cheeses (depending on flavor desired)
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Classification based on of strains
Single strain culture One well-characterized
strain

Multiple strain culture A defined mixture of
several well-characterized strains
Mixed strain culture An undefined mixture of
unknown or poorly characterized strains
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Classification based on preservation method
The starter culture manufacturer propagates
culture and preserves it in one of several forms.
Liquid Freeze-dried Concentrated,
freeze-dried Concentrated, frozen

Form purchased by food manufacture depends on
inoculation method.later
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Large-scale production and preservation of
L.A.B. starter cultures

Liquid starter culture (108 cfu/ml)
Standarization to a specific cfu/ml
Concentration (centrifugation or ultrafiltration)
Freeze-dry
Quick-freeze
Freeze-dry
Frozen, concentrated starter culture (1010 -
1011 cfu/g)
Freeze-dried, concentrated starter culture
(1011 - 1012 cfu/g)
Freeze-dried starter culture (108 - 109 cfu/g)
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Frozen L.A.B. starter cultures
Pellet form
Solid block
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Classification based on inoculation method
Bulk starter requires preparation at the dairy
plant

Direct Vat Set does not require preparation at
the dairy plant
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Direct Vat Set Cultures

• Concentrated freeze-dried or concentrated frozen
• Procedure
• Select culture
• Purchase from culture manufacturer
• Store in freezer
• Use to inoculate fermentation vessel directly

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Cultures for bulk starter preparation

• Freeze-dried, frozen or liquid
• Procedure
• Select culture
• Purchase from culture manufacturer or get from
  company stock
• Store in freezer or refrigerator
• Propagate mother culture, intermediate cultures
  and bulk starter culture regularly
• Use bulk starter to inoculate fermentation vessel

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Bulk starter preparation Mother Culture

• Small volume culture propagated daily -
  aseptically
• Original inoculum from culture manufacturer or
  companys own stock culture
• Used to inoculate the first intermediate culture.

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Starter culture propagation in the dairy
500 1,000 L
10,000 L
100 L
10 L
1 L
500 1,000 L
500 1,000 L
10,000 L
DVS
500 1,000 L
DVS
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Bulk starter growth medium
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Preparing the bulk starter medium and inoculation
Mother, intermediate and bulk starter cultures
should be propagated in a room separate from
production facility with positive air pressure
and minimal traffic.
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Bulk Starter Traditional vs. pH-controlled
Traditional (Conventional) Bulk Starter

• No pH control
• As pH decreases, cell growth slows and
  eventually stops
• Bulk starter tank is cooled when pH reaches 4.8
  5.0 (mesophilic) or 4.2 4.6 (thermophilic)

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Bulk Starter Traditional vs. pH-controlled
pH-Controlled Bulk Starter
2-3X more active than traditional

• External pH control
• pH is controlled by an automatic pH
  meter/controller
• Keeps pH at a preset level
• 5.8-6.0 (mesophilic)
• 5.4-5.6 (S. thermophilus)
• 4.7 (Lb. helveticus, Lb. delbrueckii)

thermophilic

• Internal pH control
• A buffer is added that is insoluble at neutral
  pH
• As the pH of the medium decreases, the
  solubility of the buffer increases and slows
  further pH reduction
• Mesophilic cultures only

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Bulk starter activity
The activity of the bulk starter is evaluated to
determine how much to add to the fermentation
Tests are usually based on acid production rate.
Specific test requirements depend on product
being made.
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Commercial Culture Examples
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Examples
http//www.dsm.com/dfs/dairy/products/cultures/7E
en/index.pl
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Advantages and disadvantages
Direct Vat Set System
Bulk Starter System
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Starter Cultures
Thermophilic or mesophilic Single, multiple or
mixed strain Liquid, freeze-dried, concentrated,
freeze-dried, or concentrated frozen Direct-vat-se
t or bulk starter (traditional or pH-controlled)