Starter Cultures

1. Starter Cultures Starter culture: A concentrated preparation of live cells that is added to a raw material to initiate fermentation rapidly

2. 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

3. Criteria for strain selection Product Flavor and texture Acid production rate Reliability – ex. bacteriophage resistance

4. Classification of Dairy Starter Cultures Based on ….. Growth temperature Number of strains in culture Culture preservation method Inoculation method

5. Classification based on growth temperature Thermophilic vs. mesophilic Thermophilic dairy starter cultures: Optimum growth temperature: 92–110 F (33–43 C) S. thermophilus Lb. delbrueckii subsp. bulgaricus Lb. helveticus Yogurt, Italian cheeses, Swiss cheese, others

6. Classification based on growth temperature Thermophilic vs. mesophilic Mesophilic dairy starter cultures: Optimum growth temperature: 70–90 F (21–32 C) Lc. lactis subsp. lactis Lc. lactis subsp. cremoris Cheddar, Camembert, others

7. Classification based on growth temperature Thermophilic vs. mesophilic Citrate diacetyl, CO2, acetate Mesophilic aromatic dairy starter cultures: Optimum growth temperature: 70–90 F (21–32 C) Lc. lactis subsp. lactis biovar. diacetylactis Leuc. mesenteroides subsp. cremoris Leuc. lactis Buttermilk, sour cream, cottage cheese, other cheeses (depending on flavor desired)

8. 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

9. 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

10. Large-scale production and preservation of L.A.B. starter cultures Standarization to a specific cfu/ml Liquid starter culture (~108 cfu/ml) Concentration (centrifugation or ultrafiltration) Freeze-dry Quick-freeze Freeze-dry Freeze-dried, concentrated starter culture (~1011 - 1012 cfu/g) Frozen, concentrated starter culture (~1010 - 1011 cfu/g) Freeze-dried starter culture (~108 - 109 cfu/g)

11. Frozen L.A.B. starter cultures Pellet form Solid block

12. Classification based on inoculation method Bulk starter: requires preparation at the dairy plant Direct Vat Set: does not require preparation at the dairy plant

13. 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

14. 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

15. Day 1 Day 2 Day 3 Day 4 Day 5….. 3-4 weeks then start over Freeze-dried Culture ~1L …… First intermediate culture ~10 L Bulk starter preparation: Mother Culture • Small volume culture propagated daily - aseptically • Original inoculum from culture manufacturer or company’s own stock culture • Used to inoculate the first intermediate culture.

16. Starter culture propagation in the dairy 500 – 1,000 L 10,000 L 1 L 10 L 100 L 500 – 1,000 L 500 – 1,000 L 10,000 L DVS 500 – 1,000 L DVS

17. Bulk starter growth medium

18. 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.

19. 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)

20. 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

21. 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.

22. Commercial Culture Examples

23. Examples: http://www.dsm.com/dfs/dairy/products/cultures/%7Een/index.pl

24. Advantages and disadvantages Direct Vat Set System Bulk Starter System

25. Starter Cultures Thermophilic or mesophilic Single, multiple or mixed strain Liquid, freeze-dried, concentrated, freeze-dried, or concentrated frozen Direct-vat-set or bulk starter (traditional or pH-controlled)