166 ◾ Fundamental Food Microbiology
a strain that is resistant to several phages can be developed. Current studies on genome analysis
of lactic acid bacteria and bacteriophages will help develop phage-resistant starter strains (see
Chapter 13).
Yeast and Mold Cultures
Specific strains of yeast cultures (e.g., Saccharomyces cerevisiae) used to leaven dough in bakery
products and to produce alcohol in beer, wine, or distilled liquor have been developed. These
yeasts are produced by culture producers as well as by processors. Culture producers grow the yeast
in suitable media, concentrate the cells, and supply it in frozen or dried form.
Molds used as starter in some products are also available from culture producers. The strains
used should not produce mycotoxins. The molds are grown on the surface of a liquid or solid
(bread) media until they sporulate. The spores are collected, dried in powder form, packaged, and
supplied to processors.
Conclusion
Isolation and identification of microorganisms associated with food fermentation have helped
the use of specific species and strains in pure culture for controlled fermentation. These starter
cultures are currently produced by commercial culture producers for use by food-processing companies directly to start fermentation of raw materials. This has also helped to reduce product loss
associated with culture failure, notably from phage attack. Development of phage-resistant starter
cultures has also helped overcome the problem. Current studies on the genome sequence of lactic
acid bacteria and their bacteriophages will be useful in the future development of bacterial strains
for their efficient use in food fermentation. The use of starter culture in food fermentation is covered in Chapter 15.
QUESTIONS
1. Define starter culture.
2. Briefly list the major advances in starter-culture technology since the 1950s.
3. How are concentrated starter cultures prepared? How does this technology differ from the
making of bulk starters?
4. Briefly describe the method used in developing a phage-insensitive medium for the manufacture of bulk starters.
5. List the problems in starter cultures that can affect their performance. What difficulties can
occur because of thawing and refreezing a starter culture?
6. Define the terms lytic phage, temperate phage, prophage, lysogeny, and lytic cycle of
bacteriophages.
7. Give an example of bacteriophages of each: Lactococcus, Streptococcus, and Lactobacillus.
8. How can starter strains resistant to bacteriophages be produced?
References
1. Huggins, A.R., Progress in dairy starter culture technology, Food Technol., 38, 41–50, 1984.
a strain that is resistant to several phages can be developed. Current studies on genome analysis
of lactic acid bacteria and bacteriophages will help develop phage-resistant starter strains (see
Chapter 13).
Yeast and Mold Cultures
Specific strains of yeast cultures (e.g., Saccharomyces cerevisiae) used to leaven dough in bakery
products and to produce alcohol in beer, wine, or distilled liquor have been developed. These
yeasts are produced by culture producers as well as by processors. Culture producers grow the yeast
in suitable media, concentrate the cells, and supply it in frozen or dried form.
Molds used as starter in some products are also available from culture producers. The strains
used should not produce mycotoxins. The molds are grown on the surface of a liquid or solid
(bread) media until they sporulate. The spores are collected, dried in powder form, packaged, and
supplied to processors.
Conclusion
Isolation and identification of microorganisms associated with food fermentation have helped
the use of specific species and strains in pure culture for controlled fermentation. These starter
cultures are currently produced by commercial culture producers for use by food-processing companies directly to start fermentation of raw materials. This has also helped to reduce product loss
associated with culture failure, notably from phage attack. Development of phage-resistant starter
cultures has also helped overcome the problem. Current studies on the genome sequence of lactic
acid bacteria and their bacteriophages will be useful in the future development of bacterial strains
for their efficient use in food fermentation. The use of starter culture in food fermentation is covered in Chapter 15.
QUESTIONS
1. Define starter culture.
2. Briefly list the major advances in starter-culture technology since the 1950s.
3. How are concentrated starter cultures prepared? How does this technology differ from the
making of bulk starters?
4. Briefly describe the method used in developing a phage-insensitive medium for the manufacture of bulk starters.
5. List the problems in starter cultures that can affect their performance. What difficulties can
occur because of thawing and refreezing a starter culture?
6. Define the terms lytic phage, temperate phage, prophage, lysogeny, and lytic cycle of
bacteriophages.
7. Give an example of bacteriophages of each: Lactococcus, Streptococcus, and Lactobacillus.
8. How can starter strains resistant to bacteriophages be produced?
References
1. Huggins, A.R., Progress in dairy starter culture technology, Food Technol., 38, 41–50, 1984.