Starter cultures antibiotics

Commercially available yeast extracts are made from brewers yeast, from bakers yeast, from alcohol-grown yeast (C. utilis) and from whey grown yeast (K fragilis). Extracts are used ia fermentation media for productioa of antibiotics, ia cheese starter cultures, and ia the productioa of viaegar. They are also exteasively used ia the food iadustry as condiments to provide savory flavors for soups, gravies and bouillon cubes, and as flavor intensifiers ia cheese products. 

Many of the organisms employed are extremely sensitive to antibiotic residuals in the milk. As shown in Table III, as little as 0.05 to 1.0 lU/ml of penicillin and 0.05 to 10.0 microgram/ml of aureomycin inhibited the growth of 19 cheese starter cultures (18). Lower levels are capable of affecting the flavor and texture properties of the product (14, 19) as well as promoting the growth of undesirable antibiotic resistant coliforms (14, 20). 

Apart from public health impacts, residual antimicrobials in animal products can bring about technoeconomic losses in the food processing industry. It has long been known that the presence of some antimicrobial compounds in milk can dramatically affect the production of fermented dairy products such as yogurt, cheese, buttermilk and sour cream (72, 73). As shown in Table 10.2, even minute concentrations of antibiotics in milk can cause inhibition of the growth of commonly used dairy starter cultures (74). 

Table 10.2 Minimum Inhibitory Concentrations of Antibiotics for Common Dairy Starter Cultures and B cillus ste rothermophilus...

Production of antibiotic-like substances in cultured dairy products has been associated with homo- and heterolactic streptococci, some of the lactobacilli, and Brevibacterium linens. Production may be unwanted and fortuitous, as in commercial starter cultures, or it may be desired and encouraged. 

Relationship between Starter Cultures and Streptococcal Antibiotics. When antibiotic-producing and non-antibiotic-producing strains of S. lactis and S. cremoris from commercial starter cultures were mixed in equal proportions, the antibiotic-producing strains soon predominated (Hoyle and Nichols 1948). Domination occurred after 24 to 48 hr. (Collins 1961). Emergence of a predominant strain may be accompanied by a loss of starter activity and renders the starter more susceptible to complete inactivation by bacteriophage. 

As shown in Table I, antibiotics may be added to foods directly for technological reasons, indirectly through treated animals and feeds or naturally through lactic starter culture biosynthesis. Recent increases in antibiotic use for food production as well as for disease control poses certain risks. 

These include the emergence of potentially dangerous antibiotic resistant microorganisms, the possibility of toxic or allergic reactions in sensitive individuals and/or technological problems of starter culture inhibition associated with antibiotic residues in food products. This paper summarizes the risks, as well as some of the benefits, of antibiotics in foods and feeds. 

Inhibition of Starter Cultures. The primary cause of antibiotic residues in milk and milk products is the failure of producers to withhold milk from the market for a sufficient time period following veterinary therapy for mastitis or other diseases in dairy cattle. Consumption of antibiotic-supplemented feed may also lead to residues in the milk. These antibiotics are quite stable and remain in the milk even after manufacturing pro-cessses including pasteurization, drying or freezing. Marth and Ellickson (22), Marth (23) and Mol (17) have reviewed extensively problems in the dairy industry associated with antibiotic residues in the fluid milk supply. 

The production of natural antibiotics by lactic starter cultures has been well documented (40) Some of these compounds have been isolated and identified as noted in Table IX. 

Shortly after their development in the 1940s, antibiotics were used in veterinary medicine, first to prevent or treat mastitis in cows and later for the treatment of other diseases. Initial concern about antibiotic residues in milk was not a public health issue but came from dairy processors who noticed inhibition of starter cultures used in the production of cheese and yogurt, thus generating a need for screening tests to examine milk for antibiotic residues. " Since inhibition of starter cultures by penicillin in milk was the main problem, the earliest microbial inhibition assays were based on growth inhibition of lactic acid bacteria. Spores of Bacillus species were also utilized spores are easier to handle and far more stable than the vegetative cells. 

Naturally. Nisin, for example, is a naturally occurring antibiotic, which is sometimes found in milk. Thus, it is noteworthy that gassy fermentations in raw cheese made with milk containing clostridia are controlled by the use of nisin-producing starter cultures. 

Galesloot, T. E. and Pette, J. W. 1956. The estimation of the nisin content of antibiotic starters and cultures and of cheese made by means of antibiotic starters. Ned. Melk. Zuiveltijdschr. 10, 137-142. (Dutch)... 

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