Lactic Bulk Culture System Utilizing a Whey-Based Bacteriophage Inhibitory Medium and pH Control. I. Applicability to American Style Cheese

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Abstract
Fresh Cheddar cheese whey was fortified with 1% (NH4)H2PO4, 1% Na2HPO4, and .32% yeast extract, then heated 45 min at 89.degree. C. The phosphate-treated whey medium was compared with unmodified whey, reconstituted pretested nonfat dry milk and a commercial bacteriophage inhibitory medium. The phosphate whey medium inhibited bacteriophage and stimulated culture [Streptococcus lactis, S. cremoris and Leuconostoc sp.] growth. To improve culture activity the medium was reformulated, the phosphate content reduced and the bulk culture system provided with pH control. When coupled with anhydrous ammonia injection to maintain pH 6.0, the medium produced a lactic streptococci culture with activity superior to that of conventional bacteriophage inhibitory or milk media. Amounts required for inoculation of Monterey cheese milk were 20-33% of the requirements for whole milk culture. No differences in cheese yields were detected. Direct inoculation of bulk substrate with freeze-dried seed cultures, bypassing intermediates, was successful. An ammonia injection recorder tracing provided cheese makers with a continuous history of culture activity and guidelines for required inocula adjustments. Culture activity remained nearly constant for a longer time than in conventional cultures. Differential pH electrode systems with built-in transmitters were remarkably stable even though subjected to normal heating and cooling of the substrate.