Internal pH control starter media: use in culture preservation and for multiple strain growth Public Deposited

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  • Several bulk starter media, consisting of two experimental blends and four commercial preparations, were examined for each medium's ability to grow, preserve, and/or recover lactic streptococcal starter cultures. Nonfat milk was used as a control. Results showed that cultures which had the greatest survival rate in frozen storage had been grown in a medium capable of providing relatively high cell numbers, acid production, and pH prior to storage. However, those media supplying good initial culture growth did not necessarily possess good preservative properties as well. Only three of the seven media proved capable of satisfying most of the above parameters. Of those three media, the most effective medium composition contained twice as much whey as any of the other media and was the only one that utilized NH₄OH as a buffering agent. Cultures demonstrating the greatest survival in liquid storage @ 4° C were those grown in a medium capable of furnishing high pH during storage. The existence of strain dominance in a multiple-strain lactic acid starter culture was examined using the streptomycin-resistant mutants of two Streptococcus lactis and four Streptococcus cremoris strains. Six different combinations of the six-strain mix (each containing a different mutant) and a control (containing all six parent strains) were grown over a 10 hr incubation period in two different types of bulk starter media. Samples were taken every two hours and then plated onto M17 with streptomycin (enumerated mutants only) and without streptomycin (enumerated total cell count). Evidence of dominance was seen in one medium but not the other. Where dominance was present, only one of the six strains studied was found to be suppressed when grown in association with the other strains.
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