Proteinase Negative Variants of Streptococcus cremoris for Cheese Starters

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Abstract
Proteinase negative variants of S. cremoris HP and 104 propagated in a fortified whey-based medium with pH control produced 93% of the cell mass of their proteinase positive counterparts. Buffered milk substrates fortified with yeast extract were poor media and varied markedly in their ability to support growth of proteinase negative cells. High concentrations of proteinase negative variants produced sufficient acid in milk at 38.degree. C in 5 h to qualify them for use in Cheddar cheese manufacture. Generation times of proteinase negative cells were 3.5 times as long in cheese milk as those of proteinase positives, suggesting a probable reduction of phage and antibiotic problems. Exclusive use of proteinase negative cultures is suggested for cheese making.