Preparation of Concentrated Lactic Streptococcus Starters

Abstract

Single-strain cultures of Streptococcus cremoris were grown in a semisynthetic medium with automatic p H control. After centrifugation, the cells were resuspended in sterile nonfat milk (2% of the original volume). There was no significant difference in the maximum population attained when cultures were grown at p H values of 5.5, 6.0, or 6.5 with sodium hydroxide as the neutralizer. With ammonium hydroxide as the neutralizer, maximum populations obtained were increased about twofold. In most cases, the acid-producing ability of the culture concentrates was comparable to that of fresh-milk cultures. There was some variation among strains of S. cremoris with respect to the effects of different neutralizers and levels of p H control on the biological activity of the culture concentrates. The culture concentrates were stored in liquid nitrogen for as long as 231 days without significant loss in biological activity.