Bacteriological Studies of Cultured Buttermilk. II. Progressive Changes in the Numbers of Leuconostoc Citrovorum and Streptococcus Cremoris as Associated with pH and Acetlymethylcarbinol Plus Biacetyl Levels

Abstract

An investigation was made, using 2 starters, in which progressive changes were followed throughout the fermentation period of cultured buttermilk in the numbers of Leuconostoc citrovorum and Streptococcus cremoris. pH value and acetylmethylcarbinol plus biacetyl content. The enumeration and differentiation were made by a plate culture technique described in the first paper of this series. At all stages, L. citrovorum represented only a small percentage of the total flora as compared with S. cremoris. It was at the lowest level near the coagulating point of the milk and then increased beyond this point. The L. citrovorum population continued to increase after the S. cremoris population had reached a maximum level. Maximum levels for L. citrovorum were not reached until 35 hours of continuous incubation or longer. No significant production of acetylmethylcarbinol plus biacetyl occurred prior to coagulation of the milk. After that time, the rate of increase was rapid to the end of the 24-hour period. The results obtained with the 2 starter cultures were comparable.