Acidic free amino compounds formed in various lactic acid starter cultures as measured by ion exchange chromatography.

The role of starter organisms in the ripening of various cheese varieties has been the subject of extensive study in recent years (Deane, 1951; Peterson et al., 1948; Baribo and Foster, 1952; and Van der Zant and Nelson, 1954a). The accumulation of various free amino compounds during cheese ripening has been attributed primarily to enzymes of bacterial origin (Peterson et al., 1948; Deane, 1951; Harper and Gould, 1952). Most of the previous studies have been limited to the organism Streptococcus lactis (Hansen, 1941; Morgan and Nelson, 1951). Baribo and Foster (1952) determined some of the characteristics of the endocellular proteinases of one strain each of S. lactis, Lactobacillus casei, and Micrococcus freudenreichii. Van der Zant and Nelson (1953a and 1953b) investigated the proteolytic activity of S. lactis and a cell-free extract of this organism prepared by sonic vibration. Recently, Van der Zant and Nelson (1954a, 1954b) reported using paper chromatography to investigate the presence of amino acids and peptides in skimmilk inoculated with S. lactis, and to study some of the characteristics of the endocellular peptidases of this organism. In the present study, ion exchange chromatography was applied to investigate the proteolytic activity as measured by the presence of various acidic free amino acids of several lactic acid starter organisms; napiely, Lactobacillus bulgaricus, Lactobacillus lactis, and Streptococcus thermophilus.