STIMULATING EFFECT OF MILK CASEIN HYDROLYSATES ON THE GROWTH OF STREPTOCOCCUS-THERMOPHILUS

To develop an effective utilization of milk casein, casein hydrolysate preparations of various average peptide lengths (APL) were prepared enzymatically with endo/exo-protease, and the stimulating effects on the qrowth of Streptococcus thermophilus by these hydrolysates were examined. The stimulating effects on S. thermophilus were compared among trial preparations and six kinds of commercial peptones. The results obtained were summarized as follows: (1) It was found that the hydrolysate preparation having APL of 1.5 showed the best stimulating effect on the growth of S. thermophilus among the samples examined. The free amino acid content of this preparation was about 50%. (2) It was presumed that the poor effect of domestic commercial peptones on the growth of S. thermophilus was due to their short APL and the lack of stimulating factors, such as vitamins. Therefore, it was concluded that the trial preparation having appropriate APL and sufficient vitamins content was the most suitable peptone for the cultivation of S. thermophilus.