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Comparison of Milk Proteolysis by Bacillus subtilis Protease and by Pseudomonas fluorescens^1,2,

Department of Dairy and Poultry Science, Kansas State University, Manhattan 66502

ABSTRACT

In preliminary tests using a ninhydrin method as a measure of protein breakdown, proteolysis of milk by a Bacillus subtilis enzyme appeared to differ from that by Pseudomonas fluorescens. Further study showed that with P. fluorescens, ninhydrin values were higher than with the enzyme at comparable nonprotein nitrogen levels, and the differences became greater as nonprotein nitrogen increased. The linear trend for the relationship between ninhydrin value and nonprotein nitrogen was closer for P. fluorescens than for B. subtilis enzyme. Although absorbancy patterns (at 280 m) from fractionation on G-25 Sephadex were basically similar, there were several differences. Due to differences in the breakdown products formed in the two hydrolysates, the ninhydrin method used was not a satisfactory index of protein digestion by the B. subtilis enzyme.

¹ Contribution no. 751, Department of Dairy and Poultry Science, Kansas Agricultural Experiment Station, Manhattan.

² Supported in part by a grant from the American Dairy Association, Chicago.