Proteinase Profiles of Lactococcus lactis ssp. cremoris Using High Performance Liquid Chromatography

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Abstract
Proteinase-positive or proteinase-negative Lactococcus lactis ssp. cremoris cultures propagated in M17 broth were centrifuged, washed, mixed with 2.5% rennet-casein solution, and incubated at 30.degree.C for 24 h. High performance liquid chromatography analysis of the filterd extracts was conducted using an acetonitrile solvent gradient. Four major peaks, eluting at 8, 13, 19, and 25 min, were selected to characterize 26 strains. These four peaks were totaled to indicate the amount of casein solubilization. A fifth peak of soluble casein, eluting at 34 min, exhibited marked decreases in peak area for many of the strains. Different profiles developed for each proteinase-positive strain and its proteinase-negative variant. Most proteinase-positive strains were more proteolytic than their proteinase-negative variants. Four strains were atypical, the protein-negative variant had larger peak area totals for the four peaks selected than the proteinase-positive parent strain. These results were consistent with previous yield studies for these strains. The HPLC casein test shows potential for selecting strains for maximum yield potential.