Proteolytic activity of some Lactobacillus paracasei strains in a model ovine-milk curd system: Determination of free amino acids by RP-HPLC

Curd slurries were prepared from ovine milk to study the proteolytic properties of various strains of Lactobacillus paracasei. A commercial industrial starter and the strains to be tested in this study, Lb. paracasei strains Pa1, Pa2, Pa3, were inoculated in separate slurries. Free amino acids were analysed on days 0, 2, 5, 7, and 10. As ripening progressed, total free amino acids increased significantly (P < 0.01); content ranged from 150 mg/100 g dry matter (DM) on day 0 to 600 mg/100 g DM on day 10. Generally speaking, CIT, GLN, LEU, ASN, PRO, and 4-HYPRO were the main free amino acids in all four slurries tested, accounting for 60–82% of the total free amino acids. The slurries made using strains Pa1 and Pa3 were similar to the control slurry, and these three slurries exhibited the highest proteolysis levels. Differences between the strains of the species tested were observed.