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Letters in Applied Microbiology ISSN 0266-8254 ORIGINAL ARTICLE Degradation of milk-based bioactive peptides by yogurt fermentation bacteria* M. Paul and G.A. Somkuti Eastern Regional Research Center, Agricultural Research Service, US Department of Agriculture, Wyndmoor, PA, USA Keywords Abstract bioactive peptide, RP-HPLC, yogurt bacteria. Aims: To analyse the effect of cell-associated peptidases in yogurt starter Correspondence culture strains Lactobacillus delbrueckii ssp. bulgaricus (LB) and Streptococcus Moushumi Paul, Eastern Regional Research thermophilus (ST) on milk-protein-based antimicrobial and hypotensive Center, Agricultural Research Service, US peptides in order to determine their survival in yogurt-type dairy foods. Department of Agriculture, 600 East Mermaid Methods and Results: The 11mer antimicrobial and 12mer hypotensive milk- Lane, Wyndmoor, PA 19038, USA. protein-derived peptides were incubated with mid-log cells of LB and ST, E-mail: moushumi.paul@ which are required for yogurt production. Incubations were performed at pH *Mention of trade names or commercial 4Æ5 and 7Æ0, and samples removed at various time points were analysed by products in this publication is solely for the reversed-phase high-performance liquid chromatography (RP-HPLC). The pep- purpose of providing specific information and tides remained mostly intact at pH 4Æ5 in the presence of ST strains and mod- does not imply recommendation or erately digested by exposure to LB cells