71A-30 |
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P. LIMPISATHIAN and P. D. Courtney. Dept. of Food Science and Technology, The Ohio State Univ., 2015 Fyffe Rd, Columbus, OH 43210-1007 Dairy Propionibacterium strains have proteolytic activities capable of hydrolyzing casein-derived peptides to small peptides and amino acids which contribute to cell growth and cheese flavor. The diversity of peptidase activities among dairy Propionibacterium strains is not well characterized. The objective was to evaluate the intracellular peptidase activities of dairy Propionibacterium strains. Twenty-nine different Propionibacterium freudenreichii strains from commercial starter cultures and cheeses were selected for analysis. Cells were grown to mid-exponential phase and cell-free extracts were analyzed using the following: p-nitroanilide labeled peptides as substrates: pro-pNA, lys-pNA, ala-pro-pNA, and glu-pNA. Using each chromagenic substrate, the liberation of p-nitroanilide was monitored spectrophotometrically at 410 nm in each cell-free extract in 20 mM Tris-HCl buffer, pH 7.0, at 30 °C. The Bio-Rad protein assay established the protein concentration in each cell-free extract which was used to calculate the enzyme specific activity. Proline iminopeptidase (PepI) activity on the pro-pNA substrate ranged from 0 to 158 mmol/min/mg protein. Six strains had no or very low PepI activity. Aminopeptidase activity on the lys-pNA and the glu-pNA substrates ranged from 0 to 79.7 and from 0 to 5.2 mmol/min/mg protein, respectively. X-prolyl dipeptidyl aminopeptidase (PepX) activity on the ala-pro-pNA substrate ranged from 0 to 73.3 mmol/min/mg protein. Most strains, 23 of 29 strains, were higher in PepI activity than other activities. One strain with no PepI activity had the highest PepX and aminopeptidase activities. The intracellular peptidase activities of dairy Propionibacterium strains varied in specificity and activity levels. These differences may contribute to flavor and growth rate variations observed in cheeses manufactured with different Propionibacterium strains.
Session 71A, Dairy Foods: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |