91A-6 |
Application of MALDI-TOF mass spectrometry to screen primary and adjunct cultures used in cheese manufacture |
E. SOERYAPRANATA1, J. R. POWERS1, K. M. Weller1, W. F. Siems, III2, and H. H. Hill, Jr.2. (1) Department of Food Science and Human Nutrition, Washington State University, PO Box 646376, Pullman, WA 99164-6376, (2) Department of Chemistry, Washington State University, PO Box 644630, Pullman, WA 99164-4630 Selection of lactic cultures is crucial to prevent bitterness of cheese. A previous study using aged Cheddar cheese demonstrated the ability of matrix-assisted laser desorption / ionization time-of-flight (MALDI-TOF) mass spectrometry to differentiate primary cultures and adjunct cultures, based on the concentration of bitter peptide, b-casein f193-209. The speed and sensitivity of MALDI-TOF may be useful for rapid screening of lactic cultures for propensity to produce bitter cheese. The objective of our study was to demonstrate the application of MALDI-TOF to in vitro assay to screen primary and adjunct lactic cultures. b-casein was incubated with chymosin in citrate buffer (pH 5.4, 4% NaCl) followed by incubation with cell free extract (CFE) from primary or adjunct culture, previously used in the aged cheese study. Lactococcus lactis #56 and #105 were primaries representing bitter and non-bitter cultures, respectively. Lactobacillus helveticus WSU19 and W900R represent adjunct cultures having high and low debittering activities, respectively. Proteolysis pattern and concentration of b-casein f193-209 after incubation with CFE were determined using MALDI-TOF at 0, 4, 8, 16, and 24 hours. Degradation of b-casein by chymosin produced b-casein f193-209 as a major product. Proteolysis by CFE from WSU19 produced b-casein f194-209 with and without cyclization of Gln-194, f193-207, f195-209, and f195-206. This pattern is characteristic of aminopeptidase N, endopeptidase, aminopeptidase A, and/or pyrollidone carboxylyl peptidase activities. Proteolysis by CFE from W900R produced b-casein f194-209, f194-206, and f193-206, indicating aminopeptidase N and endopeptidase activities. Proteolysis patterns of CFEs from #56 and #105 were similar to W900R. The rates of b-casein f193-209 hydrolysis by CFEs from WSU19, W900R, #56, and #105 were 3.67, 0.20, 0.21, and 0.12 µM/h, respectively. MALDI-TOF is a rapid in vitro qualitative and quantitative tool complementing chromatographic techniques for screening of lactic cultures used in cheese manufacture.
Session 91A, Food Chemistry: Enzymes, vitamins and plant pigments
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