11-3 |
Evaluation of impacts of freezing and thawing on protein degradations of caprine milk cheeses by SDS-PAGE analysis |
S. J. LEE, Agricultural Research Station, Fort Valley State Univ., 1005 State University Dr., Fort Valley, GA 31030-4313, Y. W. Park, Agricultural Research Program, Fort Valley State Univ., College of Agriculture, Home Economics & Allied Programs, 1005 State University Dr., Fort Valley, GA 31030-4313, A. Kalantari, Fort Valley State University, Fort Valley, GA 31030, and D. L. Van Hekken, Dairy Processing & Products Research Unit, USDA-ARS-Eastern Regional Research Center, 600 E. Mermaid Ln., Wyndmoor, PA 19038-8598. Protein degradation during cheese maturation is affected by several factors including plasmin, chymosin, protease, pH of curd, storage temperature and time, salt-to-moisture ratio and humidity, etc. Impacts of freezing on proteolysis and shelf life of caprine milk cheeses has little been studied. The purpose of the study was to determine effects of freezing and thawing on changes in protein moieties of plain soft and Monterey Jack (MJ) goat milk cheeses. Two varieties of caprine cheeses were prepared in 3 batches: commercially purchased plain soft variety and MJ cheeses manufactured at the University dairy pilot plant. Each lot of both varieties was subdivided into two portions. One half as fresh control was immediately stored at 4oC for 0, 14, and 28 days, and the other was immediately frozen (-20oC for 24 hr), thawed at 4oC, then subjected to the identical refrigeration treatment as control. Cheese proteins were extracted, and specific degradative protein bands were analyzed by SDS-PAGE and Kodak 1D Image Analysis Software System. No statistical differences were found in electrophoretic patterns of all proteins in frozen-thawed cheeses compared to those of corresponding proteins in controls. Regardless of freezing and storage periods, soft cheeses exhibited distinctive 8 bands of alpha-s2-, beta- and gamma 1-caseins, beta-lactoglobulin and some polypeptides degraded from caseins. MJ cheeses revealed greater number of protein (9-12) bands, presumably due to the 6 wks aging prior to freezing experiment. Alpha-s2- and beta-caseins were two major proteins for both cheeses, where 14 and 57%, and 1.5-17 and 35-40% for soft and MJ cheeses, respectively. Alpha-s2-casein in MJ cheeses varied between the 3 batches. It was concluded that freezing and thawing had minimal impacts on protein degradation toward shelf life of the goat cheeses, whereby frozen-storage may have a strong potential for practical application for extending storage life of caprine cheeses.
Session 11, Food Chemistry: Proteins I
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