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Freezing, thawing have a little impact in cheese protein degration.

The manner in which proteins degrade as cheese matures is affected by several factors, including plasmin, chymosin, protease, the pH of curd, storage temperature and time, the salt-to-moisture ratio and humidity. Unfortunately, the effect and impact of freezing on the proteolysis and shelf life of caprine milk cheeses has not been extensively studied.

The goal of researchers in Georgia was to determine the effects of freezing and thawing on changes in the protein moieties of plain soft and Monterey Jack (MJ) goat milk cheeses. The scientists prepared two varieties of caprine cheeses in three batches: a commercially purchased plain soft variety and MJ cheeses manufactured at Georgia's Fort Valley State University dairy pilot plant.

Each lot of both varieties was subdivided into two portions. One half as a fresh control was immediately stored at 4 C for 0, 14 and 28 days. The other half was immediately frozen at -20 C for 24 hours, thawed at 4 C and then subjected to the identical refrigeration treatment as the control. The scientists extracted cheese proteins. They analyzed specific degradative protein bands using commercial image analysis software.

The investigators did not find any statistical differences in the electrophoretic patterns of all of the proteins in the frozen-thawed cheeses and those of the corresponding proteins in the controls. Regardless of the extent of freezing and storage time, the soft cheeses exhibited eight distinctive bands of alpha-s2-, beta- and gamma 1-caseins, beta-lactoglobulin and some polypeptides degraded from caseins. MJ cheeses had a greater number of protein bands--9 to 12. This was probably caused by six weeks of aging prior to the freezing experiment. Alpha-s2- and betacaseins were two major proteins for both cheeses. The amount of alpha-s2-casein in MJ cheeses varied among the three batches.

The researchers determined that freezing and thawing had little impact on protein degradation and the shelf life of the goat cheeses. Their frozen-storage methodology may have strong potential for extending the storage life of caprine cheeses.

Further information. Sung Lee, Agricultural Research Station, Fort Valley State University, 1005 State University Dr., Fort Valley, GA 31030; phone: 478-825-6865; fax: 478-825-6376; email:
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Publication:Emerging Food R&D Report
Date:May 1, 2006
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