71A-60 |
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J. W. MONTELLA and P. S. Tong. Dairy Products Technology Center, California Polytechnic State Univ., 1 Grand Ave., San Luis Obispo, CA 93407 Cheese manufacturing is traditionally a batch process. Ultrafiltration could be applied to make cheesemaking a continuous process. To develop the continuous process, it is important to determine the factors affecting the compositional and rheological changes of retentate and its rennet coagulation time (RCT). Our objectives are to study the effects of heat treatment of whole milk and ultrafiltration temperature on composition of retentate, and the influence of compositional change on rheological properties and RCT of retentate. Whole milk was ultrafiltered using a 10,000 molecular weight cut-off polysulfone membrane until the retentate volume was 1/3 the original volume of whole milk. Two filtration temperatures were used: 10 and 50 °C. Whole milk was heat-treated before ultrafiltration or was ultrafiltered before heat treatment. In all cases, heat treatment was applied at 63 °C for 30 min. RCT was determined at 30 °C using a rheometer equipped with a bob and cup geometry. For all experiments, the retentate was standardized to 24.75% total solids content using UF permeate. The results of heat treatment before filtration at 50 °C show the calcium content in retenate increased by 50% and the whey protein content in retentate increased by 45%, compared to heat treatment after filtration at 10 °C. RCT increased by 200% under the same conditions. For heat treatment before filtration at 50 °C, the increase in calcium content in retentate was due to the binding of calcium to the casein micelles. Denatured whey proteins can associate with micelles. The subsequent increase in casein micelle size leads to a hindrance of the enzyme activity of rennet; consequently, this results in a longer rennet coagulation time.
Session 71A, Dairy Foods: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |