Effect of Dehydration on the Specific Heat of Cheese Whey
Differential scanning calorimetry was used to determine the specific heat of cheddar cheese whey as a function of water content and thereby provide fundamental data useful for the further development of dried whey products. The specific heat of fluid cheddar cheese whey, which contains 7% solids, was 0.951 ± .036 cal/g/°C at 12°C. A linear relationship was maintained between specific heat and moisture content when dried whey solids were re-hydrated to moisture levels between 3 and 93% H2O. The apparent partial specific heat of the whey solids was 0.328 cal/g/°C and that of the water was 0.995 cal/g/°C, a value close to that of bulk water. An inflection, however, was noted in the relation between specific heat and water content at 50% H2O when the specific heat data were obtained with concentrated whey samples prepared by evaporation of water from fluid whey. These data yielded apparent partial specific heat values for water of 0.966 cal/g/°C above 50% H2O and 1.203 cal/g/°C below 50% H2O. Apparently the water is in a more structured form in concentrated systems provided that the solids are initially fully hydrated. This conforms to the concept that a critical amount of water must be present in a proteinaceous system for the water to be held in a quasi-solid or “icelike” structure.
KeywordsDifferential Scanning Calorimeter Bulk Water Cheese Whey Sorbed Water Excess Heat Capacity
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