88C-15 |
Thermophysical properties of restructured sweetpotato puree at freezing and refrigeration temperatures |
O. O. FASINA, W. M. Walter, Jr., and H. P. Fleming. USDA-ARS, NC State University, Box 7624, Raleigh, NC 27695-7624
About 60% of harvested roots of sweetpotatoes (SP) are sold and consumed fresh because of texture control problems. Restructuring of SP puree with alginate and calcium sulfate has been shown to be an effective method to control SP product textural characteristics. French fry-type and simulated baked SP products have been developed from the restructured puree. Freezing and refrigeration is one of the unit operations essential to the production of high quality restructured SP puree. The objective of this study was to determine the thermophysical (apparent specific heat, enthalpy of melting and unfreezable water content) properties of SP puree at freezing and refrigeration temperatures. SP puree was obtained by steam cooking peeled, cut roots (slices of 0.95 cm thick). The cooked slices were then pureed using a hammer mill fitted with a 0.15 cm screen. Restructured SP puree was prepared by the addition of alginate, calcium chloride, tetrasodium phyrophosphate and sucrose to steam-cooked SP puree. Thermophysical properties were determined using a differential scanning calorimeter within the temperature range of –40 and 20C. Results showed that the presence of alginate/calcium complex bound some water in the puree. This increased the amount of water in the puree that is unavailable for freezing (0.56 g water/g solids for restructured and 0.44 g water/g solids for non-restructured) and reduced the amount of energy required to freeze the texturized SP puree (358 kJ/kg versus 403 kJ/kg for non-restructured SP puree). During phase change, the specific heat of the restructured SP puree increased from about 1.9 kJ/kg K to about 90 kJ/kg K. The results obtained from this study will be used in the design and selection of systems for the freezing and refrigeration of restructured SP puree and in estimating the time required for freezing and thawing of restructured SP puree.
Session 88C, Food Engineering: Physical and Chemical Properties
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