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S. ZHU1, H. S. Ramaswamy1, and A. Le bail2. (1) Dept. of Food Science and Agricultural Chemistry, McGill Univ., 21111 Lakeshore Road, Sainte-Anne-de-Bellevue, Montreal, QC H9X 3V9, Canada, (2) LGPA, ENITIAA, Rue de Geraudiere, BP 82225-44322, Nantes, Cedex 3, France High Pressure (HP) has interesting effects on water phase transition, but not much attention has been paid to its role in food processing applications. Understanding phase transition behavior of water in foodstuffs during HP processing can aid process development and food quality improvement, but available scientific information in this area is very limited. The objective of this work was to evaluate/compare phase transition behavior in different foods/food materials (potato, salmon, pork, Tylose and pure water). HP Differential Scanning Calorimetry (DSC) was used in this study. Small specimens (0.48-0.72 g, vacuum-packaged in polyethylene pouches) of test sample were subjected to isothermal pressure scan (P-scan, 0.3 MPa min-1) at –5, –7, –10, –15, and –18° C. Pressure, temperature and calorimetric signals were recorded every 5 s during the test. Phase transition temperature/pressure and latent heat were determined based on each heat-flow peak. Each P-scan test created a reliable heat-flow peak reflecting the nature of phase transition and amount latent heat of test sample at the test temperature. A polynomial regression equation was established for each test sample, showing a good relationship between pressure and phase change temperature as well as latent heat. Measured latent heat of food samples had a trend different from that of pure water due to temperature dependence of ice content in frozen food samples. However, ice-mass based latent heat values showed no significant difference (P>0.05) from latent heat of pure water (Ice I) under pressure. Higher moisture levels in foods (e.g., potato) had a higher phase transition point and obviously a higher latent heat during a P-scan test at any givin temperature. It was found that the phase transition point (either temperature or pressure) of pure water was significantly depressed (P<0.05) when associated with foods. Moisture content was the major factor affecting phase transition and latent heat during HP processing. P-scan technique is a powerful tool to study the pressure-dependent phase transition phenomena in foods.
Session 34, Nonthermal Processing: General I
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |