36G-4 |
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E. K. DERMESONLOUOGLOU, M. C. Giannakourou, and P. S. Taoukis. School of Chemical Engineering, National Technical Univ. of Athens, Iroon Polytechniou 5, Athens, 15780, Greece Osmotic Dehydration (OD) prior to freezing has been proposed for improving frozen tissue quality and stability during storage. Such increased stability was previously demonstrated for frozen tomato slices osmoconcentrated in alternative osmotic solutions. The increase on the average molecular mass of the tomato matrix due to water removal and impregnation of solids during OD leads to a solute-dependent increase of glass transition temperature (Tg'), thus contributing to the stabilization of the final product. The objective was to study glass transitions of osmodehydrofrozen tomato samples. OD with aqueous solutions of different carbohydrates having different glass transition properties was applied as a pretreatment. Low molecular weight carbohydrates of special functional and/or nutritional characteristics that are compatible to the sensory characteristics of the osmo-preconcentrated tissue were studied. Tomato slices were osmodehydrated in 56.5% (wt/wt) syrups of carbohydrates at 35° C for 1 hr. Glucose, oligofructose, tagatose, trehalose/oligofructose (50% to 50%) and a high DE maltodextrin (HDEM) were used in the osmotic solutions, combined with NaCl (3.5%) and CaCl2 (1.5%). Moisture, soluble solid, and insoluble solid contents were measured. Phase transitions at subzero temperatures for the osmotic syrups used, as well as for tomato samples, were studied with differential scanning calorimeter equipped with liquid nitrogen cooling accessory. The Tg' values of osmodehydrofrozen samples were between –49.0 and –55.4° C. The HDEM treatment led to the highest increase of Tg' of the vegetable matrix and the glucose treatment to the lowest one. The melting point for OD samples was depressed as compared to untreated tomato samples (from -3.9 to –9.2° C). Tg' was correlated to water activity and moisture content. The results suggest that the addition of carbohydrates into tomato tissue modified its low-temperature phase transitions. The increase of Tg' could partly account for the quality stabilization that was observed in the osmodehydrofrozen samples and correlates to the decrease of the difference between storage T and Tg'.
Session 36G, Refrigerated & Frozen Foods: General
2005 IFT Annual Meeting, July 15-20 - New Orleans, Louisiana |