Effect of microwave thawing on microstructure and physicochemical stability of low fat white sauces made with soy protein

Abstract

The microstructural and physicochemical stability of white sauces made with soy protein and modified waxy maize starch was evaluated after subjecting them to a freezing-thawing process in a conventional or microwave oven. The microstructure of sauces revealed a structured matrix of soy protein and starch polymers where fat globules and swollen starch granules remain dispersed. Both thawing methods affected the fat globule size and morphology but they did not affect the starch granules. The SDS-PAGE analysis did not show any apparent changes between sauces thawed by both methods. Moreover, a similar pattern was found in the soy protein isolate used as a raw material indicating that this type of protein was also stable to the cooking process. There were no significant differences (P > 0.05) in the reducing power of the sauces regardless of the thawing method used. However, the acidity index and the k 232 parameter were significantly higher (P < 0.05) in conventionally thawed sauces. Finally, syneresis was negligible and no significant differences (P > 0.05) were found among different frozen storage periods. In conclusion, the formulation of the sauce is appropriate to develop low fat, vegetarian meals which can be subjected to frozen storage and microwave reheating.