Preparation and characterization of edible soya protein films

Abstract

Soya bean has more protein (about 38-44%) than the protein content (8-15%) of cereal grains. Most of the protein of soya is classified as globulin and is available as a low cost co-product of the oil processing industry. Although soya protein has been studied in combination with other proteins such as wheat gluten, the film forming ability of the soya protein isolate alone has not been studied in detail. In this report, the thermal, mechanical and water sorption properties of soya protein films are discussed. Water was used as the solvent to make casting solutions and glycerol was used as the plasticizer. The pH of the casting solution was adjusted by adding 2M HC1. Similar to other grain protein films, the properties of the soya protein isolate film largely depend on the relative humidity of the environment. Tensile strength values of soya protein films were found to be comparable with those of conventional packaging materials such as low density polyethylene. Moisture absorption isotherms were found to be similar in behavior to other proteins such as zein, wheat, gluten, etc. These values fitted well to the GAB model proposed for the moisture absorption of grain proteins.