Effect of heating cast kafirin films on their functional properties

Abstract

Edible films can be produced from kafirin but the diverse food product requirements necessitate modification of the films. To modify their functional properties, kafirin films were cast, with and without plasticizer, from glacial acetic acid (GAA) and aqueous ethanol (AE), then heated using microwave energy. A power of 80 W for 2 min caused an approximately two- and fourfold increase in the tensile strength of non-plasticized and plasticized films, respectively. Film glass transition temperature increased approximately by 15%. Film biodegradability was slowed. However, only the digestibility of the non-plasticized films cast from AE heated for the longest time (4 min) was decreased, by about 25%; while that of the other films was not affected. GAA cast films had higher digestibility than AE cast ones, possibly as a result of acid-mediated deamidation of kafirin. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicated heat-induced kafirin oligomers. Scanning electron microscopy of heated plasticized films showed more wrinkled structures compared to non-heated films, whereas the non-plasticized films appeared more brittle with heating. The results indicate that heat-induced intermolecular disulfide cross-linking was involved in modifying the properties of kafirin films.