Influence of Glass Transition on Oxygen Permeability of Starch-Based Edible Films

摘要

Starches from different sources have distinctly different molecular weights. In addi-tion, the high temperatures and shear stresses involved in starch-film solution casting, compression molding, and extrusion reduce the starch molecule chain length. This research investigated the effect of starch chain length on oxygen permeability (OP) and glass transition temperature (T_g) of starch films. Solution-cast starch films made from tapioca-based and rice-based starches having different chain lengths were used in this study. Starch, noncrystallizing sorbitol (the partial hydrolysis product of starch with subsequent hydrogenation under pressure), and deionized water were mixed, heated to 95°C and held for 30 min to gelatinize the starch, cast on high-density poly-ethylene plates, and dried at ambient conditions to form films. Results showed that both tapioca-starch and rice-starch chain length affected OP. Films made from long-chain starch had lower OP than did those made from short-chain starch. The T_g of starch tended to decrease with decreasing degree of polymerization. Shorter-chain starch had lower T_g, which correlated with an increase in the OP of starch films. From these experiments, it can be concluded that the T_g of starch could be used to explain the change in OP of starch films related to starch chain length.