Physical and Mechanical Properties of High‐amylose Rice and Pea Starch Films as Affected by Relative Humidity and Plasticizer

Abstract

ABSTRACT: The tensile properties, water vapor permeability, oxygen permeability at different relative humidities (RH), and water solubility of edible films made of high‐amylose rice starch (RS) or pea starch (PS) were measured and compared with the most commonly used edible films. Photomicrography of starch films shows amylopectin‐rich gels and amylose‐rich granules. The addition of glycerol into starch films made amylose‐rich granules swollen and continuously dispersed between amylopectin‐rich gels. Tensile strength of RS and PS films decreased when RH increased from 51% to 90%, whereas elongation‐at‐break (E) of both films increased when RH increased. Water vapor permeabilities of both films were similar, resulting in 130 to 150 g mm/m2/d /kPa. Oxygen permeability of RS and PS were very low (< 0.5 cm3μm/m2/d/kPa) below 40% RH, and 1.2 to 1.4 at 45% RH. Water solubility of PS film was 32.0%, which is lower than that of RS film (44.4%). Overall high‐amylose rice and pea starch films possess an excellent oxygen barrier property with extremely high stretchability.