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

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.