Effects of Liquid Okara Substitution for Water on the Quality and Staling Characteristics of Gluten-Free Rice Flour Bread

Abstract

This study investigated the nutritional, physical, and staling properties of gluten-free rice flour bread prepared with varying levels of liquid okara substitution (0-50%; 0% as control). Liquid okara, obtained by diluting, grinding, and heat-sterilizing raw okara, contained approximately 95% moisture and 5% solids, with dietary fiber as the predominant component followed by proteins. At 50% substitution, the dietary fiber content doubled compared with the control, while the specific volume peaked at 2.25 cm³/g at 25% substitution (vs. 2.04 cm³/g in the control). Bread hardness decreased by up to 30%, resulting in a softer and less adhesive texture. Scanning electron microscopy revealed smaller, more uniformly dispersed particles, and viscoelastic analysis indicated increased storage and loss moduli with higher substitution levels. Breads with 25% and 50% substitutions retained more moisture and springiness during storage. These improvements were attributed to enhanced water retention, delayed starch retrogradation, and structural stabilization. Overall, substitution at approximately 25% provided the optimal balance of nutritional enhancement, textural quality, and storage stability.