Does protein deamidation enhance rice protein concentrate's ability to produce and stabilize high internal phase emulsions?

Rice is one of the most consumed grains in the world. Rice protein has great nutritional value as a hypoallergenic protein and due to its high lysine content, a limiting amino acid in several other plant protein sources. However, rice protein has low solubility, hampering its use in many applications in the food industry. In this context, alkaline deamidation (0.5 h, 343 K, and pH 11) was applied to modify the protein structure of rice protein concentrate (RPC). After deamidation, two protein powders were produced: (i) one containing the whole protein fraction recovered after RPC deamidation (DT) and (ii) another containing only the soluble fraction recovered after RPC deamidation (DS). Protein dispersions were characterized by SDS-PAGE, zeta potential, solubility, surface hydrophobicity, and capacity to hold water and oil. RPC could not structure canola oil into a high internal phase emulsion (HIPE) due to its low solubility. DT and DS dispersions displayed solubility much higher than RPC and enabled the structuration of HIPEs with 75 % (w/w) canola oil and 25 % of DT or DS dispersions (2, 4, and 6 % w/w). HIPEs were characterized regarding particle size, microstructure, Turbiscan and oil loss stabilities, and rheological behavior for 60 days. Turbiscan analysis and oil loss measurements showed high stability, and the thixotropy tests showed high recovery in all HIPEs. Higher protein concentrations and DS dispersions produced HIPEs with smaller particle sizes. However, rheological measurements indicate that HIPEs produced with DT dispersions had better results, maintaining their structure over the 60 days. Furthermore, DT is cheaper to produce; therefore, DT 4 and 6 % w/w were the most promising for producing HIPEs. The HIPEs produced in this study displayed great potential as fat replacers.