Sorghum proteins: Effect of extraction pH on physicochemical properties and emulsion formation

Abstract

Extraction methods suitable for food applications should be studied to obtain new plant protein isolates. This study aimed to evaluate the effect of pH (8.0, 10.0, and 12.0) and temperature (20 and 40 °C) during alkaline extraction on the yield and functional and physicochemical characteristics of sorghum protein isolates and to test their ability to stabilize emulsions. The best extraction yield (58.52 %) was at pH 12.0 and 40 °C. The obtained isolates had protein concentration superior to 4-fold as compared to the raw material. Electrophoresis showed mainly prolamins, with some globulin, glutelin, and higher molecular weight polypeptides (>250 kDa). Sorghum protein isolate obtained at pH 12.0 had improved solubility (64.77 %) compared to the isolates obtained at pH 8.0 (14.50 %) and pH 10.0 (17.68 %). Emulsions with 70 % (w/w) of oil showed no phase separation during storage, and those produced with the isolate obtained at pH 12.0 were more stable, with smaller droplet sizes after the 7-day storage (25.17–44.77 μm), lower creaming index, higher emulsion stability index (ESI), and less flocculation. The study demonstrated the functional ability of sorghum protein isolates obtained by alkaline extraction to form concentrated oil-in-water emulsions, avoiding using organic solvents.