Changes in protein and starch digestibility in sorghum flour during heat-moisture treatments.

Abstract

Heat-moisture treatment (HMT) has been used to modify properties of sorghum starches. However, information is limited on the effects of HMT on the digestibility of starch and the concurrent changes in protein in sorghum flour. The objectives of this research were to identify heat-moisture conditions to increase the resistant starch (RS) content of sorghum flour and investigate changes in sorghum proteins and starch structure. Sorghum flours with different moisture contents (0, 125, 200, and 300 g kg-1 w.b.) were heated at three temperatures (100, 120 and 140 °C) and times (1, 2 and 4 h). HMT of sorghum flour increased its RS level. The flour treated at 200 g kg-1 moisture and 100 °C for 4 h had a high RS content (221 g kg-1 vs. 56 g kg-1 for the untreated flour). Starch was not gelatinized when sorghum flours heated at moisture content of 200 g kg-1 or below. Sorghum protein digestibility and solubility decreased during HMT. The increase in RS of sorghum flour upon HMT was attributed to enhanced amylose-lipid complexes and heat induced structural changes in its protein fraction. HMT can be used to increase RS content in sorghum flour without gelatinizing its starch, thereby providing sorghum flour with unique food applications. © 2017 Society of Chemical Industry.