Removal of starch granule-associated lipids alters the physicochemical properties and in vitro digestion of wheat starches from different grain hardness

Abstract

Starch granule-associated lipids (SGALs) are closely associated with wheat grain hardness, which significantly influences the physicochemical properties of starch. In this study, the effects of removing SGALs on the physicochemical properties and in vitro digestion of hard-grain starch (HGS), medium-grain starch (MGS), and soft-grain starch (SGS) were systematically evaluated. SGS was characterized by a higher unsaturated fatty acid content, in which oleic acid was found to be particularly enriched (19.89 mg/g). When the SGALs were removed, the apparent amylose and damaged starch contents were increased in all samples, leading to pitted surfaces on the starch granules and an obvious decreased particle size. The relative crystallinity decreased to 22.80% for defatted hard-grain starch (DHGS), 11.39% for defatted medium-grain starch (DMGS), and 14.14% for defatted soft-grain starch (DSGS), which was accompanied by lower thermal stability. In particular, DHGS showed a significant decrease in gelatinization enthalpy (0.74 J/g) and exhibited the maximum thermal degradation rate (2.67%/°C). Furthermore, the breakdown and setback viscosities decreased by 47.70% and 18.75%, respectively. These alterations reduced the resistance to enzymatic hydrolysis. After 11 h of in vitro digestion, the digestion rate of DHGS, DMGS and DSGS increased to 61.17%, 68.49% and 53.82%, respectively. These findings provide a theoretical basis for quality improvement in starch-based products.