Impact of ultrasonication on the physicochemical properties of sorghum kafirin and in vitro pepsin-pancreatin digestibility of sorghum gluten-like flour

Abstract

Sorghum is a nutritionally dense grain but its nutritional quality is limited by its poor digestibility. The objective was to determine the effects of ultrasonication on the physicochemical properties of kafirin, major protein in sorghum, and its stability against pepsin-pancreatin hydrolysis (PPH). Ultrasonication for 10min at 40% amplitude increased the solubility of purified kafirin from 6.5μg/mL to 173.3μg/mL. Ultrasonication altered the secondary structure of kafirin as evaluated by circular dichroism and Fourier-transform infrared red spectroscopy. In pepsin-pancreatin hydrolysates, 14.7% increase in molecules with molecular weight between 0.075 and 0.5kDa was detected in size-exclusion chromatogram after ultrasonication at 40% amplitude, 10min. The degree of hydrolysis was also increased after ultrasonication by 17.7%, 127.6%, 346.6% as measured by o-phthaldialdehyde derivatization, trichloroacetic acid precipitation and hydrochloric acid hydrolysis, respectively with improved antioxidant property. Our results showed the potential of ultrasonication to improve digestibility and biological properties of sorghum flour.

Keywords: 2,2-Diphenyl-1-picrylhydrazyl; Antioxidant; Iso-2-propanol; Kafirin; Nitric oxide; O-phthaldialdehyde; Pancreatin; Pepsin; Pepsin-pancreatin hydrolysis; Secondary structure; Sorghum; Trolox; Ultrasonication.