Effect of brewers spent grain addition and screw speed on the selected physical and nutritional properties of an extruded snack

Abstract

The effect of screw speed (100–300 rpm) and addition of brewers spent grain (BSG, 0–30% based on the maize flour used) on the approximate composition (crude protein, crude fat, total starch, crude fibre), physical (expansion, hardness, bulk density, SME, water absorption and solubility indexes), nutritional (total antioxidant capacity, TAC; total phenolic compounds, TPC; phytic acid, PA; protein in vitro digestibility, PIVD; resistant starch, RS) and colour (Hunter L, a, b) properties of an extruded snack food was investigated. A decrease in hardness was observed at increased screw speeds whereas scattered data was obtained with increasing BSG levels. Results indicated that addition of BSG resulted in reduced expansion and increased PA, PIVD and RS values ( P < 0.05). On the other hand, addition of BSG to the samples has no significant effect on the TAC and TPC values ( P < 0.05). Increased screw speeds resulted in increased expansion and decreased RS values ( P < 0.05). Screw speed has no significant effect on the TAC, TPC, colour, PA and PIVD values of BSG added samples ( P < 0.05). Addition of BSG caused a decrease in the Hunter L values giving darker samples.