Effect of roasting process on enzymes inactivation and starch properties of highland barley

Abstract

Roasting may be beneficial to extend the shelf life by inactivating the lipases and peroxidases in highland barley, but it may lead to the deterioration of starch quality. In this study, the pre-treatment techniques of pearling and tempering were tried to improve the efficiency of inactivation, and different roasting treatment parameters were compared to obtain the optimum treatment conditions, under which thermally degraded starch may be less. Pearling had been proved to be an effective means in reducing enzyme content, and tempering could improve the sensitivity of enzymes to heat. Synergism of the two pre-treatment methods increased the inactivation of lipase and peroxidase in highland barley to 80% and 100%, respectively, and the optimal pre-treatment and roasting condition was P20M16T16 (20% pearling rate, 16% moisture, and 16 min treatment time) at 180 °C. Under this condition, the starch quality was basically consistent with those of control starch. For roasting treatment starch, the birefringence intensity, swelling power, and solubility slightly decreased and the polarized cross also still existed, while the relative crystallinity slightly increased and the crystal type unchanged. Roasting treatment starch showed higher pasting temperature and lower paste viscosity, and the increasing To, Tp, and the decreasing enthalpy.