Effects of Heat-Moisture Treatment on Nutritional Quality and Dough Properties of Legume Flours

Heat-moisture treatment (HMT) was evaluated for its effects on the antioxidant, nutritional and dough properties of different legume flours. The results showed that the contents of total phenols and flavonoids and the antioxidant capacity of adzuki bean and pea flour initially increased and then decreased with the increase in HMT time, reaching the maximum at 0.5 and 1.0 h, respectively; whereas the contents of total phenols and flavonoids of white kidney bean flour increased with HMT time up to 8.0 h. HMT had consistent effects on the scavenging activity against 2,2’-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) cation radical and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and the contents of total phenols and total flavonoids. The major fatty acids in all three legume flours were palmitic acid, stearic acid, linoleic acid, cis-11-eicosatetraenoic acid and oleic acid. HMT for 2.0 h and longer had a significant effect on the contents of oleic acid, linoleic acid and cis-11-eicosatetraenoic acid in white kidney bean flour. After HMT, the contents of free amino acids in red and white kidney bean flour decreased significantly due to its involvement in the Maillard reaction, while bound amino acids in pea flour were released, thereby increasing the amount of free amino acids. Scanning electron microscopy (SEM) showed pores in and protein adhesion on the starch granules due to protein denaturation and partial gelatinization of starch with increasing HMT time. The recrystallization of starch resulted in a decrease in peak, trough and setback viscosity, and poorer shear resistance of legume flour. The results of dough water distribution showed that the relaxation times T₂₁ and T₂₂ of adzuki bean flour increased after HMT, and the dough formation of adzuki bean flour was better than that of the other two flours. Thermomechanical analysis showed that HMT enhanced protein weakening in mixed legume-wheat flour doughs and inhibited starch retrogradation, thus improving product quality.