Abstract: The effects of different heat treatments: steaming at atmospheric pressure (SAP) and boiling at atmospheric pressure (BAP) on the physicochemical properties of Chinese yam flour were analyzed by rapid viscosity analysis (RVA), rheometry, Fourier transform infrared (FTIR) spectroscopy and scanning electronic microscopy (SEM). The results showed that the wettability and dispersibility were improved by both heat treatments, which decreased from 7.77 and 4.68 min to 2.11 and 0.52 min after 30 min of SAP, respectively. After heat treatment, the pasting temperature, peak viscosity, minimum viscosity, breakdown value, and final viscosity decreased, while the iodine blue value increased with the increase in heat treatment time. The apparent viscosity of heat-treated yam flour declined steeply and then tended to stable with increasing shear rate, exhibiting shear thinning. Heat treatment destroyed the structure of yam flour, decreased the degree of structural orderliness and resulted in an irregular appearance. It was also found that the change of color caused by atmospheric boiling was smaller than that caused by atmospheric steaming, while the change of solubility caused by atmospheric steaming was smaller than that caused by atmospheric boiling. After steaming, the solubility increased from 16.05 to 17.89 g/100 g. The solubility of SAP treated sample was higher than that of the sample subjected to BAP for the same durations. The boiling treatment resulted in a significant decrease in the contents of functional components; that is, the contents of polysaccharides, total polyphenols, total flavones and allantoin decreased from 2.67, 0.076, 0.084, 0.445 g/100 g to 1.75, 0.070, 0.071 and 0.288 g/100 g after 30 min, respectively, while the steaming treatment resulted in losses of total polyphenols and flavonoids, which decreased from 0.076 and 0.084 g/100 g to 0.055 and 0.061 g/100 g after 30 min, respectively. Compared with BAP, SAP was a better processing method for cooked Chinese yam flour.

Key words: Chinese yam flour, heat treatment, steaming at atmospheric pressure, boiling at atmospheric pressure, physicochemical properties