Impact of acid and heat–moisture treatment combination on physicochemical characteristics and resistant starch contents of sweet potato and yam starches

Abstract

The objective of this study is to investigate formation of slowly digestible starch (SDS) and resistant starch (RS) and change in physicochemical properties of sweet potato and yam starches under a combination of acid and heat–moisture treatments using three mild organic acids including acetic acid, lactic acid and citric acid and heating temperature at 110°C for 8 h. The results show that the SDS and RS in sweet potato starch significantly increased from 6.6 and 14.7% in native starch to 8.7–13.2% and 37.5–42.1% in acid and heat–moisture treated starches, respectively. Likewise, the SDS and RS in yam starch increased from 4.7 and 21.6% in native starch to 10.0–11.3% and 39.0–46.4% in the treated starches, respectively. The RS content in the acid and heat–moisture treated starches was also significantly higher than that of the heat–moisture treated starches without acid hydrolysis. Yam starch produced higher amount of RS under acid and heat–moisture treatment as compared to sweet potato starch at the same condition. Swelling power and viscosity of starches significantly decreased, whereas the solubility significantly increased after treatments. The citric acid had the most impact on RS formation and starch properties, followed by lactic acid and acetic acid. As a result, the combination of acid and heat–moisture treatment is a useful method to produce higher amount of resistant starch, which can be applied for functional foods.