Air Oxidation of Corn Starch: Effect of Heating Temperature on Physicochemical Properties and In Vitro Digestibility

Abstract

Corn starch is heated (100, 120, 140, and 160 °C) under air convective conditions for 4 h. Scanning electron micrograph images show that the treatment produced pores and fractures on the granule surface. Hydroxyl groups of starch molecules are oxidized to carboxyl and carbonyl groups. Increasing heating temperature conditions lead to significant increases in the carboxyl and carbonyl groups contents. Solubility profiles increase while the apparent viscosity of the starch gels (5% w/v) decreases as heating temperature increases. X-ray diffraction shows that the modified starch heated at 160 °C has a crystallinity of 6.42% and a short-range ordering of 0.14 as revealed by Fourier-transform infrared ratio 1047/1022, which is significantly lower than the respective values of 24.42% and 0.2 exhibited by native starch. The onset, peak, conclusion gelatinization temperatures, and enthalpy of the modified starches tend to decrease slightly with increasing temperature. The air oxidation treatment affects the digestibility of corn starch, and as temperature increases, the rapidly digestible and slowly digestible starch fractions decrease, while the resistant starch fraction increases significantly. Overall, the results show that heating of corn starch at mild temperature conditions lead to important modifications of the molecular organization and to moderate oxidation of starch chains.