Structural Characteristics and In Vitro Digestibility of Malic Acid-Treated Corn Starch with Different pH Conditions

The objective of this study was to investigate the influence of pH value on the in vitro digestibility of malic acid-treated corn starch in relation to its structural properties. Varying pH values (1.5-8.5) of 2 M malic acid solution were combined with corn starch in a forced-air oven at 130 degrees C for 12 h. Using Fourier-transform infrared spectroscopy (FT-IR), carbonyl groups were detected in malic acid-treated corn starch, indicating cross-linking through esterification. As the pH value of malic acid-treated corn starch decreased from 8.5 to 1.5, the resistant starch content increased from 18.2 to 74.8%. This was the result of an increased degree of substitution and was maintained after gelatinization. The granular structure of malic acid-treated corn starches was not destroyed, and the starches maintained birefringence. This malic acid-treated corn starch could be utilized in heat processed foods such as bread and cookies as well as in products with reduced calories.