Effect of water content of high-amylose corn starch and glutinous rice starch combined with lipids on formation of starch–lipid complexes during deep-fat frying

Abstract Moisture affects the combination of starch granules and fatty acids in deep-fat frying. In this study, high-amylose corn starch (HACS) and glutinous rice starch (GRS) with various water contents were fried in rapeseed oil at 170 °C for 7 min. The complex index (CI) of the GRS–lipid and HACS–lipid complexes improved as the moisture content increased from 6% to 40%; however, further increasing the water content from 40% to 60% led to a decrease in the CI. At a moisture content of 40%, the CI of the HACS–lipid complexes was higher than that of the GRS–lipid complexes. Fatty acid content analysis revealed that the total fatty acid content at different moisture contents in the HACS–lipid complexes was higher than that in the GRS–lipid complexes both before gelatinization and after enzyme hydrolysis. In addition, the total fatty acid content in the HACS–lipid complexes and GRS–lipid complexes at 40% moisture content was the highest among all the measured moisture contents. Scanning electron microscopy revealed that both the HACS and GRS granules lost their integrity after deep-fat frying, and no free lipid droplets were noted among the starch granules after defatting. Both Fourier-transform infrared spectroscopy and fluorescence microscopy verified that HACS combined with lipids yielded a stronger lipid-binding capacity than that of GRS at a moisture content of 40%. The study results may be potentially useful in the deep-fat frying of starchy food to produce foods with lower fatty acid content.