Characterizing the chemical features of lipid and protein in sweet potato and maize starches

AbstractThe chemical features of lipid and protein in sweet potato and maize starches were investigated by comparing their IR and NMR spectra before and after hydrolysis by lipase or alkali protease. The results showed that the absence of C–H stretching vibration near 2930 cm−1 in IR spectra of sweet potato and maize starches hydrolyzed by lipase or protease was probably due to an interaction of amylose and amylopectin without lipid or protein. The results of 13C NMR showed that the lipid and protein were attached to each other in those two starches and both connected with maize starch, but only lipid connected directly with sweet potato starch. Lipid in starch probably inhibits crystal formation of starches, but protein in starch promotes the process. The characteristic fatty acids for sweet potato starch were CH3(CH2)13COOH + Lys + Glucose (G) and CH3(CHCH)4(CH2)4COOH + G, for maize starch, CH3(CHCH)6(CH2)29COOH. The typical peptides for sweet potato starch might be Lys + Phe + Ala + G + G and Leu + Lys + Leu + G, for maize starch, they were Asp + Val + Leu + Val and Asp + Glu + Leu + Glu.