Enzymatic digestion of amylose and high amylose maize starch inclusion complexes with alkyl gallates

The interactions between starch and phenolic compounds have a great impact on the physicochemical and nutritional properties of starch-containing foods. One particular form of the interaction is starch-guest inclusion complexation, which is a specific non-covalent interaction formed between starch and guest molecules. This study investigates complexation ability and enzymatic digestibility profiles of amylose and high amylose maize starch (HAMS) inclusion complexes with gallic acid (GA) and alkyl gallates of various chain lengths, including butyl (BG), octyl (OG), dodecyl (DG), hexadecyl (HG), and octadecyl (SG) gallates. The formation of inclusion complex was examined by complementary techniques including differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. The digestibility profiles, represented as rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) contents, were obtained through simulated in vitro enzymatic digestion assays. The results showed that while GA, BG, and OG were not capable of forming inclusion complex with either amylose or HAMS, gallates with longer alkyl chains were able to form more stable inclusion complexes. Precipitated amylose and HAMS samples without inclusion complex formation contained the lowest RDS and highest SDS + RS, probably due to starch retrogradation. Amylose and HAMS inclusion complexes with long alkyl chain, particularly HG and SG, also possessed the lowest RDS and highest SDS + RS, but higher SDS proportions than the non-complexed starch samples. It was suggested that the inclusion complexes, especially amylose-HG and SG, and HAMS-DG, HG, and SG, might have contributed to the increase in SDS content. The water insusceptibility and high thermal stability of these inclusion complexes helped retard the starch digestion. The resistant yet steady digestion behavior of the starch-gallate inclusion complexes has significant implications in modulating glycemic response, as well as enabling a slow and sustained release of bioactive guest compounds into the gastrointestinal tract.