Self-assembly Of Caffeic Acid And Starch And Its Effects On Physicochemical Properties And In Vitro Digestibility Of Starch

Starch is the main source of carbohydrate in our daily life.Inhibition of starch digestibility by adding functional components into starch can meet the requirement of the diabetics.Caffeic acid is a kind of small molecular phenolic acid which can inhibit the activity of a-glucosidase and a-amylase.In the present study,the effect of caffeic acid on the activities of a-glucosidase and a-amylase was determined,and the complexes of different starch and caffeic acid were prepared by thermosol method.The particle morphology,crystallinity,thermodynamic properties,molecular structure and in vitro digestibility of starch-caffeic acid complexes were analyzed.The main results are as follows.(1)Caffeic acid dose-dependently inhibited the activity of a-glucosidase and a-amylase,and the half-inhibitory concentrations(IC50)of a-glucosidase and a-amylase were 0.031 and 1.208 mg/mL,respectively.The inhibition type of caffeic acid on a-glucosidase and a-amylase was reversible anti-competitive inhibition and irreversible inhibition,respectively.(2)The highest inclusion rate of caffeic acid in starches was 30.84%in waxy maize starch,followed by 13.27%in normal maize starch and 8.67%in high amylose maize starch,but no inclusion rate was detected in potato starch.Compared with the control group,the amylose content of caffeic acid-potato starch increased by 4.91%,and that of caffeic acid-high amylose maize starch increased by 10.95%,indicating that thermosol treatment of caffeic acid in starch can improve the amylose content of starch.The relative crystallinity of potato starch,common corn starch,and waxy corn starch decreased after interaction with caffeic acid,suggesting that caffeic acid may delay or inhibit starch retrogradation.The stretching vibration of O-H in FTIR spectra of caffeic acid-waxy maize starch was enhanced.The results of 1H-NMR showed that the hydroxyl peak of potato starch and waxy corn starch in 4.4-5.6 ppm was enhanced when they were combined with caffeic acid.These results indicated that caffeic acid may interact with starch molecules by forming hydrogen bonds and more readily form hydrogen bonds with amylopectin.(3)After the combination of caffeic acid with starches,the content of resistant starch increased slightly,and the glycemic index decreased.Caffeic acid inhibited the digestibility of waxy maize starch most significantly,the resistant starch content of waxy maize starch increased by 3.2%and the glycemic index decreased by 8.77%.After self-assembly of caffeic acid and starch,the crystallinity and digestibility of starch all decreased,and the results of correlation analysis showed that the digestibility and crystallinity of starch were significantly negatively correlated.Therefore,the decrease of digestibility of starch-caffeic acid complex is less related to the change of starch structure after self-assembly,but mainly attributed to the inhibition of caffeic acid on amylase.