Study on internal structure and digestibility of jackfruit seed starch revealed by chemical surface gelatinization

Abstract

To understand the contribution of the molecular structure to the digestibility of jackfruit seed starches (JSS) from a new perspective, the starch samples were subjected to chemical surface gelatinization by 4.0 M CaCl 2 solution. After the removal of surface gelatinized part, the remaining JSS granules were obtained with approximately 0%, 15%, 30%, 40%, 50%, 60%, and 70% gelatinization degrees (DG), respectively. The DG values of these starches were calculated by integral optical density (IOD) method that was more accurate and efficient compared to traditional weighing method. The structure features (amylose content, particle morphology, relative crystallinity, short-range ordered structure, thermal properties) and in vitro digestion of JSS were studied and correlated as Pearson's matrix. The morphology of remaining JSS granules showed a rough surface with a lamella structure. The distribution of amylose content in the middle layer was slightly higher than that in the periphery and tended to be more uniform. The resistant starch content of JSS granules was in a fluctuant decrease trend from the periphery to the core, which was consistent with the distribution of relative crystallinity. The remaining JSS granules with higher degrees of gelatinization exhibited lower gelatinization temperature and enthalpy. The results imply that the JSS is hydrolyzed by hydrolase from the dense periphery to the relatively loose interior. And, the lower susceptibility of starch to hydrolase is mainly ascribed to the stable double helix structure of outer layer and alternating crystalline structure. • Surface gelatinized remaining jackfruit seed starch granules were obtained. • Integral optical density method was practical to monitor the gelatinization degree. • The molecular structure and digestibility were correlated as Pearson's matrix. • The relative crystallinity is related to resistant starch of jackfruit seed starch. • Jackfruit seed starch was hydrolyzed from the dense periphery to loose interior.