Octenylsuccinic anhydride group distribution in esterified maize starches with different granular structure and its effect on starch digestibility

Abstract

This study aimed to investigate the distribution of octenylsuccinic anhydrid (OSA) groups in different maize starch granules and its effect on starch digestibility. OSA starches with two substitution degrees (DS) about 0.02 and 0.05 were prepared. Confocal Laser Scanning Microscopy and Confocal Raman spectra showed that OSA groups distributed mainly on the granules surface at low DS of all the starches. The content of OSA groups in center area increased with the increasing DS for A-type starch, while the content of OSA groups decreased from the surface to inner at both low and high DS for B-type starch. This demonstrated that OSA reagent could travel through the granule pores and channels to arrive at the cavity in the A-type starch. However, due to a dense internal structure for B-type starch, OSA groups could graft into the granule only by penetration. Analysis of X-ray Diffraction showed that the degree of crystallinity slightly decreased as the increasing DS of OSA starch. The content of rapidly digestible (RDS) and slowly digestible starch (SDS) decreased, but that of resistant starch (RS) increased in the raw OSA starches with the increasing DS (RDS: 23.0%, RDS: 8.3%, RS: 72.3% for the raw waxy maize starch with 0.05 DS). It indicated that the hydrolysis of the OSA starches was influenced by the distribution of OSA groups.