Morphology and structure of chestnut starch isolated by alkali and enzymatic methods

The structure and morphology of starch from fruits of two chestnut (Castanea sativa Mill.) varieties, Martainha and Longal, isolated by alkaline (A3S) and enzymatic (ENZ) methods were assessed. Chestnut starch granules were found to be round and oval in shape, consisting of medium/small granules, with a mean granule size ranging between 9 and 13 μm. Isolated chestnut starch appeared to the naked eye as a white powder, with high values of L^∗, and the Longal variety produce starches duller than Martainha. No differences between samples were observed by FTIR analysis. The X-ray patterns of isolated starches are of C-type (more specifically of C_b type) with a relative crystallinity between 31.5% and 39.8%. The ¹³C CP/MAS NMR spectra are similar for both varieties but different for the used isolation methods. The amorphous phase in the starch granules isolated by A3S methods was lower than that of the starch extracted by the ENZ method, making the B-type allomorph in the C-type starch granules more evident than in the A-type. Those differences in the structure of isolated starches are shown by a lower degree of damage, and a higher level of crystallinity of starches isolated by the A3S method, which means that its original structure is less affected or partially destroyed. This study would be helpful to better understand the relationships among structure and functional properties for a eventual industrial application of chestnut starches.