Genotype specific starch characteristics in relation to resistant starch formation in table potatoes

Abstract

Table potatoes are important staple foods with a higher satiety index than rice or pasta, but also reach a higher glycemic index (GI), leading to contradictory dietary recommendations. Previous studies identified resistant starch (RS) content as primary criterium for the GI. Hence, the relevance of starch molecular properties for genotype specific RS formation was investigated. Six common table potato varieties were used to investigate the starch pasting and digestibility in whole tubers and their isolated starches. A Micro-Visco Amylograph was used to simulate the cooking process for isolated starches and determine their pasting curves. In vitro starch digestibility was determined for raw freeze-dried cooked tubers kept at 4 °C for up to 72 h and for isolated starches. Moreover, important molecular starch properties, including granule size distribution, molar mass distribution, amylose content and inter- and intra-molecular structures were determined. The results show substantial differences in starch digestibility and pasting characteristics among genotypes. Soraya starch showed small and low-branched amylopectin and small granule size as characteristics for rapid RS formation in isolated starch, which was not evident in the whole tuber. In contrast, Huckleberry Gold formed RS in the tuber already shortly after cooking, whereas slow RS formation was evident in the isolated starch. The results suggest, that starch structural characteristics play a role in RS formation, but non-starch constituents of the tuber have to be considered as well. The results help to identify breeding goals for varieties with low GI and high nutritional value.