Insights into the multi-scale structure and in vitro digestibility changes of rice starch-oleic acid/linoleic acid complex induced by heat-moisture treatment

The study presents an innovative approach using heat-moisture treatment (HMT) to prepare rice starch-oleic acid (OA)/linoleic acid (LOA) complex. Relationship of the multi-scale structure- in vitro digestibility of rice starch-OA/LOA complex induced by HMT was established in this work. Herein, HMT induced the formation of single helices complex between OA/LOA and amylose or long side chains of amylopectin, which formed more V-type crystallite. HMT assisted complexation with OA/LOA resulted in higher ordered molecular chain aggregations in amorphous amylose background area, reduced the amorphous lamellae and made the double helices and A-type crystallite perfectly arranged. These structural alternations inhibited the molecular interactions (e.g., binding ability, catalyzed location) between rice starch and α-amylase, which eventually increased the resistant starch (RS) content and decreased the slow digestible starch (SDS) content. Moreover, HMT treated rice starch formed type II complex with OA and type I complex with LOA, and all the referred changes went more obvious with the increasing amount of OA than LOA. The results suggested that the OA/LOA was inserted inside the amylose spiral cavity and the amorphous lamellae of rice starch. The current study exhibited an in-depth research of the multi-scale structure within rice starch-OA/LOA complex and proposes a promising approach to ensure the starch products have designated digestibility.