Understanding the dual impact of oat protein on the structure and digestion of oat starch at pre- and post-retrogradation stages

Although extensive research has been conducted on the effects of protein-starch interaction on the gelatinization and microstructure of starch gels, the starch retrogradation process and protein component has been overlooked. Moreover, the dual regulatory effects of oat protein on starch gel microstructure and starch digestibility pre-and post-retrogradation still remains largely unexplored. In this study, the gelation behaviors, structure, and digestibility of oat protein-oat starch mixtures pre- and post-retrogradation were determined. The oat proteinstarch samples exhibited lower setback values (314 cP) and higher relaxation peak time T-23 (363.62 ms) compared to the oat starch samples (1994 cP and 160.51 ms), indicating that oat protein effectively delayed the short-term retrogradation and weakened the water-binding capacity of starch gel. Morphological and rheological analyses revealed that prior to retrogradation, oat protein promoted the formation of a looser network structure with weak shear resistance and consistency, while, after 7 d of retrogradation, an appropriate protein content (<30 %) facilitated the formation of an orderly and uniform honeycomb porous gel structure. Furthermore, oat protein increased the resistant starch content (RS) from 18.16 % to 32.66 % before retrogradation. After retrogradation, oat protein slowed down the increase in RS content by inhibiting the formation of starch crystal structure. Noteworthy, different oat protein components play various roles in starch gelatinization and retrogradation process.