Effect of protein types on structure and digestibility of starch-protein-lipids complexes

Ternary systems of starch, lipids, and protein have been extensively investigated for modulating starch digestibility recently. Nevertheless, how the proteins influenced the formation of starch-protein-lipids complexes was not resolved. This study aimed to investigate the effects of proteins with different isoelectric points (whey protein isolate and A-type gelatin) on structures and digestibility of starch-protein-linoleic acid (LA) complexes. Results showed that proteins and LA significantly increased starch ordered structures and reduced the digestibility. Due to the emulsifiability of proteins, they increased LA solubility in water and thereby promoted the formation of starch-protein-LA complexes. Accordingly, the starch-lipids-protein complexes had more ordered structures and a lower starch digestibility than did the LA- and proteins-complexed starches. Comparing with starch-GE-LA complexes, the starch-WP-LA complexes had more short-range ordered structure, helical structure, and crystals and a lower starch digestibility. The mechanism underlying such an observation should attribute to the differences in intrinsic properties (e.g., isoelectric point) between GE and WP. Proteins (e.g., GE) with an isoelectric point higher than 7.0 may easily compete with starch for LA and retard the formation of starch-protein-lipids complexes comparing with the protein has an isoelectric point lower than 7.0.