Small and large oscillatory shear behaviors of gelatin/starch system regulated by amylose/amylopectin ratio

Abstract

This work explores the influence of starch amylose/amylopectin ratio on the gel-related features of gelatin/starch system using small and large amplitude oscillation shear methods. The higher self-aggregation and self-entanglement ability of amylose reduced the miscibility of gelatin and starch, and increases zero-shear viscosity (ŋ0) and reduces sol-gel transition temperature (Tgel) by enhancing the difficulty of molecule movement and thus the difficulty of gel formation. The gelatin/amylopectin-rich system has higher gel hardness and wider linear viscoelastic region, which are related to the higher integrity and uniformity of network structure. The gelatin/amylose-rich system shows enhanced ability to resist deformation against external shear forces (suggested by higher storage and complex modulus) under small amplitude oscillatory shear (SAOS), which is ascribed to the larger rigidity and entanglement degree of amylose. At strain amplitude up to 50% (middle amplitude oscillatory shear, MAOS), gelatin/amylose-rich system exhibits reduced structure recovery ability (reflected by larger semi-minor axis of ellipse, and lower strain amplitude for inflexion of elastic stress) under MAOS, but enhances restructuring capacity at strains of 500% and 1000% (large amplitude oscillatory shear, LAOS) (indicated by occurrence of secondary loop) than gelatin/amylopectin-rich system. Those seemingly contradictory phenomena are correlated with the preference of hydrogen bond forming ability among amylose rather than with gelatin. This weakens interactions between amylose and gelatin and thus inhibits recovery of bulk structure under MAOS, but is favor for the formation of amylose aggregations, which is helpful for the local structure restructuring and thus enhances structure restructuring capacity under LAOS. The results help us comprehensively understand the gel-related properties of gelatin/starch system and are valuable for rational design of gelatin/starch systems with improved gel-related features.