Persimmon tannins enhance the gel properties of high and low methoxyl pectin

•Persimmon tannins increased pectin's gel strength.•All tannin-pectin complex gels showed a rapid formation with G′ > G′′.•Pectin/tannin complex gels had aggregated network.

The effects of persimmon tannins with different average degrees of polymerization (DP26 and DP5) on the rheological and microstructural properties of high- and low-methoxyl (HM/LM) pectin gel were investigated. The gel properties were analyzed by large-deformation and dynamic rheological measurements, and the complex gels microstructure was also characterized using scanning electron microscopy (SEM). Persimmon tannins (DP26/5) could significantly enhance the strength of HM and LM pectin gels (p < 0.05) that was about twice that of pectin alone, especially with high concentrations of tannins (2 g/L). Besides, the rheological results indicated that the addition of persimmon tannins increased the gelling ability of HM/LM pectins, and all tannin-pectin complex gels displayed a typical weak gel-like (G′ > G″) structure. Furthermore, SEM analyses revealed the heterogeneous and aggregated network of the gels containing persimmon tannins, because of the intermolecular cross-linking between the carboxyl groups of pectin molecule and the phenolic hydroxyl groups of tannins through hydrogen bonds and hydrophobic interaction. Overall, DP5 tannins enhanced gel properties of HM/LM pectins more than DP26 tannins, probably due to the larger size, steric hindrance and self-association of DP26 tannins.