Functional properties and in vitro antioxidant and antibacterial effectiveness of pigskin gelatin films incorporated with hydrolysable chestnut tannin

Abstract

The impact of the incorporation of 10 wt.% of hydrolyzable chestnut tannin (CT) into pigskin gelatin (G) films plasticized with glycerol (Gly) on the physico-chemical properties as well as the in vitro antioxidant and antibacterial effectiveness against food-borne pathogens such as Escherichia coli and Streptococcus aureus was investigated. A higher tendency to both, redness (a*) and yellowness (b*) coloration characterized gelatin films incorporated with CT. The reduced lightness (L) and transparency of gelatin-CT films plasticized with 30 wt.% Gly might be associated with certain degree of phase separation which provoked the migration of the plasticizer to the film surface. The incorporation of CT and glycerol affected the chemical structure of the resultant films due to the establishment of hydrogen interactions between components as revealed by Fourier transform infrared spectroscopy. These interactions reduced gelatin crystallinity and seemed to be involved in the substantial decrease of the water uptake of films with tannin, irrespective of the glycerol level. Such interactions had minor effect on tensile properties being similar to those of the control films (without CT) at the same glycerol level. Films modified with 10wt.% CT showed significant (P<0.05) DPPH radical scavenging activity, c.a. from 0±0.033 % to 87.1±0.002% for CT-free and CT-congaing gelatin films. The limited inhibitory activity films incorporated with 10wt.%CT against the selected bacteria evidenced by disk diffusion method probably resulted from the interactions within the film restricting the diffusion of the active agent into the agar medium. The more modest protective effect observed against a Gram-positive bacterium (S. aureus) was also discussed.