Cross-linking of gelatin using plant phenolics for gelatin fabrication

Abstract

Phenolic compounds, natural plant metabolites, are known to react under oxidizing conditions with side chain amino groups of peptides producing complexes with modified properties. In this study, the total phenolics content, expressed in term of gallic acid equivalent (GAE), of crude extract from several local grown phenolic-rich plants were determined. The three highest phenolics-containing crude aqueous extract, which were light roast coffee, butterfly pea and pomegranate solution were used in cross-linking of gelatin. The effect of cross-linking degree on gelling properties of gelatin solutions was studied. The viscosity of 6.67% gelatin solutions and free amino groups were found to deceased when increasing polyphenol:NH₂ molar ratio. Cross-linking of gelatin using gallic acid and the extract of pomegranate and light roasted Arabica coffee caused the gelation and melting temperature to decrease. Butterfly pea extract was the most effective cross-linker that caused gelling and melting complex viscosities to decrease. The swelling ratios of cross-linked gelatin films decreased when increasing polyphenol:NH2 molar ratio. The tensile strength and elongation to break of cross-linked gelatin films increased compared with native gelatin while Young’ modulus decreased (p<0.05). Lower lightness (L*) value, yellowness (b*) and whiteness but higher redness (a*) were observed in cross-linked gelatin films (p<0.05).