Vanillic acid and coumaric acid grafted chitosan derivatives: improved grafting ratio and potential application in functional food

Abstract

Chemically modified biofunctional chitosan derivatives may open up new applications in functional food and nutraceuticals development. Two new conjugates, namely vanillic acid and coumaric acid grafted chitosan derivatives were developed and comparative evaluation of their antioxidant and antimicrobial activities was carried out with ferulic acid and gallic acid grafted chitosan. The synthesized water soluble (1.0–4.5 mg/mL) chitosan-phenolic acid conjugates showed characteristic FTIR-spectroscopy band at around 1644 and 2933 cm−1. Free phenolic acid was not observed in TLC plate of the chitosan-phenolic acid conjugates and UV–vis spectra showed primary absorption peak of the corresponding phenolic acids confirming the grafting reaction. Total antioxidant activity of the chitosan-phenolic acid derivatives ranged from ~12 to 29 g ascorbic acid equivalent/100 g of the conjugate. Minute quantity of the derivatives (~57–162 μg and 82–109 μg respectively) could give 50 % inhibition of 2, 2′-diphenyl-1-picrylhydrazyl radical and hydroxyl free radical. Broad spectrum antibacterial activity was observed for all four derivatives against an array of foodborne pathogens and spoilage bacteria. Coumaric acid grafted chitosan showed promise as a food preservative as it inhibited the growth of several foodborne pathogens and spoilage bacteria, including Staphylococcus aureus. Among all the four derivatives, ferulic acid and gallic acid grafted chitosan had lowest minimum inhibitory concentration against Staphylococcus aureus and Pseudomonas aeruginosa respectively.