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.
Therapeutic potential of water soluble vitamins has been known for long and in recent times they are being widely supplemented in processed food. Phenolic acid-grafted chitosan derivatives can serve as excellent biofunctional encapsulating materials for these vitamins. As a proof of concept, thiamine and pyridoxine loaded ferulic acid-grafted chitosan microspheres were developed. Ferulic acid was successfully grafted on chitosan by a free radical mediated reaction and the structure was confirmed by FTIR and NMR analysis. When compared to FTIR spectra of chitosan, intensity of amide I (at around 1644 cm(-1)) and amide II (at around 1549 cm(-1)) bands in spectra of ferulic acid-grafted chitosan were found increased, indicating formation of new amide linkage. Strong signals at δ = 6.3-7.9 ppm corresponding to methine protons of ferulic acid were observed in NMR spectra of ferulic acid-grafted chitosan, suggesting the successful grafting of ferulic acid onto chitosan. Grafting ratio of the derivative was 263 mg ferulic acid equivalent/g polymer. Positively charged particles (zeta potential 31 mv) of mean diameter 4.5 and 4.8 μ, corresponding to number distribution and area distribution respectively were observed. Compact microspheres with smooth surfaces and no apparent cracks or pores were observed under scanning electron microscope. Efficient microencapsulation was further proved by X-ray diffraction patterns and thermal analysis. Preliminary anti-inflammatory activity of the vitamin-loaded microspheres was demonstrated.
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