Study On Antioxidant And Antibacterial Activities Of Dialdehyde Microcrystalline Cellulose

Dialdehyde microcrystalline cellulose (DAMC) is a cellulose oxide derivative. With highly active dialdehyde functions which makes the material has high reactivity, DAMC can react with amino and generate Schiff base. There are some advantages in physical and mechanical properties, biocompatibility and biodegradability of DAMC. In addition, it is environmentally friendly and low toxicity. This character enables DAMC to be widely employed in biological medicine, environmental protection and paper making applications.The aim of this study was to investigate the antioxidant and antibacterial activities of DAMC with different aldehyde contents to provide a theoretical basis for the development of a new type of antioxidants and antimicrobial agents.In this work, DAMC with varied aldehyde contents were prepared from microcrystalline cellulose (MCC) by periodate oxidation for ditferent reaction time. A series of characteristic analyses of products and MCC were carried out. The antioxidant activity and the antibacterial activities of DAMC were studied as well. The results of scanning electron microscopy (SEM) indicated that the particle size of DAMC became shorter than that of unoxidized MCC, and the surface erosion of MCC molecules was observed. The formation of aldehyde and hemiacetal groups of the DAMC was confirmed by Fourier transform infrared spectroscopy (FT-IR) spectra. The results of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and powder X-ray diffraction demonstrated that the degree of crystallinity and thermal stability of DAMC decreased as their aldehyde contents increased. The antioxidant activity assays demonstrated that the DAMC with 6.59 mol/g of aldehyde content showed the highest scavenging effect on DPPH, ABTS, and hydroxyl radicals with half-inhibitory concention(IC50) values of 5.9 mg/mL, 5.6 mg/mL and 8.1 mg/mL; its reducing power was also the best among the other samples. The best reaction conditions for DAMC combined with protein was that the aldehyde content of DAMC is 6.59 mmol/g, pH＝8, the temperature is 40℃ and the reaction time is 4h. Under the reaction conditions, the protein adsorption rate for DAMC had been reached 46.58%. The antimicrobial activity test results showed that DAMC with high aldehyde contents (more than 5.14 mmol/g) exhibited the strongest antibacterial activity against S. aureus, B. subtilis, E. coli and S. typhimurium, and their MIC values were 15, 15, 15, and 30 mg/mL, respectively. Under the condition of 37℃ and atmospheric pressure, the antibacterial kinetics model of the DAMC with 6.59 mmol/g of aldehyde content accords with the mathematical model. For the constant k, we found k =16.83 h-1, 15.98 h-1, 44.70 h-1 and 40.79 h"1 for S. aureus, B. subtilis, E. coli and S.typhimurium, respectively. It can be seen that the DAMC with high aldehyde content exhibited significant antioxidant and antimicrobial properties which can be used as potential additives and coating materials in the food and pharmaceutical industry.