Abstract: This study aimed to explore the effect of carboxymethylation modification of wheat bran arabinoxylan (AX), prepared by alkaline extraction, on its physicochemical properties. The effects of NaOH concentration, molar ratio of AX to sodium chloroacetate (SMCA) to NaOH, reaction temperature, and reaction time on the degree of substitution of carboxymethylated AX were investigated through single-factor experiments. The structures, monosaccharide compositions, molecular masses, viscosities and thermal stabilities of carboxymethylated AX with different degrees of substitution were studied. The results showed that when NaOH concentration, AX-SMCA-NaOH ratio, reaction temperature and reaction time were respectively 100 mg/mL, 1:2:2, 65 ℃ and 4 h, the highest degree of substitution of 0.66 was obtained. Infrared spectroscopy analysis proved the success of the carboxymethylation reaction. The total content of xylose and arabinose in carboxymethylated AX with the highest degree of substitution was 14.72%, and the molecular mass was 4.18 × 105 Da, both of which were lower than those (88.72% and 6.07 × 105 Da) of the unmodified arabinoxylan. In addition, when the degree of substitution was increased, the shear viscosity of carboxymethylated AX showed a significant decrease, while the thermal stability was increased obviously, as demonstrated by an increase in the temperature for the maximum thermal decomposition rate from 285 to 306 ℃. The results of this study indicated that the physicochemical properties of carboxymethylated wheat bran AX were quite different from those of the original form. This paper can provide a theoretical basis for studies on the carboxymethylation of wheat bran arabinoxylan and its application.

Key words: wheat bran; arabinoxylan; carboxymethylation; carboxymethylated arabinoxylan; physicochemical properties