Acetylation Modification of the Polysaccharides from Portulaca oleracea L. and Their Antioxidant Activities
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Abstract:
Portulaca oleracea L. was used as the raw material. Polysaccharides from Portulaca oleracea L. (POP) were extracted by hot water, and acetylated with acetic anhydride to yield Ac-POP. Taking the degree of substitution as an index, the effects of reaction time, reaction temperature and material-liquid ratio on the degree of substitution of Ac-POP were investigated by the single factor experiments. The conditions for acetylation modification of POP were further optimized, and the antioxidant activities of POP and Ac-POP were evaluated. The experimental results showed that the optimal conditions for the acetylation modification of POP were: reaction time 2.78 h, reaction temperature 51.90 ℃, material-liquid ratio 1: 28.15 (g/mL). Under such optimal modification conditions, the degree of substitution of Ac-POP was 0.60. The infrared spectroscopy analysis of the original polysaccharide and acetylated polysaccharide showed that the acetylation of the polysaccharide from Portulaca oleracea L. was successful. The POPs before and after modification had a certain ability to scavenge free radicals and exhibited a certain dose-dependent relationship. In the range of 0.05~5.0 mg/mL, the maximum scavenging rates were 69.73% and 64.54% for POP and Ac-POP against DPPH free radicals, respectively, 43.48% and 25.04% against ·OH, respectively, and 78.86% and 79.16% against O2-·, respectively. As the concentration increased, the antioxidant activity of Ac-POP increased gradually. Antioxidant activity studies revealed that compared with POP, the scavenging capacities of Ac-POP against DPPH free radicals and ·OH decreased, but that against O2-· increased.
