Extraction processing optimization of polyphenols and polysaccharides from rapeseed protein processing waste liquor

Abstract: Rapeseed protein processing waste liquor contains a variety of natural antioxidant products, which include polyphenol, polysaccharide, peptide, and so on. To realize the comprehensive utilization of rapeseed protein processing waste liquor and gain high value-added products to improve the overall economy, the extraction efficiency and the antioxidant activities of polyphenols and polysaccharides in waste liquid from production of rapeseed protein were researched in this paper. First of all, effects of extraction temperature, ethanol concentration and extraction time on the extraction rate of polyphenols and polysaccharides from waste liquid were investigated by single-factor experiments to acquire the appropriate ranges of extraction parameters. Then a Box-Behnken design (BBD) was applied to evaluate the effects of extraction temperature, ethanol concentration and extraction time on the extraction efficiency and their interactions at 3 equidistant levels. The ranges of the 3 independent variables i.e. extraction temperature, ethanol concentration and extraction time were 50-70 ℃, 50%-70% and 15-45 min, respectively, which were based on the results of single-factor experiments. The result indicated that ethanol concentration was the most significant variable, followed by extraction temperature and time according to the regression coefficient significance of the equation and the gradient of slope in 3D (three-dimensional) response surface map. The optimum conditions could be modified as follows: Extraction temperature of 60 ℃, ethanol concentration of 65% and extraction time of 31 min. Under the optimal conditions, extraction ratios of polyphenols and polysaccharides were 2.19% and 8.14%, respectively, which were well-matched with the predicated values of 2.19% and 8.18% obtained from the models. The results revealed that the regression equations and models were reliable to predict the influences of factors on extraction ratios of polyphenols and polysaccharides. In addition, anti-oxidative activities of polyphenols extract and polysaccharides extract in vitro were evaluated by scavenging activity of DPPH (1,1-diphenyl-2-picrylhydrazyl radical 2,2-diphenyl-1-(2,4,6- trinitropheny) hydrazyl) and hydroxyl radical as well as reducing power. The result showed that the DPPH radical scavenging abilities of polyphenols extract and polysaccharides extract increased from 32.63% to 93.53% and from 18.65% to 77.97% with the increasing of their concentrations from 0.10 to 0.50 mg/mL and from 0.40 to 2.40 mg/mL, respectively. Half inhibitory concentrations of polyphenols extract and polysaccharides extract for scavenging DPPH were 0.20 and 1.45 mg/mL respectively according to their regression equation. Hydroxyl radical scavenging abilities of them increased from 36.92% to 83.62% and from 13.59% to 78.60% with the increasing of their concentrations from 5.00 to 30.00 mg/mL and from 0.80 to 3.80 mg/mL, respectively. Half inhibitory concentrations of polyphenols extract and polysaccharides extract for scavenging hydroxyl radical were 10.85 and 2.38 mg/mL respectively according to their regression equation. The reducing abilities also increased with the increasing of the concentrations of polyphenols extract and polysaccharides extract. In contrast, reducing ability of polyphenols extract was stronger than that of polysaccharides extract. From these results, for different free radicals, the scavenging ability of polyphenols and polysaccharides was different, and showed a good dose-effect relationship in the range of mass concentrations. The DPPH free radical scavenging rate and reducing ability of polyphenols extract were both significantly higher than that of polysaccharides extract under the same mass concentration, while the polysaccharides extract had a stronger scavenging ability to hydroxyl radical than polyphenols extract. In the end, the phenolic ingredients in samples were analyzed by HPLC (high performance liquid chromatography). The result indicated that polyphenols extract was rich in phenolic compounds such as cumaric acid, syringic acid, pcoumaric acid, sinapinic acid and benzoic acid. The concentration of cumaric acid was 2.65 mg/g and that of sinapinic acid even reached 5.57 mg/g.