Optimization of extraction and characterization of physicochemical, structural, thermal, and antioxidant properties of mucilage from Hollyhock’s root: a functional heteropolysaccharide

Abstract

In this study, the effect of root powder to water (RP/W) ratio (0.05, 0.10, and 0.15% w/v), temperature (30, 60, and 90 °C) and pH (3, 7, and 11) were investigated by response surface methodology to extract mucilage. The optimized conditions of mucilage extraction were the RP/W ratio (0.104% w/v), temperature 50.54 °C, and pH 3.00. The maximum content of protein, carbohydrate, and fat achieved at a temperature of 30 °C. The maximum content of dry mucilage, total phenolic and antioxidant activity obtained at a temperature of 90 °C while it was at a temperature of 60 °C for total flavonoids contents. The maximum protein, carbohydrate, fat, total phenolic contents and antioxidant activity was obtained at pH 3. The maximum content of dry mucilage was achieved at pH 11. The rise in the Hollyhock’s RP/W ratio caused an increase in the content of total phenolic, total flavonoids, and protein content of extracted mucilage, but the reduction in fat and carbohydrate contents. Differential scanning calorimetry proves that the heat profile of the sample is endothermic. Thermal gravimetric analysis indicated that a decrease of the sample’s weight to the amount of 70.22%, occurred in the temperature range of 480.96 °C to 536.37 °C. The Fourier transform infrared spectroscopy spectrum confirmed the existence of carboxyl groups in polysaccharide of Hollyhock’s root mucilage. The results of this study approved that mucilage of Hollyhock’s root is a natural antioxidant compound and has the potential for utilization in the food and drug industry as a new ingredient.