Optimization of polysaccharide extraction from olive leaves and evaluation of its antioxidant and rheological properties

Central composite design response surface methodology was used to optimize polysaccharide extraction from olive leaves. Effect of three independent variables [extraction time (3- 7 hours), extraction temperature (60- 100°C) and water-to-raw material ratio (5-25 mL/g)] on extraction yield were studied. Extracted polysaccharide was evaluated for antioxidant properties, total phenolic and flavonoid content and its structure and functional groups were studied using FTIR. Rheological properties and flow behavior of polysaccharide were determined by fitting to power law model. The most important parameter in experimental ranges was temperature and the lowest effect was seen in extraction time. Highest extraction yield was obtained at extraction time of 2 hours, extraction temperature of 80.96°C and water-to-raw material ratio of 17.94 mL/g. Antioxidant properties of extracted polysaccharide were measured using DPPH radical at 517 nm that showed notable antioxidant properties. Rheological property of extracted polysaccharide was studied at 1, 2.5 and 5% concentration. Results showed that at high concentration, polysaccharide shows shear thinning behavior. One of the most important obstacles in native polysaccharide applications is their extraction yield. Extract of olive leaf polysaccharide is highly affected by extraction temperature. Extracted polysaccharide showed good antioxidant properties comparing to BHT and phenolic extract of olive leaf. Moreover it could be used for increasing solution viscosity at higher concentrations.