Optimization of ultrasonic-assisted extraction of polysaccharides from purple glutinous rice bran (Oryza sativa L.) and their antioxidant activities

Abstract

Purple glutinous rice bran (Kum Doi Saket rice (KUM)) contains high content of edible polysaccharides and anthocyanins and has an excellent antioxidant activity. This research aimed to optimize the extraction of crude polysaccharides from defatted purple glutinous rice bran using an ultrasonic-assisted extraction (UAE) and compared with a hot water extraction (HWE). Results showed that optimal extraction condition was as follows: a defatted rice bran to water ratio of 1:20 w/v, extraction temperature and time of 70 °C for 20 min. Under the optimal extraction condition, the yield of polysaccharide of UAE (4%) was significantly higher than that obtained from the HWE (0.8%). Additionally, antioxidant activities of extracted polysaccharide including IC₅₀ value DPPH, IC₅₀ value ABTS, and FRAP value were 1.09 mg/mL, 2.80 mg/mL and 197 µM Fe²⁺/g, respectively. It is suggested that the UAE process is promising method to decrease the processing time and to enhance extracted polysaccharide yields by 4 times.

Figure 1

Tri-dimensional response surface contour plots showing the experimental factors: (X₁) ratio KUM-DB to water, (X₂) extraction temperature and (X₃) extraction time on yield (a–c), IC₅₀ of DPPH assay (d–f), IC₅₀ of ABTS assay (g–i) and FRAP assay (j–l).

Figure 2

Overlay plot of the response surface regression model between the ratio of KUM-DB to water and extraction temperature; fixed extraction time at 20 min.