Ultrasonic-Assisted Extraction, Structural Characteristics, and Antioxidant Activities of Polysaccharides from Alpinia officinarum Hance

Alpinia officinarum Hance, a well known agricultural product in the Lei Zhou peninsula, is generally rich in polysaccharides. In order to enhance the use of A. officinarum Hance polysaccharides (AOP) in functional food, AOP was extracted using an ultrasonic-assisted extraction method, and the ultrasonic extraction parameters of AOP was optimized. Furthermore, this study investigated the physicochemical and antioxidant activities of AOPs. In addition, the structural properties were preliminarily determined using Fourier-transform infrared spectroscopy (FTIR), high performance size exclusion chromatography, and a Zetasizer. Ultimately, this study explored the mechanism underlying the antioxidant activities of AOP. The results showed that the optimal ultrasonic-assisted extraction parameters were as follows: ultrasonic time, 6 min; ratio of water to material, 12 mL/g; and ultrasonic power, 380 W. Under these conditions, the maximum yield of AOPs was 5.72%, indicating that ultrasonic-assisted extraction technology is suitable for extracting AOPs due to the reduced time and water usage. Additionally, AOPs were purified using graded alcohol precipitation, resulting in three fractions (AOP30, AOP50, and AOP70). AOP30 had the lowest molecular weight of 11.07 kDa and mainly consisted of glucose (89.88%). The half inhibitory concentration (IC50) value of AOP30 and AOP70 was lower than that of AOP50 in the ability to scavenge the ABTS radical, while a reverse trend was observed in reducing ferric ions. Notably, the antioxidant activities of AOPs were highly correlated with their polydispersity index (Mw/Mn) and Zeta potential. AOP30, a negatively charged acidic polysaccharide fraction, exhibited electron donating capacities. Additionally, it displayed strong antioxidant abilities through scavenging 2,2′-azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) radicals and reducing ferric ions. In conclusion, the present study suggests that AOP30 could be developed as an antioxidant ingredient for the food industry.