###### Abstract  
In this study, ultrasound-assisted extraction of green pea pod polysaccharide (GPPP) was investigated and optimized using a central composite response surface design coupled with a numerical optimization technique. The effects of ultrasonic power (50-150 W), sonication time (20-80 min), ratio of water to raw material (20:1-40:1 mL/g) and extraction temperature (40-80 \({}^{\circ}\)C) on polysaccharide extraction yield were studied. The maximum extraction yield was obtained with a sonication power of 135.34 W, extraction time of 48.61 min, ratio of water to raw material of 33.6:1 mL/g and extraction temperature of 68.25 \({}^{\circ}\)C. Under these conditions, the experimental yield was 7.37% \(\pm\) 0.13%, which was in close agreement with the predicted value (7.20%). The GPPP has been analyzed in order to identify a variety of chemical properties. The FT-IR spectrum demonstrated obvious characteristic peaks of polysaccharides. Furthermore, antioxidant activity of GPPP was evaluated by various antioxidant assays in vitro. The results revealed that GPPP possessed considerable DPPH free radical scavenging activity (91.03%), reducing power (0.63) and ferric reducing antioxidant power (0.34 mmol/L) at a total amount of 0.9 mg/mL. These findings indicated that GPPP extracted using an ultrasound-assisted extraction technique has potential as a novel source of natural antioxidant agent for future applications. green pea pod; polysaccharide; ultrasound-assisted extraction; antioxidant activity +
Footnote †: journal: _foods_  
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the need for waste disposal but also provides an economically viable alternative resource for natural polysaccharide production. Polysaccharides are high molecular weight macromolecules which can be easily separated from various sources such as plants, microorganisms and algae using water under appropriate conditions [6; 7]. In recent years, studies on polysaccharide extraction from natural resources has gained increasing attention, as they can modulate rheological properties of foods and are generally used as natural food thickeners, gelling agents, coating agents, texture modifier, stabilizers, and emulsifiers for various applications [8]. Conventionally, plant polysaccharides are extracted by hot water procedures. Despite its simplicity and safety, hot water procedures generally require high temperatures and long processing time which may lead to the degradation of the polysaccharides and a decrease of biological activity of target compounds and also extraction yield is reduced due to destruction of polysaccharides [9; 10; 11]. Ultrasound-assisted extraction (UAE) has been successfully implemented in the extraction of polysaccharides from various plant material due to reducing solvent usage, lowering extraction temperature and enhanced extraction efficiency [12]. Recently, several studies have reported the possibility of using ultrasound technology in extraction of polysaccharide from food waste and their by-products including _Nephelium lampaceum_ L. fruit peel [13] and pomegranate peel [14]. The mechanism of ultrasound-assisted extraction is attributed to cavitation, mechanical and thermal effects which can result in particle size reduction, disruption of cell walls and enhanced mass transfer across cell membranes [12]. Therefore, UAE provides increased extraction yield, increased rate of extraction, reduced extraction time and higher processing throughput along with the advantage of usage of reduced temperature and solvent volume which is very useful for the extraction of heat labile compounds [14]. On the other hand, use of an optimization technique such as response surface methodology (RSM) in the extraction processes can be very interesting because fewer experimental trails are needed compared to the single-factor method.