Abstract
In the present study, ultrasound-assisted extraction (UAE) of crude polysaccharides (PSP) from pumpkin seeds was optimized by response surface method (RSM). The polysaccharide yield (2.29 ± 0.14%), which agreed closely with the theoretical predicted value 2.40%, was obtained under the optimal extraction conditions: extraction time 24 min, extraction temperature 50 °C, ultrasonic power 347 W, and liquid to solid ratio 23 mL/g. After further purification by two-step column chromatography, a novel polysaccharide (PSP-1) was isolated from pumpkin seeds. PSP-1 was composed of mannose, glucose, and galactose in a molar ratio of 1.00:4.26:5.78 with molecular weight of 3728 g/mol. 1D and 2D NMR spectroscopy analysis revealed that the backbone of PSP-1 was mainly formed by β→6)-β-d-Galp-(1→, →6)-α-d-Glcp-(1→, and →3,6)-β-d-Manp-(1→ with branching at O-3 and O-6 of →3,6)-β-d-Manp-(1→. Branch linkages were composed of α-d-Glcp-(1→ and →4)-α-d-Galp-(1→.
Highlights
Pumpkin seeds have been so commonly used in functional foods or medicines, which was ascribed to the valuable functional components [1]
Discovery and assessment of polysaccharides extracted from plants, microorganisms, and animals have become an area of research focus [9,10,11]
The results indicated that longer extraction time can induce degradation of the polysaccharides and corresponding decrease in the yield of PSP [22]
Summary
Pumpkin seeds have been so commonly used in functional foods or medicines, which was ascribed to the valuable functional components [1]. Previous studies showed that pumpkin seeds had health protective values, such as antioxidant, immunomodulatory, diuretic and anti-inflammatory activities [3,4]. The parameters of hot water extraction were investigated by RSM, and the yield of crude polysaccharides from pumpkin seeds was 2.18%, which agreed well with the predicted value [18]. There was no study about UAE optimization of polysaccharides from pumpkin seeds. Ultrasonic-assisted extraction of the polysaccharides from pumpkin seeds was investigated. The effects of four variables (extraction time, extraction temperature, ultrasonic power, and liquid to solid ratio) on the yield of PSP were optimized by RSM. After two-step column isolation from PSP, the purified fraction (PSP-1) was obtained and analyzed for detailed structure by FT-IR, periodate oxidation, Smith degradation, and NMR (1 H, 13 C, COSY, HSQC, and HMBC)
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