Isolation and characterization of pectic polysaccharides from the seeded fruit of oil pumpkin ( Cucurbita pepo L. var. Styriaca)

Abstract

Seeded fruit of oil pumpkin ( Cucurbita pepo L. var. Styriaca) represents a rich source of pectic polysaccharides. Pectic polysaccharides were isolated by a three-step extraction procedure at various reaction conditions, where 0.01 M ethylendiaminotetraacetic acid was used as extractant in the first step and 1% and 5% NaOH in the second and third steps. A classical extraction procedure (60 min) or and two procedures (U- and UP-experiments) with short applications of ultrasound (5–10 min) were used in the first extraction step. In comparison to the classical extraction, higher or similar yields of low-esterified pectic polysaccharide fractions were obtained from the short ultrasound-assisted extraction, where after sonication the extraction process in the first step was stopped (U-experiments). Prolongation of the extraction time after sonication in the first step to 60 min (UP-experiments) resulted in more than 2% higher yields of polysaccharides from the first and second steps, the last representing non-esterified pectic polysaccharides. The major portion of polysaccharides was obtained in the first and second steps, representing 80–89% of the total isolated polysaccharides. In the third step, pectic polysaccharides containing considerable amounts of hemicelluloses were isolated. All polysaccharide fractions were contaminated to various extents with protein. The sonication treatment had no effect on the total phenolics content (0.6–2.0%). The overall antioxidant activity in the 2,2-diphenyl-1-picrylhydrazyl (DPPH ) assay of fractions from first and second steps of the classical and ultrasound-assisted extractions was very low. In contrast, the pectin/hemicellulose fractions from the third step, particularly of the U-experiment, exhibited considerable “efficient concentrations” (EC 50) ranged from 14 to 21 when compared to that of quercetin (EC 50 = 0.14) used as positive control. EC 50 is defined as the concentration of substrate that causes 50% loss of the DPPH activity. The results suggested that the pumpkin polysaccharide fractions represent dietary fibers with a high content of pectin and/or beneficial antioxidant properties, which might be suitable for functional food applications.