Functional, physicochemical properties of sodium carbonate-soluble polysaccharides from the bulbs and foliage leaves of yellow and red onion.

The oil and water holding capacities, surface activity, and gelling ability of sodium carbonate-soluble pectin (NSP) extracted from the cell wall of bulb and foliage leaves of yellow and red onion (Allium cepa L.) were investigated and compared with those of commercial citrus pectin. Pectin chemical composition and properties its aqueous dispersions (e.g. the viscosity, pH) were studied. Homogalacturonan was the main component of the low-methoxylated pectin, with a small amount of rhamnogalacturonan I (more branched in the bulb pectin). Both the oil (35-41 g/g.) and water (20 g/g) holding capacities of NSP were higher than citrus pectin (1 and 17 g/g, respectively). The surface activity of NSP was comparable (foliage leaves; surface tension (γ) decrease to 62 mN/m) or higher (bulb; γ decrease to 56 mN/m) than commercial pectin. The ability of NSP, especially extracted from the bulb, to form larger structures with increasing viscosity and neutralizing the negative surface charge, was significantly higher than that of citrus pectin. Therefore, NSP of bulb and foliage leaves may be useful as a carrier of oil- or water-soluble substances, a surface active agent, texturizer and gelling agent in the food, pharmaceutical, cosmetic and agricultural branches of industry.