Soluble Polysaccharides Isolation and Characterization from Rabbiteye Blueberry (Vaccinium ashei) Fruits

Abstract

Five soluble polysaccharide fractions were sequentially extracted with water, EDTA, Na 2 CO 3 , 4% KOH, and 14% KOH solutions at room temperature for 4 h from cell wall material of rabbiteye blueberry (Vaccinium ashei) fruits, and their physicochemical properties were examined. The sequential treatments yielded a total 36.02% soluble polysaccharides of the dry cell wall material. HPAEC and spectroscopy (FT-IR, NMR) analyses indicated that water-, EDTA-, and Na 2 CO 3 -soluble polysaccharide fractions were mainly composed of pectins, followed by lower amounts of arabinogalactans and glucans, while the two KOH-soluble fractions were mainly composed of hemicelluloses. Homogalacturonan was proven to be the predominant component in the isolated blueberry fruit pectic substance. The isolated blueberry fruit hemicelluloses could be defined as a linear β-(1→4)-linked-xylopyranosyl, in which xylose was the predominant neutral sugar (69.98 to 77.16%), followed by lower amounts of galactose, glucose, arabinose, and mannose. Keywords INTRODUCTIONBlueberry (Vaccinium ashei) fruits are known for their health-promoting substances and are thus gaining wide popularity with the public (Lila 2004;. Like other berry fruits, blueberry fruits are rich sources of bioactive compounds with antimicrobial activities against human pathogens (Puupponen-Pimiä et al. 2001, 2005. These bioactive compounds include flavonoids, such as flavonols (Häkkinen and Törrönen 2000), anthocyanins, and others , all having antioxidant activity. It has been shown that dietary supplementation with blueberry fruit extracts may decrease the enhanced vulnerability to oxidative stress that accompanies aging (Joseph et al. 2005). Joseph reported that treatments with extracts from blueberries reduced oxidative stress and age-related declines in normal function in vitro and in vivo (Joseph et al. 1998). In recent decades, consumer consciousness of food nutritional value has increased and this awareness has increased the popularity of blueberries.Pectins are an important family of heterogeneous polysaccharides in fruit cell walls (Bansal et al. 2011). The major pectic polysaccharide is homogalacturonan (HG), a linear homopolymer consisting of α-(1→4)-bound galacturonic acid (GalA) residues. The carboxyl moieties of the polymer are esterified to a certain degree with methanol at C-6 (Voragen et al. 2009). The degree and pattern of the methoxylation are important parameters for pectin functionality (Willats et al. 2006). Next to HG, two types of (Lv et al. 2010). In the plant cell walls, hemicelluloses are associated with cellulose and lignin by hydrogen bonds and covalent bonds (mainly ether and ester linkages), respectively. Therefore, isolation of hemicelluloses in a pure form from plant cell walls involves hydrolysis of ester and ether linkages followed by extraction of them into aqueous media (Xu et al. 2007). It has been recently observed in tomato tissue that hemicellulose polymers are present at cell junctions, imparting a role in cell adhesion (Ordaz-Ortiz ...

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