Pectic polysaccharides from mature orange (Citrus sinensis) fruit albedo cell walls: Sequential extraction and chemical characterization Academic Article uri icon

abstract

  • The orange albedo alcohol insoluble solids (AIS) wall preparation, material prepared from the albedo tissue of mature orange fruit, contained 55mol% pectic polysaccharides, including homogalacturonan (HG), rhamnogalacturonan I (RG I) and rhamnogalacturonan II (RG II) together with Type I arabinogalactan (AG) and arabinan. It also contained cellulose (22mol%) and other non-cellulosic polysaccharides (14mol%), including xyloglucans (XGs) (10mol%), heteromannans (2mol%) and heteroxylans (2mol%). Sequential extraction of the AIS performed with NaOAc, CDTA, Na₂CO₃, 1M KOH and 4M KOH produced soluble fractions (Frs.) with different relative proportions of these polysaccharides. The NaOAc and CDTA Frs. were composed predominantly of pectic polysaccharides (89 and 97mol%, respectively) with only very low proportions of other non-cellulosic polysaccharides. Na₂CO₃ (50mM) released highly ramified pectic polysaccharides, whereas stronger alkali (1M and 4M KOH) liberated mostly non-cellulosic polysaccharide, comprised predominantly of XG. The NaOAc, CDTA and Na₂CO₃ Frs. contain low levels of 2-O-methyl-Fuc and 2-O-methyl-Xyl, suggesting the presence of RG II. To obtain the RG II for structural characterization, the NaOAc fraction was digested with a combination of endo-polygalacturonase (endo-PG; PG I and PG II) and exo-PG, and the degradation product was fractionated by anion exchange and size exclusion chromatography. The isolated product (approx. 0.5% of orange albedo AIS) contained all six diagnostic sugars and has a glycosyl linkage composition consistent with the structural model of RG II.

authors

publication date

  • February 2011

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