Physical and Chemical Properties of the Polysaccharides Extracted from the pericarp of Citrus grandis Osbeck

Abstract

Citrus grandis Osbeck belongs to Rutaceae of the Subfamily Aurantioideae of the Archicitrus Tanaka of the Cephalocitrus Tanaka. Many studies have pointed out that the essential oil extracted from the Citrus grandis Osbeck peel provides antioxidant and antibacterial effects. However, researches on the physicochemical properties of Citrus grandis Osbeck peel polysaccharide are quite limited. The objective of this study was to explore the extraction solvents (deionized water, 0.14M NaHCO3, 6 % citric acid) on the physical and chemical properties of Citrus grandis Osbeck polysaccharide. The results showed that the yield of the acid-extracted hydrocolloid was the highest, but the crude protein and ash content as well as the relative content of sodium ions of the alkaline-extracted hydrocolloid was the highest. Monosaccharide composition analysis by HPLC-UV method revealed the ionic nature of Citrus grandis Osbeck polysaccharide. The galacturonic acid (GalA) content was the highest for the water-extracted hydrocolloids, and the GalA content in the polysaccharide extracted from the mesocarp and exocarp was 238.24 mg / g and 223.10 mg / g, respectively. On the other hand, neutral sugar content was the highest for the alkaline-extracted hydrocolloids (68.33% and 67.26% for the polysaccharide extracted from the exocarp and mesocarp, respectively), mainly galactose, arabinose, xylose and rhamnose. Intrinsic viscosity determination by four methods revealed that Chou & Kokini and Solomon-Gotesman methods showed better linear relationship. In contrast, Huggins and Fuoss & Strauss methods seemed not to be applicable to the sample. Analysis of the molecular size by gel permeation chromatography (GPC) showed that the weight average molecular size of Citrus grandis Osbeck polysaccharide was in the range of 1.31 105~4.89 105, regardless of the extraction methods.

文旦柚（Citrus grandis Osbeck）屬於芸香科（Rutaceae）之柑橘亞科（Subfamily Aurantioideae）之初生柑橘亞屬（Archicitrus Tanaka）之第4區柚區（Cephalocitrus Tanaka）。許多研究指出，由柚子皮所提煉出的精油，具有抗氧化及抗菌作用，但對於柚子皮的多醣特性研究甚少，故本研究擬探討以不同溶劑（deionized water、0.14M NaHCO3、6％ citric acid）萃取方式對文旦柚多醣的理化特性之影響。結果發現，以檸檬酸萃取的產率最高，但粗蛋白及灰分部份則以碳酸氫鈉萃取的含量最高，相對的金屬離子鈉元素的含量也是最高。以HPLC-UV方法測定文旦柚多醣的單糖組成發現，離子多醣之半乳糖醛酸以水萃方式的含量最高，文旦柚中果皮及外果皮含量分別是238.24 mg/g及223.10 mg/g；中性糖則以鹼萃方式含量最高，文旦柚外果皮及中果皮含量分別是68.33％及67.26％，其中以半乳糖、阿拉伯糖、木糖及鼠李糖含量最高。四種分析固有黏度的方式中，以Chou & Kokini及Solomon-Gotesman方式有較好的線性關係，而Huggins及Fuoss & Strauss方式不適用本研究的樣品。以膠體過濾層析分析文旦柚多醣的分子量，不論是何種萃取方式，文旦柚外果皮及中果皮多醣的重量平均分子量大約介於1.31 × 105~4.89 × 105。