*1.1.1 Structure of pectin*

The pectin is a complex carbohydrate polymer of galacturonic acid residues having esterified carboxylic groups with methanol. The degree of esterification of carboxylic groups of the pectin has been changed from different sources. Pectin consisted of four polysaccharides including homogalacturonan, RGI (xylogalacturonan rhamnogalacturonan I) and RGII (rhamnogalacturonan II) (**Figure 2**) [11, 12]. The homogalacturonan is the main linear chain of galacturonic acids linked through α-1, 4 linked and makes the main chain of pectin polymer. RGI formed through the linkage of ragmnopyranose residues by α-1, 2 bond and makes the branches with the polymer. D-apiose, 2-O-methyl-D-xylose-and 2-O-methyl-L- fructose side chain generates the RGII region of pectin polymer [13]. The C-2 or C-3 position of galacturonic acid chain is acetylated in rhamnogalacturonan 1 region of pectin polymer, and most of the chains are consisted of D-galacturonic acids. In aqueous conditions the pectin polymer stand in pure form conformation with great flexibility and do not form straight conformation. This composition of pectin was varied among different sources [14]. The properties of pectin are strongly depending on methylation of galacturonic acids residues, which is usually 70%.

**Figure 2.** *Basic structure of pectin [10].*
