J Microbiol Biotech Food Sci / Saptadip Samanta 2019 : 9 (2) 248-266 249 a gel structure after cross-linking with calcium ions. The gelling properties mainly depends on the interaction between calcium ions and the unesterified carboxyl groups of pectin; moreover, the other determining factors like temperature, pH, types of pectin, degree of esterification and acetylation, presence of sugar and other solutes are also important (Pedrolli et al., 2009). Homogalacturonan (HG) Homogalacturonan is a

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... inear homopolymer of D-galacturonic acid residues attached through α-(1-4) glycosidic bonds and contains as many as 200 galacturonic acid units with a length of about 100 nm long. The acetyl esterification and methyl esterification of D-galacturonic acid can also be done at C-2 or C-3 position and C-6 position respectively (Fig.1) . The methyl esterification determines physical properties of pectin and also sensitive to Ca 2+ cross-linking. According to esterification level the molecules are classified into three groups: a) pectin, in which 75% of its carboxyl groups are methylated; b) pectinic acid which carries less than 75 % methylated carboxyl groups; c) pectic acid or polygalacturonic acid, which does not carry any methyl group at the carboxylic end. (Jayani et al., 2005) .