**3.2 Esterase**

Esterase, which removes methoxyl and acetyl esters from pectin forming polygalacturonic acid. Where catalyzes the de-esterification of pectins. These enzymes from fungal originate work by arbitrarily eliminating the methyl groups via a multi-chain mechanism, while from plant source work by attacking either the next terminal to a free carboxyl group or the non-reducing-end and progressing linearly through a single-chain mechanism [35]. Esterase enzymes are producing mainly from microorganisms and have a negligible effect on the viscosity of a pectin solution without divalent cation as barium (Ba2+), calcium (Ca2+), and strontium (Sr2+). However, it is reported that the presence of Ca2+ ions releases a maximum effect at either small or large preparations [36].

Some of the purified esterase acting against the reducing end. While others are targeting the non-reducing-end of pectin. The molecular weight for these enzymes ranges from 22 to 90 kDa, referring to the difference of the protein confirmations. For the work efficiency of esterase, various ranges of pH (5-11) and temperature (40 – 70°C) should be applied. However, the product optimization of the fungal esterase has a lower pH value versus the bacterial one [37]. Depending on the functional group target, pectinesterase is classified into:

1.*Methyl-esterase*, which divides the methyl ester group of pectin. Freeing methanol and converting pectin into pectic acid or pectate via a single-chain mechanism. The chain length of pectin polymer is not reduced [38]. Various

isoenzymes of pectin methylesterases are isolated and characterized from different sources, considering the functional group's target [39]. Two types of pectin methylesterase A (PmeA) and B (PmeB), were isolated from *Erwinia chrysanthemi* [40] and *E. chrysanthemi* 3937 [41] and were well-studied. The PmeA acting functionally to be extracellular, while the PmeB enzyme acting on the outer membrane.

2.*Acetyl-esterase*, which catalyzes the hydrolysis of acetyl ester residues of pectin, forms acetate in pectic acid [42].
