Pectins apple, molecular weight

For apple maceration, the main activity is the endopectinlyase (PL) which decreases the viscosity due to the colloidal pectin by decreasing tlie molecular weight of this substrate methylated at about 90%. In association to this PL, exo B and endoarabanase (ARAs), pectinacetylesterase (PAE), rhamnogalacturonase (RG) and other hemicellulases allow to hydrolyse side chains of the pectin, decrease the steric hindrance and make the access of pectinases to the rhamnogalacturonic backbone more easy. 

The first probable values for the molecular size of the native pectins from apple and sugar beet were obtained by Schneider and co-workers.71 These workers prepared the nitro- and acetyl-derivatives in order to avoid the anomalous behavior due to charge effects which occurred using the unsubstituted polysaccharides. From osmotic and viscometric measurements on the nitrate, values for the molecular weight of 30,000-100,000 were found, the constant Km in Staudinger s equation being 6(10)-4. Viscometric measurements indicated that there was little difference in size between the two derivatives. 

The molecular weight distribution curves for apple and lemon pectins were obtained similarly by Owens, Miers and Maclay.79 These workers were not satisfied that the preparation of the nitrate involved no degrada-... 

Liquidification of starches for free flow Recovery of sugar from candy scraps Remove starches to increase sparkling properties Remove starches to increase sparkling properties An aid in preparation of pectin from apple pomace Conversion of starches to low molecular weight dextrins (corn syrup)... 

Recently Ishii and Yokotsuka 170, 171,172) reported that a purified pectin lyase from AspergiUus sojae initiated the clarification reaction in apple juice. This enzyme has a molecular weight of 32,000 and a pH optimum of 5.5 for 68% esterified pectin (pH 7.0 for 98% esterified pectin). Divalent cations stimulated activity and shifted the pH optimum towards neutrality. The enzyme was stable between pH 4 and 7. One mg of purified pectin lyase (76.5 units of activity) could clarify 30-40 liters of apple juice within one hour at 40°C [0.018-0.024 units needed to clarify 10 ml (172)]. At the point of complete clarification 50% of the pectin in the juice had been converted to a form soluble in 75% ethanol. 

Pectins, the gelling agents used in making jams and jellies, are ubiquitous in plants and are produced commercially from apple skin or citrus rind. They are structural polysaccharides, with molecular weights between 20,000 and 400,000, containing galactose, galacturonic acid, rham-nose, xylose, and arabinose. 

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