Protopectin

Renard, C. M. G. C., Searle-van Leeuwen, M. J. F., Voragen, A. G. J., Thibault, J.-F. and Pilnik, W. (1991a). Studies on apple protopectin. II. Apple cell wall degradation by pure polysaccharidases and their combinations. Carbohydr Polymers 14, 295-314. 

The conversion of protopectin, the water-insoluble parent pectic substance, into soluble pectin and pectate and, further, into their cleavage products, is one of the mechanisms playing a role in the plant during its maturation, as well as in the process of infection of the plant. In the plant, protopectin has the function of an intercellular adhesive and, hence, its conversion into the soluble form results in a disruption of tissue rigidity, and in cell separation that is reflected in softening and subsequent liquefaction of the plant material. 

FIG. 15 Texture modification (percentage of raw fruit texture) and protopectin content (mg/100 g wet weight) before (BF) and after (AF) freezing of strawberry slices not pretreated (NT) or air dried at 80 °C up to 60% weight reduction without (AD) or following 60-min osmotic dehydration (OAD) in 60% (w/w) sucrose solution at 25 °C at atmospheric pressure (Brimar, 2002). 

Z. I. Kertesz, Note on the nature of protopectin. Paper given at the Memphis, Tennessee, meeting of the Am. Chem. Soc., April, 1942. 

There is no major advance which can be reported in our knowledge of protopectinases. The possibility of the existence of a protopectinase different from PG seems now somewhat more remote than it was ten years ago. As stated above, the trend in thinking about protopectin is definitely in the direction that protopectin is not a specific cellulose-pectinic acid compound but pectinic acid which is insoluble either on account of large molecular size or due to the effect of polyvalent cations or both. In this sense there is really no need to assume the existence of a separate protopectinase. There is little doubt that this uncertainty is in a large degree attributable to the lack of precise knowledge of protopectin. 

The prevailing concept is that, in the softening that accompanies ripening, textural changes occur as insoluble, wall-bound protopectin of high molecular weight, after partial de-esterification by pectin methyl... 

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