Pectin degradation, causing the softening of ripening fruit, has been proposed to be partly enzymic and partly due to non-enzymic scission by hydroxyl radicals (•OH).
Airianah et al. applied a recently developed fluorescent fingerprinting method to detect the ‘collateral damage’ inflicted when •OH acts on pectins. Six true fruits revealed •OH-attacked pectin, increasing during ripening. Three false fruits (strawberry, pear, apple) showed little or none. Non-enzymic attack on fruit polysaccharides is thus supported experimentally, and is predominantly a feature of ovary-wall (not receptacle) tissue.
Othman B. Airianah, Robert A. M. Vreeburg, Stephen C. Fry, 2016, 'Pectic polysaccharides are attacked by hydroxyl radicals in ripening fruit: evidence from a fluorescent fingerprinting method', Annals of Botany, vol. 117, no. 3, pp. 441-455 http://dx.doi.org/10.1093/aob/mcv192