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Potato peelings
The potato has come a long way since Raleigh brought some back to England from the 'New World' to impress the queen. It is still a significant source of carbohydrate in many meals but it also finds extensive use in a variety of snacks. Diseased potatoes are less desirable than healthy ones both for direct consumption and for manufacture of snack foods and there is also an increasing demand, especially from supermarkets, for high 'visual quality' with no obvious damage. A very common form of damage is abrasion of the immature periderm, the skin of the tuber, leading to local dehydration and providing a possible entry route for disease. As described by Sabba and Lulai of the USDA lab at Fargo (pp. 1-10), the periderm consists of a secondary meristem, the phellogen, that generates an outer layer of phellem and an inner layer of phelloderm. During maturation, the meristematic activity of the phellogen declines, the phellem suberizes and then dies, leading to the formation of a protective layer. Thus only the immature periderm is especially susceptible to abrasion. The cytological basis for this is the fracture of the radial walls of the immature phellogen. In unwounded periderm, there is a decrease in the proportion of esterified pectin during maturation which, the authors suggest, allows for calcium pectate formation and wall strengthening. When immature periderm is abraded, the wound is sealed by suberin and a new phellogen is formed. This wound phellogen has less pectin than native phellogen and there is no decrease in the proportion of esterified pectin as the wound periderm matures; there is also less cell wall peroxidase in wound periderm. However, despite the care and detail of the authors' analysis of periderm cell wall biochemistry, we are no nearer to preventing abrasion damage of the potato. Anyone for chips?
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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