Invertase & invertase inhibitor in potato

Abstract

The pattern of changes in sugar composition which occur when potatoes are stored at low temperatures or are irradiated (18, 19) suggests that the reducing sugars mnay arise as the consequence of the hydrolytic action of invertase on sucrose. During cold temperature storage there is a rapid increase in sucrose content followed bh an increase in redlucing sugars relative to the sucrose content. Furthermore a survey of the literatur-e indicates that, for many varieties of potatoes, the ratio of glucose to fructose is close to unity (luring at least part of the time of storage (17). If invertase is indleed a factor in the accumulation of reducing sugars, information concerning the characteristics of this enzyme and the inhibitor here reported could conceivably lead to nmeans for controlling the reducing sugar content of potatoes (20). The literature on potato invertase is rather sparse. Tn 1903, Kastle and Clark (9) detected invertase in sprouted but not in unsprouted potatoes. In 1928, MlcGuire and Falk (13) showed that the invertase action of potato juice was higher at pH 4 than at pH 5 and 6. Denny et al (5) found that the invertase activity of potato juice from tubers treated with ethylene chlorohvdrin was significantly greater than that fronm untreated controls. A few reports have suggested that the level of invertase activity depends on the elemental nutrition of the plant [potassium (24), boron (4), chlorine & sulfur (10)1. Bois and Savary (3) and MIcCready (12) in more recent years have detected invertase in potatoes, although the latter author could fin(d activity only in sprouted andl not in unsprouted tubers. The presenlt paper describes our experience in attempting to (letect invertase in crude potato macerates. In general, the results confirnm the scattered findings of the older literature but also point to the presence of an endogenous inhibitor of the enzymiie. A preliminary report of some of the present results has been publishedl elsewlhere (21).