CHLOROPHYLL, CHLOROGENIC ACID, GLYCOALKALOID, AND PROTEASE INHIBITOR CONTENT OF FRESH AND GREEN POTATOES

Exposure of commercial White Rose potatoes to fluorescent light for 20 days induced a time-dependent greening of potato surfaces; an increase in chlorophyll, chlorogenic acid, and glycoalkaloid content (alpha-chaconine and alpha-solanine); and no changes in the content of inhibitors of the digestive enzymes trypsin, chymotrypsin, and carboxypeptidase A. The maximum chlorophyll level of the light-stored potatoes was 0.5 mg/100 g of fresh potato weight. Unstored potatoes contained no chlorophyll. Storing potatoes in the dark did not result in greening or chlorophyll formation. Chlorogenic acid and glycoalkaloid levels of dark-stored potatoes did increase but less than in the light-stored potatoes. In the light, chlorogenic acid concentration increased from 7.1 mg/100 g of fresh potato weight to a maximum of 15.8 mg after greening. The corresponding values for alpha-chaconine are 0.66 and 2.03 mg and for alpha-solanine 0.58 and 1.71, respectively, or an approximately 300% increase for each glycoalkaloid. The trypsin, chymotrypsin, and carboxypeptidase A concentrations, respectively, of about 1000, 375, and 100 units/g of dehydrated potato powder were not changed. Experiments on delay of greening by immersion in water suggest that (a) chlorophyll formation and glycoalkaloid synthesis are unrelated physiological processes and (b) the concentration of chlorophyll is 26 times greater, of chlorogenic acid and glycoalkaloids 7-8 times greater, and of protease inhibitors about 2-3 times lower in the peel of the green potatoes than in the whole tuber. The described compositional changes should help define consequences of potato greening for plant physiology, food quality, and food safety.