| Light stimulates both chlorophyll and glycoalkaloid synthesis in potatoes (Solanum tuberosum L.) through independent biochemical processes. Green potatoes are rejected by markets because of the expected higher glycoalkaloid content. Towards a further understanding of light-induced glycoalkaloid and chlorophyll synthesis in potato tubers, variety tests and postharvest practices were investigated in this thesis.;In the variety tests, thirty-three varieties or experimental lines of potato tubers grown in California were examined for total glycoalkaloid and chlorophyll concentrations after 6 days of fluorescent light exposure at 20°C. Average glycoalkaloids in the thirty-three varieties increased from 5.24 to 8.24 mg as a result of light exposure; however, the increases were not significant in fourteen of the varieties and none of the varieties contained higher than 20 mg/100g, considered the food safety limit. Significant increases in chlorophylls were observed in all but one purple variety (P < 0.05). By separating the varieties into three types, russet, yellow and red, significantly higher total glycoalkaloids and chlorophylls were observed in russet type tubers after light exposure, but there were no differences in the red and yellow varieties.;Oil treatment, controlled atmosphere, and modified atmosphere packaging were the postharvest practices evaluated as potential treatments for mitigating chlorophyll and glycoalkaloids accumulation in potatoes in this thesis. Oil treatment significantly inhibited light-induced greening of potato tubers. Wiping tubers with 40 microg olive oil reduced greening by 70% after 3 days of light exposure. Low oxygen (O2) concentrations had inhibiting effects on glycoalkaloid and chlorophyll synthesis. There was complete inhibition on chlorophyll and glycoalkaloid synthesis in tubers stored in O2 levels lower than 1% and 5%, respectively, after 8 days under light. However, decay may develop in tubers stored in O2 lower than 5% depending on variety. Carbon dioxide (CO2) levels of 6% or more also inhibited light-induced glycoalkaloids, but to reduce chlorophyll synthesis, the levels had to be higher than 12%. Modified atmosphere packaging (Scanfresh(TM)) with average 8% O2 and 10% CO2 also reduced the rate of light-induced glycoalkaloid and chlorophyll formation in tubers. The different types of greening suggested that the inhibitory effects of chlorophyll and glycoalkaloid synthesis with low O2 and high CO2 may be controlled by different mechanisms. |
