COMPARISON OF GLYCOALKALOID CONTENT OF FRESH AND FREEZE-DRIED POTATO LEAVES DETERMINED BY HPLC AND COLORIMETRY

As part of a program to control the biosynthesis of Solanum glycoalkal oids in potatoes, we used an HPLC assay to measure the specific alpha- chaconine and alpha-solanine content of greenhouse-grown potato leaves at different stages of maturity. Comparative studies were done with t he bromophenol blue titration assay for total glycoalkaloids. We found that foliar glycoalkaloids can be extracted with 5% aqueous acetic ac id, that analysis of glycoalkaloids with freeze-dried leaf powders was more reproducible than with fresh leaves, and that the bromophenol co lorimetric method gave higher values than HPLC. As little as one leaf from a growing plantlet can be analyzed with the HPLC assay. Large var iations in both alpha-chaconine and alpha-solanine contents of fresh l eaves suggest that potato foliar glycoalkaloids should be determined b y HPLC from freeze-dried rather than fresh leaves.