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 glycoalkaloids 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 the bromophenol blue titration assay for total glycoalkaloids. We found that foliar glycoalkaloids can be extracted with 5% aqueous acetic acid, that analysis of glycoalkaloids with freeze-dried leaf powders was more reproducible than with fresh leaves, and that the bromophenol colorimetric method gave higher values than HPLC. As little as one leaf from a growing plantlet can be analyzed with the HPLC assay. Large variations in both alpha-chaconine and alpha-solanine contents of fresh leaves suggest that potato foliar glycoalkaloids should be determined by HPLC from freeze-dried rather than fresh leaves.