Alpha-solanine and alpha-chaconine glycoalkaloid assay in Solanum tuberosum extracts by liposomes and time-resolved fluorescence

Glycoalkaloid contents in potatoes are potentially toxic, and therefore there is a strong need for a method to control stressed potatoes and to monitor the potato transgenic cultivars, which requires the screening of many samples. This paper describes a new assay method for α-solanine and α-chaconine detection in the leaf, sprout, skin and tuber extracts of different potato cultivars. The method makes use of a europium chelator entrapped in phosphatidylcholine/cholesterol containing liposomes. Fluorescence detection after liposome lysis is linear in a calibration range of α-solanine and α-chaconine (1:1 w/w) between 3 and 10 μg. This method is unsuitable for evaluating each glycoalkaloid separately, but it is cheap and rapid: it can therefore be applied in the first screening for total glycoalkaloid content of the samples. In the assayed samples, α-solanine and α-chaconine concentration was undetectable in peeled tubers, but attained values higher than 200 mg/100 g fresh weight in the leaf extracts. Comparison with HPLC was made by adding areas of peaks corresponding to α-solanine and α-chaconine; the methods showed a good agreement (R2=0.998).