Stability of potato glycoalkaloids under heating conditions - Reactions with fatty acids

Glycoalkaloids (GA) are endogenous metabolites of the plant family Solanaceae and considered as contaminants. However, their stability and reactivity during high-temperature food processing such as frying and deep-frying of potatoes has not been comprehensively studied. Consequently, the aim of this study was to characterize the reactivity of GA in heat-induced reactions by investigating the formation of novel reaction products. Based on the assumption that GA may be present in cell membranes and may react with lipids and amphiphilic compounds, in conjunction with the results of preliminary screening measurements for reaction products, this work focused on reactions with (endogenous) lipids. For this purpose, pure GA were incubated with fatty acids (palmitic, stearic, oleic, linoleic and α-linolenic acid) at temperatures commonly applied during deep-frying (180 °C). Reaction products formed were characterized by multi-stage high-resolution mass spectrometry and liquid chromatography-coupled tandem mass spectrometry. Two novel reaction pathways were identified and described - esterification of GA with fatty acids via hydroxyl groups of the sugar moiety and oxidation of the steroidal alkaloid moiety. Additionally, the formation of these products was verified in processed potato matrices, without the addition of frying oil, which indicates that the ester formation originates from the tuber's endogenous fatty acids. Consequently, the findings presented herein contribute to the understanding of the chemical fate of GA during thermal processing of potato products. However, the total amounts formed must still be determined, and a toxicological study must then be conducted to assess the extent to which the reaction products affect on human nutrition.