Investigation of the effect of the drying techniques on the volatile constituents’ profiles of sow thistle (Sonchus oleraceus L.) using headspace solid-phase microextraction with comprehensive two-dimensional gas chromatography–time of flight mass spectrometry (HS-SPME–GC × GC–ToFMS)

Sonchus oleraceus L. is a leafy vegetable commonly consumed in traditional Mediterranean diets as a wild edible plant for its nutritional, sensory, and health benefits. This study aimed to track changes in the volatile constituents of S. oleraceus after oven and microwave drying in correlation with the plant’s proximate analysis, amino acid profile, sugar content, and fatty acid analysis to predict the main pathways of volatile generation during thermal processing. Comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry was used for the volatile analysis. A total of 247 compounds belonging to 13 different classes were identified. Alcohols, terpenes, and esters were the most abundant groups in the fresh sample. Levels of the products of thermal oxidation of fatty acids, such as aldehydes and ketones, increased dramatically at the expense of alcohols and terpenes. Additionally, the number of N- and O-heterocycles formed through the Maillard reaction increased, corresponding to the reduction of amino acids and sugars. After drying, sulfur-containing compounds were generated as products and intermediates of methionine Strecker degradation. Oven-dried plant displayed the highest contents of ash (19.86%), protein (26.21%), and fat (3.89%), following moisture reduction to 3.82%. A downward trend in the amino acid profile was noted during drying, particularly in oven-dried plants, including arginine, tyrosine, valine, cysteine, isoleucine, and phenylalanine. Microwave-dried plant retained higher levels of these amino acids compared to oven-dried ones. The sugar content varied based on the drying method; the oven-dried plant had lower levels of sucrose, glucose, and fructose than the microwave-dried plant. Based on Gas Chromatography analysis, palmitic, stearic, and linolenic acids were predominant in fresh and dried samples. This study clarifies the metabolic changes that occur during drying, which are crucial for ensuring safety and shelf life.