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Hydrogen sulphide (H2S), viewed as a deadly environmental pollutant, is now intensively researched as the third gaseous signalling molecule, ubiquitously present and with a myriad of physiological functions. We studied garlic (Allium sativum L.) scapes, the underexplored yet widely consumed “flower stalks” of garlic, for their organosulphide constituents and H2S-releasing activity. Oils obtained from pH-adjusted (pH 3.0–9.0) puree contained 15 organosulphides that showed sensitivity to the pH values of the processing media. Disulphides are significantly higher in the oil obtained at basic pH while trisulphides and cyclic organosulphides were much higher in the oils isolated at the acidic to weakly acidic pH values. A cell-based fluorescent method was used to quantify the H2S-releasing capacity, expressed as diallyl trisulphide equivalents (DATS-E in mmol DATS/g). DATS-E values significantly increased with increasing concentrations of trisulphides and tetrasulphides but showed inverse relationship with the increase in disulphides concentration. Common cooking method of stir-frying resulted in loss of more than 96% of the organosulphides and the oil obtained had an 85-fold lower DATS-E value.