Formation of Previously Undescribed ?(7)-Phytosterol Oxidation Products and Tocopherylquinone Adducts in Pumpkin Seed Oil during Roasting, Screw-Pressing, and Simulated Culinary Processing at Elevated Temperatures

The influence of pumpkin seed roasting conditions (110-140 degrees C) and screw-pressing on the formation of previously undescribed delta(7)-phytosterol oxidation products and tocopherylquinone adducts with nucleophilic phosphatidylethanolamine species was investigated. The roasting process of pumpkin seed paste at a temperature above 120 degrees C for 30 min considerably enhanced the formation of delta(7)-oxysterols. Targeted analysis [electron impact mass spectrometry (MS), 1D-nuclear magnetic resonance] led to the identification of five novel markers of pumpkin paste roasting, among which (3 beta,5 alpha,22E,24S)-stigmasta-7,22-dien-6-one-3-ol (6-oxo alpha-spinasterol), stereoisomers of (3 beta,5 alpha,22E)-7,8-epoxystigmast-22-en-3-ol (7,8-epoxy-alpha-spinasterol), and (3 beta,5 alpha)-22,23-epoxys-tigmast-7-en-3-ol (7,8-epoxy-alpha-spinasterol) were reported in edible oils for the first time. Simulated culinary processing provided novel stereoisomers of (3 beta,5 alpha,22E)-stigmasta-7,22-dien-3,6-diol, unusual (3 beta,5 alpha,22E)-stigmasta-7,22-dien-6,15-dione-3-ol, and (5 alpha,22E)-stigmasta-7,22-dien-3-one accompanied by minor stereoisomers of (3 beta,5 alpha)-7,8;22,23-diepoxystigmastan-3-ol. Moreover, a clear relationship between the pumpkin seed oil stability index and synergistic effect of glycerophospholipids with present tocochromanols was found. High-resolution atmospheric pressure chemical ionization-MS experiments clearly demonstrated the formation of various gamma-tocopherylquinone adducts with primary amines, namely, octylamine. The mitigation strategy of potentially detrimental oxysterols from pumpkin seed oil included optimization of processing parameters while maintaining the formation of desirable sensory-active compounds.