Mechanistic elucidation of the degradation and transformation of hydroxy-α-sanshool and its conformers as the pungent dietary components in Sichuan pepper: A DFT study

Abstract

To better understand the structural changes of sanshool pungent dietary components during the process and preservation of Sichuan pepper and pungent foods, the mechanistic insights into the intrinsic degradation and transformation of 16 hydroxy-α-sanshool conformers have been explored computationally. Our results have revealed that increasing the cis-CC bond numbers in the most stable all-trans hydroxy-β-sanshool structure causes the maximum 34.21 kJ/mol conformational energetic difference, and the existent probability of C2nnn would be lower than that of C1nnn (n = 1,2). The isomerization between the conformers could be much easier when they are excited by light radiation, as the strength of the CC bonds and their connected CC bonds becomes significantly close, and the relative energies among conformers are largely reduced. Besides, the different combination of cis/trans-CC bonds changes the delocalization degree of molecular Frontier orbitals, which consequently causes the different photochemical stability. Finally, the possible molecular oxidation degradation mechanism is proposed.

Keywords: Conformation; Mechanism; Pepper; Pungency; Sanshool.