Identification of the key flavor-active compounds in roasted and non-roasted Zanthoxylum piperitum
Creators: name: Ji, Yue
Publisher: name: No Publisher Supplied
Year: 2022

description: Sichuan pepper is a widely used spice in Asian cuisine because of its unique flavor profile. The aroma of Sichuan pepper can be described as citrus, woody, spicy, floral, fresh, peppery with over 200 volatiles have been identified across different species in previous studies. Besides the pleasant aroma, Sichuan pepper gives a unique tingling and numbing sensation upon consumption. Previous studies showed that a group of alkylamides are responsible for eliciting the chemesthetic sensation in Sichuan pepper. Around 35 alkylamides have been identified and a few of them were studied from sensory perspective¹⁻⁸. Thermal treatments, including roasting, boiling, and frying, are often applied to Sichuan pepper to bring out its optimal flavor profile, however what’s driving the flavor differences between thermally treated and nontreated Sichuan pepper hasn’t been fully explored.This study aims to investigate how chemical change drives flavor difference between dried Sichuan pepper pericarp (Z. piperitum) before and after roasting. The objective can be further divided into two parts: first, to establish a standardized aroma vocabulary and connect each attribute with volatile components to understand how aroma changes with thermal treatment of Z. piperitum. Second, to develop and validate the analytical method to quantify four alkylamides, hydroxy-α-sanshool (α-SOH), hydroxy-β-sanshool (β-SOH), hydroxy-γ-sanshool (γ-SOH) and γ-sanshool (γ-S) and conduct kinetic study to understand how the four alkylamides degradate through thermal treatment.69 volatile compounds were identified in aromatic extract of non-roasted Z. piperitum sample extract, and 50 compounds were identified roasted Z. piperitum extract. 30 odor active volatiles with a FD factor above 2 are identified between the roasted and non-roasted Z. piepritum. Among the identified aroma active volatiles, linalool, eucalyptol, and geraniol are the strongest odorants with the highest dilution factor. The formation of 2, 5-dimethyl pyrazine, 2, 6-dimethyl pyrazine, 2, 3-dimethyl pyrazine, 2-ethyl-3, 5-dimethyl pyrazine is responsible for the evident roasted nutty aroma in roasted sample.An LC-MS method is developed to quantify the target alkylamides, and a series of method validation tests, including precision, recovery, system suitability tests, were conducted to assess the accuracy of the method. The overall validation data suggest that the method is precise and rugged.Kinetic study results suggested the degradation of α-SOH follows first order reaction with the activation energy of 33.89 kcal/mol. Pseudo-zero order reaction was observed with γ-SOH and γ-S with an activation energy of 30.02 and 24.11 kcal/mol respectively. No apparent reaction order is observed with β-SOH. Specifically, the concentration of β-SOH decreases and then increase as processing time increase under a certain temperature. The increase in β-SOH could be explained with the isomerization of α-SOH to β-SOH during roasting.Overall, a standardized aroma vocabulary is established for Z. piperitum sample with and without thermal treatment, and each aroma character is linked to a group of responsible volatile compounds. An LC-MS method was developed and validated. Kinetic models are built for α- SOH, γ-SOH and γ-S. This provides important understanding in guiding the processing condition of Z. piperitum and other alkylamides containing spices to retain the flavor active compounds and provide a scientific basis for flavor design and future food products development.