Roasting pretreatment of walnut (Juglans regiaL.) kernels: improvement of the oil flavor profile and correlation with the chemical composition

The present study focused on the role of roasting pretreatment in improving the flavor of WOs. In total, 71 volatile compounds were detected, 35 odorants were perceived, and 17 aroma-active compounds were identified in WOs by using headspace-solid phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) and aroma extract dilution analysis of gas chromatography-olfactometry (AEDA/GC-O). The results indicate that extended roasting pretreatment is effective in generating aldehydes and pyrazine aroma-active compounds in WOs. The correlation between the aroma-active compounds and chemical composition was identified by Pearson correlation analysis. The branched-chain aldehyde, 3-methylbutanal, is a Maillard reaction product with ribose as a precursor. Pyrazine aroma-active compounds were also related to ribose, with absolute correlation coefficients of 0.85 to 0.96; among pyrazine compounds, 2-ethyl-5-methylpyrazine showed strong correlation with isoleucine and arginine, while 2-methylpyrazine and 2,3,5-trimethylpyrazine showed strong correlation with glycine, lysine, and histidine. The determination of the effect of roasting on aroma-active compound alteration and the study of aroma precursors will be helpful for walnut oils' flavor quality control, which directly enable their industrial application.