Identification of Volatile Oxidation Compounds as Potential Markers of Walnut Oil Quality

Abstract

In this study, a 10-day accelerated storage at 60 °C was carried out to investigate the evolution of volatile profiles of walnut oils from three cultivars (cvs. Santai, Xiangling, Qingxiang). Eighteen volatile oxidation compounds, including three alcohols, 11 aldehydes, one furan, one ketone, and two acids, were identified in all oil samples. Data from the three cultivars were combined and the analysis showed that 2-heptenal and 1-octen-3-ol exhibited the strongest linear correlations with peroxide value (PV), p-anisidine value (p-AnV), and the residual content of total tocopherols (R_tocos ). The contents of both compounds were also proved to be significant variables for PV, p-AnV, and R_tocos , according to the jack-knife uncertainty test applied in partial least squares analysis. Hence, 2-heptenal and 1-octen-3-ol could be used as potential markers of walnut oil quality. Besides, the oleic-derived compounds such as octanal and nonanal were suggested to be used to indicate notable decrease of PUFAs during walnut oil oxidation, since they showed the strongest negative correlations with the residual content of PUFAs (R_PUFAs ). PRACTICAL APPLICATION: Nowadays a large-scale planting of walnut has taken place in China. Since walnut contains more than 60% of oil, the development of walnut oil is of great significance. Volatiles such as aldehydes are secondary oxidation products. Study on the dynamic changes of their types and contents could be helpful to understand the process of walnut oil oxidation. The measurement of walnut oil quality could also be more convenient and predictable with the use of volatile markers. Hence, this research provides insights for the future development of online quality control system for walnut oil.

Keywords: accelerated storage; marker; peroxide value; volatile oxidation compound; walnut oil.