Walnut (Juglans regia L.) oil chemical composition depending on variety, locality, extraction process and storage conditions: A comprehensive review

This review presents a comprehensive synthesis of walnut oil chemical composition data (major and minor compounds) collected from the literature according to the varieties and the geographic origins of walnuts, and to the oil extraction processes. Considered as influencing factors, pre- and post-harvest treatment parameters of in shell-walnut and kernels were identified and works on oil stability were discussed according to walnut pre-treatment, oil extraction processes and their storage conditions. Most studies dealt with the quantification of fatty acids and tocopherols. There has been less interest in the triacylglycerol composition and minor components (sterols, volatiles, phenolic compounds) of the oil. The volatile compound profiles were mainly determined to define the oxidative degree of oil and to better understand the effect of the fatty acid degradation on the organoleptic properties of oil. Unfortunately, sensory analyses were rarely performed. This review highlights a lack of knowledge on walnut sampling before oil analysis and a distortion between some results of chemical compounds. Impact of walnut variety, walnut storage and oil extraction process was documented but few studies have considered the temporal factor of harvest, the packaging and the storage conditions of oil, which influence its chemical composition and consequently its nutritional and taste qualities.