Identification and quantification of phytosterols in black walnut kernels

This study aimed to identify and quantify phytosterols of six black walnut (Juglans nigra L) varieties, and compare the levels of these phytosterols between black walnuts and English walnut (Juglans regia L.). Totally, 13 phytosterols were identified in the black walnut kernels, with j3-sitosterol predominating over the other sterols. The analysis also revealed the presence of 3 phytosterols, Delta(5,23)-stigmastadienol, cycloeucalenol and 28-methylobtusifoliol, which have never been reported in black walnuts. The average levels of total sterols ranged from 1236.0 mg/kg to 1542.3 mg/kg. No significant differences were noted in total sterol levels between the studied black walnut varieties and English walnut. Through untargeted metabolomics analysis, five additional glycosylates and hydroxycinnamates of phytosterols were putatively identified in the black walnuts. The findings from this research suggest black walnuts are rich in phytosterols most of which have been demonstrated to exert bioactivities. Future studies should be focused on seasonal and geographic variations in phytosterol content of black walnuts, and bioassay-guided purification to assess potential health-promoting properties of these phytosterols.