Antioxidant properties, profile of polyphenolic compounds and tocopherol content in various walnut (Juglans regia L.) varieties

The aim of this work was to characterize antioxidant properties, establish the profile of polyphenolic compounds and evaluate the content of tocopherols in walnut fruits. The research material consisted of eleven walnut varieties which were examined for dry matter content, fats and minerals content. Their antioxidant capacity was determined by the ABTS, DPPD and FRAP assays. The profile of polyphenolic compounds was established by means of ultra-high performance liquid chromatography coupled with a mass detector (UPLC-PDA-ESI-MS). In addition, tocopherols (, , and ) were quantified using high-pressure liquid chromatography (HPLC). Walnut fruits differed significantly in terms of their physicochemical parameters, antioxidant properties and the content of bioactive compounds. Walnuts of the Lake cultivar exhibited the strongest antioxidant potential, while those of the U02 had the highest content of total polyphenols (2.07g/100g). Phenolic acids, among which gallic acid, protocatechuic acid, syringic acid, and genistinic acid were identified, dominated in the polyphenol profile. In turn, the spectrum of tocopherols contained four isoforms: , , and . In the examined walnuts, the total tocopherol content ranged from 19.83mg/kg (U17) to 126.00mg/kg (Lake) and - and -tocopherols were present in major quantities.