Impact of the Degree of Maturity of Walnuts (Juglans regia L.) and Their Variety on the Antioxidant Potential and the Content of Tocopherols and Polyphenols

Abstract

The aim of the study was to characterize the antioxidant properties; establish the profile of polyphenolic compounds and evaluate the content of tocopherols in walnuts of three varieties (Leopold; Apollo; Resovia) differing in the degree of maturity (harvest date). The profile of polyphenolic compounds was established by UPLC-PDA-ESI-MS. The content of tocopherols was determined by HPLC-FLD. It was found that the content of dry matter and fat increased and the antioxidant properties decreased with the maturation of nuts. Walnuts of the Leopold cultivar harvested in July exhibited the highest content of total polyphenol (2149.08 mg/100 g dry mass). In their polyphenolic profile; 26 compounds were identified; mainly belonging to the class of ellagitannins. The polyphenolic content decreased with the maturation of nuts. The total content of tocopherols in the tested nuts increased with ripening and ranged from 1.76 mg/100g (Apollo VII) to 18.30 mg/100g (Resovia IX)

Changes in Antioxidant Activity, Profile, and Content of Polyphenols and Tocopherols in Common Hazel Seed (Corylus avellana L.) Depending on Variety and Harvest Date

“…Even so, the literature lacks information on the influence of the degree of maturity on the fat content of hazelnuts. Among data from Pycia et al [10], a similar correlation was found between the fat content of walnut fruits and their harvest date. The quoted authors indicate that the content of this ingredient increased with the ripening and in walnuts harvested in September it was on average 22.64 g/100 g d.m.…”

“…The analysis of polyphenolic compounds profile was performed by ultra-efficient liquid chromatography coupled with a mass detector (UPLC-PDA-ESI-MS) (Waters, Micromass, Manchester, UK) [10,16,17]. The study used the Aquity liquid chromatograph (Waters, Micromass, Manchester, UK), coupled with a photodiode array (PDA) and a tandem quadrupole detector (TQD).…”

“…Tocopherols (α, β, γ, δ) were analyzed by high-performance liquid chromatography (HPLC) using SYKAM chromatograph (Eresing, Germany) equipped with a fluorescence detector (Shimadzu RF 353) and 5C18-MS-II column (200 mm × 4.6 mm i.d., 5 µm Cosmosil) [10,17]. The column was developed in the isocratic system of methanol (100%) at a flow rate of 0.5 cm 3 /min.…”

“…On the other hand, Marzocchi et al [25] reported that the content of polyphenols in the dry hazelnut seeds of the Kataloński variety was 1245.27 mg/100 g d.m., and the value of this parameter increased with higher temperatures and longer baking times. Pycia et al [10] analyzed the effect of the degree of maturity of walnuts on the content of polyphenols and antioxidant capacity. A similar tendency was demonstrated to see a decreased level of antioxidant properties with the acquisition of maturity.…”

“…Then the content of phenolic compounds changes dynamically. When fully ripe, edible parts of a walnuts fruit have a significantly lower level of polyphenols compared to unripe fruits [10]. However, the content of colored anthocyanins in the fruit skin or nut shell increases significantly.…”