Effect of Climate and Roasting on Polyphenols and Tocopherols in the Kernels and Skin of Six Hazelnut Cultivars (Corylus avellana L.)

Abstract

Poland is one of the largest producers of hazelnuts in Europe; however, information about the contents of biologically active compounds in hazelnuts grown in Poland is limited. The aim of this study was to analyze and compare the concentrations of phenolic acids, flavonols, and tocopherols in raw and roasted hazelnut kernels and their skin, in addition to determining the effect of the cultivar and year of cultivation. The experiment was carried out in 2016–2018, and the nuts of six hazelnut cultivars were used for research purposes. Among the detected phenolic acids, p-coumaric acid was the most abundant in roasted and unroasted kernels, whereas the apigenin content represented 43%–45% of the total flavonols. The harvest year had a significant effect on the polyphenol content of hazelnuts, whereas roasting had a minor impact. The hazelnut skin contained 168- to 378- fold higher contents of total phenolic compounds than the raw and roasted nuts. Gallic acid was the most abundant phenolic acid in hazelnut skin, contributing 95.0% of the total polyphenols on average. α-Tocopherol was the most abundant tocopherol in the hazelnut cultivars, followed by β + ƴ-tocopherol and δ-tocopherol in hazelnut cultivars. The statistical analysis showed that roasting and year of cultivation did not affect the tocopherol contents of the investigated samples.

Morphological Traits and Chemical Composition of Hazelnut from Different Geographical Origins: A Review

“…The lowest tocopherol concentration is observed in cultivars from Turkey (69-87%) [10], whereas the highest concentration is from Croatia and Portugal, 96% and 92-94%, respectively [9,74]. The highest α-tocopherol concentration is found in hazelnuts from Poland and Croatia, 25.77-29.60 mg/100 g, and 26.8 mg/100 g, respectively [35,75]. γ-tocopherol and δ-tocopherol are only present at low levels and are even undetectable in certain cultivars.…”

“…Moreover, information regarding minor tocopherol isomer content, mainly δ-tocopherol, is limited (Table 3). According to current reports, the order tocopherol isomer content in hazelnut oil is as follow: α-tocopherol > β-tocopherol > γ-tocopherol > δ-tocopherol [8,35]. The major tocopherol isomer, α-tocopherol, represents 69%-96% of total tocopherols.…”

“…Although many hazelnut cultivars have been intensively investigated, especially those cultivated in Turkey [10,[25][26][27] and Italy [28][29][30][31], so have those from new producing countries such as Chile [32], Iran [15,33], and Poland [34][35][36][37]. To the best of our knowledge, reviews on hazelnut physio-chemical properties are limited.…”

Evaluating the Suitability of Hazelnut Skin as a Feed Ingredient in the Diet of Dairy Cows

“…Besides differences in analytical procedures, hazelnut varieties and harvest time have been reported as significant factors influencing the tocopherols content [49]. Regarding the effect of roasting on tocopherols content in hazelnut and its skin, contrasting results are available in literature [50].…”

Polyphenols Extracted from Chinese Hickory (Carya cathayensis) Promote Apoptosis and Inhibit Proliferation through the p53-Dependent Intrinsic and HIF-1α-VEGF Pathways in Ovarian Cancer Cells

“…The flesh of the walnut seed is surrounded by a brown leathery coating, called the skin or the seed coat, which protects the walnut kernel from oxidation and microbial contamination. Component analysis shows that polyphenols are mainly present in the skin of nuts [ 14 , 15 ]. Research on these polyphenols will help the comprehensive utilization of Chinese hickory, but there is little research on the seed skin of Chinese hickory nuts to evaluate anti-tumor activity.…”