Roasting Affects Phenolic Composition and Antioxidative Activity of Hazelnuts (Corylus avellana L.)

Abstract

The potential effect of skin removal and roasting on individual and total phenolic content, and on antioxidative potential of 6 hazelnut cultivars were investigated. HPLC-MS identification of individual phenolics confirmed the presence of 7 flavan-3-ols (catechin, epicatechin, 2 procyanidin dimers, and 3 procyanidin trimers), 3 flavonols (quercetin pentoside, quercetin-3-O-rhamnoside, and myricetin-3-O-rhamnoside), 2 hydrobenzoic acids (gallic acid, protocatechulic acid), and 1 dihydrochalcone (phloretin-2'-O-glucoside). Flavonols were only detected in whole hazelnut kernels. The content of individual phenolics, with the exception of gallic acid, was always highest in whole unroasted hazelnuts and was significantly reduced after skin removal. Similarly, total phenolic content and antioxidative potential decreased when skin was removed. Roasting had a significant negative effect on individual phenolics but not on the total phenolic content and antioxidative potential of kernels. From a health promoting phytochemical composition of hazelnuts the consumption of whole unroasted kernels with skins should be preferential to peeled kernels either roasted or unroasted. Practical Application: A significant reduction in the antioxidative potential and total phenolic content is detected after hazelnut skin removal but not after roasting, suggesting that hazelnut kernels should be consumed whole. In hazelnut skin, many phenolic compounds are located, which are not present in flesh and, therefore, the health properties of hazelnuts are strongly affected by skin removal. Thermal processing and roasting conditions used in this study had a lesser effect on the individual phenolic composition of the kernel and thus roasted and unroasted hazelnuts without skin contain comparable amounts of health promoting compounds.

Tree nut phytochemicals: composition, antioxidant capacity, bioactivity, impact factors. A systematic review of almonds, Brazils, cashews, hazelnuts, macadamias, pecans, pine nuts, pistachios and walnuts

“…Hazelnuts. Schmitzer et al (91) reported that roasting had a negative effect on individual phenolics but not on the total phenolic content and TAC (determined by DPPH) of hazelnuts. They found that the roasting decreased protocatechulic acid, phloretin-2-O-glucoside, catechin and epicatechin contents in whole hazelnuts of six genotypes harvested in Maribor, Slovenia.…”

The Mineral Source for Human Nutrition of Nuts in Different Hazelnut (Corylus avellana L.) Cultivars

“…According to the daily microelement requirements, 100 g of Turkish hazelnut cultivars has supplied about 50% for Fe and Cd, 41% for Mo, 32% for Zn, 21% for Se, 21% for Cr, 5% for B, 1% for Ni of the recommended daily amount (Özkutlu et al, 2011). Hazelnut is the best source of essential elements, amino acids, vitamin B and E among tree nuts (Açkurt et al, 1999;Oliveira et al, 2008;Xu and Hanna, 2011) and serves as a good source of natural antioxidants (Açkurt et al, 1999;Contini et al, 2008;Schmitzer et al, 2011). Several studies indicated that the nut composition of hazelnut is affected by cultivar, harvest year, soil and geographical origin (Açkurt et al, 1999;Amaral et al, 2006;Dundar et al, 2002;Seyhan et al, 2007).…”

“…Hazelnut fruits are different in morphologic characteristics and mineral composition with an extremely high variability among genotypes of different origins (Ferreira et al, 2010;Rovira et al, 2005). They are a rich source of main nutritive matter that seem to have positive effect on human health (Cristofori et al, 2008;Oliveira et al, 2008;Schmitzer et al, 2011;Silva et al, 2007). Regarding mineral composition, Alasalvar et al (2003) considered that the major minerals in hazelnut were potassium, phosphorus, calcium, magnesium, and selenium.…”

Stability of Dietary Phenolics and Antioxidant Properties of Vegetables Depends on Cooking Methodology

“…Duration of cooking and methods also have been found to have a negative impact on phenolic content and antioxidant activity (15)(16)(17)(18)(19).…”