Hazelnut kernel

Alasalvar, C., Karamac, M., Amarowicz, R., and Shahidi, R, Antioxidant and antiradical activities in extracts of hazelnut kernel (Corylus avellana L.) and hazelnut green leafy cover, J. Agric. Food Chem., 54, 4826-4832, 2006. 

Tree Nuts Composition, Phytochemicals, and Health Effects Hazelnut hard shell Hazelnut kernel (with skin)... 

Hazelnut kernel (without skin) Hazelnut green leafy cover... 

Although antioxidant activity and phenolic constituents of hazelnut (hazelnut kernel) [4,26-28] and some of its by-products [29-31,100] have been reported, little is known about phenolic phytochemicals and their potential health benefits in hazelnut and hazelnut by-products. Therefore, this chapter provides detailed information on nutraceuticals, phytochonicals, and health aspects of hazelnut and hazelnut by-products and evaluates their antioxidant activities by a number of indicators. Taxanes present in hazelnut by-products are discussed in detail. Where possible, the health benefits of relevant phytochemicals are described. 

Contents of Phenolics and Total Antioxidant Activity in Extracts of Hazelnut Kernel and Hazelnut By-Products... 

Five soluble phenolic acids (free and esterifled), one of which is a hydroxylated derivative of benzoic acid (gallic acid) and four are cinnamic acid derivatives (caffeic, p-coumaric, ferulic, and sinapic acids), have been studied and tentatively identified in ethanolic extracts of hazelnut kernel and hazelnut by-products (Table 13.2) [31]. The order of total phenolic acid concentration was as follows hazelnut hard shell > hazelnut green leafy cover > hazelnut tree leaf > hazelnut skin > hazelnut kernel. Different phenolic acids predominate in each plant part examined. Among the identified phenolic acids, p-conmaric acid was most abundant in hazelnut kernel, hazelnut green leafy cover, and hazelnut tree leaf, whereas gallic acid was most abundant in hazelnut skin and hazelnut hard shell, possibly implying the presence and perhaps the dominance of tannins in the latter samples (Table 13.2). The same number, but different concentration, of phenolic acids have also been reported in hazelnnt kernel and hazelnut green leafy cover [30]. 

The content of condensed tannins in hazelnut (kernel), expressed as milligrams of CE per gram of extract, varies quite markedly, from a low of 40.5 for 80% ethanolic extract to a high of 320 for 80% acetone extract. Acetone is a more effective solvent for the extraction of condensed tannins as tannins are relatively high-molecular-weight compounds and ethanol is not necessarily suitable for their extraction [30]. The reason for this is that tannins are relatively high-molecular-weight compounds and the polarity of ethanol is too low for total extraction of these polar compounds from plant sources. 

Recently, Shahidi et al. [31] found that total antioxidant activity of hazelnut extracts ranged from 29 to 148 xmol TE/g of ethanolic extract, with lowest activity in hazelnut kernel aud highest in hazelnut tree leaf (Table 13.1). The total antioxidaut activity of hazelnut by-product extracts were approximately 4-to5-fold higher than that of hazelnut kernel at the same extract concentration. At a given concentration, hazelnut by-product extracts would serve as a more effective antioxidant than hazelnut kernel extract. Consideration of defatted hazelnut (on an extract basis) and hazelnut (as is weight basis) make the quantitative comparison between the studies of Wu et al. [4] and Shahidi et al. [31] impossible. 

Siriwardhana and Shahidi [33] evaluated the Trolox equivalents antioxidant capacity (TEAC) of almond and its by-product extracts and found that ethanolic extracts, at the same concentration the TEAC values, followed the order of brown skin > green shell cover > whole seed (kernel). Values of brown skin and green shell cover extracts were 12.6- and 9.8-fold higher than that of whole seed extract, respectively. Alasalvar et al. [30] observed that hazelnut kernel and its green leafy cover extracts from 80% (v/v) ethanol were characterized as having significantly lower (P < 0.05) total antioxidant activity compared to those of extracts obtained from 80% (v/v) acetone. 

Yurttas et al. [26] measured the antioxidant activity of both hydrolyzed and nonhydrolyzed Turkish and American hazelnut kernel extracts in a linoleic add-buffer system. Results showed that... 

Several free radical scavenging activity tests (hydrogen peroxide, superoxide, and DPPH) have been employed to evaluate the extracts of hazelnut kernel and hazelnut by-products. This information... 

FIGURE 13.2 Antioxidant activity in extracts of hazelnut kernel and hazelnut by-products in the 3-carotene-linoleate model system. (From Shahidi, R, Alasalvar, R, and Liyana-Pathirana, C.M., J. Agric. Food Chem., 55,1212, 2007. With permission.)... 

Certain species of hazelnut trees produce as much as one-tenth of the paclitaxel found in the Pacific yew trees. For every dry weight gram of bark of the Pacific yew, about 50 to 70 j,g of paclitaxel can be extracted, while in branches and leaves of the hazelnuts, about 5 to 7 of paclitaxel can be extracted per gram dry weight. Hazelnut kernel (raw) and shells have also been reported to contain small amounts of paclitaxel (<0.05 (ig/g extract) [93]. 

Small amounts of paclitaxel were also isolated from Turkish Tombul hazelnut tree leaf (0.05 J.g/g extract) and hard shell (0.08(tg/g extract). In addition to paclitaxel, 10 deacetyl baccatin III and cephalomannine (leaf and hard shell) and baccatin III (green leafy cover) were found in the extracts (Table 13.10). Taxanes were not detected in the extracts of hazelnut kernel and hazelnut skin from Turkish Tombul cultivar. 

Sim ek, 0., Arid, M. Demir, C. (2002) Mycoflora of hazelnut (Corylus avellana L.) and aflatoxin content in hazelnut kernels artificially infected with Aspergillus parasiticus. Nahrung/Food 46(3), 194-196. 

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