Corylus avellana L. Husks an Underutilized Waste but a Valuable Source of Polyphenols
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ORIGINAL PAPER
Corylus avellana L. Husks an Underutilized Waste but a Valuable Source of Polyphenols Sandra Cabo1 · Alfredo Aires1 · Rosa Carvalho2 · Núria Pascual‑Seva3 · Ana Paula Silva1 · Berta Gonçalves1 Received: 31 January 2020 / Accepted: 16 September 2020 © Springer Nature B.V. 2020
Abstract Bioactive potential of hazelnut husks was determined as a function of their cultivar source and extraction solvent. Hazelnut husks from four hazelnut cultivars (Butler, Grada de Viseu, Lansing and Morell) were picked in a hazelnut orchard at harvest and extracted with five solvents with different polarity: water, methanol, acetone, ethyl acetate and hexane. Phenolics were identified by HPLC–DAD and antioxidant activity was determined by three complementary methods: DPPH, FRAP and inhibition of lipid peroxidation. A total of 11 phenolics were identified in studied cultivars and grouped in five main classes namely, ellagitannin (ellagic acid), benzoic acids (gallic acid, protocatechuic acid and vanillic acid), flavonols (kaempferol-3,7-O-diglucoside, kaempferol-3-O-[6-acetylglucoside]-7-O-glucoside, kaempferol-3-O-[6acetylglucoside]7-O-rhamnoside and quercetin-3-O-rutinoside), flavone (luteolin-7-O-rutinoside) and flavan-3-ol (epicatechin). Cultivar and extraction solvent influenced significantly (p methanol (32.6) > acetone (21.1) > ethyl acetate (6.0) > hexane (1.89)] [28]. Although water shown the highest eluent strength (> 1) and dielectric constant (78.45) compared to other solvents [27], its ability to remove phenolics from plant matrices
seems to be lower when compared with methanol but higher than acetone. It has been widely accepted that high polarity always-mean high extraction and better phenolics solubility into extraction solvent [30], however, differences in structures of phenolics can also influence its own solubility. Moreover, factors like extraction temperature, time and method can be critical for phenolic extraction and solubility. Regarding the content of photosynthetic pigments (Table 2), as expected, chlorophylls were better extracted with acetone, whilst carotenoids were exclusively extracted with methanol. Under the other solvents, the average content
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Solvent
1.18 ± 0.00c 1.91 ± 0.15d 1.08 ± 0.07b 0.50 ± 0.02a n.d. *** 0.82 ± 0.02b 1.63 ± 0.02d 1.07 ± 0.06c 0.29 ± 0.05a n.d. *** 1.45 ± 0.01c 2.62 ± 0.19d 1.01 ± 0.10b 0.42 ± 0.00a n.d. *** 0.20 ± 0.01c 0.70 ± 0.02d 0.17 ± 0.01b 0.04 ± 0.00a n.d. *** *** *** ***
0.25 ± 0.02b 0.36 ± 0.01c 0.11 ± 0.01a n.d. n.d. *** 0.21 ± 0.04c 0.61 ± 0.02d 0.15 ± 0.01b 0.03 ± 0.00a n.d. *** 0.33 ± 0.00b 0.63 ± 0.01c 0.09 ± 0.01a n.d n.d. *** 0.19 ± 0.00b 0.37 ± 0.00c 0.04 ± 0.00a n.d. n.d. ***
*** *** ***
*** *** ***
0.05 ± 0.00a 0.32 ± 0.02d 0.18 ± 0.00c 0.07 ± 0.01b n.d. *** 0.02 ± 0.00a 0.32 ± 0.01c 0.10 ± 0.01b n.d. n.d. *** 0.07 ± 0.00b 0.39 ± 0.05d 0.16 ± 0.01c 0.05 ± 0.00a n.d. *** 0.02 ± 0.00a 0.44 ± 0.02d 0.13 ± 0.01c 0.05 ± 0.01b n.d. *** *** *** ***
n.d. 3.06 ± 0.38b 0.57 ± 0.13a n.d. n.d. *** 1.95 ± 0.00b 14.39 ± 1.23d 4.12 ± 0.59c 0
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