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Identification of Key Antioxidants of Free, Esterified, and Bound Phenolics in Walnut Kernel and Skin

Walnut is a natural source of antioxidants. Its antioxidant capacity is determined by the distribution and composition of phenolics. The key phenolic antioxidants in various forms (free, esterified, and bound) in walnut kernel (particularly seed skin) are unknown. The phenolic compounds in twelve wa...

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Autores principales: Wu, Shutian, Mo, Runhong, Wang, Ruohui, Li, Qingyang, Shen, Danyu, Liu, Yihua
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2023
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9956992/
https://www.ncbi.nlm.nih.gov/pubmed/36832900
http://dx.doi.org/10.3390/foods12040825
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author Wu, Shutian
Mo, Runhong
Wang, Ruohui
Li, Qingyang
Shen, Danyu
Liu, Yihua
author_facet Wu, Shutian
Mo, Runhong
Wang, Ruohui
Li, Qingyang
Shen, Danyu
Liu, Yihua
author_sort Wu, Shutian
collection PubMed
description Walnut is a natural source of antioxidants. Its antioxidant capacity is determined by the distribution and composition of phenolics. The key phenolic antioxidants in various forms (free, esterified, and bound) in walnut kernel (particularly seed skin) are unknown. The phenolic compounds in twelve walnut cultivars were analyzed using ultra-performance liquid chromatography coupled with a triple quadrupole mass spectrometer in this study. A boosted regression tree analysis was used to identify the key antioxidants. Ellagic acid, gallic acid, catechin, ferulic acid, and epicatechin were abundant in the kernel and skin. The majority of phenolic acids were widely distributed in the free, esterified, and bound forms in the kernel but more concentrated in bound phenolics in the skin. The total phenolic levels of the three forms were positively correlated with antioxidant activities (R = 0.76–0.94, p < 0.05). Ellagic acid was the most important antioxidant in the kernel, accounting for more than 20%, 40%, and 15% of antioxidants, respectively. Caffeic acid was responsible for up to 25% of free phenolics and 40% of esterified phenolics in the skin. The differences in the antioxidant activity between the cultivars were explained by the total phenolics and key antioxidants. The identification of key antioxidants is critical for new walnut industrial applications and functional food design in food chemistry.
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spelling pubmed-99569922023-02-25 Identification of Key Antioxidants of Free, Esterified, and Bound Phenolics in Walnut Kernel and Skin Wu, Shutian Mo, Runhong Wang, Ruohui Li, Qingyang Shen, Danyu Liu, Yihua Foods Article Walnut is a natural source of antioxidants. Its antioxidant capacity is determined by the distribution and composition of phenolics. The key phenolic antioxidants in various forms (free, esterified, and bound) in walnut kernel (particularly seed skin) are unknown. The phenolic compounds in twelve walnut cultivars were analyzed using ultra-performance liquid chromatography coupled with a triple quadrupole mass spectrometer in this study. A boosted regression tree analysis was used to identify the key antioxidants. Ellagic acid, gallic acid, catechin, ferulic acid, and epicatechin were abundant in the kernel and skin. The majority of phenolic acids were widely distributed in the free, esterified, and bound forms in the kernel but more concentrated in bound phenolics in the skin. The total phenolic levels of the three forms were positively correlated with antioxidant activities (R = 0.76–0.94, p < 0.05). Ellagic acid was the most important antioxidant in the kernel, accounting for more than 20%, 40%, and 15% of antioxidants, respectively. Caffeic acid was responsible for up to 25% of free phenolics and 40% of esterified phenolics in the skin. The differences in the antioxidant activity between the cultivars were explained by the total phenolics and key antioxidants. The identification of key antioxidants is critical for new walnut industrial applications and functional food design in food chemistry. MDPI 2023-02-15 /pmc/articles/PMC9956992/ /pubmed/36832900 http://dx.doi.org/10.3390/foods12040825 Text en © 2023 by the authors. https://creativecommons.org/licenses/by/4.0/Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Wu, Shutian
Mo, Runhong
Wang, Ruohui
Li, Qingyang
Shen, Danyu
Liu, Yihua
Identification of Key Antioxidants of Free, Esterified, and Bound Phenolics in Walnut Kernel and Skin
title Identification of Key Antioxidants of Free, Esterified, and Bound Phenolics in Walnut Kernel and Skin
title_full Identification of Key Antioxidants of Free, Esterified, and Bound Phenolics in Walnut Kernel and Skin
title_fullStr Identification of Key Antioxidants of Free, Esterified, and Bound Phenolics in Walnut Kernel and Skin
title_full_unstemmed Identification of Key Antioxidants of Free, Esterified, and Bound Phenolics in Walnut Kernel and Skin
title_short Identification of Key Antioxidants of Free, Esterified, and Bound Phenolics in Walnut Kernel and Skin
title_sort identification of key antioxidants of free, esterified, and bound phenolics in walnut kernel and skin
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9956992/
https://www.ncbi.nlm.nih.gov/pubmed/36832900
http://dx.doi.org/10.3390/foods12040825
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