Journal
FOOD CHEMISTRY
Volume 350, Issue -, Pages -Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.foodchem.2021.129217
Keywords
Walnut kernel; Solvent extraction; Esterified phenolics; Bound phenolics; Antioxidant activity
Funding
- Fundamental Research Funds of CAF [CAFYBB2019QD002, CAFYBB2017QC002]
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The majority of phenolic compounds in walnut kernels exist in the free form, showing high radical scavenging activity. There is a strong correlation between the antioxidant activities of phenolics and their contents. Acetone is effective for extracting soluble phenolics, while methanol is better for extracting insoluble bound phenolics.
The free, esterified and bound forms of 37 phenolic compounds (including hydroxybenzoic acid, hydroxycinnamic acids, flavanols, flavonols and flavones) from walnut kernel (Juglans regia L.) were investigated in this study. Results showed that the majority of walnut phenolics were presented in the free form (51.1%-68.1%), followed by bound (21.0%-38.0%) and esterified forms (9.7%-18.7%). Ellagic acid, gallic acid, ferulic acid, sinapic acid and caffeic acid were widely distributed in three forms. Differently, jeuglone, kaempferol, quercetin-7-o-beta-D-glucoside and dihydroquercetin were only found in free phenolics. Among the three forms, free phenolics had the highest radical scavenging activity (IC50: DPPH, 15.5 mu g/ml; ABTS, 13.6 mu g/ml). The correlation co-efficients between the antioxidant activities of phenolics and their corresponding contents were 0.82-0.92. More soluble phenolics (free and esterified forms) could be extracted by acetone, while methanol was better at extracting insoluble bound phenolics.
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