A Review on Phytochemical Composition and Potential Health-promoting Properties of Walnuts

Walnuts are among the commonly consumed oil nuts in the world. The nuts typically contain 40–70% oil, and are a rich source of fatty acids, phenolics, phytosterols, tocopherols and carotenoids. The levels of unsaturated fatty acids and tocopherols in walnuts were significantly higher than those of many other widely consumed oil nuts. The presence of phytochemicals in walnuts gives rise to multiple bioactivities, such as antioxidant, anti-inflammatory properties, and cholesterol lowering activity. The addition of walnut to a diet could enable delay of the onset of neurodegenerative disorders, protection against the development of certain cancers. Agronomic practices, environmental and climatic conditions, geographic locations, harvesting and postharvest handling practices have impacts upon phytochemical levels in walnuts.Abbreviations: LDL: low-density lipoprotein; HDL: high-density lipoprotein; GC-FID: gas chromatography-flame ionization detector; GC-MS: gas chromatography-mass spectrometry; HPLC-DAD: high-performance liquid chromatography-diode array detector; LC-MS/MS: liquid chromatography-tandem mass spectrometry; CE-MS: capillary electrophoresis–mass spectrometry; NMR: nuclear magnetic resonance; Aβ: amyloid beta protein; ROS: reactive oxygen species; DCF: dichlorofluorescein; DCFH-DA: dichlorofluorescin diacetate; SOD: superoxide dismutase; CAT: catalase; GR: glutathione reductase; GPx: glutathione peroxidase; GST: glutathione S-transferase; GSH: glutathione; LDH: lactate dehydrogenase; VCAM-1: vascular cell adhesion molecule: ICAM-1: intracellular adhesion molecule; TNF-α: tumor necrosis factor α; IL-6: interleukin 6; NF-κB: nuclear factor kappa light chain enhancer of activated B cells; IL-1β: interleukin 1β; IL-8: interleukin 8; IL-10: interleukin 10; MCP-1: monocyte chemoattractant protein 1; mTOR: mammalian target of rapamycin; ATG7: autophagy related 7; MAP1BLC3: microtubule-associated proteins 1A/1B light chain 3; PMA: phorbol 12-myristate 13-acetate; LPS: lipopolysaccharide; iNOS: inducible nitric oxide synthase; COX-2: cyclooxygenase 2; IGF-1: plasma insulin-like growth factor 1; GSTT2: glutathione S-transferase theta 2; GSK3β: glycogen synthase kinase 3 beta; ALA: α-linolenic acid; CD133: CD133 antigen; CD44: CD44 antigen; DLK1: Protein delta homolog 1; EPA: eicosapentaenoic acid; DHA: docosahexaenoic acid; Bcl-2: B-cell lymphoma 2; IL-1α: interleukin 1α; MAO-B: monoamine oxidase B; MPTP: 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; MPP+: 1-methyl-4-phenylpyridinium; BLM: bleomycin; CSE: cigarette smoke emission.