a1 Department of Nutritional Sciences, University of Connecticut, 3624 Horsebarn Road Extension, Unit 4017, Storrs, CT 06269, USA
a2 Antioxidants Research Laboratory, Jean Mayer USDA Human Nutrition Research Center on Aging, Tufts University, 711 Washington Street, Boston, MA 02111, USA
Tree nuts contain an array of phytochemicals including carotenoids, phenolic acids, phytosterols and polyphenolic compounds such as flavonoids, proanthocyanidins (PAC) and stilbenes, all of which are included in nutrient databases, as well as phytates, sphingolipids, alkylphenols and lignans, which are not. The phytochemical content of tree nuts can vary considerably by nut type, genotype, pre- and post-harvest conditions, as well as storage conditions. Genotype affects phenolic acids, flavonoids, stilbenes and phytosterols, but data are lacking for many other phytochemical classes. During the roasting process, tree nut isoflavones, flavanols and flavonols were found to be more resistant to heat than the anthocyanins, PAC and trans-resveratrol. The choice of solvents used for extracting polyphenols and phytosterols significantly affects their quantification, and studies validating these methods for tree nut phytochemicals are lacking. The phytochemicals found in tree nuts have been associated with antioxidant, anti-inflammatory, anti-proliferative, antiviral, chemopreventive and hypocholesterolaemic actions, all of which are known to affect the initiation and progression of several pathogenic processes. While tree nut phytochemicals are bioaccessible and bioavailable in humans, the number of intervention trials conducted to date is limited. The objectives of the present review are to summarise tree nut: (1) phytochemicals; (2) phytochemical content included in nutrient databases and current publications; (3) phytochemicals affected by pre- and post-harvest conditions and analytical methodology; and (4) bioactivity and health benefits in humans.
Abbreviations: CRP, C-reactive protein; DPPH, 2,2-diphenyl-2-picrylhydrazyl; eBASIS, BioActive Substances in Food Information System; EuroFIR, European Food Information Resource; FRAP, ferric-reducing antioxidant power; GAE, gallic acid equivalent; HT, hydrolysable tannin; ICAM-1, intercellular adhesion molecule-1; LC, liquid chromatography; ORAC, oxygen radical absorbance capacity; PAC, proanthocyanidin; PE, Phenol-Explorer; SR-23, USDA National Nutrient Database for Standard Reference, release 23; TAC, total antioxidant capacity; USDA, US Department of Agriculture; VCAM-1, vascular cell adhesion molecule-1