Tree nut phytochemicals: composition; antioxidant capacity; bioactivity; impact factors. A systematic review of almonds; Brazils; cashews; hazelnuts; macadamias; pecans; pine nuts; pistachios and walnuts

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.