Pecan kernel antioxidant capacity and oil composition are affected by mechanical pruning and by nut position in tree canopy

Pecan kernels have high antioxidant capacity and high levels of unsaturated fats, which are known to aid in the prevention of various chronic and age-related diseases. Concentration of human health-promoting biochemicals in plant tissues may be influenced by environmental factors. Our objective was to characterize relationships of pecan kernel antioxidant capacity and fatty acid composition to the local level of light exposure in the canopy. Our study was conducted in three major US pecan-producing states: Georgia ('Stuart' cultivar), Texas ('Pawnee' cultivar), and New Mexico ('Western' cultivar). In each state, study plots were subjected to a range of treatments paralleling conventional canopy light management practices. Nuts were collected at maturity from three canopy zones having distinct light regimes (increasing light with increasing canopy zone height). Kernels were defatted, fatty acids were derivatized to methyl esters, and resultant fatty acid methyl esters were analyzed by gas chromatography. Total kernel oil content and oleic acid content increased with height in the tree canopy and with pruning, whereas linoleic acid content, to a lesser degree, showed the opposite pattern. For example, in New Mexico the most intensely pruned treatment had total oil content of 71.1% compared with 67.8% for the unpruned control. Kernel antioxidant capacity was assessed by the Total Phenolics Content (TPC) and Oxygen Radical Absorbance Capacity (ORAC_FL) assays. Kernel antioxidant capacity showed a positive relationship with light exposure. These data suggest that implementation of pecan canopy light management programs may benefit pecan consumers through enhanced kernel nutritional properties.