Kernel oxidation susceptibility and pellicle darkening are among the biggest concerns regarding walnut quality. Monitoring oxidation is crucial to preserve quality from production to consumption. Chemical oxidation parameters (peroxide value and UV absorbances), fatty acid profile, tocopherols, phenols, and volatiles in ‘Chandler’ and ‘Howard’ kernels were studied at different time points during 28 weeks of storage to evaluate potential oxidation markers. During storage, peroxide value, UV absorbances, and volatiles concentration increased; oxidative stability, phenols, and tocopherols decreased, while fatty acid profile was unaffected. ‘Chandler’ had a lower peroxide value, K232, and K268; and higher kernel and oil oxidative stability compared to ‘Howard’. Phenols and tocopherols decreased 1.2-fold in ‘Chandler’ and 1.3-fold in ‘Howard’. Using multivariate analysis, samples were discriminated in three groups according with their oxidative levels. Increases of volatiles in oil and kernel were associated with higher oxidative levels. Pentanal, 2-methylpropanal, hexanal, (E)-2-pentenal, 3-octanone, octanal, (Z)-2-penten-1-ol, hexanol, (E)-2-octenal, 1-octen-3-ol, benzaldehyde, (E,E)-2,4-nonadienal, and hexanoic acid in kernels were adequate at distinguishing oxidation levels and as oxidative markers in walnuts. Kernel volatiles is a useful measurement for walnut oxidation during storage without any prior fat extraction.

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BACKGROUND: While both maturity and light exposure are important factors determining olive fruit physiology, the relationship between maturity, canopy position and optimal harvesting time has not been well-studied. To understand the interaction of these factors, olive fruits from upper and lower layers of the canopy were harvested from September to January. Maturity, moisture and fat content of the fruit as well as the quality and minor components of the oil extracted were measured. RESULTS:Lower light interception at the lower canopy positions resulted in differences in the fruits and oil extracted between canopy layers. Upper layer presented 60% of the overall production; fruit had one unit more of maturity index, 3% less moisture and 5% more fat content. Oil extracted from the upper layers presented higher concentration of oleuropein and ligstroside aglycone. Fruits from upper layers at maturity index of two had higher fat content and more total phenols in the oil extracted when compared with fruits from lower layer with the same maturity index. CONCLUSIONS: Differences in oil composition between layers do not correlate with differences in the fruit maturity index;instead, fruit position is a determining factor for physiological processes related to fruit growth and oil composition.brix, 16 dry matter 17 or fruit respiration. 18 Studies have also found that there are connections between fruit maturation and specific sterols and fatty acids present in the fruit pulp. 19 Additionally, non-destructive methods have been developed by measuring anthocyanin content in the peel 20 or using fruit external color and texture. 21 Olive oil quality parameters, such free fatty acidity, peroxide value, specific UV absorbances and sensory attributes have also been shown to change along fruit maturation. 22,23 Previous studies were performed to study how temperature, 24 incident light, 25,26 maturation or canopy position 6,7 in the fruit influence productivity and composition on the oils extracted. However, there is a lack of understanding on how canopy management can influence fruit maturation along harvest season in order to understand if there are possible interactions between these factors. Therefore, the aim of this research was to investigate the effect of fruit canopy position on fruit maturation and oil composition and to determine which parameters are determinant for the optimal harvesting time. MATERIAL AND METHODS Plant material and experimental designThe study was carried out at the Wolfskill Experimental Orchard Field Station from University of California, Davis (Winters, CA, USA) (38.502920, −121.977120). Trees of Arbequina cultivar of ten years old, managed under sprinkler irrigation were used in this experiment. The trees were trained to vase system (5 m × 6 m) with a single trunk with two main branches, oriented along the row, starting by 0.5 m height above ground. Two more couples of main branches were inserted at 150 and 230 cm above ground respectively. The average height of the trees was 3 m and the averag...

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