Fatty acid composition of olive oil in response to fruit canopy position and artificial shading

Abstract

The fatty acid composition of olive oil is greatly affected by geographical origin, and olive oil is often promoted by health experts because of its high oleic acid concentration. Unfortunately, recent evidence has shown that oleic acid (%) can be low in many non-Mediterranean regions due to high temperatures. Thus, management tools related to irrigation, fertilization, and canopy management are being sought that might improve fatty acid composition in such regions. The objectives here were to: 1) evaluate the relationships between fatty acid composition in fruit at different canopy positions and both the photosynthetically active radiation (PAR) and red-to-far red ratio (R/FR) measured at these same positions; and 2) determine the response functions of the fatty acid concentrations to PAR using multiple shading levels applied at different fruit growth phases. Fruit samples were taken from 60 canopy positions in a large olive hedgerow (cv. Arbequina) to achieve the first objective, and different shading levels (3, 20, 40, 70% PAR) were applied using shade cloth over the northern portion of large individual trees (cv. Arbequina) for the second objective. The oleic acid concentration (%) showed a significant exponential decay with increasing daily PAR values obtained from the different canopy positions. Maximum values of about 60% oleic acid were observed at low PAR and minimum values of 50% occurred at high PAR. Based on the artificial shading treatments, the high oleic acid at shaded canopy positions appeared to be related to less fruit maturation. The other main fatty acids did not differ by canopy position, and no significant relationships between individual fatty acids and R/FR ratio were found. However, severe artificial shading under shade cloth did increase stearic and linolenic acid concentrations. Despite oleic acid being about 10% higher in the more shaded parts of the canopy, cultivating olive trees at low PAR values in order to meet international olive oil trade standards would likely not be commercially feasible due to low flowering and yields. Careful cultivar selection, early harvesting when fruit are less mature and oleic acid is higher, and blending of oils from different cultivars are recommended to improve fatty acid composition in warm regions.