Summer deficit-irrigation strategies in a hedgerow olive cv. Arbequina orchard: effect on oil quality

Treated Unconventional Waters Combined with Different Irrigation Strategies Affect 1H NMR Metabolic Profile of a Monovarietal Extra Virgin Olive Oil

The agricultural sector is facing a decrease in water supply and water quality at a global level and this is a problem that strictly affects all the Mediterranean olive growing areas. The aim of this work was to evaluate, for the first time, by NMR Spectroscopy and multivariate data analysis the metabolic profiling of the oils produced under different irrigation schemes. Arbosana olive oils were obtained from the use of saline reclaimed water (RW) and treated municipal wastewater (DW), combined with: full irrigation (FI) and regulated deficit irrigation (RDI). The results show a higher relative content of saturated fatty acids in EVOOs obtained from RDI strategy, regardless of the water source. Moreover, an increase in unsaturated fatty acids, a ω6/ω3 ratio content was observed in EVOOs obtained from RW when compared with DW water. Furthermore, the RW–RDI showed an increase in secoiridoid derivatives and hydroperoxides with respect to DW–RDI. A sustainable irrigation management, by combining a deficit irrigation strategy and saline reclaimed water source, could be crucial in order to overcome the problem of water scarcity and to guarantee the olive oil nutraceutical properties. The 1H NMR-based metabolomic approach proved a powerful and versatile tool for this specific investigation.

Specialized Functions of Olive FAD2 Gene Family Members Related to Fruit Development and the Abiotic Stress Response

Three different cDNA sequences, designated OepFAD2-3, OepFAD2-4 and OepFAD2-5, encoding three microsomal oleate desaturases (FAD2) have been isolated from olive (Olea europaea cv. Picual). Sequence analysis and functional expression in yeast of the corresponding cDNAs confirm that they encode microsomal oleate desaturases. Gene expression and lipid analysis indicate that these three genes are not involved in the linoleic acid present in seed lipids, while OeFAD2-5, together with OeFAD2-2, contributes mostly to the linoleic acid present in the mesocarp and, therefore, in the olive oil. Our results have also shown that olive FAD2-3, FAD2-4 and FAD2-5 gene expression is not only spatially and temporally regulated in olive fruit, but also is cultivar-dependent, as well as regulated by water regime, temperature, light and wounding. All these data suggest specialized physiological roles for the olive FAD2 gene family members with respect to both aspects of the biosynthesis of the linoleic acid, either present in storage lipids that constitute the olive oil or being part of membrane lipids, which are involved in the response to abiotic stresses, and highlight the differences on FAD2 gene regulation between oilseeds and oil fruits.

Olive tree physiology and chemical composition of fruits are modulated by different deficit irrigation strategies

BACKGROUND

Cropping practices focusing on agronomic water use efficiency and their impact on quality parameters must be investigated to overcome constraints affecting olive groves. We evaluated the response of olive trees (Olea europaea, cv. 'Cobrançosa') to different water regimes: full irrigation (FI, 100% crop evapotranspiration (ET_c )), and three deficit irrigation strategies (DIS) (regulated (RDI, irrigated with 80% of crop evapotranspiration (ET_c ) in phases I and III of fruit growth and 10% of ET_c in the pit hardening stage), and two continuous sustained strategies (SDI) - a conventional SDI (27.5% of ET_c ), and low-frequency irrigation adopted by the farmer (SDIAF, 21.2% of ET_c ).

RESULTS

The effects of water regimes on the plant water status, photosynthetic performance, metabolite fluctuations and fruit quality parameters were evaluated. All DIS treatments enhanced leaf tissue density; RDI and SDI generally did not affect leaf water status and maintained photosynthetic machinery working properly, and the SDIAF treatment impaired olive tree physiological indicators. The DIS treatments maintained the levels of primary metabolites in leaves, but SDIAF plants showed signs of oxidative stress. Moreover, DIS treatments led to changes in the secondary metabolism, both in leaves and in fruits, with increased total phenolic compounds, ortho-diphenols, and flavonoid concentration, and higher total antioxidant capacity, as well higher oil content. Phenolic profiles showed the relevance of an early harvest in order to obtain higher oleuropein levels with associated higher health benefits.

CONCLUSION

Adequate DIS are essential for sustainable olive growing, as they enhance the competitiveness of the sector in terms of olive production and associated quality parameters. © 2019 Society of Chemical Industry.

Ripening Indices, Olive Yield and Oil Quality in Response to Irrigation With Saline Reclaimed Water and Deficit Strategies

The 70% worldwide surface of olive orchards is irrigated. The evaluation of non-conventional water resources and water-saving techniques has gained importance during the last decades in arid and semiarid environments. This study evaluated the effects of irrigation with two water sources: low-cost water DEsalination and SEnsoR Technology (DESERT) desalinated water (DW) EC_w ∼1 dS m^-1) and reclaimed water (RW) (EC_w ∼ 3 dS m^-1) combined with two irrigation strategies: full irrigation (FI) (100% of ET_c) and regulated deficit irrigation (RDI, 50% of ET_c) on fruit yield, ripening indices, and oil yield and quality of olive trees cv Arbosana planted in Mediterranean conditions. Our results showed that RW without water restrictions increased the fruit yield by 35% due to a slight increase in the fruit weight and, mainly, to a greater fruit set than the control trees; although this did not result in a higher oil yield (g tree^-1) since the oil content per fruit dry weight was reduced. The RDI strategy did not decrease the fruit yield despite the fact that olive weight tended to decrease, and it increased the oil yield by ∼14.5%. The combination of both stresses (RW and RDI) neither decreased the fruit yield; however, it significantly reduced oil yield (25% less in 2018) since oil content per fruit dry weight was strongly reduced (40%) compared to control trees. Both RDI treatments, regardless water source, determined acidity levels in olive paste lower than in FI treatments; however, it reduced oil extractability and fatty yield. The finding about oil quality indicated that olive exposure to RW, regardless of the water amount, decreased oil quality mainly due to the reduction of oleic acid and the increase of C18:2/C18:3 ratio and peroxides; on the contrary, both RW and RDI improved the total polyphenols. In all cases, the parameters met the legislation. In short, with appropriate management, RW and RDI have great potential to manage oil olive production; nevertheless, studies subjected to long-term use of these techniques should be experienced to ensure the sustainability of oil yields and quality.

Drought Stress Effects and Olive Tree Acclimation under a Changing Climate

Increasing consciousness regarding the nutritional value of olive oil has enhanced the demand for this product and, consequently, the expansion of olive tree cultivation. Although it is considered a highly resilient and tolerant crop to several abiotic stresses, olive growing areas are usually affected by adverse environmental factors, namely, water scarcity, heat and high irradiance, and are especially vulnerable to climate change. In this context, it is imperative to improve agronomic strategies to offset the loss of productivity and possible changes in fruit and oil quality. To develop more efficient and precise measures, it is important to look for new insights concerning response mechanisms to drought stress. In this review, we provided an overview of the global status of olive tree ecology and relevance, as well the influence of environmental abiotic stresses in olive cultivation. Finally, we explored and analysed the deleterious effects caused by drought (e.g., water status and photosynthetic performance impairment, oxidative stress and imbalance in plant nutrition), the most critical stressor to agricultural crops in the Mediterranean region, and the main olive tree responses to withstand this stressor.

Quality Attributes and Fatty Acid, Volatile and Sensory Profiles of "Arbequina" hydroSOStainable Olive Oil

The use of deficit irrigation techniques on olive orchards is the main trend aiming to optimize water savings while improving functional and sensory characteristics of oils from trees under deficit irrigation techniques. The brand hydroSOStainable has been defined for crops produced under water restriction conditions. HydroSOStainable olive oils obtained under two new regulated deficit irrigation and one sustained deficit irrigation treatments in "Arbequina" olive trees were evaluated by analyzing quality parameters, antioxidant activity, total phenol content, fatty acid profile, volatile compounds, and sensory descriptors. Results showed that some of these irrigation strategies improved the phenol content at "moderate" stress levels, slightly enriched the fatty acid profile (~3.5% increased oleic acid and simultaneously decreased saturated fatty acids), and increased some key volatile compounds and also several key sensory attributes. Therefore, hydroSOStainable olive oil may be more attractive to consumers as it is environmentally friendly, has a higher content of several bioactive compounds, and has improved sensory characteristics as compared to control (fully irrigated) oils.

Yield and Water Productivity Responses to Irrigation Cut-off Strategies after Fruit Set Using Stem Water Potential Thresholds in a Super-High Density Olive Orchard

An increase in the land area dedicated to super-high density olive orchards has occurred in Chile in recent years. Such modern orchards have high irrigation requirements, and optimizing water use is a priority. Moreover, this region presents low water availability, which makes necessary to establish irrigation strategies to improve water productivity. An experiment was conducted during four consecutive growing seasons (2010-2011 to 2013-2014) to evaluate the responses of yield and water productivity to irrigation cut-off strategies. These strategies were applied after fruit set using midday stem water potential (Ψstem) thresholds in a super-high density olive orchard (cv. Arbequina), located in the Pencahue Valley, Maule Region, Chile. The experimental design was completely randomized with four irrigation cut-off treatments based on the Ψstem thresholds and four replicate plots per treatment (five trees per plot). Similar to commercial growing conditions in our region, the Ψstem in the T1 treatment was maintained between -1.4 and -2.2 MPa (100% of actual evapotranspiration), while T2, T3 and T4 treatments did not receive irrigation from fruit set until they reached a Ψstem threshold of approximately -3.5, -5.0, and -6.0 MPa, respectively. Once the specific thresholds were reached, irrigation was restored and maintained as T1 in all treatments until fruits were harvested. Yield and its components were not significantly different between T1 and T2, but fruit yield and total oil yield, fruit weight, and fruit diameter were decreased by the T3 and T4 treatments. Moreover, yield showed a linear response with water stress integral (SΨ), which was strongly influenced by fruit load. Total oil content (%) and pulp/stone ratio were not affected by the different irrigation strategies. Also, fruit and oil water productivities were significantly greater in T1 and T2 than in the T3 and T4. Moreover, the T2, T3, and T4 treatments averaged 37, 51, and 72 days without irrigation which represented 75-83, 62-76, and 56-70% of applied water compared with T1, respectively. These results suggest that using the T2 irrigation cut-off strategy could be applied in a super-high density olive orchard (cv. Arbequina) because it maintained yields, saving 20% of the applied water.

Virgin olive oil quality of hedgerow 'Arbequina' olive trees under deficit irrigation

BACKGROUND

Regulated deficit irrigation (RDI) is used in hedgerow olive orchards to achieve a sustainable balance between water savings, tree vigor and oil production. Its effects on the presence of compounds responsible for the taste of the oil and its nutritional value are controversial. The present 3-year study was conducted in an 'Arbequina' orchard (1667 trees ha^-1 ) under a full irrigation (FI) treatment (470.1 mm year^-1 of water) and two RDI treatments scaled to replace 60% and 30%, respectively, of FI. The quality parameters, antioxidant contents and volatiles of the extracted virgin olive oil (VOO) were analyzed.

RESULTS

In general, oils from the 30% RDI treatment had higher contents of pigments and phenolic compounds, a higher oleic/linoleic ratio and the highest oxidative stability, despite their lower tocopherol content. FI oils showed higher (E)-2-hexenal, 1-penten-3-one, ocimene, E-2-pentenal and pentene dimer contents than 30RDI oils, but lower contents of (E)-2-pentenol and volatile esters.

CONCLUSION

The results of the present study suggest that a RDI strategy supplying 30% of the total irrigation needs induces an increase in natural antioxidants in VOO. Neither yield, nor the rest of the quality parameters were affected by the reduced irrigation. However, abundant autumn precipitation can over-ride these effects of 30% RDI treatment on oil quality. © 2016 Society of Chemical Industry.

The Role of Polyphenoloxidase, Peroxidase, and β-Glucosidase in Phenolics Accumulation in Olea europaea L. Fruits under Different Water Regimes

Olive fruits and oils contain an array of compounds that contribute to their sensory and nutritional properties. Phenolic compounds in virgin oil and olive-derived products have been proven to be highly beneficial for human health, eliciting increasing attention from the food industry and consumers. Although phenolic compounds in olive fruit and oil have been extensively investigated, allowing the identification of the main classes of metabolites and their accumulation patterns, knowledge of the molecular and biochemical mechanisms regulating phenolic metabolism remains scarce. We focused on the role of polyphenoloxidase (PPO), peroxidase (PRX) and β-glucosidase (β-GLU) gene families and their enzyme activities in the accumulation of phenolic compounds during olive fruit development (35-146 days after full bloom), under either full irrigation (FI) or rain-fed (RF) conditions. The irrigation regime affected yield, maturation index, mesocarp oil content, fruit size, and pulp-to-pit ratio. Accumulation of fruit phenolics was higher in RF drupes than in FI ones. Members of each gene family were developmentally regulated, affected by water regime, and their transcript levels were correlated with the respective enzyme activities. During the early phase of drupe growth (35-43 days after full bloom), phenolic composition appeared to be linked to β-GLU and PRX activities, probably through their effects on oleuropein catabolism. Interestingly, a higher β-GLU activity was measured in immature RF drupes, as well as a higher content of the oleuropein derivate 3,4-DHPEA-EDA and verbascoside. Activity of PPO enzymes was slightly affected by the water status of trees during ripening (from 120 days after full bloom), but was not correlated with phenolics content. Overall, the main changes in phenolics content appeared soon after the supply of irrigation water and remained thereafter almost unchanged until maturity, despite fruit growth and the progressive decrease in pre-dawn leaf water potential. We suggest that enzymes involved in phenolic catabolism in the olive fruit have a differential sensitivity to soil water availability depending on fruit developmental stage.

Water deficit during pit hardening enhances phytoprostanes content, a plant biomarker of oxidative stress, in extra virgin olive oil

No previous information exists on the effects of water deficit on the phytoprostanes (PhytoPs) content in extra virgin olive oil from fruits of mature olive (Olea europaea L. cv. Cornicabra) trees during pit hardening. PhytoPs profile in extra virgin olive oil was characterized by the presence of 9-F1t-PhytoP, 9-epi-9-F1t-PhytoP, 9-epi-9-D1t-PhytoP, 9-D1t-PhytoP, 16-B1-PhytoP + ent-16-B1-PhytoP, and 9-L1-PhytoP + ent-9-L1-PhytoP. The qualitative and quantitative differences in PhytoPs content with respect to those reported by other authors indicate a decisive effect of cultivar, oil extraction technology, and/or storage conditions prone to autoxidation. The pit hardening period was critical for extra virgin olive oil composition because water deficit enhanced the PhytoPs content, with the concomitant potential beneficial aspects on human health. From a physiological and agronomical point of view, 9-F1t-PhytoP, 9-epi-9-F1t-PhytoP, and 16-B1-PhytoP + ent-16-B1-PhytoP could be considered as early candidate biomarkers of water stress in olive tree.