Effects of pre-harvest deficit irrigation during the oil accumulation period on fruit characteristics, oil yield extraction, and oil quality in olive cv. Genovesa in an arid region of Argentina
Introduction
Olive oil consumption has been steadily increasing worldwide over the last 20 years (IOC, 2016). This is due to different reasons, mainly consumers’ growing knowledge about its organoleptic, nutritional, and therapeutic properties within the Mediterranean and non-producing countries (Sala-Vila et al., 2015). Numerous studies have shown evidence that the beneficial properties of olive oil are related to the high content of antioxidant compounds and monounsaturated fatty acids (eg. Sala-Vila et al., 2015). Recently, the phenolic compounds of olive fruits and oil and their relation to antioxidant, anti-carcinogenic, and organoleptic (bitter and pungent) attributes have attracted considerable attention (Llorente-Cortés et al., 2010). Olive oil phenolic compounds, in particular, and oil quality in general are affected by many factors such as cultivar, environmental conditions, orchard management, and processing technology (Servili et al., 2004).
Among cultural practices, the influence of irrigation on oil quality has been extensively investigated in different olive cultivars and environments. In olive crop, a general pattern was observed in which water deficit application during any fruit growth period led to slight or no impact on oil free acidity, peroxide value, spectrophotometric indices, and fatty acid composition but to marked increases in oil phenolic compounds (Caruso et al., 2014, Patumi et al., 1999). However, this relationship is far from universal, and the oil quality response can vary according to water deficit exposure time, severity, and duration. Water deficit applied during early fruit development seems to produce a more consistent increase in oil phenolic concentration regarding high responsiveness of fruit phenolic synthesis (Alagna et al., 2012, Lémole et al., 2018). By contrast, the effect of water deficit applied during the fruit oil accumulation period on oil phenolic concentration is less clear. There is evidence of increase (e.g. Gómez-Rico et al., 2007; Vidal et al., 2019) or reduction (e.g. García et al., 2020) where environmental conditions and harvest time play a key role (Sainz et al., 2019).
Water deficit before harvest may increase the concentration of oil phenolic compounds by a reduction of fruit moisture leading to lower losses of fruit phenolic compounds during oil extraction (Dag et al., 2008). Olive fruits have high phenolic concentration. However, only a very low proportion (0.1–2%) is transferred to olive oil during the industrial process, mainly because phenolic compounds are more soluble in the water than oil phase (Jerman Klen et al., 2015). Talhaoui et al. (2016) evaluated the phenolic concentration and composition of fruits and derived oil from six olive cultivars. The authors found that the transfer rate from fruits to oil was highly associated with fruit moisture rather than phenolic concentration in fruits.
In arid environments, such as those used for olive cultivation in Argentina, deficit irrigation strategies could be managed in different fruit growth periods depending on irrigation objectives, such as vegetative growth control and water savings (Trentacoste et al., 2019). Pierantozzi et al. (2020) evaluated four irrigation levels applied 2 months prior to pit hardening (i.e. late-spring) in an intensive olive cv Genovesa orchard in central-western Argentina under similar conditions to those reported here. The authors observed that spring water deficit affected vegetative growth with a slight effect on oil production, although no information was provided on oil quality. Few studies have focused on evaluating water deficit strategies carried out before harvest. This can be explained by the fact that pre-harvest water deficit is related to a reduction in fruit oil accumulation (Tognetti et al., 2006, Hueso et al., 2019) and lower efficiency of mechanical harvesting (Dag et al., 2008). In addition, autumn rainfall is frequent in the Mediterranean climate where much of the olive research has been carried out. From an industrial viewpoint, pre-harvest water deficit could reduce fruit moisture and increase oil extraction, compensating for lower fruit oil content. It has the additional advantage of a potential increase in the transfer of phenolic compounds, although other characteristics such as fatty acids profile must also be evaluated (García et al., 2020).
Fruit moisture is highly responsive to plant water status and environmental conditions (Trentacoste et al., 2012). Dag et al. (2015) observed in some experimental seasons that the response of oil phenolic concentration to water deficit regimes was altered by a change in fruit moisture just before harvest as a consequence of rainfall. Understanding the influence of irrigation regimen and environmental conditions is fundamental to designing irrigation strategies focused on olive oil quality. The aims of the present study were to determine the impact of pre-harvest deficit irrigation applied during the oil accumulation period in olive cv. Genovesa on (i) maturity, oil, water, and flavonoid compounds in fruit and (ii) on yield extraction, fatty acids, and phenolic compounds in oil. To deepen the knowledge about the effect of fruit moisture on oil quality, an additional treatment was incorporated in which distilled water was added during the industrial processing of olives from the severe water deficit treatment.
Section snippets
Site and orchard
The study was carried out during seasons 2017–2018 and 2018–2019 in a commercial olive (cv. Genovesa) orchard in Cañada Honda Valley (31º 58′S, 68º 32′W, 614 m.a.s.l.), San Juan, Argentina. The orchard was established in 2011 with rows oriented N-S and trees spaced 3.5 m x 7.0 m (408 trees ha-1). The climate of the region is arid with an annual rainfall of 195 mm concentrated in the summer months and an average annual temperature of 18.5 °C. The soil is sandy-loam with high gravel content less than
Seasonal conditions, water applied, and dynamics of fruit weight and moisture
Daily and accumulated seasonal rainfall is shown in Table 1 and Fig. 1. Rainfall in 2017–2018 (193 mm) and 2018–2019 (174 mm) was close between the two periods and the long-term average of 195 mm (period 2014–2019). As usual in San Juan province, rainfall was concentrated between December and May. Additionally, about 50% of the total rainfall occurred during Period II (January to early April) when deficit irrigation treatments were applied (Table 1). The main difference between seasons was
Discussion
Different irrigation treatments from end of pit hardening to harvest were applied to generate a wide range of variation in fruit moisture as a useful framework to investigate fruit moisture impacts on other fruit materials (oil and mass), oil extraction and quality. The study area is characterized by scarce annual rainfall (lower than 200 mm) and a summer-autumn period (Period II) with high evaporative demand and some intense rainfall events (e.g. early April 2018).
Conclusions
The present study indicates that pre-harvest water deficit can be used to manage fruit moisture, but responsiveness is highly dependent on rainfall events occurring just before harvest. This experiment has identified that fruit moisture of about 50% at harvest leads to maximum oil yield extraction and phenolic compounds concentration. Further work with paste obtained from fruits with a wider moisture range and from other olive cultivars is required to confirm these conclusions. The fatty acids
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
We are grateful to Miguel Zuccardi from “Finca Zuelo-Familia Zuccardi” for allowing access to the olive orchards where this research was conducted. We also thank Miguel Ballester and Guillermo Ojeda for their technical assistance in the management of olive hedgerows, as well as Octavio Contreras and Walter Galarza for their help with olive collection and laboratory work and Silvia Barbuzza for her help with proofreading.
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2021, Journal of Food Composition and AnalysisCitation Excerpt :Frantoio) orchard under different irrigation regimes (full, deficit, complementary) showed negligible influence of watering on free acidity, peroxide value and fatty acid composition, but strong effect on phenolic concentration (Caruso et al., 2014). A recent study using RDI during the active oil synthesis period, once pit development is complete, showed had lower moisture, dry mass and oil deposition, and higher pulp flavonoid content in 30 % ETc-RDI than in 50 %-RDI and full-irrigated treatments (Monasterio et al., 2021). So far and to the best of our knowledge, studies evaluating irrigation effects on chemical components of olive seeds have not been addressed yet.