**1. Introduction**

Virgin olive oil (VOO) is a valuable product obtained mechanically without any refining processes, so it keeps olive fruit compounds such as antioxidants [1] as well as compounds responsible for its typical colour and flavour. Olive oil flavour depends on the content in bitter-tasting compounds, such as phenolic compounds, but also on the volatile compounds, which are responsible for the typical odour notes and potential defects.

The most important VOO volatile compounds are formed through the lipoxygenase (LOX) pathway [2], C5 and C6 LOX compounds being the major contributors to the essential green sensory attribute [3]. When olives are released from the trees (either by falling down spontaneously or by harvesting them), progressive cell disruption takes place, which triggers the LOX pathway [3] and, therefore, the generation of C5 and C6 compounds and the development of the typical olive oil flavour. Factors affecting the activity of the enzymes involved in the LOX pathway, such as the fruit cultivar and the agronomic and processing conditions, may influence the volatile compound profile [2,3],

and thus the flavour traits [4]. In addition, fruit decay favours chemical oxidation and microbial enzyme activity, which cause an increase in fermentation compounds, volatile phenols and chemical oxidation compounds [4], which are involved in most of the defective flavours of olive oil [3,5].

Over the last decades, organic agriculture has increased in importance. Regulation 834/2007 [6] (soon to be replaced) defines it as a system combining the best environmental practices, a high biodiversity level, the preservation of natural resources, animal welfare, and production methods based on natural substances and processes. Each State within the European Union have set up a control system to ensure that the organic agriculture comply with this regulation. It has been reported not to improve the sensory quality of food [7]. In the case of olive oil, results are not consistent. At small scale, it has been shown that restrictions in the use of chemicals (e.g., fertilisers) result in changes in the phenol content, some volatile compounds and sensory traits [8]. However, at large scale results do not seem to indicate a clear trend, which might be due to further differences in the agronomic practices [9]. In addition, little information about the effect of the organic practices on oil from unirrigated orchards and its volatile compounds is available [9], even though unirrigated and traditionally farmed systems tend to be based on more sustainable practices. In traditionally farmed orchards, harvesting is usually performed manually from the trees. Although not advisable for the production of high quality oil [10], harvesting the fruits from the ground is still resorted to in traditional systems when other methods are not feasible. It is currently performed when hand-picking is not convenient (then, the fruits are knocked down with a pole, e.g., when the fruits are scarce, scattered or difficult to access), or when the fruits fall down due to over-ripening or after climatic events such as strong winds. As ground fruits yield poor quality oils that usually cannot be marketed as virgin oil and need chemical refining, they are managed separately, and often undergo longer storage times, which favour further decay. It would be convenient to know if differences in the quality and the volatile compounds of oil when comparing both harvesting methods are consistent over the harvesting season. The harvesting time is of great interest for the industry. Early harvesting facilitates high prices in the market. However, as fruit ripeness increases, oil content rises, although in contrast oil quality worsens [11,12]. Little information is available about the effect of harvesting time on the volatile compounds, especially in the case of organic production [13].

About 1,800,000 tons of olive oil were produced in Spain in the 2018–2019 session [14]. The more abundant cultivars in Spain are Picual (over a million ha) and Hojiblanca (about 270,000 ha). Verdial de Badajoz is also among the main Spanish olive cultivars, with about 30,000 ha [15], being farmed mainly in the west (Extremadura region).

To date, most research about the effect of organic production and harvesting conditions has been focused on oil from irrigated orchards. More information on how these factors affect oil characteristics throughout the harvesting season is advisable to ensure the highest oil quality when there is no irrigation, which is more environmentally sustainable. Therefore, the aim of this study was to research the effect of organic production under traditional agronomic practices, the traditional harvesting methods (tree-picked vs. ground-picked fruits), and the harvesting time (over a six-week period) on the chemical and physical-chemical parameters and on the volatile compound profile of the olive oils produced from olives from the Verdial de Badajoz cultivar in a commercial olive mill.
