World production of table olives (Olea europaea L.) has shown a steady increase for the last 20 years at an average rate of 100,000 t/year, reaching 2,526,000 tons in 2011–12 [International Olive Council (IOC), 2012]. In parallel, world consumption of table olives is rising as well. The major producing countries are Spain (21%), Egypt (20%), Turkey (16%), Syria (7%), and Morocco, Greece, and Italy, each producing 3% to 4% of the total world production (IOC, 2012).
Table olives are traditionally harvested manually. However, the shortage of manpower for harvesting on the one hand and increasing labor costs on the other (Birger et al., 2008; Ferguson et al., 2010; Vega Macias et al., 2005) have encouraged researchers and growers to test different mechanical-harvesting approaches for processing at a reasonable cost with low labor demand. Mechanical harvesting of table olives has been studied since 1975 (Ferguson et al., 2012; Vega Macias et al., 2005; Zion et al., 2011). However, use of this method is still very limited (Vega Macias et al., 2005). In contrast, mechanical harvesting of oil olives has become a common practice in intensive orchards (Tous, 2011; Vossen, 2007). Most of the old, traditional oil olive orchards are still harvested manually, often aided by small-scale mechanical means such as rod beating or different types of combs operated by man and driven by electric, pneumatic, or two-tact engines. However, most of the oil olive orchards planted in the last few decades have been designed and shaped for mechanical harvesting by trunk shakers, overhead straddle-type harvesters, or canopy-contact shakers (Ferguson et al., 2010).
The application of mechanical harvesting to table olives is more complex. Green table olives are harvested before the fruit reaches physiological maturity and therefore the force required to detach the fruit from the tree is high (Burns et al., 2008; Ferguson et al., 2005). This usually leads to low harvesting efficiency. In addition, mechanical-harvesting techniques generally result in a certain degree of fruit injury compared with traditional, manual harvesting (Ferguson, 2006; Rosa et al., 2009; Vega Macias et al., 2005). Severely injured olives cannot be used by the industry for processing as a result of consumer preferences. As a result, the use of mechanical harvesting for table olives is very limited and with increasing labor costs and decreasing availability of workers, the industry is in danger in some producing countries (Ferguson et al., 2012).
To alleviate the two major difficulties involved in the mechanical harvesting of table olives, i.e., harvesting efficiency and fruit injury, attempts have been made to use abscission agents to reduce fruit-detachment force (FDF), thereby increasing harvest efficiency (Martin, 1994) and reduce the vibration intensity used in mechanical harvesting, thereby reducing the percentage of injured fruit and the severity of the defects (Burns et al., 2008; Rosa et al., 2009; Vega Macias et al., 2005). Although various substances have been tested as abscission agents, the ones in current use are based on ethylene-releasing compounds (Hartman et al., 1970; Martin et al., 1981) or ethylene-releasing precursors (Banno et al., 1993; Birger et al., 2008; Goren and Huberman, 1998). The use of abscission agents has been shown to reduce FDF and increase harvest efficiency in many studies (Barranco et al., 2004; Ferguson et al., 2010), but it is accompanied, in many cases, by moderate to severe leaf drop (Martin et al., 1981). In addition, the efficiency of abscission agents is dependent on cultivar, temperature, and stress, so that in some cases, their application damages the tree canopy and in others, it does not affect FDF or harvest efficiency (Burns et al., 2008; Klein et al., 1978; Martin, 1994; Martin et al., 1981).
In the traditional manual harvesting of green table olives, the picked olives are usually stored in bins and transported to the processing plant shortly after harvest. After cleaning and sorting, the process at the plant depends on the desired final product. The most common product in table olives is the Spanish-style green olive (Luh et al., 2005). At the processing plant, the olives are immersed in a solution of NaOH at a relatively high concentration (2.5%) to remove bitterness. Once the solution has penetrated approximately two-thirds of the distance between the skin and the pit, the olives are rinsed and stored in brine for fermentation. Other common products are California-style black ripe olives and Greek-style naturally ripened olives (Luh et al., 2005). In Israel and neighboring countries, a product called “cracked olives” is very popular. In this process, the sorted olives are passed through a machine that presses the fruits to obtain flesh cracking. The cracked fruits are then kept in 11% brine solution, similar to Greek-style ripe olives (Luh et al., 2005). After fermentation, the olives are canned. This process is dependent on variety—it is not suitable for ‘Manzanilla’, for example, but is very suitable for the local cultivar Souri. This process is hereafter referred to as “Oriental processing.”
The number of injured fruit in manually picked olives is usually small and injury intensity is generally not severe. The NaOH treatment conceals most of the light visible injuries. In mechanically harvested olives, the number of injured fruit is higher as is the intensity of the injuries (Ferguson et al., 2010). To minimize the number of non-cannable fruit, a preliminary field treatment has been proposed, consisting of immediate immersion of the harvested olives in a dilute solution of NaOH, transportation in liquid to the processing plant, and completion of the process at the plant (Vega Macias et al., 2005).
The current work evaluated mechanical harvesting of two common table olive products: Spanish-style green olives and cracked olives. Mechanical harvesting of four cultivars with trunk shakers (with and without rod beaters) was compared with manual picking during 2 successive years in the presence and absence of abscission agents. Harvest efficiency and fruit quality were assessed.
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