GRASAS Y ACEITES, 57 (1), ENERO-MARZO, 16-24, 2006, ISSN: 0017-3495

The postharvest of mill

By José M. García and Khaled Yousfi

Departamento de Fisiología y Tecnología de Productos Vegetales Instituto de la Grasa, CSIC, Avda. Padre García Tejero 4 - 41012 Sevilla, Spain.

RESUMEN include the washing, grinding, beating, pressing, decantation, or filtration, without being La postcosecha de aceituna de molino mixed with oils of another nature. In the same way, it El mayor deterioro del aceite de oliva es debido a la inade- seems logical to relate the quality of an orange juice cuada manipulación de las aceitunas durante el tiempo que to the physiological state of the fruits wherefrom it is media entre su cosecha y su procesado. El almacenamiento de obtained; the quality of virgin oil is directly related las aceitunas se lleva acabo mediante el simple amontona- to the quality of the fruit from which it is extracted. In miento del fruto, esperando su procesamiento. Estos frutos this chapter the consequences of the postharvest desarrollan toda clase de procesos degenerativos en un corto manipulation on the olive physiology and on the oil periodo de tiempo. Los aceites obtenidos a partir de estos fru- tos exhiben deterioros hidrolíticos y oxidativos característicos, quality will be studied. In general, the postharvest confirmados por sus valores altos de acidez, de índice de pe- period of a fruit includes all the processes that the róxidos o de absorbancia en la región ultravioleta a 232 y 270 olive is subjected to, from harvesting up to its sale in nm. Para evitar esta situación, la industria intenta reducir al the market or its industrial transformation. Thus, máximo el intervalo entre la cosecha y el procesado del fruto, normal activities such as packaging, transportation, mediante un aumento de la capacidad de molturación. Sin em- selecting, sorting, cleaning, antifungal treatments, bargo, el equipo necesario para prevenir la acumulación de fru- grading, or storage are all associated with this period. to en Enero no se precisa para el resto de la campaña. En es- te capítulo, la refrigeración de las aceitunas o el uso de Traditionally, olives have been treated from the tratamientos físicos, que permiten el procesado de frutos poco moment of harvesting until their processing with the maduros, son analizados como alternativas posibles. same sensitivity that construction material such as sand or gravel might receive (Figure 1). The degree of PALABRAS-CLAVE: Aceite de oliva - Calidad - Olea eu- excellence of virgin is directly related to the ropaea - Refrigeración - Tratamiento de calor. physiological state of the fruit at the moment of its processing, and this is the most determinant factor to SUMMARY its level of quality. Unfortunately, obtaining the best quality virgin olive oil is not rewarded by a sufficient The postharvest of mill olives increase in the market value of this oil in comparison to that reached for other virgin oils from a lower quality The greatest deterioration of olive oil is due to poor category (Fundación del Olivar, 2005a). Frequently, handling of the olives during the time between harvesting extra virgin olive oil is sold only about 3% more and processing. Storage of olive fruits is carried out by simple heaping in fruit piles, waiting their processing. These expensive than the so-called “lampante”, which can fruits develop all kinds of degenerative processes in a short not be commercialized for human consumption period of time. Oils obtained from them show characteristics without previous refining and, in fact, oil of the “virgin” hydrolytic and oxidative deteriorations confirmed by their category can reach a better price than “extra virgin” high acidity values, peroxide value or ultraviolet absorbance oil, in spite of its lower level of quality (Fundación del at 232 and 270 nm. To avoid this situation, the industry is Olivar, 2005b). Therefore, to address the olive currently reducing the interval between harvesting and processing, through an increase in milling capacity. However, industry on the goal of obtaining a high quality olive oil the equipment necessary for preventing the accumulation of fruit in January would be unnecessary for the rest of the season. In this chapter, refrigeration of the olive fruits, or the use of physical treatments, to allow the processing of unripe fruits, are analysed as possible alternatives.

KEY-WORDS: Heat treatment - Olive oil - Olea europaea - Quality - Refrigeration.

1. INTRODUCTION

Virgin olive oil is by definition the oil obtained from Figure 1 the olive fruit through physical procedures, which Olive pile. Source: J. Alba

16 THE POSTHARVEST OF MILL OLIVES

may seem utopia. Nevertheless, it is an indisputable produced respectively by lipases, lipoxygenases and fact that olive oil will never be able to compete in price liases of both olive and parasitic origin (González- with other oils, due to the high cost of its harvesting Cancho, 1957; Mazuelos-Vela, 1972; García and and the scanty yield that is obtained from its physical Streif, 1991). The oil obtained also develops an extraction (25 % of the initial weight, at best). The undesirable sensory attribute called “atrojado” competitiveness of olive oil comes from its intrinsic (fusty), due to the presence of a high content in quality, superior to any another edible oil (Touzani volatile acids, such as acetic or butyric and in fat 2004). The increasing value that the Mediterranean alcohols, such as 1-octen-3-ol and 2-octen-1-ol diet is acquiring among nutrition specialists has (Gutiérrez et al., 1981; Olías et al., 1988; Olías and contributed to an international rise in the demand for García, 1997). virgin olive oil (Wahrburg et al. 2002). For this reason, To avoid this physical and biological deterioration in spite of the scarce profit margin rendered from its of the fruit, which determine the subsequent price, the production and sale of virgin olive oil is production of a low quality virgin oil, the industry is increasing systematically (Grapevines et al. 2003). currently following a main strategy of reducing the Throughout this chapter the postharvest strategy that interval between harvesting and processing, as the olive industry has selected for obtaining a high much as possible and recommends three steps for quality product will be discussed and the utilization of the olive during this period: Firstly, the separation of other alternative systems will be proposed. harvested olives from the ones previously falling onto the soil is strongly recommended. For this purpose the use of canvases on the soil for the 2. POSTHARVEST OF OLIVES: CURRENT reception of the harvested fruits is commonly used. SITUATION AND FUTURE TRENDS Secondly, the use of perforated boxes is recommended for keeping the olives: a larger format Historically, the greatest deterioration of olive oil is of 100 x 100 x 120 cm3 for a short storage period due to poor handling of the olives during the time (≤ 48 h) (Figure 3) and a small one (50 x 30 x 40 cm3) between harvesting and processing. After specially for longer periods of storage (Figure 4) harvesting, which is normally done with the cheapest (Tous et al. 2005). Finally, the main recommendation process called “vareo” (shaking the olive branches that the olive industry is following consists in an with rods), the olives, laying on the soil from the increase in milling capacity in order to avoid a wait beaten branches, are picked up and put in dump period ≥ 24 h from the harvesting to the oil extraction truck boxes, sometimes even using digging (de Toro et al. 2002). machines (Figure 2). Storage of these olives is The separation of healthy from decayed fruit is carried out by simple heaping in fruit piles on the one of the basic premises of postharvest courtyard of the olive mills, awaiting their processing. technology in order to guarantee that it will arrive to In these conditions all kinds of degenerative the market or processing plant in good condition. It processes and pathogenic infections develop in the is especially important for the sensory quality of fruit in a short period of time. Anaerobic micro- virgin oils. The human nose is very sensitive to the organisms act in the internal zone of the pile and odours developed in infected olives. A small aerobic ones in the outermost areas. At the same presence of these undesirable attributes could time, the metabolism of the accumulated fruits contaminate a large amount of oil, resulting in a results in a considerable increase in temperature in serious loss of quality. On the other hand, these the pile, autocatalyzing the degenerative processes infected fruit randomly placed in the olive pile are and accelerating fruit degradation. Normally, oils infection nests from which the parasitic micro obtained from these fruits are characterized by organisms, mainly fungi, can rapidly proliferate presenting hydrolytic and oxidative deteriorations among the rest of the fruit. This progressive measured by their high acidity values, peroxide value deterioration is accelerated by the presence of or ultraviolet absorbance at 232 and 270 nm, mechanically damaged fruits, which are especially

Figure 2 Figure 3 Figure 4 Digging machine used Container for table olives. Olives packed in a 22 kg able in olive harvesting. Source: P. García perforated plastic box. Source: J. Alba. Source: Tous et al. 2005

GRASAS Y ACEITES, 57 (1), ENERO-MARZO, 16-24, 2006, ISSN: 0017-3495 17 JOSÉ M. GARCÍA AND KHALED YOUSFI

sensitive to the fungi infection. The use of “vareo” time and olive tree alternation (Table 1). Olive causes a high incidence of fruit damage and, harvesting is done during a relatively short period of indirectly, facilitates oil deterioration. time, when fruit offer a better yield for oil production. Unfortunately, the use of perforated plastic boxes Thus, in the last five seasons, almost 40 % of oil to contain the olives during their postharvest period is production has been concentrated in the month of not yet an extended practice. Normally, the use of January. The machinery necessary for preventing boxes is limited to transporting the olives from the accumulation of fruit waiting oil extraction during harvesting to the dump truck boxes, but even this peak production in January would be excessive for simple measure can suppose a considerable the rest of the season, when it would have to work improvement in the maintaining fruit integrity in at 50 or 60 % of its capacity. Furthermore, the olive comparison to the use of diggers for this task. In crop is highly variable; one season with a high yield addition to the reduction of mechanical damage, the of olives will be followed by one with a very poor main aim of this system is to avoid deterioration due fruit production. For this reason, the processing to excessive fruit accumulation. The holes in the capacity for a crop during a high production season boxes are very important to allow for ventilation of the to avoid fruit accumulation, would only work at 50% olives, delaying the fermentation processes in the of its performance during seasons of lower fruit stored fruit. The use of boxes for the storage of olives production. intended for oil would mean a significant improvement in quality for the olive oil industry. It implies the introduction of the palletization system, habitually 3. COLD STORAGE. AN ALTERNATIVE used for other commodities, such as oranges, apples, pears, etc. For instance, palletization, in addition to a The use of refrigeration in fruit storage is based better preservation of the fruit to damage caused by on the reduction of the speed of the metabolic handling , allows for quick cargo removal in minutes processes induced by low temperatures. Thus, using a forklift, more efficient olive storage, higher enzymatic activity such as celulases and quantity in a lower space, and better organization of galacturonases, responsible for fruit softening, or the olives, which could be classified by their different chlorophylases, which act in skin colour changes characteristics: origin, quality, harvesting system, are delayed, allowing a longer commercial life for variety, etc. However, the main advantage of this the commodity. However, the main metabolic effect system is that it would facilitate the traceability of the of cool temperature is the decrease in the olive oil from the olive tree to the bottle of virgin olive effectiveness of fruit respiration. This process oil. Thus, producers, who obtain the highest quality supplies the energy necessary for the development virgin olive oil, could sell their product at a higher price of fruit maturation. A high level of respiration than other oils of inferior quality. This system should determines two undesirable effects: a shorter be an affective tool for securing the characteristic of commercial life for the product stored and a loss in quality of a determined denomination of origin. weight and nutritional value, because this process The acceleration of fruit processing through the consumes energy metabolites such as sugars, increase of milling capacity is the least imaginative lipids, or organic acids. Furthermore, refrigeration and the most expensive solution to prevent olive oil delays the deterioration activity of the pathogens, deterioration caused by the use of damaged and/or which are mainly responsible for postharvest loss of decayed fruits, which have been stored in poor fruits. In olives, decreasing the temperature from 18 conditions. Historically, the olive oil industry has to 5 °C led to a decrease in CO2 production of suffered two traditional impediments, which somewhat more than twenty-fold (García and Streif, condition its quality production: Reduced harvesting 1991). This suggests that the lag provoked in all the

Table 1 Spanish olive oil production during five seasons. The alternation of production and its concentration in determined months was evident. Source: Spanish Ministerio de Agricultura, Pesca y Alimentación

Spanish Olive Oil Production (Tm x 1000) Months 2000/01 2001/02 2002/03 2003/04 2004/05 Total % November 40 93 55 89 70 347 6.1 December 200 388 282 430 315 1615 28.6 January 270 535 324 568 422 2119 37.5 February 320 295 144 240 145 1144 20.2 March 110 67 48 71 26 322 5.7 April 30 27 5 16 4 82 1.5 May 5833120 0.4

Total 975 1413 861 1417 983 5649 100.0

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metabolic activities that require energy produced by evaluation of its oil. Storage at 5°C allows for respiration should be equally delayed. maintaining the initial sensory quality of oils extracted Some fruits are sensitive to low temperature and from fruit stored for 30 days at laboratory scale during cold storage develop a physiological disorder (Gutiérrez et al. 1992; Garcia et al. 1996a, García et commonly named “chilling injury”. The cause of this al. 1996b). problem has been attributed to a non programmed The sensitivity to low temperature diminishes accumulation of succinic acid in the Krebs cycle. with fruit maturity. Agar et al. (1999) did not Succinic-dehydrogenase should be more affected appreciate any chilling injury incidence on black by a low temperature than the other of this ripe ‘Manzanillo’ olives stored for up to 6 weeks at 0, metabolic system and its toxic substrate would 2.2, 5, or 16 °C. However, fruit of this maturity level destroy the fruit cell (Kader, 1985). At the same time, decayed more rapidly than the green-mature one, low temperatures could affect the permeability of the and after 4 weeks of cold storage the oil obtained plasmatic membranes, altering the physical from those exceeded the limit value of acidity properties of its main constituent, the phospholipids. established for “extra” virgin category of quality. In general, a fruit is considered cool-sensitive, if it Cold storage can be supplemented by the develops chilling injuries at temperatures slightly modification of the atmosphere within the room higher than its freezing point. Unfortunately, the fruit where the fruits are kept. Habitually, this modification of the Olea europaea is one of them. Chilling injury consists of an increase in the concentration of CO2 symptoms in olives begin as an internal browning of and/or a decrease of O2. This system allows a better the flesh around the pit, subsequently, external control of both: development of fruit maturation and pitting appears dull in colour on the skin of this area, pathogen proliferation, extending the commercial life browning becomes darker and, finally, progressively of the stored product and better maintaining of its occupies all the internal flesh and the skin surface. initial level of quality. Atmospheric manipulation can The chilled olives are especially sensitive to fungi also be useful to delay the physiological changes infection and rot rapidly (Kader 1996; Nanos 2002). due to chilling sensitive crops, as these cannot be Maxie (1964), Woskow and Maxie (1965) and stored for a long time at low temperatures. Kader (1989) in different works identified the Nevertheless, the use of these atmospheres can temperature of 5° as the barrier for the cold storage induce other physiological disorders, or aggravate for different table olives. Below this temperature chilling injury, depending on the commodity (Kader, these fruits developed severe chilling injury. 1986; Nanos et al. 2002). If the new concentrations Subsequently, García (1993a) found that this of these gases in the refrigerated room are temperature was also useful for storing mature-green permanently regulated, the system of storage is '' fruits, the most highly cultivated Spanish named “controlled atmosphere” (CA), whereas the variety of olives intended for oil.. However, after a absence of this control determines the use of a prolonged storage of 2 months at 5 °C this variety “modified atmosphere” (MA) storage. exhibited a 10 % incidence of chilling injury. For the CA storage has been tested in table olives in storage of olives intended for oil, temperature is the California and in Greece, obtaining different results main determining factor for maintaining physiological according to the cultivar used. Thus, ‘Mission’ conditions of the fruit intact and, subsequently, to green-mature olives have benefited from CA extract from it oil with the same level of quality as it storage at 5 °C, because these olives maintain their had initially. During storage, the incidence of fruit initial ripening stage and a good physiological and decay increases in direct relationship with the sensory quality after 10 weeks of storage under 2 to temperature selected. After a week of storage the 5% O2 and 2.5 to 10.5% CO2 at 5°C. However, the decay of ‘Picual’ olives stored at 12 °C was four times use of CA increases the sensitivity to chilling higher than at 8°C and eight times higher than at 5°C injuries of Manzanillo’ olives, which show an (García et al., 1996a). The increase of fruit decay appreciable incidence of chilled fruit after a storage determines a proportional increase in the acidity of period of 6 weeks at 10 °C under an atmosphere the oil, due to the hydrolytic action of the lipases of enriched with a concentration of 5% CO2. The the pathogens, which use this activity as the first step incidence of this disorder increased if the presence in metabolizing the oil contained in the infected fruits. of O2 was also diminished at up 2% in the storage Refrigeration at 5 °C delays fungi proliferation and, atmosphere (Woskow and Maxie, 1965; Kader et consequently, the acidity value of the oil is al., 1989). More recently, Nanos et al. (2002) also maintained within the limit established for the "extra" obtained a different answer to storage conditions, quality of the virgin olive oil (< 0.8 %) for up to a according to the table variety tested, whereas period of 30 days. Similarly, quality parameters which ‘Conservolea’ olives can be stored at 7.5 °C under evaluate the level of oil oxidation, exhibit a level of CA conditions for up to 22 days, ‘Chondrolia’ fruits deterioration proportional to the storage temperature. resulted extraordinarily sensitive to chilling injury, Thus, the values of stability to oxidation of the oils even at this relatively high temperature. obtained from olives stored at 5°C were better than Storage of mill olives under CA conditions has the ones extracted from fruit kept at higher also been assayed. García and Streif (1991), using temperatures. In the same way, the panel test also the table variety ‘Gordal’ tested the effect of showed the close relationship between the refrigeration and CA conditions on the quality of the physiological state of olive fruit and the sensory oil subsequently extracted. Both, O2 reduction or CO2

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increasing induced chilling on fruit stored at 5 °C and delay fruit deterioration due to internal or external the incidence of this disorder increased; when both factors. The air inside the room must be renewed CA conditions were combined. In contrast, fruit often, to avoid undesirable accumulations of CO2 stored at the same temperature did not suffer any due to fruit respiration. As the external aspect of the physiological damage. Affected fruit decayed rapidly fruit is not relevant for mill olives, maintaining a high and, in consequence, the best quality oil was level of relative humidity (RH) is not necessary, but obtained from the olives refrigerated in air. the level of fruit dryness could be easily controlled Subsequently, using ‘Picual’ olives the effects of CA during fruit cold storage regulating the speed of conditions were studied on fruit physiology ventilation and the RH inside the room. It would be (Castellano et al., 1993; García, 1993a), on interesting for future studies to clarify the effect of polyphenol content (Maestro et al., 1993) and oil the level of fruit dryness induced by cold storage on quality (Gutiérrez et al., 1992; Pérez-Camino et al., oil quality. It can be a non-polluting system to 1992; García, 1993b) in the Instituto de la Grasa. As reduce the production of waste water. All the was previously observed in table olives, CA storage material necessary for palletization required by the induced physiological disorders in olives intended for industry is also necessary, including boxes, pallets oil, being especially detrimental the use of high CO2 or forklifts and the machinery associated with it: concentrations (García, 1993a). In consequence, as Case inverters, case washing machines, etc. Finally, the use of CA storage atmospheres does not provide it is necessary to take into account that cold storage any additional advantage over refrigeration in air at is not a fruit hospital. Only healthy fruit can be 5°C for the storage of mill olives, but inducing refrigerated to obtain a high quality olive oil. The physiological disorders facilitates fruit decay and, refrigeration of damaged or rotten fruit only afterwards, the obtaining of poor quality oils, which guarantees an oil of poor quality. Consequently, this are characterized by a high acidity level and the system is only compatible with the careful presence of undesirable sensory attributes. harvesting, packing and transport of this product. One of the main factors to take into account for Refrigeration of olives intended for oil at 5°C has the use of refrigeration for the storage of olives been successfully applied by the olive oil industry intended for oil is the selection of an adequate (García et al., 1996b; Canet and García, 1999). loading unit to contain the product. Of course, for the About 1000 Tm of olives (‘Blanqueta’ and industry the use of the largest possible container ‘Villalonga’ cultivars) were hand harvested in Valle supposes an important saving in costs. However, it de Albaida (Valencia, Spain), packed in perforated may imply an excessive fruit accumulation, which plastic containers with a capacity of 14 Kg of olives does not allow for effective refrigeration of the unit. and stored for 18 days at 5 °C (Figure 5). The On the other hand, the use of small boxes facilitates commercial quality of the oil obtained (about 200 that the stored fruit acquiring the desired Tm) from the fruit stored under these conditions temperature as soon as possible, but it can be was evaluated as the best possible for virgin oils expensive in practice. Garcia et al. (1994) studied (“extra”), since the values of the quality parameters, the effect of the loading unit on fruit physiology and which measure the level of quality of these oils, on the quality of the oil from it. A loading unit with a were inside the limits established for this category capacity of 400 kg of ‘Picual’ olives stored at 5 °C of quality (Table 2). The storage at 5 °C of the olive showed a real temperature of 25 °C in the inner that could not be immediately processed allowed for zone of fruit accumulation. Consequently, the fruit the use of the mill machinery to full yield for 8 weeks stored under these conditions decayed rapidly and (Figure 6). The hypothetical increase of double the oil extracted immediately exhibited a poor level milling capacity would be not sufficient to absorb of quality. In contrast, fruit placed in containers with a storage capacity of 60 Kg showed an internal temperature of 6 °C, only 1 °C higher than the refrigerated room where it was stored and the oils obtained from it exhibited a level of quality similar to its initial level for at up 30 days of fruit storage. In summary, the best possible loading unit should be one, while as big as possible, allows efficient refrigeration of the entire stored product. The perforated plastic boxes capable of holding 22 Kg of fruit, previously recommended for prolonged olive storage are perfectly useful for cold storage. When considering the use of refrigeration for the storage of olives intended for oil, the industry must meet at least the following requirements: A cool room capable of storing the product that cannot be absorbed by the mill machinery. It should be equipped with cooling machinery able to refrigerate Figure 5 the product at the temperature required (normally 5 Olives stored at 5 °C in Cooperativa Valle de Albaida °C) over a period of time ≤ 12 hours, to immediately (Valencia). Source: M. Canet.

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Table 2 Evaluations reached by the oils obtained from olives of the varieties Blanqueta and Villalonga stored industrially for 18 days to 5°C in the parameters that define the level of quality of the virgin olive oil. aMean value ± standard deviation of three determinations analysed in three different oil extractions. Source: Canet and García (1999

Quality parameter ‘Blanqueta’ ‘Villalonga’ Acidity (% oleic) 0,53 ± 0,19a 0,44 ± 0.12 Peroxide value (mEq Oxygen/Kg oil) 3,50 ± 0,65 3,87 ± 0,98

K232 1,68 ± 0,06 1,57 ± 0,09

K270 0,12 ± 0,00 0,14 ± 0,02 Stability (hours) 51,13 ± 6,96 67,67 ± 9,59 Panel text (“1" the worst - “9" the best) 6,93 ± 0,37 7.30 ± 0,22 the harvest at highest production peak (Figure 7). An amount of 200 Tm of olives could not be processed in the sixth week of the season, and would be exposed to a serious risk of deterioration. On the other hand, under this milling capacity, the oil extraction machinery would work to full yield for only two weeks. Cold storage clearly facilitates a more economic use of disposable machinery. Considering that the next season the olive fruit production could suffer a reduction of the 50 %, due to the typical olive alternation (Figure 8). In this case, the actual milling capacity should be sufficient to process this reduced fruit production. An excessive milling capacity would be unproductive approximately every two seasons. Cold storage is more versatile and less restrictive than oil extraction machinery. It can be used for the refrigeration of Figure 7 multiple products and requires a lower maintenance Estimated data of olive processing for virgin olive oil cost. Furthermore, cold storage is more susceptible production supposing the use of a milling capacity of to renting than excess of oil extraction machinery, 64,000 kg/day in the Cooperativa Comarcal Valle de Albaida because at the moment of the peak production, (Valencia, Spain) using as reference the season 1993-94. when it is actually required, all the mills of a certain Source: Canet and García (1999). area would be occupied, working to full yield.

Figure 6 Figure 8 Data of the olive processing for virgin olive oil production using a Estimated data of olive processing for virgin olive oil production milling capacity of 32,000 kg/day in the Cooperativa Comarcal supposing a 50 % reduction of the olive crop due to the olive Valle de Albaida (Valencia, Spain) during the season 1993-94. alternation in the Cooperativa Comarcal Valle de Albaida The olives were stored at 5 °C in boxes able for 14 kg fruits. (Valencia, Spain) using as reference the season 1993-94. Source: Canet and García (1999). Source: Canet and García (1999).

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4. POSTHARVEST HEAT TREATMENT: perhaps the most important reason for the harvesting A FUTURE POSSIBILITY delay of olives intended for oil is tradition. In Andalusia, since perhaps the times of Roman During olive ripening (from the green-mature to domination, olive harvesting has begun on the same the black stage of maturity) the increase of the lipid day, December the eighth (the day of the Immaculate content is scarce (Wodner et al. 1988). Coinciding Conception, according to the catholic calendar). with this observation, the changes in the oil Both the first and the fourth reasons for biosynthesis during fruit growing and maturity, harvesting delay are not in the scope of postharvest measured by the incorporation of 14C acetate to the intervention and they are not treated in this chapter, oil of ‘Picual’ and ‘Gordal’ olives, showed at 25 weeks but the other two arguments can be clear objectives after flowering (corresponding to the green-mature or susceptible to being solved by the development of an spotted stages of olive ripening) the enzymatic adequate postharvest technology in the same way machinery responsible for the oil synthesis lost its that other fruits have been successfully treated to activity in both varieties (García and Mancha, 1992). control sensory attributes, such as the elimination of This point of ripening can be considered, in a kaki astringency or the degreening orange skin. production perspective, as the suitable one by the Oil bitterness is mainly due to of the secoiridoid beginning of the fruit harvesting, because after this derivatives of phenols (Mateos et al. 2004), these maturity level the oil accumulation in the olives is compounds, partially soluble in lipids, are given to interrupted. Furthermore, olive fruit cells have the virgin oil during its extraction, through an internal enzymatic activities, such as lipases, unknown process, in which at least two kinds of lipoxigenases or hydroperoxide liases, which can enzymes, such as glycosidases and estearases, cause hydrolytic or oxidative alterations during fruit should be involved (Tsimidou et al. 1998). ripening or/and the milling and the malaxation of the Glycosidases would break the glycosidic bond of the oil extraction process (Olías. 1992). Obviously, as the oleuropein, an extraordinarily bitter water-soluble olive matures, the possibility of these enzymes acting glycoside characteristic of the Olea europaea leaves on the stored oil increases and, in consequence, the and fruits, yielding these secoiridoid derivatives of quality of the oils tends to decline. The oil of the phenols. From oleuropein and/or secoiridoid variety '', for example, presented derivatives the estearases would yield free phenols significantly higher acidity and ultraviolet absorbance which are not bitter. A physical treatment previously when it was obtained from black fruits at the end of applied to the fruit might alter the activities of these their ripening stage, than when was extracted from enzymes, probably inhibiting them partially or totally, green-mature fruits, at the beginning of this and, consequently, controlling the level of bitter taste physiological process (Garcia et al. 1996c, Yousfi et in the oil obtained. According to this work hypothesis al. 2005). Furthermore, olives soften during fruit Garcia et al. (2001) heated green-mature Manzanilla ripening, being riper fruits more susceptible to and Verdial olives at different temperatures (30 to 50 mechanical damage and fungal infection. Thus, °C) for 24 to 72 hours in a thermostaticed room, green-mature olives resist postharvest handling observing that heating promotes a reduction of oil better than the mature ones (García and Yousfi bitterness in direct relationship to the time and the 2005). Nevertheless, in Spain the harvesting is temperature used, without any significant affect on normally carried out during the months of December, the physical and chemical parameters, which are January or February, when fruit reaches a red or used to evaluate the level of quality of olive oil. As black skin colour (Table 1), due to four main reasons: expected according to the proposal of an enzymatic Firstly, the harvesting is easier, because the inhibition, the phenol content of the oil decreased resistance of the olive to fall down decreases fruit with the intensity of the treatment and, consequently, maturity. Secondly, although the oil content is only the stability against oxidation also decreased, slightly higher in black olives, the physical although maintaining high absolute values. This extractability normally increases with the level of result did not coincide with those published before maturity. This fact is probably due to the softening of by Farag et al. (1997), who obtained a stabilization the ripe fruit which would facilitate the separation of of the olive oil by microwave heating of ‘Picual’ and the oil from the olive tissue. The third reason is the ‘Chemlalli’ olives previous to oil extraction. excess of bitterness and pungency that the oils The heat treatment by temperature air extracted from green olives show. When their transmission is difficult to adapt to the production lines presence is too high, these sensory attributes can of the industry. It requires an result in consumer rejection of the product. equipped room, a relatively long treatment time, the Especially sensitive to these attributes the use of boxes and is a discontinuous process that consumers who are accustomed to the milder taste requires the loading and unloading of treated material. of refined oils such as those from important markets Dipping in water allows for a more rapid and such as Japan, Canada, U.S.A. or the Northern efficient transmission of the heat to the fruits. Using European Countries. The green-mature stage of the this method, the heat treatment could be carried out ripening marks the beginning of a continuous in only a few minutes, and its adaptation to the reduction of the level of oil bitterness up to practically industrial production lines would be easier. It would disappearing in the most advanced stages of olive only be necessary to add a heating system to the maturity (Amiot et al. 1986 and 1989). Finally, fruit washing process normally used in the oil

22 GRASAS Y ACEITES, 57 (1), ENERO-MARZO, 16-24, 2006, ISSN: 0017-3495 THE POSTHARVEST OF MILL OLIVES

extraction lines of the industry. Following this idea the Amiot MJ., Fleuriet A., Macheix, JJ. 1986. Importance same investigation team tested hot water (60 to 72 and evolution of phenolic compounds in olive during °C) dipping of ‘Manzanilla’, ‘Picual’ and ‘Verdial’ olives growth and maturation. J. Agric. Food Chem. 34, 823- to control the presence of bitter taste of the oil 826. subsequently extracted (García et al. 2005). These Amiot MJ., Fleuriet A., Macheix JJ. 1989. Accumulation of oleuropein derivatives during olive maturation. treatments reached similar results of air heating, but Phytochemistry 28, 67-69. with a considerable saving of time. However, an Canet M., García JM. 1999. Repercusión de la excess of intensity of the heat treatment can cause a frigoconservación de la aceituna de molino en el detrimental effect on olive oil. It could produce proceso de producción de aceite de oliva virgen. emulsion of the oil during the subsequent extraction Grasas y Aceites 50, 181-184. process, or inducing a sensory attribute defined as Castellano JM., García JM., Morilla A., Perdiguero S., “cooked green beans”, which is not unpleasant, but it Gutiérrez F. 1993. Quality of' Picual' olive fruits under can not be considered as common for virgin olive controlled atmosphere. J. Agric.and Food Chem. 41, oils. Unfortunately, to establish a general optimal 537-539. treatment condition has not yet been possible, Farag RS., El-Baroty G., Abd-El-Aziz N., Basuny AM. 1997. Stabilization of olive oil by microwave heating. because it changes from season to season for each Int. J. Food Sc. Nutr. 48, 365-371. variety, and, even, for each cultivation zone. Probably, Fundación del Olivar, 2005a: www.oliva.net/poolred/ as the enzymatic activity responsible for bitter taste, Comun/GrafEvolAnual.asp, 28/09/05 as well the structural properties of the fruit (humidity, Fundación del Olivar, 2005b: www.oliva.net/poolred/ ratio flesh/stone, fruit age, oil content, consistency, Comun/precios.asp, 28/09/05 etc) responsible for the efficiency of the physical oil García JM., Streif J. 1991. The effect of controlled extraction are closely related with these factors, and atmosphere storage on fruit and oil quality of 'Gordal' the optimal intensity of the heat treatment should olives. Gartenbauwissenschaft, 56, 233-238. change according to these variables. Each olive mill García JM., Mancha M. 1992. Evolución de la biosíntesis de lípidos durante la maduración de las variedades industry would have to establish its own particular de aceituna Picual y Gordal. Grasas y Aceites 43, treatment conditions according to its own variety, 277-280. seasonal, and cultivation characteristics. García JM. (1993a). Efecto del CO2 en la atmósfera de An unexpected effect of heat treatment was the almacenamiento sobre la fisiología de la aceituna de increase in oil pigmentation. The oils obtained from molino. Grasas y Aceites. 44:81-84. treated fruits showed approximately double the García JM. 1993b. Efecto del CO2 en la atmósfera de content of carotenes and chlorophylls, compared to almacenamiento del fruto sobre la calidad del aceite that obtained from control olives in all the varieties de oliva. Grasas y Aceites. 44, 169-174. tested. As a result, the oil acquired a more intense García JM. 1994. La conservación de la aceituna de and darker green colour, which increased with the molino. Unaproliva 1(4). 19-24. García JM., Gutiérrez F., Castellano JM., Perdiguero S., temperature used in the treatment. Thus, a Morilla A., Albi MA. 1994. Storage of olive destined for paradoxical case was found in the oils obtained after oil extraction. Acta Horticulturae 368 673-681. heat treatment: The greenest oils, traditionally related García JM., Gutiérrez F., Castellano,JM., Perdiguero S., by the consumers to those obtained from unripe Morilla A., Albi MA. 1996a. Influence of storage fruits and, therefore, with high bitterness, actually temperature on fruit ripening and olive oil quality. J. presented the lowest intensity in this attribute. Agric. Food Chem. 44, 264-267. This is probably due to the heat-induced García JM., Gutiérrez F., Barrera M.J., Albi MA. 1996b. inactivation of the enzymes responsible for the Storage of mill olives on an industrial scale. J. Agric. pigment degradation during the oil extraction process. and Food Chem. 44, 590-593. Luaces et al. (2005) published a more detailed García JM., Seller S., Pérez-Camino MC.1996c. Influence of fruit ripening on olive oil quality. J. Agric. description of this phenomenon. The production of Food Chem. 44, 3516-3520. highly pigmented oils should be interesting for the García JM., Yousfi K., Mateos R., Olmo M., Cert A. 2001. industry. Carotenes have vitamin characteristics and Reduction of oil bitterness by heating of olive (Olea are antioxidants, whereas chlorophylls are oxidants in europaea) fruits. J. Agric. Food Chem. 49, 4231- 4235. the presence of light, and antioxidants in darkness García JM., Yousfi K. 2005. Non-destructive and objective (Kiritsakis et al. 1985). Maintaining these oils in methods for the evaluation of the maturation level of darkness should improve their stability. Furthermore, olive fruit. Eur. Food Res. Technol. 221, 538-541 (2005) to have this kind of oil available, greener and softer García JM., Yousfi K, Oliva J, García-Diaz MT, Pérez- should mean many different mixing possibilities Camino MC. 2005. Hot Water Dipping of Olives for Virgin Oil Debittering. J. Agric. 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Gutiérrez F., Perdiguero S., García JM., Castellano JM. Olías JM., Lozano MD., Rios, JJ., Gutierrez F.,Gutierrez 1992. Quality of oils from olives stored under controlled R. 1988. Determinación de ácidos grasos volátiles atmosphere. J. Am. Oil Chem. Soc. 69, 1215-1218. en aceites de oliva vírgenes. Grasas y Aceites, 39, Kader AA. 1985. An overview of the physiological and 77-81. biochemical basis of CA effects on fresh horticultural Olías JM. 1992. Definition of extra virgin olive oils. crops. In: Controlled atmospheres for storage and International congress on olive oil quality. Florence. Italy. transport of perishable agricultural commodities. Olías JM., García J.M. 1997. Olive. In Postharvest Fourth Nat. Contr. Atm. Res. Conf. North Carolina physiology and storage of tropical and subtropical State University. Pp: 1-9. fruits. Mitra S. Ed. CAD International. Wallingfort. UK. Kader AA. 1986. Biochemical and physiological basis for Pp: 225-239. the effects of controlled and modified atmospheres on Pérez-Camino MC., García JM., Castellano,JM. 1992. fruits and vegetables. Food Technol. 40, 99–104. Polar compound concentration in virgin oils from Kader AA., Nanos GD., Kerbel EL. 1989. Responses of stored cultivar Picual olive fruits. J. Agric. Food Chem. 'Manzanillo' olives to controlled atmospheres storage. 40, 2260-2262. Proceeding 5th International Controlled Atmosphere de Toro MD., Sanchez MT., Montes F. 2002. Olives. Post- Research Conference. Wenatchee, WA. Vol. 2. pp harvest quality. Alimentacion Equipos y Tecnologia 21 119-125. (174): 75-77 Kader AA., 1996. Olive disorders. Univ. California Tous J., Villamil J., Hermoso JF., Alber A.2005. El olivo en Perishables Handling Newsletter 86, 8–9. Uruguay. Olivae 103, 56-61. Kiritsakis AK., Dugan LR. Studies in Photooxidación of Touzani A. 2004. La calidad: importante objetivo del Olive Oil. . J. Am. Oil Chem. Soc. 1985, 62, 892-896. Consejo Oleícola Internacional. Olivae 100, 34-38. Luaces P., Pérez AG., García JM., Sanz C. 2005. Effects of Tsimidou M. 1998. Polyphenols and quality of virgin olive Heat-Treatment of Olive Fruit on Pigment Composition oil in retrospect. Ital. J. Food Sci. 10, 99-115. of Virgin Olive Oil. Food Chemistry 90, 169-174. Wahrburg U., Kratz M., Cullen P. 2002. Mediterranean Maestro R., García JM., Castellano JM. 1993. Changes in diet, olive oil and health. Eur. J. Lipid Sci. Technol. Polyphenol content of olives stored in modified 104, 698-705. atmospheres. HortScience 28, 749. Woskow M., Maxie EC. 1965. Cold storage studies with Mateos R, Cert A, Pérez-Camino MC, García JM. 2004. olives. In: 44th Annual Technical Report of the Evaluation of Virgin Olive Oil Bitterness by California Olive Association. Davis (Cal.) USA. pp. 6-8. Quantification of Secoiridoid Derivatives.J. Am. Oil Wodner M., Lavee S., Epstein E. 1988. Identification and Chem. Soc. 81, 71- 75 seasonal changes of glucose, fructose and mannitol Maxie EC., 1964. Experiments on cold storage and in relation to oil accumulation during fruit development controlled atmosphere. In: the 43th. Annual Technical in Olea europaea L. Scientia Horticulturae, 36, 47-54. Report of the California Olive Association. Davis Yousfi K., Cert RM., Garcia JM. 2005. Changes in quality (Cal.), USA. pp. 12-14. and phenolic compounds of virgin olive oils during Mazuelos-Vela F. 1972. La lipasa de hongo Gloesporium objectively described fruit maturation. European Food olivarum Alm. Grasas y Aceites 23, 432-435. Research and Technology. In press. Nanos GD., Kiritsakis AK., Sfakiotakis EM. 2002. Preprocessing storage conditions for green ‘Conservolea’ and ‘Chondrolia’ table olives Recibido: Septiembre 2005 Postharvest Biology and Technology 25, 109–115. Aceptado: Noviembre 2005

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