Malaxation: Influence on virgin olive oil quality. Past, present and future – An overview

Trends in Food Science & Technology 25 (2012) 13e23

Review

Malaxation: Influence on virgin olive oil quality. Past, present and future e An overview Maria Lisa Clodoveo* Department of Agro-Environmental and Territorial Sciences, Agriculture Faculty, University of Bari, Via Amendola 165/a, 70126 Bari, Italy (Tel.: D39 80 544 2514; fax: D39 80 544 2504; e-mail: [email protected]) The malaxation, a basic step of the mechanical olive oil extraction process, was studied by several authors, but a comprehensive investigation of its effects on the oil composition has not been accomplished yet. An effective olive paste malaxing is crucial in producing virgin olive oil (VOO) of exceptional quality. It is important to extract the optimum amount of oil, with the right quantities of antioxidants and the best possible flavour. The aim of this work is to present the state-of-the-art about malaxing technology and its influence on analytical parameters related to VOO quality, healthy and organoleptic characteristics of the product. Machinery evolution has been reported from the most traditional to the newest designs. Recent advances and future trends applied to the olive oil extraction technology are also reported.

VOO is exclusively extracted from fruits by means of mechanical techniques that include crushing, malaxation and extraction steps. Each of these technological operations, in addition to the olive fruit characteristics, affects the quality of the product. Olive paste preparation can be separated into two phases, fruit milling and paste malaxing. The fruit milling has the main objective of breaking the

* Corresponding author. 0924-2244/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.tifs.2011.11.004

plant tissues in order to liberate the oil drops contained in the mesocarp cells. Then malaxation prepares the paste for separation of the oil. Traditionally, the malaxing step consisting of a low (20e30 rpm) and continuous kneading of olive paste at a carefully monitored temperature. This phase is especially useful for achieving high and satisfactory yields of extraction. In fact this essential technological operation helps the small droplets of the oil formed during the milling to merge into large drops that can be easily separated through mechanical systems, and breaks up the oil/ water emulsions formed during the crushing operation. The increase in oil drop size favours the increase in “free oil”. In addition, this operation disrupts a proportion of the oily cells remaining uncrushed during the first step (crushing) allowing the recovery of another oil fraction. However, malaxation of olive paste must be considered much more than a simple physical separation, because a complex bioprocess takes place that is very relevant to the quality and composition of the final product. During malaxation considerable changes in the oil’s chemical composition occur because of the partition phenomena between oil and water and vice versa and the catalytic activity of fruit enzymes, which are released during the crushing step, owing to disruption of the cell tissues. This technological operation determines the balance between the quality and the quantity of the oil extracted by varying a range of parameters (time, temperature, atmosphere in contact with the olive paste, addition of lukewarm water and coadjuvants) (Amirante, Clodoveo, Leone, & Tamborrino, 2009a, 2009b). For example, it is known that malaxing conditions may modify the phenol (Ranalli, Contento, Schiavone, & Simone, 2001) and volatile (Angerosa, Mostallino, Basti, & Vito, 2001; Ranalli et al., 2001; Servili et al., 2003a) contents in VOO and, as a consequence, its properties. Employment of wrong mixing conditions compromises the healthy and organoleptic properties of the product. Malaxing machines: from the most traditional to the newest designs Traditionally, malaxation is performed in semi-cylindrical tanks equipped by a shaft with rotating arms and stainless steel blades of different shapes and sizes. Depending on the rotation axis location the malaxing machines can be classified in horizontal and vertical mixers, although, based on technical and economic reasons, horizontal mixers are

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more often used (Cini et al., 2006; Migliorini et al., 2008). The walls of the malaxing tanks are hollow allowing warm water to flow through these jackets to heat the olive oil paste. The olive paste is continuously agitated at a controlled temperature. Once the malaxing process has been completed, the paste is removed from the bottom of the tank by means of a pump that feeds the paste to a decanter centrifuge for subsequent treatment (Amirante & Catalano, 1995). For many years the malaxing machine was mainly characterized by a cradle shape and a non-hermetic closure consisting in a stainless steel grill. Amirante, Clodoveo, Dugo, Leone, Salvo, and Tamborrino. (2006), Amirante, Clodoveo, Dugo, Leone, and Tamborrino (2006) found that this type of machine caused considerable loss of phenolic and volatile compounds. In fact, due to the holes of the upper grill, the volatile compounds were dispersed into the air above the tank and, at the same time, phenolic compounds were oxidized by contact with the air. Recently, an innovative mixer has been made (Amirante, Clodoveo, Leone, & Tamborrino, 2009a, 2009b). This new machine has been developed to improve the heat transfer surface in order to reduce the malaxing time (Mt). This aspect is relevant because the malaxing step is the only discontinuous phase in a continuous extraction process. In fact, in this new malaxer, the heating surface per volume unit is 35% larger than the standard machines. The traditional cradle shape of malaxing machines causes an interspace for the heating water flow that covers 3/4 of the paste only. The new model is specifically designed with a cylindrical jacket that covers the whole internal surface of the tank, which means that paste can be conveyed and maintained at the desired temperature quicker and more efficiently through a thermo regulator that controls the water temperature and flow rate in the jacket walls. A new set of blades provides a bidirectional thrust to paste, which causes it to rotate and continuously bring new sections of paste into contact with the heating walls. A hermetic sealing ensures a perfect control of the atmosphere in contact with the paste in the malaxing machine through valves for inert gas treating (nitrogen or argon); this accessory further reduces the negative effects caused by a prolonged contact of paste with oxygen and it allows to extend Mt without damaging the produced oil. In order to clarify the effect of all malaxing condition on VOO, a prototype of new malaxing machine was projected and built by Amirante et al. (2009b) (Fig.1). This malaxing machine is equipped with a set of sensors useful to measure the water temperature in the heating jacket, the temperature of olive paste, the viscosity of the olive paste, the oxygen concentration in the headspace of the tank and inside the olive paste, and also the increase of CO2 in the headspace of the mixer. The efficiency of malaxation depends upon the rheological characteristics of olive paste and upon the technological parameters of operation, such as time, temperature and

atmosphere of malaxation, and eventually the employment of technological coadjuvants. Malaxing time: effects on VOO yield and quality VOO extraction yield Oil content varies by variety from less than 10% to about 30%. Generally, oil yield refers to the amount of oil that can be derived from 100 kg of processed olives. It is usually represented as a % (e.g., 16e18% by weight of olives). This indicator is usually named “extraction performance” (Bordons & N
u~nez-Reyesa, 2008) and obviously it must be as high as possible. Instead, “extractability” has been defined (Hermoso Fernandez et al., 1998) as the percentage of olive oil extracted from the total oil content of the fruit (on a fresh matter basis). The “extractability index” (EI) was calculated using the formula: EI ¼

Woil  100 Wolives $F

Where, Woil (kg) is the mass of extracted oil, Wolives (kg) the olive paste mass and F (%) is the fruit oil content (fresh weight) (determined by Soxhlet Method). This parameter indirectly takes in account the oil content lost in the by-products (vegetation water and pomace). How easy or difficult the olive oil extraction is, has been linked to olive variety and seasonal conditions such as the level of irrigation, time of harvesting, type and amount of fertilizer used, the amount of olives per tree or a high incidence of fruits affected by pests (for example, due to Bractocera oleae) or physiological diseases (for example, due to chilling injuries) (Cruz, Yousfi, P
erez, Mariscal, & Garc
ıa, 2007). Olive paste malaxation is an important step of olive processing since produces good oil extraction yields. In fact, increasing the malaxing time (Mt), in general, improves the oil extraction yield. Considering this economical parameter, the operators tend to increase Mt. The average Mt employed ranges from 45 to 60 min depending on olive characteristics. Many authors studied the effect of Mt on oil extraction yield (Aguilera, Beltr
an, Sanchez-Villasclaras, Uceda, & Jimenez, 2010; Hermoso Fernandez et al., 1998; Kalua et al., 2007). Generally, the oil extraction yield rises with increasing time of olive paste malaxation; however, the increase in Mt results in the decrease of some nutritional characteristics of VOO if the atmosphere in the headspace of the malaxer contains oxygen. Amirante, Cini, Montel, Pasqualone (2001) studied the influence of Mt (30, 45 and 60 min) at three different temperatures (27, 32 and 35  C) on VOO extraction yields. The curves of extraction yield as a function of Mt, for all the three malaxing temperatures, had a bell shape distribution (Fig.2). These results indicate, effectively, that initially the increase of Mt improves the extraction yield due to the action of endogenous enzymes able to degrade the wall oil-bearing cells that elude crushing. After achieving the maximum

M.L. Clodoveo / Trends in Food Science & Technology 25 (2012) 13e23

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Fig. 1. Scheme of the olive oil processing line equipped with the prototype of the innovative malaxing machine. The malaxer is equipped with a set of sensors useful to measure the oxygen concentration in the headspace of the tank (A) and inside the olive paste (B), the temperature of olive paste (C), the viscosity of the olive paste (D), the increase of CO2 in the headspace of the malaxer (E) and also the water temperature in the heating jacket (F). All the sensors are connected to a personal computer (PC) to acquire the data.

value, the curve of extraction yield decreased with the Mt increasing because of the emulsion formation due to the mixing action. These findings were in accordance with Ranalli, Pollastri, Contento, and Iannucci Elucera (2003) that reported a decrease in oil yields with time from 60 to 75 min. Commercial qualitative parameters The commercial qualitative parameters of VOO, like free fatty acids, peroxide value and specific spectrophotometric absorptions in the UV region did not change when the Mt of olive paste was increased (Ranalli et al., 2003). Polyphenol The importance of VOO is mainly attributed to its richness in phenolic compounds (PC), which act as natural

antioxidants and may contribute to the prevention of several human diseases (Bendini et al., 2007). PC are also responsible for the shelf-life of the oils (Angerosa et al., 2001) and for their typical bitter taste. The phenolic fraction of VOO consists of a heterogeneous mixture of compounds. The phenolic compounds, once released or formed during processing of olives, are distributed between the water (approximately 53% of the available pool of antioxidants in the olive fruit) and oil phases (12%). Another part of the phenolics (approximately 45%) is trapped in the solid phase (pomace) (Rodis, Karathanos, & Mantzavinou, 2002). The distribution of the released amount of the PC between water and oil is dependent on their solubility in these two phases. Consequently, only a fraction of the phenolics enters the oil phase. In general, the concentration of the PC in the

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Fig. 2. Influence of malaxing time (30, 45 and 60 min) at three different temperatures (27, 32 and 35  C) on VOO extraction yields (kg of oil/kg of olives *100). (Amirante et al., 2001).

olive oil ranges from 50 to 1000 mg/g of oil depending on the olive variety. PC are contained in the endocellular oil; malaxation is the step of the oil extraction that particularly modifies their qualitative and quantitative composition (Servili et al., 2004). In 2009, G
omez-Rico, InarejosGarc
ıa, Salvador, & Fregapane, 2009 found that Mt influences more the phenol composition of olive paste than its corresponding VOO. The PC in VOO extracted employing an industrial plant is much more affected by the malaxation temperature (MT) than the Mt. Similar results were found by Angerosa et al. (2001). Also Kalua, Bedgood, Bishop, and Prenzler (2006; Kalua et al., 2007) report no significant differences of PC concentration in VOO with Mt. Oxidative stability An important requirement, which is not reported in the regulations, is the stability to auto-oxidation of VOO, which is usually evaluated using the Rancimat method. This method provides the induction time for decomposition of hydroperoxides, produced by fat oxidation. Lercker, Frega, Bocci, and Mozzon (1999) studied the interaction between olive-paste Mt and oxidative stability of VOO. Based on their empirical experience and in order to increase oil extraction yields, the operators often tend to increase Mt which reduces the shelf-life of oils. In fact, Rancimat stability test of the oils extracted from the olive paste at increasing Mt gives evidences of a progressive reduced induction time. Volatile compounds Volatile composition of VOO is tightly related to sensory attributes and the sensory quality plays an important role in directing the preference of consumers. Changes in the content of volatile compounds (VC) can notably modify the olfactory perceptions. VC in VOO do not originate from the fruit, per se; they are formed during processing (Sanchez & Salas, 2000). Most of these aromatic VC are

formed through the action of enzymes that are released when the fruit is crushed, and continue to form during malaxation. VC production during oil processing, involves several different pathways, particularly the lipoxygenase pathway (Kalua et al., 2007). The lipoxygenases, after their release owing to cellular disruption of fruits, immediately become active and transform the unsaturated fatty acids, linolenic and linoleic acids, into C6 and C5 compounds that contribute to green odour notes (Angerosa et al., 2001). Angerosa et al. (2001) observed an accumulation of C6 and C5 VC with the prolonging of Mt, regardless of the temperature adopted. By evaluating the effect of Mt on volatile composition, it could be observed that the production of hexanal, one of the most important contributors to the olive oil flavour, seemed mainly promoted by the prolonging of Mt.

Malaxing temperature: effects on VOO yield and quality VOO quality depends both on Mt and malaxing temperature (MT). The MT has a great influence on the process yield since the oil droplets are grouped due to a reduction in the oil viscosity (Ranalli et al., 2001). However for excessive heating undesirable effects can be observed: loss of PC, loss of VC responsible for oil flavour and fragrance and accelerates its oxidative process.

Oil extraction yield An increase in MT raises extraction yields (Aguilera et al. 2010; Inarejos-Garc
ıa, G
omez-Rico, Salvador, & Fregapane, 2009), especially when the olive paste is not manageable. However, Ranalli et al. (2001) suggested that the MT should not be higher than 30  C. In fact, at this olive paste temperature level, good oil extraction yields were obtained without substantial compositional modification of the analytical oil fractions. But at 35  C there was a sensible decrease in the overall compositional oil quality, without achievement of substantial oil yield increases. Moreover, malaxing at 45  C had significantly lower yields compared to other temperatures (15, 30  C), which might be due to change in the rheology of the paste and increased interactions between lipids, proteins, and carbohydrates, culminating in the entrapment of oil in the olive paste (Kalua et al., 2007).

Commercial qualitative parameters When the MT increased from 30 to 35  C there is an increase in activity of the lipase enzymes (responsible for free acidity increase) and to an intensification of the primary oxidation processes (responsible for the increase of the k232 and peroxide index values) and the secondary oxidation processes (responsible for the increase of the k270 and carbonyl index values) (Ranalli et al., 2001).

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Fig. 3. The trend of the total HP (colorimetric method) with respect to malaxation temperature (Parenti et al., 2008).

Polyphenols PC in VOO are strongly influenced by MT. The influence of MT (Angerosa et al., 2001; Kalua et al., 2006; Lercker et al., 1999; Parenti & Spugnoli, 2002; Parenti, Spugnoli, Masella, & Calamai, 2008; Ranalli et al., 2001; Servili et al., 2003b) on VOO overall quality was widely investigated, but contrasting results have been reported on the effects of MT on the PC concentration. Several authors found more PC in VOO when the temperature was increased (Boselli, Di Lecce, Strabbioli, Pieralisi, & Frega, 2009; Parenti, Spugnoli, & Cardini, 2000), whereas others found an inverse relationship between MT and PC concentration (Angerosa et al., 2001; Servili et al., 2003b). Kalua et al. (2007) observed low concentrations of the PC at low temperatures. Probably the formation of certain PC may involve bond cleavages to release PC that are bound to other molecules in the olive fruit. Ranalli et al. (2001) observed that the concentration in PC of the oils increased with increasing levels of olive paste MT. Evidently, there was an increasing release of PC (from the vegetable tissue), which

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consequently dissolved in increasing amounts in the oil phase. The increase in PC was more significant when the MT increased from 25 to 30  C. However, the oil PC did not increase when the MT increased from 30 to 35  C. These observations are congruent with Parenti et al. (2008) that recorded the trend of total PC (by means of colorimetric method) with respect to MT (Fig. 3). A bell-shaped curve was found with a maximum at 27  C. For higher temperatures, a progressive decrement was observed, so that the total amount of PC seems to be negatively affected by the MT in the range of 30e36  C. A similar trend was observed for the secoiridoid compounds (Fig. 4) As reported in Fig. 4, approximately the same trend was recorded for all the considered compounds, i.e. a quasi-linear increment of concentrations with increasing temperature until 30  C, followed by a marked decrease in correspondence with the highest temperatures (33 and 36  C). It is likely that at the higher temperature the degradation rate of these compounds increased and therefore their concentration in the final oil was lower. Indeed, increasing temperature levels, during the olive paste malaxing process, favour the activity of oxidoreductase enzymes present in olive fruit, such as PPO and POD which is rather high at 35  C. Also LOX, that catalyses the formation of hydroperoxides, could also be responsible for an indirect oxidation of secoiridoids. Another active enzyme is b-glucosidase which could have a role in the production of phenol-aglycones (secoiridoids) through hydrolysis of the oleuropein and demethyloleuropein glycosides. No significant differences in lignans concentration were found between the different levels of MT. According to Artajo, Romero, Suarez, and Motilva (2006), this result could be explained considering the lipidic character of these compounds and their lower antioxidant activity as compared to other hydrophilic phenols (Servili et al., 2004, 2009). Volatile compounds The most negative effects of high MT were related to the minor genesis of VC. As reported by Salas and Sanchez

Fig. 4. The trend of the secoiridoid compounds with respect to malaxation temperature (Parenti et al., 2008) (Abbreviations: 3,4-DHPEA-EDA, dialdehydic form of elenoic acid linked to hydroxytyrosol; p-HPEA-EDA, dialdehydic form of elenoic acid linked to tyrosol; 3,4-DHPEA-EA, isomer of oleuropein aglycon; L-agl, ligstroside aglycon).

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(1999), temperatures higher than 25  C reduce the activity of two basic enzymes involved in the LOX pathway, such as LOX and hydroperoxide lyase. The partial inhibition of these enzymes reduces the formation of C6 saturated and unsaturated aldehydes, alcohols, and esters responsible for cut grass and floral sensory notes of VOO (Angerosa et al., 2001). Atmosphere composition inside the malaxer: effects on VOO yield and quality The feasibility of altering oxygen concentration (OxC) during processing could be a strategy to optimize the phenolic concentration in VOO. This is a fundamental aspect from a technological standpoint. In fact, due to the strong variability in phenol concentrations in the olive fruits, related to agronomic factors such as cultivar, fruit ripening, and agronomic practices, the malaxing conditions may be manipulated to obtain the optimal values of phenols in VOO without significant modifications to the aroma profile. The OxC can be regulated during malaxation by treatment with inert gases or by the use of the CO2 naturally produced by the olive pastes. Yield The use on inert gas in the headspace of the malaxers allows to extend Mt without damaging the resulting oil. The increasing of Mt can be a possible solution to obtain an increment of the oil extraction yield in the case of “difficult” pastes. Chemical composition Inert gases like nitrogen and argon have been used with sealed malaxers to increase the antioxidant activity and extend shelf life of VOO (Vierhuis et al., 2001). Sterol and fatty acid compositions of the oils were not affected by nitrogen application. However, malaxation in nitrogen atmosphere raised tocopherol but lowered carotenoid and chlorophyll contents of oils (Yorulmaz, Tekin, & Turan, 2011). Polyphenols Oxygen was found to act during malaxation on PC mainly favouring enzymatic phenomena (Migliorini, Mugelli, Cherubini, Viti, & Zanoni, 2006). The relationships between endogenous oxidoreductases, such as PPO and POD and the concentration of hydrophilic phenols in VOO are well-known (Servili et al., 2003a, 2003b; Vierhuis et al., 2001). The phenol concentration in the oils was strongly modified by O2 availability. The oleuropein, demethyloleuropein, and ligstroside derivatives were highly affected by the OxC during malaxation, whereas lignans were less modified; in fact, they seem to be independent of the O2 level in the malaxer (Migliorini et al., 2006). These results are in agreement with Masella, Parenti, Spugnoli, and Calamai (2011); their results confirmed that the reduced OxC, interfering with the activity of

some oxidative enzymes, led to oils characterized by less oxidation and a greater antioxidant concentration. Malaxation under N2 flush seemed to inhibit PPO and POD activities, resulting in an increase in the phenolic concentration (Vierhuis et al., 2001; Servili et al., 2003b). These findings are in agreement with Sanchez-Ortiz, Romero, Perez, and Sanz (2008). They report that a reduction of OxC during the industrial process to obtain VOO could produce, besides its beneficial effect on the nutritional quality, through a decrease of phenolic oxidation, an improvement of the organoleptic properties of the oil. As a result of a combined effect of decrease in the oxygen content and extension of Mt under N2 flush, Migliorini et al. in 2006 found a higher extraction of PC, probably because of a higher b-glucosidase activity. In Parenti, Spugnoli, Masella, Calamai, & Pantani, 2006 studied the emission of carbon dioxide (CO2) from olive paste during malaxation. They observed a rapid increase in the concentration of CO2 and a simultaneous O2 depletion during malaxation. The technological application of this naturally evolving CO2 should result in a considerable increase in the quality of resulting oil. Furthermore, as CO2 is the heaviest component of air (Mw: 44), it is feasible that it will stratify over the paste surface during malaxation, resulting in better protection against oxidation (Masella et al., 2011). The CO2 saturated atmosphere allows a reduction in oxidative phenomena without using inert gases. This considerably reduces the cost of the extraction process. These observations are in agreement with Amirante et al. (2009a). Volatile compounds The use of N2 during malaxation not only reduces the oxidative degradation of PC but, at the same time, modifies the VC of oil. The evolution of VC in the olive pastes during malaxation was studied to show the effect of OxC on aroma formation due to the LOX activity (Servili et al., 2008). However, the formation of VC suggests that, for the LOX pathway activation and its development during all the Mt, the amount of the oxygen incorporated by the olive pastes during crushing is probably adequate (Masella et al., 2011). Malaxing coadjuvants: effects on VOO yield and quality In the olive oil extraction process, 10e20% of oil remains inside the unsheltered cells or is left in the colloidal system of the olive paste (microgels) and some is bound in an emulsion with the vegetable water (Esp
ınola, Moya, Fern
andez, & Castro, 2009). The difficulty of freeing this ‘‘bound” oil lies mainly in the fact that the droplets of dispersed or emulsified oil are surrounded by a lipoprotein membrane (phospholipids and proteins) that keeps them in that state. When this phenomenon is more pronounced the pastes obtained are called ‘‘difficult pastes” and usually need the use of a coadjuvant, which could be added at the

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malaxation step, to break down emulsions, allowing most of the oil to be extracted. The most frequently employed coadjuvants are: lukewarm water, talc, salt and, in certain country, enzyme preparations. Water addition Lukewarm water can be added to facilitate the oil extraction (usually 50e70 L of water added to 100 kg of olive paste). The addition of water to the paste during malaxation to improve oil extractability was suggested several decades ago by Martinez, Munoz, Alba, and Lanzon (1975). Water addition had a significant effect on the quality indices of VOO (Ben-David et al., 2010). Phenols of a hydrophilic nature decrease as a function of the amount of water added. Therefore, the use of lukewarm water facilitates the oil extraction but also results in lower polyphenol level, hence a shorter shelf life (Velasco & Dobarganes, 2002). Water addition, in fact, modifies the concentrations of the soluble substances in oily and aqueous phases. In fact, during malaxation, the phenolic substances dissolve in oily and aqueous immiscible phases in contact, according to the corresponding value of the constant (K) of partition equilibrium, which is expressed by the following equation:

K¼

½Aacqueous phase ½Aoily phase

where K is the constant of partition equilibrium and [A] is the concentration of compound A, expressed as mol/l (or mg/l). The value of K, in conditions of chemicalephysical equilibrium, depends only on the temperature and, therefore, is constant at constant temperature. Of course, the law of the partition equilibrium is strictly valid for the individual compound only, and it is not valid for the total phenol content of oil and vegetable water. Many phenolic substances, in fact, are present in olive fruit, olive oil and vegetable wastewater and each of them has a specific value of the constant of partition equilibrium (K) between the concentrations in the aqueous and oily phases in contact. However, recently, in order to minimizing the loss of PC, the centrifugal three phase decanters were improved to be able to separate oil employing only a small quantity of lukewarm water (0e20 L/100 kg of olives) to dilute the olive paste. These decanters are called “water saving decanter” and they can produce oil richer in polyphenol than the traditional models. Hydrated magnesium silicate and calcium carbonate Talc (hydrated magnesium silicate) is authorized as a food additive and coadjuvant (E553b) (CE Directive 30/2001). The use of talc as coadjuvant has been proved to increase oil extraction yield (up to 24%) with no interference on oil quality (Esp
ınola et al., 2009; Fern
andez, Esp
ınola, & Moya, 2008). The addition of micronized

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talc to difficult pastes improves the paste structure, reducing emulsions (Uceda, Jim
enez, & Beltr
an, 2006). However, talc overdose can reduce the process yield. The amount of talc used ranges from 0.3% to 1% of the weight of the olives being milled. Also calcium carbonate (E170) is authorized by European Union regulations (CE Directive 30/2001); it does not react with oils because of its crystalline structure and water affinity and it is easily removed by centrifugation together with olive pomace due to its high density (2.72 g/cm3) and water affinity (Esp
ınola et al., 2009). The particle size of the coadjuvant could affect the oil yield: the extraction yield decreased as the particle size increased. For the same particle size, calcium carbonate was found to extract a greater oil amount than talc (Moya et al., 2010). Considering oil quality, no influence by either coadjuvant was detected as oil components remained unaltered during the extraction process. The sensorial evaluation gave the same result for all olive oils, no matter if a coadjuvant was used or not, indicating that these compounds only act physically on the oil extraction process. Salt Salt addition seems to be a feasible alternative for the improvement of oil extraction (P
erez et al., 2008). Cruz et al. (2007) has reported the feasibility of using common salt (sodium chloride) as a coadjuvant for the physical extraction of olive oil with similar oil yields as micronized talc and with non-significant changes in the main physico-chemical parameters of the oil. The presence of NaCl in the olive pastes increases the density and the ionic strength of the aqueous phase that could affect the solubility of certain compounds and may even modulate the activity of those enzymes actives during the malaxation process. Physico-chemical quality parameters of the VOOs were not significantly affected by the use of this coadjuvant (Cruz et al., 2007). Addition of NaCl during the extraction process was positively correlated with the presence of o-diphenol compounds and the stability of the oils obtained. Moreover the use of NaCl resulted in a significant increase in contents of pigments (b-carotene, lutein and chlorophylls a and b) and VC in the oils. The intensity of bitterness was slightly increased. Natural enzymatic complexes The excellent review written by Chiacchierini, Mele, Restuccia, and Vinci (2007) is strongly recommended to readers interested in influence that enzyme addition during olive oil extraction. Due to its recent appearance, comments in this section are limited to specific aspects which are useful to clarify the main effects of the natural enzymatic complexes on the VOO quality. Enzyme preparations were shown to increase oil extraction yields in the range 10.2e13.5 kg oil per tonne of olives, regardless of the olive variety processed; other reports showed that the enzyme treatments resulted in higher overall oil yields,

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the increase ranging from 0.9% to 2.4% wet basis, compared to untreated pastes (Najafian et al., 2009). Spain was the first country to regulate coadjuvant use (Ministerio de Sanidad y Consumo, 1986). The Spanish coadjuvant list include also the enzyme carbohydrase from Aspergillus aculeatus (Ministerio de Sanidad y Consumo, 1989). Very little is known about the specific role of the various constituent enzymes present in the enzyme preparations (Chiacchierini et al., 2007). It seems that the enzyme formulation degrades the walls of the oil-bearing cells that elude crushing and also has similar effects on the colloidal system in olive paste (pectins, hemicelluloses, proteins, etc.) that retain the droplets of oil. In this way, the oil droplets are released by phase inversion and gradually merge into larger droplets until they form a mass of free oil, which is extracted mechanically. The enzyme breaks up, not only the liquid/solid emulsions, but also the liquid/liquid emulsions mainly caused by crushing the fruits (Mınguez-Mosquera et al., 2002). It also has a positive effect on the rheological characteristics of the paste, as a result of which the phases (liquids and solids) are separated more thoroughly. Systematic studies carried out in the 1980s, revealed that no single enzyme was adequate for the efficient maceration and extraction of oil from olives. Three types of enzymes, pectinases, cellulases and hemicellulases were found to be essential for this purpose. It’s now accepted that enzymatic treatment of olive paste could have important implications for olive oil storage, as well as sensory and nutritional benefits. The main advantages of using macerating enzymes during olive oil extraction are (1) increased extraction (up to 2 kg oil per 100 kg olives) under cold processing conditions; (2) better centrifugal fractionation of the oily must; (3) oil with high levels of antioxidants and vitamin E; (4) slow induction of rancidity; (5) overall improvement the wastewater. The qualitative and quantitative results achieved by exploiting biotechnologies during olive oil extraction seem to be economically advantageous (despite its cost) as well as environmentally friendly.

Conclusions and future trends Malaxation in recent years has been recognized as one of the most critical points in the mechanical extraction process for VOO and the design of malaxing machine has undergone great changes due to the numerous scientific studies published in the last twenty years. Many of these studies have been carried out to investigate this crucial phase and its influence on VOO quality. Malaxing conditions, such as time, temperature and the composition of the atmosphere in contact with the olive paste, can influence the activity of the enzymes that are responsible for the healthy and organoleptic properties of the product. The results reported in more than 80 articles can be resumed in the following summary point:

a) Mixing conditions such as time, temperature and the composition of the atmosphere in contact with the olive paste can influence the activity of the enzymes that are responsible for the healthy and organoleptic properties of the product. b) In order to obtain the best quality from the olive fruits, the malaxing machine should be hermetically closed during the extraction process to strategically control the oxygen concentration also employing inert gases. c) The use of inert gas during malaxation reduces the oxidative degradation of phenolic compounds and allows to extend Mt without damaging the produced oil. Moreover, the increasing Mt permits an increment in the oil extraction yield, mainly in the case of “difficult” pastes. d) A low MT (<30  C) and a Mt between 30 and 45 min are recommended to obtain good olive oil quality without compromising the yields. e) The use of the CO2 naturally produced by the olive pastes during malaxation could be used as a method to obtain a natural inertization of the headspace in the malaxer, allowing a large reduction in the costs derived by the use of inert gases. f) The addition of lukewarm water to the paste during malaxation can improve oil extractability but at the same time phenols of a hydrophilic nature decrease as a function of the amount of water added. g) The use of talc as coadjuvant has been proved to increase oil extraction yield (up to 24%) with no interference on oil quality. h) Enzymatic preparations increase olive oil yield and could have important implications for olive oil storage, as well as sensory and nutritional benefits. The quality of VOO could be even more improved by regulating the malaxing parameters and monitoring the chemical/biochemical changes of olive paste precisely: in many olive oil mills the process is controlled manually or with single control loops that maintain some flows and temperatures at constant values, since there are many factors that affect production. Usually operators must use their experience to have the process under control. The automatic control of the extraction of oil out of olives is still an open field. In the next future malaxing machine could be equipped by a series of sensors able to monitor in real time the extraction parameters and to operate the right correction of the process to achieve the best quality of VOO. Therefore, process automation is needed to obtain a high quality product, optimal process yields at low costs. The use of sensors and detectors to continuously measure important chemical properties could have significant technical benefits. Near-infrared (NIR) transmittance spectroscopy could be applied to on-line control quality and characterization of VOOs (Jim
enez Marquez, Molina
ıaz, & Pascual Reguera, 2005). At present, new sensors based on NIR and microwave technologies are being developed. They will help to know the process

M.L. Clodoveo / Trends in Food Science & Technology 25 (2012) 13e23

performance and its regulation. Regarding the VOO aroma, electronic noses could be used for analyzing olive pastes (Esposto et al., 2006; Garc
ıa-Gonz
alez, Tena, & Aparicio, 2007). On-line monitoring of the evolution of VC during VOO processing could be very useful for defining the operative conditions of malaxation (i.e. time, temperature and atmosphere) in order to improve the VOO sensory quality according to product type (i.e. variety, ripening stage, sanitary aspects, etc.). Electronic tongues are also promising techniques in olive oil extraction process control (Apetrei et al., 2010). Acknowledgement I would like to acknowledge the debt I owe to Paolo Amirante, Full Professor of Agricultural Engineering, Agriculture Faculty, University of Bari- Italy. I have learnt much from working with him on food technology and food processing machinery. This paper is dedicated to the memory of Gian Luca Montel, deceased on 20 September 2008. At the time of his death he was 41 years old. He was assistant Professor of Agricultural Engineering, Agriculture Faculty, University of Foggia- Italy. During his academic career Prof. G. L. Montel developed research activities in many areas, especially in the field of olive oil, food industrial plant, recycling of agro-food by-products, and waste management. Appendix Abbreviations used VOO Mt MT PC PPO POD LOX VC OxC

Virgin olive oil Malaxation time Malaxation temperature Phenolic compounds Polyphenol oxidase Peroxidase Lipoxygenase Volatile compounds Oxygen concentration

References Aguilera, M. P., Beltr
an, G., Sanchez-Villasclaras, S., Uceda, M., & Jimenez, A. (2010). Kneading olive paste from unripe ‘Picual’ fruits: I. Effect on oil process yield. Journal of Food Engineering, 97, 533e538. Amirante, R., & Catalano, P. (1995). Extraction of olive oil by centrifugation: fluid-dynamic aspects and assessment of new extraction plant solutions. Olivae, 57, 44e49. Amirante, R., Cini, E., Montel, G. L., & Pasqualone, A. (2001). Influenza della miscelazione e di estrazione. sulla qualita vergine di oliva. Grasas Aceites y, 52, 198e201. Amirante, P., Clodoveo, M. L., Dugo, G., Leone, A., Salvo, F., & Tamborrino, A. (2006). New mixer equipped with control atmosphere system: influence of malaxation on the shelf life of extra virgin olive oil. Italian Journal of Food Science215e220, Special issue.

21

Amirante, P., Clodoveo, M. L., Dugo, G., Leone, A., & Tamborrino, A. (2006). Advance technology in virgin olive oil production from traditional and de-stoned pastes: influence of the introduction of a heat exchanger on oil quality. Food Chemistry, 98, 797e805. Amirante, P., Clodoveo, M. L., Leone, A., & Tamborrino, A. (2009a). Malaxer machine and its evolution of the enhancing olive oil quality. In Artemis. (Ed.), Proceedings of XXXIII CIOSTA-CIGR V conference 2009 technology and Management to Ensure Sustainable Agriculture, Agro-systems, Forestry and Safety 17e19 June 2009 Reggio Calabria e Italy, Vol. 1 (pp. 55e59), Reggio Calabria e Italy. Amirante, P., Clodoveo, M. L., Leone, A., & Tamborrino, A. (2009b). Una gramola innovativa per l’ottimizzazione del processo di estrazione meccanica e per enfatizzazione del ruolo funzionale degli oli vergini di oliva. In IX Convegno Nazionale A.I.I.A. Ricerca e innovazione nell’ingegneria dei biosistemi agro-territoriali. Ischia Porto, 12e16 settembre 2009, ISBN 978-88-89972-13-7. Cd-Printed. Angerosa, F., Mostallino, R., Basti, C., & Vito, R. (2001). Influence of malaxation temperature and time on the quality of virgin olive oils. Food Chemistry, 72, 19e28. Apetrei, C., Apetrei, I. M., Villanueva, S., de Saja, J. A., GutierrezRosales, F., & Rodriguez-Mendez, M. L. (2010). Combination of an e-nose, an e-tongue and an e-eye for the characterisation of olive oils with different degree of bitterness. Analytica Chimica Acta, 663(1), 91e97. Erratum in: Analytica Chimica Acta. 2010 Jul 19;673(2):212. Artajo, L. S., Romero, M. P., Suarez, M., & Motilva, M. J. (2006). Partition of phenolic compounds during the virgin olive oil industrial extraction process. European Journal of Lipid Science and Technology, 225, 617e625. Ben-David, E., Kerem, Z., Zipori, I., Weissbein, S., Basheer, L., Bustan, A., et al. (2010). Optimization of the Abencor system to extract olive oil from irrigated orchards. European Journal of Lipid Science and Technology, 112, 1158e1165. Bendini, A., Cerretani, L., Carrasco-Pancorbo, A., Gomez-Caravaca, A. M., Segura-Carretero, A., Fernandez-Gutierrez, A., et al. (2007). Phenolic molecules in virgin olive oils: a survey of their sensory properties, health effects, antioxidant activity and analytical methods. An overview of the last decade. Molecules, 12, 1679e1719. ~ ez-Reyesa, A. (2008). Model based predictive Bordons, C., & N
un control of an olive oil mill. Journal of Food Engineering, 84, 1e11. Boselli, E., Di Lecce, G., Strabbioli, R., Pieralisi, G., & Frega, N. G. (2009). Are virgin olive oils obtained below 27  C better than those produced at higher temperatures? LWT-Food Science and Technology, 42, 748e757. Chiacchierini, E., Mele, G., Restuccia, D., & Vinci, G. (2007). Impact evaluation of innovative and sustainable extraction technologies on olive oil quality. Trends in Food Science and Technology, 18, 299e305. Cini, E., Magni, J., Migliorini, M., Mugelli, M., Pasquini, M., & Recchia, L. (2006). Sperimentazione di una gramola ad asse verticale nell’estrazione dell’ olio di oliva. Rivista di Ingegneria Agraria. [Journal of Agricultural Engineering], 1, 1e19. Commission of the European Communities, 2001 (2001). Commission directive 2001/30/EC of 2 May 2001 amending directive 96/77/EC laying down specific purity criteria on food additives other than colours and sweeteners. Official Journal of the European Communities, L 146, 1e23. Cruz, S., Yousfi, K., P
erez, A. G., Mariscal, C., & Garc
ıa, J. M. (2007). Salt improves physical extraction of olive oil. European Food Research and Technology, 225, 359e365. Esp
ınola, F., Moya, M., Fern
andez, D. G., & Castro, E. (2009). Improved extraction of virgin olive oil using calcium carbonate as coadjuvant extractant. Journal of Food Engineering, 92, 112e118. Esposto, S., Servili, M., Selvaggini, R., Ricc o, I., Taticchi, A., Urbani, S., et al. (2006). Discrimination of virgin olive oil defects. Comparison

22

M.L. Clodoveo / Trends in Food Science & Technology 25 (2012) 13e23

of two evaluation methods: HS-SPME-GC/MS and electronic nose. In M. A. Petersen, & W. L. P. Bredie (Eds.), Flavour science: Recent advances and trends. Developments in food science, Vol. 43 (pp. 315e318). The Netherlands: Elsevier B.V. Publisher. Fern
andez, D. G., Esp
ınola, F., & Moya, M. (2008). Influencia de diferentes coadyuvantes tecnol
ogicos en la calidad y rendimiento del aceite de oliva virgen utilizando la metodolog
ıa de superficies de respuesta. Grasas y Aceite, 59, 39e44. Garc
ıa-Gonz
alez, D. L., Tena, N., & Aparicio, R. (2007). Characterization of olive paste volatiles to predict the sensory quality of virgin olive oil. European Journal of Lipid Science and Technology, 109, 663e672. G
omez-Rico, A., Inarejos-Garc
ıa, A. M., Salvador, M. D., & Fregapane, G. (2009). Effect of malaxation conditions on phenol and volatile profiles in olive paste and the corresponding virgin olive oils (Olea Europaea L. cv. Cornicabra). Journal of Agriculture and Food Chemistry, 57, 3587e3595. Hermoso Fernandez, M., Uceda Ojeda, M., Garcia-Ortiz Rodriguez, A., Morales Bernardino, J., Friaz Ruiz, L., & Fernando Garcia, A. (1998). In Elaboracion del aceite de oliva de calidad. Obtencion por el sistema de dos fases (pp. 65e71). Sevilla (Spain): Junta de Andalusia, Apuntes n. 11/94. Inarejos-Garc
ıa, A., G
omez-Rico, A., Salvador, M. D., & Fregapane, G. (2009). Influence of malaxation conditions on virgin olive oil yield, overall quality and composition. European Food Research and Technology, 228, 671e677. Jim
enez Marquez, A., Molina
ıaz, A., & Pascual Reguera, M. I. (2005). Using optical NIR sensor for on-line virgin olive oils characterization. Sensors and Actuators B, 107, 64e68. Kalua, C. M., Allen, M. S., Bedgood Jr., D. R., Bishop, A. G., Prenzler, P. D., & Robards, K. (2007). Olive oil volatile compounds, flavour development and quality: a critical review. Food Chemistry, 100, 273e286. Kalua, C. M., Bedgood, D. R., Bishop, A. G., & Prenzler, P. D. (2006). Changes in volatile and phenolic compounds with malaxation time and temperature during virgin olive oil production. Journal of Agriculture and Food Chemistry, 54, 7641e7651. Lercker, G., Frega, N., Bocci, R., & Mozzon, M. (1999). Volatile constituents and oxidative stability of virgin olive oils: influence of the kneading of olive-paste. Grasas Y Aceites, 50, 26e29. Martinez, S. J., Munoz, A. E., Alba, M. J., & Lanzon, R. A. (1975). Informe sobre utilizacion del Analizador de Rendimientos ‘‘Abencor’’. Grasas y Aceites, 26, 379e385. Masella, P., Parenti, A., Spugnoli, P., & Calamai, L. (2011). Gramolazione della pasta di olive in condizioni sigillato. Journal of the American Oil Chemists Society, 88, 871e875. Migliorini, M., Mugelli, M., Cherubini, C., Viti, P., & Zanoni, B. (2006). Influence of O2 on the quality of virgin olive oil during malaxation. Journal of the Science of Food and Agriculture, 86, 2140e2146. Migliorini, M., Zanoni, B., Berti, A., Cherubini, C., Cini, E., Daou, M., et al. (2008). In Protocolli innovativi per la produzione di olio extra vergine nella realta aziendale toscana. Firenze: Camera di Commercio di Firenze. Maggio 2008. Mınguez-Mosquera, I., Gallardo-Guerrero, L., & Roca, M. (2002). Pectinesterase and polygalacturonase in changes of pectic matter in olives (cv. Hojiblanca) intended for milling. Journal of the American Oil Chemists Society, 79, 93e99. Ministerio de Sanidad y Consumo (1986). Ministerio de Sanidad y Consumo, ORDEN de 13 de enero de1986 por la que se aprueba la lista positiva de aditivos y coadyuvantes tecnol
ogicos para uso en laelaboraci
on de aceites vegetales comestibles. Bolet
ın Oficial del Estado, 19, 3089e3090. Ministerio de Sanidad y Consumo (1989). Ministerio de Sanidad y Consumo, ORDEN de 30 de noviembre de 1989 por la que se modifica la lista positiva de aditivos y coadyuvantes tecnol
ogicos autorizados en la elaboraci
on de aceites vegetales comestibles. Bolet
ın Oficial del Estado, 301, 39066.

Moya, M., Esp
ınola, F., Fern
andez, D. G., de Torres, A., Marcos, J., Vilar, J., et al. (2010). Industrial trials on coadjuvants for olive oil extraction. Journal of Food Engineering, 97, 57e63. Najafian, L., Ghodsvali, A., Khodaparast, M. H. H., & Diosady, L. L. (2009). Aqueous extraction of virgin olive oil using industrial enzymes. Food Research International, 42, 171e175. Parenti, A., & Spugnoli, P. (2002). Influence of olive oil paste temperature on polyphenols content of the extracted oils. La Rivista Italiana Delle Sostanze Grasse, 79, 97e100. Parenti, A., Spugnoli, P., & Cardini, D. (2000). Gramolazione e qualita dell‟olio di oliva. La rivista italiana delle sostanze grasse, 77, 61e64. Parenti, A., Spugnoli, P., Masella, P., & Calamai, L. (2008). The effect of malaxation temperature on the virgin olive oil phenolic profile under laboratory-scale conditions. European Journal of Lipid Science and Technology, 110, 735e741. Parenti, A., Spugnoli, P., Masella, P., Calamai, L., & Pantani, O. L. (2006). Improving olive oil quality using CO2 evolved from olive pastes during processing. European Journal of Lipid Science and Technology, 108, 904e912. P
erez, A. G., Romero, C., Yousfi, K., & Garc
ıa, J. M. (2008). Modulation of olive oil quality using NaCl as extraction coadjuvant. Journal of the American Oil Chemists’ Society, 85, 685e691. Ranalli, A., Contento, S., Schiavone, C., & Simone, N. (2001). Malaxing temperature affects volatile and phenol composition as well as other analytical features of virgin olive oil. European Journal of Lipid Science and Technology, 103, 228e238. Ranalli, A., Pollastri, L., Contento, S., & Iannucci Elucera, L. (2003). Effects of olive paste kneading time on the overall quality of virgin olive oil. European Journal of Lipid Science and Technology, 105, 57e67. Rodis, P. S., Karathanos, V. T., & Mantzavinou, A. (2002). Partitioning of olive oil antioxidants between oil and water phases. Journal of Agricultural and Food Chemistry, 50, 596e601. Salas, J. J., & Sanchez, J. (1999). The decrease of virgin olive oil flavor produced by high malaxation temperature is due to inactivation of hydroperoxide lyase. Journal of Agricultural and Food Chemistry, 47, 809e812. Sanchez, J., & Salas, J. J. (2000). Biogenesis of olive oil aroma. In J. Harwood, & R. Aparicio (Eds.), Handbook of olive oil: Analysis and properties. Gaithersburg, Maryland, USA: Aspen Publications, Inc. Sanchez-Ortiz, A., Romero, C., Perez, A. G., & Sanz, C. (2008). Oxygen concentration affects volatile compound biosynthesis during virgin olive oil production. Journal of Agricultural and Food Chemistry, 56, 4681e4685. Servili, M., Esposto, S., Fabiani, R., Urbani, S., Taticchi, A., Mariucci, F., et al. (2009). Phenolic compounds in olive oil: antioxidant, health and organoleptic activities according to their chemical structure review. Inflammopharmacology, 17, 76e84. Servili, M., Selvaggini, R., Esposto, S., Taticchi, A., Montedoro, G. F., & Morozzi, G. (2004). Health and sensory properties of virgin olive oil hydrophilic phenols: agronomic and technological aspects of production that affect their occurrence in the oil. Journal of Chromatography A, 1054, 113e127. Servili, M., Selvaggini, R., Taticchi, A., Esposto, S., & Montedoro, G. (2003a). Air exposure time of olive pastes during the extraction process and phenolic and volatile composition of virgin olive oil. J Journal of American Oil Chemists Society, 80, 685e695. Servili, M., Selvaggini, R., Taticchi, A., Esposto, S., & Montedoro, G. F. (2003b). Volatile compounds and phenolic composition of virgin olive oil: optimization of temperature and time exposure of olive pastes to air contact during the mechanical extraction process. Journal of Agricultural and Food Chemistry, 51, 7980e7988. Servili, M., Taticchi, A., Esposto, S., Urbani, S., Selvaggini, R., & Montedoro, G. F. (2008). Influence of the decrease in oxygen during malaxation of olive pastes on the composition of volatiles and phenolic compounds in virgin olive oil. Journal of Agricultural and Food Chemistry, 56, 10048e10055.

M.L. Clodoveo / Trends in Food Science & Technology 25 (2012) 13e23 Uceda, M., Jim
enez, A., & Beltr
an, G. (2006). Olive oil extraction and quality. Grasas y Aceites, 57, 25e31. Velasco, J., & Dobarganes, C. (2002). Oxidative stability of virgin olive oil. European Journal of Lipid Science and Technology, 104, 661e676. Vierhuis, E., Servili, M., Baldioli, M., Schols, H. A., Voragen, A. G. J., & Montedoro, G. (2001). Effect of enzyme treatment during mechanical extraction of olive oil on phenolic compounds and polysaccharides. Journal of Agricultural and Food Chemistry, 49, 1218e1223. Yorulmaz, A., Tekin, A., & Turan, S. (in press). Improving olive oil quality with double protection: destoning and malaxation in

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nitrogen atmosphere. European Journal of Lipid Science and Technology. doi:10.1002/ejlt.201000481.

Maria Lisa Clodoveo is assistant professor with tenure in Food Science and Technology, Department of Agro-Environmental and Territorial Sciences, Agriculture Faculty, University of Bari, Italy. She teaches classes on Food science and technology and Food quality control. She also teaches a specialized course in olive-oil processing plants. Her research interests include innovation in optimization of agro-food industry plants and process settings, influence of industrial processes on food quality, real time control of processes, recycling of agro-food by-products, and waste management.