ANALYTICAL CARACTERISTICS OF OLIVE OILS PRODUCED BY TWO DIFFERENT EXTRACTION TECHNIQUES in Portuguese olive variety
121L. VAZ-FREIRE, J. GOUVEIA, A. M. COSTA FREITAS*
1 Departamento de Fitotecnia, Instituto de Ciências Agrárias e Mediterrânicas, Universidade de Évora, Apt 94, 7002-554 ÉVORA, PORTUGAL
2 Departamento de Agro-Indústrias e Agronomia Tropical, Instituto de Agronomia Universidade Técnica de Lisboa, Tapada da Ajuda, 1349-017 Lisboa, PORTUGAL
ANALYTICAL CARACTERISTICS OF OLIVE OILS PRODUCED BY TWO
DIFFERENT EXTRACTION TECHNIQUES in Portuguese olive variety
A metal hammer- decanter (HD) olive processing line was compared to a traditional metal hammer-press (HP) line, a discontinuous method that, if properly used, yields high-quality virgin olive oils. Galega olives (traditional Portuguese variety) were used. Olives were picked at a predetermined maturation stage and plagues and oil content were evaluated before processing. Years, extraction technology, data replicates, and years*extraction, analytical results were compared using statistical treatment. In spite significant differences among the results obtained only acidity gave results that, besides being statistically different, were sufficient to classify the produced olive oil in a lampante category.
KEY WORDS: olive oil, extraction technique, technology, Galega Vulgar
CARACTERISTICAS ANALÍTICA DE LOS ACEITES DE OLIVA PRODUJIDO
POR DOS DIVERSAS TÉCNICAS DE EXTRACCIÓN PARA LA VARIEDADE
PORTUGUESA Galega Vulgar.
Se han comparado dos líneas de procesamiento de aceite utilizando un sistema de prensas (SP) y un decantador centrífugo (DC). El procesamiento que recurre al sistema de prensas es un sistema discontinuo que, sin embargo, permite obtener aceites vírgenes de gran calidad. Para este estudio se ha utilizado la variedad Portuguesa Galega común. Las aceitunas fueron tratadas
contra el ataque de plagas, y recogidas en un punto de maduración predeterminado. Del mismo modo, se evaluó el porcentaje de aceite obtenido de la cosecha. Se han considerado los resultados analíticos teniendo en cuenta la determinación de la influencia de la extracción en el producto final. Este punto ha sido evaluado por medio de un tratamiento estadístico. Aunque se han observado diferencias significativas entre los resultados de algunos de los parámetros analizados, sólo las diferencias verificadas en el grado de acidez son susceptibles de modificar la clasificación final del aceite, situándolo en la categoría lampante.
Palabras clave: aceite, técnicas de extracción, tecnología, Galega vulgar
Olive oil production is one of the most traditional agricultural industries in Portugal, and is still of primary importance for the rural economy, local heritage and environment of most Mediterranean countries. Portugal it’s the forth productor in the European Union, that it’s the leading world producer, producing around 80 % of the world’s olive oil and consuming also around 70 %.(Gouveia, 1995; Leguen De Lacroix - European Commission Directorate-General for Agriculture, 2003).
Olive trees belong to Olea europea L. family but among them different cutivars
with different characteristics can be found in the world production zones. The most important cultivars used in Portugal are Galega Vulgar, Carrasquenha,
Cordovil, Cobrançosa and Verdeal (Bartolini et al., 1998).
Portuguese cultivars with major interest in olive oil industry are those responsible for the generation of olive oil under the classification of Protected Denomination Origin (DOP) (Bartolini et al., 1998; Gouveia et al., 2002), where the predominant variety is Galega Vulgar, representing 80% of the olive patrimony in Portugal (Gemas et al., 2002).
In general terms olive oil quality is related to olive ripeness, olive sanitary condition andd processing but also to origin, variety ande store. (Vinha et al.,
2005; Torres et al., 2006).
Processing is, in fact, a major factor affecting olive oil quality. Pressed oil obtained under the proper processing conditions is usually of great quality. Press extraction was almost the only olive oil extraction process used for centuries. Olive oil processing has, however, progressed significantly since the
beginning of the seventies, when the centrifugation system appeared. Since than many articles compare the so-called three-phase centrifugation system extraction with two-phase centrifugation system (Vlyssides et al.,2004). When
compared to the press system these processes are sometime considered as producing olive oils of inferior quality (Rannalli et al., 2001)
To verify olive oil quality chemical and sensorial analysis can be used. Several studies have been carried out comparing aroma compounds, oxidative stability, phenolic compounds, colour and others chemical parameters (Boskou, 1996; Ranalli et al., 1997; Aparicio and Luna, 2002).
In this work the two different extraction technologies decanter and pressing by hydraulic press were evaluated, by means of routine regulated analysis, with the aim of verifying if differences could be significant enough to classify the olive oil under different classificationsthus reducing or affecting not only their intrinsic quality but also its commercial value.
Technological studies similar to this can provide important information to determine not only the differences among the produced olive oils but also can be a powerful help to improve technologies.
Experiments were carried out by processing under defined conditions mechanically picked olives from the Portuguese cultivar Galega Vulgar. All
olives were picked at proper and controlled sanitary conditions. Olives were picked during the harvests of 2001, 2002, 2003 and 2004.
A 120Kg sample was collected. Fruits were stored in open boxes at ambient temperature (5-15ºC) with reasonable air flow and without direct light incidence. Extraction was made during the next 24h. Before extraction, leaves and dirt (soil, stones, etc) were removed by washing under cold running water.
Maturation index was determined according to Hermoso et al. (1991). Fat yield
and humidity percentage were also determined before extraction. For these olives the percentage of Gloeosporium olivarum Alm. or Dacus oleae Rossi
(olive fly) attack was determined by visual inspection. Three replicates for each extraction procedure (pressing and centrifugation) were made for each collected sample with an exception on 2001 were only two replicates were made due to severe climatic conditions.
An homogeneous 20 Kg sample was processed (each time) for each one of the technologies under study: a hammer-mill press line (Vieirinox, Portugal) and a hammer-mill integral decanter line (Oliomio, Italy) were used. No water was added to the olive paste in both systems and malaxing time, about 1 h, was equal for both methods as well. For the pressing system the liquid-liquid separation was made by natural process, decantation. Three replicates were made for each extraction process.
Analysis for the Olive Oil
Acidity was determined according to EC regulation nº2568/91 annexe II, Spectrofotometry UV absorption was made according to EC regulation nº2568/91 annexe IX; Peroxide value followed EC regulation nº2568/91 annexe III; Rancidity was analyzed according to the Portuguese rule NP 4158 de 1991;
Sterols, uvaol and eritrodiol were according to EC regulation nº2568/91 annexe V; fatty acids EC regulation nº2568/91 annexe XB waxes regulation EC nº2568/91 annexe IV and triglycerides EC regulation nº2568/91 anexe VIII.
For Polyphenols analyses an internal method developed at Instituto Superior de Agronomia, based on the Folin Ciocalteu's method, .was followed (internal proceeding IT065, Lab. de Estudos Técnicos, ISA, UTL. Lisboa Portugal),
Value of tocopherols was determined according to the method described by P. Rovellini et al. (1997), which uses High Performance Liquid Chromatography; connected to a ultraviolet detector (HPLC-UV).
For the ANOVA, General Linear model analysis the software used was the Minitab version 12 for Windows (Minitab Inc., State College, USA)
Results and discussion
The results obtained for the olives (tables 1 and 2) show the homogeneity of the samples in terms of maturatio, fat content, humidity and dry matter. According to the results in table 1 we might consider that harvest was made at similar maturation stages. The same can be stated as far as humidity percentage is concerned but not for the fat content. In fact for fat content a standard deviation of 11, 20 was obtained.
The results obtain for the pests control Gloeosporium olivarum Alm. or Dacus
oleae Rossi (olive fly) show a significant difference between both years (table III), however an acceptable sanitary state could still be considered. The different
sanitary state might probably justify the difference verified for the fat content (Boskou, 1996; Barranco et al., 2001).
For the olive oil results (table 4-8) we might consider that most data, for the entire studied parameters, lie in the legal intervals considered for extra virgin olive oil classification with one exception. For the olive oil obtained from the Press system the acidity value is above 2 in the last three years of analysis thus the resulting oil should be classified as “lampante” olive oil in agreement with
).CE regulation (Regulation nº1989/2003
The above conclusions were taken only from an analytical point of view and were not based on any statistical treatment. To allow reliable conclusions an ANOVA treatment was applied. Extraction technologies as well as replicates were the target variable (Table 9). The interaction extraction*replicates was also tested. The statistical analysis was made using the software Minitab the ANOVA General Linear Model, with a significance level of 95%. Table IX presents only the interactions where significant differences were detected. From this table we could conclude that data replicates didn’t show significant
differences, with an exception in acidity values, probably due to an extra time contact, with water coming from the separation process, that occurs when the pressing technology is used. The separation time is also longer when the press system is used which might also account for the differences observed. Extraction technology, on the other hand, has a significant impact on some of the data obtained (table 9).
For sterols analysis, extraction technology has a significant impact on the results only for the Uvaol+Eritrodiol and total sterols. The slight differences
verified in individual data (table 8) are common in the same variety (Alves et al.,
For fatty acids (table 4) only the heptadecenoic acid (C17:1) presents results out of the regulation for extra virgin olive oils. These values were detected only for one extraction system (two phase decanter) although only on the year of 2004, but if we considered the covariance for the heptadecenoic acid (C17:1), we verify that it’s not higher then 5% for the bigger allowed value according with the regulation (Regulation (CE) nº 1989/2003). Also in table 4 trans-palmitoleic acid is above the regulated value for all the oils, however, when this value is considered combined with the trans-linolenic acid the final value lies in the allowed range for extra virgin olive oil.
In table 9 significant differences, due to extraction system were observed for C16:1, C17:0, C17:1, C18:1, C18:2, C20:0 e C18:3 acids.
Table 5 shows significant differences for the C40, C42, C44 as well as for Total Wax content ,however (table 5) total Wax is always < 250 mg/kg, thus the resulting oils can always be classified as extra virgin.
For the triacylglycerols in all the studied oils for both methods the quantitative sequence mention by Boskou (1996), where OOO has the highest amount followed by POO, OOL e POL was observed (Table 6). The impact of extraction procedure was significant for some data (PoOL, OOL+LnPP, POL+StLL, OOO, POO, PPO and StOO+StOSt). These results are in accordance to others, previously reported, in which , in addition to cultivar, other rather important factors affecting total fatty acid composition, and especially oleic acid content, are latitude, climatic conditions, and the ripening stage of the fruit at harvest
(Ranalli et al., 1997; Aparicio and Luna, 2004, Aranda et al., 2004) fas well as
extraction method (Salvador et al.,2001).
From these results we can conclude that extraction methods might be responsible for some of the differences observed in olive oil qualities since for the same raw material different final product could be obtained.
Taking into account the olive oil classification from EC Regulation Nº 1989/2003
Thfrom November 6 it is clear, however, that, besides acidity, all the significant differences among the parameters studied are not enough to change the oil classification. Acidity differences are enough to depreciate the oil in terms of classification.
The high acidity obtained for the oil from press extraction is probably due to an extreme hydrolysis of fat due to the excessive contact time of the oil with vegetation water during the decanting step.
Fundação para a Ciência a e Tecnologia – MCTES
Projecto Agro 824 - MADRP