WO2012160226A1 - Method for preventing total or partial crystallization of olive oil during storage at low temperature - Google Patents

Abstract

The invention relates to a method for preventing the total or partial crystallization of olive oil during storage at low temperature, while retaining the physical/chemical and sensory properties, which includes the application of ultrasonic energy to said olive oil. The invention also relates to the olive oil obtained from said method.

Description

 PROCEDURE TO AVOID THE TOTAL OR PARTIAL CRYSTALLIZATION OF OLIVE OIL DURING ITS LOW CONSERVATION

FIELD OF THE INVENTION TEMPERATURE

The present invention relates to a method for preventing the total or partial crystallization of olive oil by using power ultrasound in the form of electronic pulses, while maintaining the physical-chemical and sensory properties of said oil during its preservation. low temperature, for a period not less than 16 months. The present invention also relates to olive oil obtained by this process.

BACKGROUND OF THE INVENTION

Olive oil is a product that has extremely complex organoleptic and chemical-physical characteristics. Therefore, special care must be taken when handling, storing and preserving it, since if poor conditions are used the oil may undergo changes that may alter its properties (1).

Currently, the main concern of producers of extra virgin olive oil is to be able to guarantee the stability and quality of the oil, as long as possible. In the particular case of olive oil, oxidation is the main cause of the loss of quality, and the speed with which this process takes place is one of the most important factors that determine the shelf life of this product (2).

In order to maintain the quality of volatile and non-volatile components (phenols and minor components) responsible for the organoleptic characteristics and nutritive properties so appreciable of olive oil during storage, it is absolutely essential to control each and every one of the factors that affect the lipid oxidation

The high oxidative stability of extra virgin olive oil with respect to other vegetable oils is mainly due to the fatty acid composition, in particular, the high ratio between mono- and polyunsaturated fatty acids and the presence of some minor components that play a very important role in the preservation of oxidation (3).

Despite the high stability of extra virgin olive oil, it is also susceptible to oxidative processes, such as enzymatic oxidation, which normally occurs during the extraction process and during frying, photo-oxidation, when the oil It is exposed to light and the self-oxidation that occurs mainly when the oil is in contact with oxygen during processing, packaging and storage (4, 5, 6).

Lipid oxidation is a consequence of the interaction between the fatty acid triacylglycerol and the molecular oxygen present in the oil matrix. The main product of the reaction is hydroperoxides that are generated by a mechanism that includes the appearance of free radicals. This oxidation reaction has a high activation energy, this causes the reaction to increase its speed in the presence of precursors such as traces of metal or the action of light. It has also been observed how the storage temperature of the oil can significantly influence lipid oxidation reactions (1). A fact that should be noted is the increase in lipid oxidation in the presence of free fatty acids and traces of metals such as iron and copper (7). In contrast, phenolic compounds and carotenes decrease these self-oxidation reactions, while tocopherols, chlorophylls and phospholipids demonstrate their anti-pro-oxidant activities depending on the oil and storage conditions (8, 9).

In the document of Masón, TJ, Paniwnyk, L., Lorimer, JP "The uses of ultrasound in food technology", Ultrasonics Sonochemistry, 3 (1996), 253-256 a review of the different applications of ultrasound in the agri-food field In the case of power ultrasounds, which are those used in the present invention, the possibility of using them for the preservation of oils is not mentioned. Even unlike the present invention, it is indicated that power ultrasound can cause an increase in nucleating agents. In the paper by Patrick, M., Blind, R., Janssen, J. "The effect of ultrasonic intensity on the crystal structure of palm oil ", Ultrasonics Sonochemistry, 11 (2004), 251-255, the influence of the intensity of power ultrasound on the texture in palm oils is described, but no procedure for attenuation is mentioned or eliminate the crystallization process during the conservation of low temperature oils.

In WO0205921 different methods for obtaining fats in solid or emulsified form by applying power ultrasound are described. However, this document does not mention or suggest a procedure to attenuate or eliminate the crystallization process during the conservation of low temperature oils.

SUMMARY DESCRIPTION OF THE INVENTION A first objective of the present invention is to disclose a method capable of allowing an optimal preservation of olive oil at low temperature avoiding its total or partial crystallization and, in turn, maintaining the physicochemical properties and intact sensory attributes. The process described in the present invention allows to fulfill this objective and thus obtain an olive oil with said properties.

BRIEF DESCRIPTION OF THE FIGURES The figure represents the qualification of the positive attributes of the initial untreated sample and the initial sample treated with power ultrasound (Panell de Tast Oficial de Catalunya).

 Figure Ib represents the qualification of the possible defects of the initial untreated sample and the initial sample treated with ultrasound (Panell de Tast Oficial de Catalunya).

 Figure 2 shows the evolution of the degree of acidity for each of the olive oil samples packaged under different conditions.

 Figure 3 shows the evolution of the Peroxides index for each of the olive oil samples stored under different conditions.

Figure 4 shows the evolution of parameter K ₂₃₂ for each of the samples of Olive oil packaged under different conditions.

Figure 5 shows the evolution of parameter K ₂₇ or for each of the olive oil samples packaged under different conditions.

 Figure 6 shows the evolution of oxidative stability for each of the samples packaged under different conditions.

Figure 7 shows the comparison of the crystallization of a sample of extra virgin olive oil treated with ultrasound (left) and an untreated sample (right), after 4 months of storage at 4-6 ° C temperature.

Figure 8 represents the degree of crystallization of the samples stored at low temperature (4-6 ° C) with ultrasonic treatment (left bottle) and without ultrasound treatment (right bottle) after 16 months of storage.

DESCRIPTION OF THE INVENTION The present invention relates to a method for preventing the total or partial crystallization of olive oil, preferably extra virgin olive oil, during its low temperature preservation while maintaining both physical-chemical and sensory properties, which It includes the application of power ultrasound on said olive oil.

In particular, said procedure comprises the steps of:

 a) Application of ultrasonic pulses on olive oil present in opaque glass bottles at a power between 300 and 350 W and at a temperature below 30 ° C.

 b) Elimination of the air present in the internal oil matrix.

 c) Storage of said olive oil at a refrigeration temperature between 4 and 6 ° C.

In step (a) the ultrasonic pulses are preferably applied for 10 minutes.

This procedure uses the power ultrasound technique, applied in the form of ultrasonic pulses, to partially or totally eliminate gases, mainly oxygen, loose in extra virgin olive oil, minimizing or avoiding oxidation reactions. that take place during the preservation process of extra virgin olive oil and that may originate during the period of conservation the loss of quality of the same and its disqualification as such.

Thus, olive oil pretreated with ultrasonic pulses and kept at low temperature, does not show alterations in the physical-chemical properties, or in the sensory attributes (at least for a period of 16 months), also reducing significantly the process of crystallization of fats that occurs when olive oils are stored at low temperature.

The removal of air from step (b) is preferably carried out by displacing the air with an inert gas denser than the air, for example argon.

The present invention also relates to olive oil obtained by the process described in any of the above embodiments. Said olive oil is preferably extra virgin olive oil.

The present invention also relates to the use of power ultrasound on olive oil in a method to avoid the total or partial crystallization of olive oil, preferably extra virgin olive oil, during cold storage while maintaining the properties physicochemical and sensory. In particular, said process comprises the steps of:

 a) Application of ultrasonic pulses, preferably applied for 10 minutes, on the olive oil present in opaque glass bottles at a power between 300 and 350 W and at a temperature below 30 ° C;

 b) Elimination of the air present in the internal matrix of the oil, preferably by displacement with an inert gas denser than the air, for example argon;

c) Storage of said olive oil at a refrigeration temperature between 4 and 6 ° C. The present invention is illustrated below by examples that are not intended to limit the scope of the invention. EXAMPLES

 Materials: variety of olives and elaboration of extra virgin olive oil

To carry out this study, an extra-monovarietal extra virgin olive oil from olives of the variety called Empeltre or Mallorcan has been used. The oil was produced in the Agricultural Cooperative of Sóller "San Bartolomé" located in the town of Sóller (Mallorca). The olives were collected from a farm affiliated with the Sóller cooperative, located in the Sierra de Tramuntana (north of the Island of Mallorca). In order to minimize the time between harvest and oil extraction, oil processing was carried out on the same day. Approximately 30 liters of extra virgin olive oil were obtained, through the continuous three-phase process, with this system maximum quality oils are obtained, both in terms of the physical-chemical properties and the characteristic sensory attributes of the extra virgin olive oil

Procedure: Once the extra virgin olive oil is obtained, it is poured into 250 ml opaque glass bottles, which are placed in an ultrasonic tank (340W power), at a controlled temperature (below 30 ° C throughout moment) and for 10 minutes the oil samples are subjected to ultrasonic pulses, eliminating partially or totally the dissolved oxygen in the olive oil matrix. After the ten minutes have elapsed, the air present between the surface of the oil and the lower part of the bottle cap is removed, by displacing it with an inert gas (argon, in our case), and closing it with an airtight cap . Finally, to guarantee the opacity of the bottle, it is covered with aluminum foil and kept in a refrigerator at refrigeration temperature (4-6 ° C).

Study of the possible effect of the application of ultrasound on the quality of extra virgin olive oil The sample of olive oil treated with ultrasound was subjected to different physical-chemical and sensory determinations in order to check if the ultrasound treatment of power had a significant influence on the main characteristics of the initial oil. The main quality indices: degree of acidity, peroxide index, K ₂₇₀ index and K ₂₃₂ index, were determined for the same samples (original sample and ultrasound treated sample) in three Different laboratories (Agrifood Engineering Laboratory of the University of the Balearic Islands, Agrifood Laboratory of Granada and Official Agrifood Laboratory of Catalonia, located in the city of Reus), following the regulations corresponding to the specific EU Regulation No. 2568/91 for olive oils.

Table 1. Characterization of the quality parameters corresponding to the initial sample of virgin olive oil and the sample treated with Ultrasound

As can be seen in Table 1, the results obtained in the three laboratories did not show significant differences in any of the quality parameters mentioned, which indicates that the application of ultrasound had no influence on the main physical-chemical indicators of the quality of the oil.

This fact was also reflected in the results obtained in the sensory analysis carried out in the Agrifood Laboratory of Granada (table 2). In this laboratory, the tasting panel, recognized by the International Olive Council (IOC) and authorized by the Ministry of Agriculture, Fisheries and Food (MAP), gives a global score to the average of positive attributes, as well as the average of Possible defects In both cases the results were completely coincident, being 5.4 the value of the positive attribute and 0 that of defects. Table 2. Sensory characterization of the initial olive oil and the sample treated with ultrasound. (Agrifood Laboratory of Granada)

In the case of the Official Tasting Panel of Catalonia, also recognized by the IOC and authorized by the MAP, the sensory description of both positive and negative attributes is more detailed. The main organoleptic characteristics of the two samples analyzed are shown in the figure. As can be seen the coincidence between both samples in the characteristic positive attributes of the oil of the instep variety (fruity olive, spicy, sweet, bitter and leaf green) is almost total, being also zero, in both cases, the value of the possible defects (figure Ib). Therefore, the most important conclusion of this study prior to the conservation of extra virgin olive oil, is that the application of ultrasonic pulses under the indicated conditions (power 340W, temperature <30 ° C, time 10 min) does not alter Significantly forms the physicochemical and sensory characteristics that determine the quality of extra virgin olive oil. Packaging of extra virgin olive oil. Procedures evaluated

Once the oil was prepared and the suitability of the use of power ultrasound in the form of ultrasonic pulses as pretreatment was checked, the olive oil was packaged using commercial dark glass bottles with a capacity of 250 ml. It was decided to bottle the unfiltered oil, with this, despite the initially cloudy appearance, its sensory properties are guaranteed to the maximum (10). In order to verify the effectiveness of the new preservation procedure, different procedures were used based on the use of modified atmosphere, absence of light and low temperature (all without pretreatment with ultrasound). Specifically, 24 bottles were allocated for each of the different storage procedures under study described below.

The oil packaging methodologies or techniques used were the following:

• Control [1]: this sample aims to simulate the oil that a regular consumer can keep, despite this the samples (250 ml dark glass bottles) were kept at 20 ° C to avoid sudden temperature changes over the long period of storage.

 • Atmosphere [2]: this sample was stored in 250 ml dark glass bottles in an inert atmosphere. This was achieved by displacing the air present between the oil surface and the bottle cap with argon. The storage temperature was 20 ° C.

· Opaque [3]: this sample was kept inside 250 ml glass bottles coated with several layers of aluminum foil to guarantee total opacity, avoiding the presence of light. The storage temperature was 20 ° C.

 • Temperature [4]: since olive oil is nothing more than a fruit juice, this sample is stored in 250 ml dark glass bottles at refrigeration temperature (4-6 ° C).

The results obtained by these four treatments were compared to the procedure object of this invention:

• Ultrasound [5]: this sample was pre-treated with power ultrasound (340 W); ultrasonic pulses were applied for 10 minutes in an ultrasonic bath thermo statized, the bath temperature never exceeded 30 ° C and the samples were stored in 250 ml dark glass bottles at refrigeration temperature (4-6 ° C), in modified atmosphere (Ar) and total absence of light. Samples [1], [2] and [4] were preserved in the presence of light. The light conditions used, in 12-hour cycles, were the following: compact spiral fluorescent lamp of 11W of power, 595 of lumen (light flow), class A of daylight.

The oil samples stored under different storage conditions were subjected to periodic control of the main physical-chemical and sensory parameters in order to determine the influence of the different variables: inert atmosphere, absence of light and low temperature on the quality of the Olive oil, in addition to incorporating the sample pretreated with ultrasound, since, as it has been demonstrated, this treatment does not modify the characteristics (chemical and sensory) of olive oil.

During the monitoring of the evolution of the different oil samples, the main chemical quality indicators established by the regulation (EEC Regulation No. 2568/91) of olive oils, that is, the degree of acidity, peroxide index, and spectrophotometric indexes K ₂₃₂ and K ₂₇₀ . In addition to the mentioned parameters, despite not being included in the legislation, but given its importance, the oxidative stability of the different oil samples was also evaluated. For the determination of this parameter, a Rancimat 679 mark (Metrohm Ltd CH-9101, Herisau, Suissa) has been used, following the method described by Gutiérrez-Rosales (11) and Velasco and Doborganes (12).

On the other hand, the organoleptic characteristics of the oils were also monitored with an approximate frequency of 3 months. For the sensory characterization and organoleptic classification the descriptive tasting method without repetitions was used, described by the International Olive Council, applying the CE norm N ° 640/2008, of July 4, 2008. Evolution of olive oil quality during storage: physical-chemical parameters

Degree of acidity (GA)

In the case of triglycerides, the biologically synthesized matter is neutral, therefore the existence of free fatty acids in the oil matrix is an anomaly or molecular disorder resulting from a poor state of preservation of fruits, an incorrect process of elaboration or poor conservation. The evolution of the GA for each of the different oil samples as a function of storage time is shown in Figure 2.

In figure 2 the maximum value that the GA can reach above which the olive oil would not obtain the extra virgin qualification has been represented in red. As can be seen, the initial analysis is already at a value very close to 0.8% oleic acid. This fact, in addition to giving little room for variation so as not to lose the category of extra virgin oil (Regulation EEC 2568/91), implies the presence of anomalies, that is to say free fatty acids with pro-oxidant capacity if the storage conditions used do not They prevent it.

As can be seen in Figure 2, only the GA corresponding to the temperature (low temperature) and ultrasound (low temperature + ultrasound) samples practically did not experience significant variations during the 16 months in which the evolution was monitored of the GA, always staying below the limit established for the category of extra virgin olive oil.

The same did not happen with samples kept under an inert atmosphere and in an opaque container, as well as with the control sample. How can the samples preserved in an inert atmosphere be observed and the control sample experienced a sharp increase in GA between the second and fourth month of storage, while in the case of the sample conserved in the absence of light, the increase was more gradual, although, at the second month, the value of the GA determined was already 0.82% oleic acid, that is to say slightly higher than the limit established by the European regulation for extra virgin olive oil. Several authors have studied the evolution of this parameter (GA) under different storage conditions such as the absence / presence of light (13, 14), the use of inert atmosphere and the application of different temperatures (15), All authors mentioned They have the same conclusion: the GA of olive oil increases as the shelf life elapses due to the appearance of compounds generated during triglyceride degradation reactions. In most of the previous studies, a smaller increase in GA was observed when potentially oxidative sources were minimized; that is, for the same temperature, the increase in GA of an olive oil preserved in an inert atmosphere was smaller than that corresponding to another sample not preserved under similar conditions and the same occurs when the oil was kept in the absence of light or low temperature. These trends seem to be true when the starting oil has a relatively low GA, where oxidation reactions initiated by external factors (light, inert atmosphere, temperature) predominate over oxidation reactions generated by the presence of free fatty acids, consequence of the process of elaboration or the state of the fruits at the time of the extraction of the oil. In all the studies cited above, the starting oil had a GA less than or equal to 0.3% oleic acid, making them prioritize external factors over oxidation reactions.

Oils that have a relatively high initial GA, as in our case (0.7% oleic acid), have a relatively large amount of free fatty acids that, given their pro-oxidant character, can promote subsequent oxidation reactions, as a result to protect them from oxygen or light, it is not possible to minimize oxidation processes (1). The results of this study indicate that the degree of oxidation, in these types of oils, can be minimized if the storage temperature is decreased, since this affects the mobility of the molecules. This fact could explain why in our study, the control samples and those kept in an inert atmosphere and in an opaque container, exhibited a greater increase in the value of GA during storage. Peroxide Index (IP)

This parameter provides information on the oxidation state of olive oil. A high value of the IP indicates that the oil contains a considerable amount to its matrix of active oxygen and therefore there can be different oxidation reactions or what is the same the oil can lose its quality more quickly. The IP is expressed as milli equivants of active oxygen per kilogram of oil (meq.0 ₂ / kg of oil).

Figure 3 shows the evolution of this index for the different oil samples stored over a period of sixteen months. All samples, except for control at 16 months of storage, the value of the IP was kept below the legislated limit (red line at 18 meq. 0 ₂ / kg oil). In general, a progressive increase of this parameter is observed, accelerating from the tenth month on most of the samples.

However, it can be clearly seen how the sample pretreated with ultrasound showed the best performance, presenting the lowest values for this index, without reaching 15 meq of 0 ₂ / kg of oil at any time during the period of evaluated storage.

The increase in IP during storage has been observed by other authors (13, 14, 15) in studies based on the effect of light, inert atmosphere and temperature on the storage conditions of olive oil.

In most of the studies reviewed, a progressive increase in this parameter was observed over time, and as in the case of GA, the increase was smaller when oxidizing conditions were minimized. This fact seems to be in apparent contradiction with what is observed in the present study with the instep variety. A possible explanation of this contradiction could be due to the fact that the GA is based on an oil with a relatively high GA (higher than those of the olive oils of the mentioned studies), since this implies a factor to be taken into account. it counts on the increase of autooxidation reactions, even more important than the oxidations promoted by external factors.

K232 extinction coefficient

The K ₂₃₂ index allows the presence of primary oxidation compounds (peroxides and hydroperoxides) to be detected. Figure 4 shows the evolution of the K ₂₃₂ extinction coefficient for the different oil samples during the storage period. The value of the red line corresponds to the limit value that an olive oil can present to be classified as an extra virgin.

The values corresponding to the K ₂₃₂ index increased progressively but moderately throughout the 16 months of the study. In this case, no large differences were observed between the oil sample pretreated with ultrasound and the other samples. In addition, it is interesting to note that the values of this parameter were found, at all times and for all samples, clearly below the maximum legislated value, a fact that can be attributed to the high stability of the olive oil of the Empeltre variety. Other authors have observed gradual increases in this parameter during the storage of olive oils under different conditions (13), in addition to a good correlation with the value of the IP parameter (15).

It should be noted that the sample pretreated with ultrasound, and therefore with a lower oxygen content in the oil matrix, presented values below 2.0 during the entire storage period.

Extinction coefficient K ₂₇ or Unlike the previous parameter, the K ₂₇₀ index allows the detection of secondary oxidation products (aldehydes, ketones, etc.).

The evolution of the extinction coefficient at 270 nm is shown in Figure 5. As the values of K ₂₇₀ can be observed, they do not show significant variations over the storage time, for any of the different storage methodologies tested.

Similar to what was observed with parameter K ₂₃₂ , and taking into account the maximum value (0.22) that an oil can reach without losing the extra virgin rating, it can be seen as the experimental values in all analysis and for all conservation methods are clearly far from this value. No significant differences were observed between the ultrasound treatment and the other treatments for this value. These observations are, in general, in accordance with the works of Di Giovacchino (15), which also did not observe significant changes during the storage of two samples of virgin olive oil, a sample conserved with an atmosphere with inert gas and another with air. In addition, in the study of Caponio (13) where the effect of the presence of light on the conservation of olive oil was analyzed, no significant changes of parameter K ₂₇₀ were also detected over time in the case of an oil sample conserved in opaque container

Oxidative stability Rancimat Method Some researchers claim that the oxidative stability measured from the Rancimat method, despite not being considered a quality parameter, provides valuable information on the shelf life of olive oil (16).

The oxidative stability of an oil is defined as the time necessary for the oil to begin to show symptoms of thickening. This stability depends on the characteristics of the oil, such as the degree of unsaturation, the content of natural antioxidants (polyphenols) and the presence of metal traces, the oxidation state, etc. (14). In addition, this parameter may vary depending on the conditions used for its conservation: temperature, presence of light, presence of oxygen, type of container, etc.

Figure 6 shows the evolution of oxidative stability over time for each of the conservation methods applied. The observed decrease in oxidative stability, for all storage methodologies, could be attributed to the degradation of minor components such as polyphenols or carotenes (14) during the storage period.

However, in figure 6 it is clearly seen how the cold preservation method combined with ultrasound presents, throughout the sixteen months of storage, the highest values for the oxidative stability of olive oils.

Sensory analysis of oil samples packaged under different conditions during the storage period

The initial oil sample used for the procedures called control, inert atmosphere, opaque container and low temperature presented the same values, both for the average of the fruity attribute (5.4) and for the value related to the absence of defects, which the initial sample pretreated with power ultrasound (ultrasound + low temperature).

 Table 3. Sensory analysis of the samples during the storage period

 Storage (months)

 Initial Procedure 3 6 9 12 16

 Defects 0.0 ± 0.0 0.0 ± 0.0 1.4 ± 0.1 1.9 ± 0.1 2.3 ± 0.1 2.7 ± 0.1

(1) Control Frutado 5.4 ± 0.1 4.0 ± 0.2 3.2 ± 0.1 2.7 ± 0.2 2.5 ± 0.1 2.1 ± 0.2

(20 ° C) Rating Virgin Virgin Virgin Virgin Virgin Virgin

 Extra extra

 Defects 0.0 ± 0.0 0.0 ± 0.0 1.0 ± 0.1 1.4 ± 0.1 2.0 ± 0.1 2.4 ± 0.3

(2) Fruity Atmosphere 5.4 ± 0.1 3.7 ± 0.1 3.9 ± 0.1 3.7 ± 0.2 3.6 ± 0.1 2.9 ± 0.1 inert Virgin Rating Virgin Virgin Virgin Virgin Virgin

 Extra extra

 Defects 0.0 ± 0.0 0.0 ± 0.0 1.1 ± 0.2 1.6 ± 0.2 2.0 ± 0.2 2.3 ± 0.2

(3) Fruit Pack 5.4 ± 0.1 3.6 ± 0.1 3.8 ± 0.1 3.5 ± 0.2 3.4 ± 0.1 2.9 ± 0.2 opaque Virgin Rating Virgin Virgin Virgin Virgin Virgin

 Extra extra

 Defects 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0

(4) Low Fruity 5.4 ± 0.1 4.8 ± 0.2 4.7 ± 0.2 4.6 ± 0.1 4.6 ± 0.2 3.8 ± 0.2 temperature Virgin Rating Virgin Virgin Virgin Virgin Virgin

 Extra Extra Extra Extra Extra Extra

Defects 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0 0.0 ± 0.0

(5) Ultrasound Fruity 5.4 ± 0.1 4.9 ± 0.1 5.2 ± 0.3 5.3 ± 0.2 5.6 ± 0.2 3.9 ± 0.3

+ low Rating Virgin Virgin Virgin Virgin Virgin Virgin temperature Extra Extra Extra Extra Extra Extra As can be seen in Table 3, the sensory analysis, corresponding to the third month of storage, for each of the conservation methods reflects that the samples did not show any defects. However, if the values of the positive attributes are analyzed, and we compare them with the values of the initial analysis (median evaluation of the positive attributes = 5.4), it can already be clearly observed as the procedure under which the samples Oil preserves the fruity attribute better corresponds to the preservation at refrigeration temperature (without ultrasonic treatment), as well as to the sample treated with ultrasound + low temperature. In fact, the samples preserved in an inert atmosphere and in an opaque container are the ones that have suffered the most alterations from the organoleptic point of view, since they have a more pronounced decrease in the fruity attribute. This aspect is in accordance with the values of the GA obtained by these samples during the first months of storage.

As can be seen in Table 3, in the organoleptic analysis corresponding to the six months of storage, defects appear for the samples identified as control (20 ° C), and for the samples preserved in modified atmosphere and in total absence of light. For this reason, these samples, in accordance with current legislation, would modify their category, moving from the extra virgin category to the virgin category. On the other hand, as can be seen in Table 3, the samples stored at refrigeration temperature (with and without pretreatment with ultrasound), do not present any defect, staying within the highest-level legislated margins (extra virgin). In addition, if the average of positive attributes is observed, it looks like these are similar to those obtained from the initial sample. And, in fact, it is the sample treated with ultrasound that has the highest median assessment of positive attributes.

In the ninth and twelfth month of storage the results were very similar to those obtained for the sixth month. Thus, for the control samples, inert atmosphere and opaque container defects were detected, slightly increasing the average value of the same in the three samples. While the average of the fruity attribute was decreasing, being the most pronounced decrease in the control sample. On the other hand, the samples kept at low temperature (with and without ultrasound treatment) showed no defects, maintaining an average of 4.6-4.7 fruity for low temperature preservation and 5.3-5.6 for low temperature preservation + ultrasound.

In the sixteenth month of storage, the oils stored at low temperature (with and without ultrasound treatment), from an organoleptic point of view, maintained the category of extra virgin (defects = 0, positive attributes> 0), although the assessment Median positive attributes decreased compared to the analysis performed at 12 months. This decrease was most noticeable in the case of the sample pretreated with ultrasound, going from a rating of 5.6 to 3.9. On the other hand, for the sample kept at low temperature without pretreatment with ultrasound, the evaluation went from 4.6 to 3.8.

The samples kept at 20 ° C (control), under an inert atmosphere and in the absence of light, maintained, after sixteen months, the category of virgin olive oil, since despite the assessment of the negative attributes increased with respect to the control carried out at 12 months, none of the samples exceeded the assessment of 3.5.

The crystallization process of the samples stored at low temperature during the storage period

Analyzing together the results of the physical-chemical and sensory analyzes, carried out throughout the evolution of olive oil conservation, it seems clear that the most appropriate methodology for the conservation of extra virgin olive oil from olives The Empeltre or Mallorcan variety and with an initial degree of acidity of 0.7 is, without a doubt, low temperature conservation. However, it should be noted that when olive oil is within the range of temperatures between 0 and 8 ° C, the formation of a white-yellowish precipitate is observed due to the crystallization of triglycerides (TAGs) , that is, fatty acids.

The variety of fatty acids that form the triglycerides present in olive oil are partly responsible for the complexity of crystallization (17). If it is considered that fatty acids represent approximately 99% by weight of olive oil and that of these the majority (65-80%) is oleic acid, this will be the main component that will condition the process of crystallization of olive oil . Taking into account this important aspect, it was more than foreseeable that the samples kept at refrigeration temperature, as the storage time passed, showed symptoms of crystallization, and in fact, this was clearly observed in this type of samples .

The samples stored at refrigeration temperature, both the one treated with ultrasound and the one that was not treated, as already mentioned in the packaging section, were stored at an approximate temperature of 4-6 ° C. During the periodic analyzes to which they were subjected, as of the fourth month, important differences in the degree of crystallization that both samples presented began to be detected. Thus, in spite of the dark color of the glass, it was observed that the samples preserved at refrigeration temperature without prior ultrasonic treatment presented more crystallization symptoms than the samples preserved at the same temperature, but treated with ultrasonic pulses.

In Figure 7, the difference in the degree of crystallization between an ultrasound treated sample (left test tube) and an untreated sample (right test tube) can be observed after being preserved for a period of 4 months to 4-6 ° C. In this test experience, a modified atmosphere was applied for both samples.

With what has been described above, it is understood that by carrying out a pretreatment with ultrasonic pulses and storing the oil in optimal conditions, it can be a good conservation method, since apart from maintaining the physicochemical and organoleptic properties, the oil is kept longer in state liquid at refrigeration temperature, since it avoids a characteristic problem of oils preserved at low temperature such as the crystallization of fat. Figure 8 shows the clear difference between these samples after 16 months of storage.

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Claims

1. - Procedure to avoid the total or partial crystallization of olive oil during its conservation at low temperature while maintaining the physical-chemical and sensory properties, which includes the application of power ultrasound on said olive oil.

 2. - Method according to claim 1 comprising the steps of:

 a) Application of ultrasonic pulses on olive oil present in opaque glass bottles at a power between 300 and 350 W and at a temperature below 30 ° C;

 b) Elimination of the air present in the internal oil matrix;

 c) Storage of said olive oil at a refrigeration temperature between 4 and 6 ° C.

 3. - Method according to claim 2 wherein the ultrasonic pulses are applied for 10 minutes.

 4. - Method according to any of the preceding claims wherein said olive oil is extra virgin olive oil.

 5.- Olive oil obtained through said procedure.