Malaxation Time Research Articles

Effects of Pulsed Electric Field on Yield Extraction and Quality of Olive Oil

The effect of the application of pulsed electric field (PEF) treatments of different intensities (0–2 kV/cm) on Arbequina olive paste in reference to olive oil extraction at different malaxation times (0, 15, and 30 min) and temperatures (15 and 26 °C) was investigated. The extraction yield improved by 54 % when the olive paste was treated with PEF (2 kV/cm) without malaxation. When the olive paste was malaxated at 26 °C, the application of a PEF treatment did not increase the extraction yield as compared with the control. However, at 15 °C, a PEF treatment of 2 kV/cm improved the extraction yield by 14.1 %, which corresponded with an enhancement of 1.7 kg of oil per 100 kg of olive fruits. The application of a PEF treatment could permit reduction of the malaxation temperature from 26 to 15 °C without impairing the extraction yield. Parameters legally established (acidity, peroxide value, K232, and K270) to measure the level of quality of the virgin olive oil were not affected by the PEF treatments. A sensory analysis revealed that the application of a PEF treatment did not generate any bad flavor or taste in the oil.

Modelling of virgin olive oil extraction using response surface methodology

Summary Malaxation of the paste is the most important step for virgin olive oil extraction because it affects both oil yield and quality. In this work the influence of temperature and mixing time on oil yield, quality parameters and oil composition in photosynthetic pigments and total polyphenols is assessed by using Response Surface Methodology. Seven Picual-variety olive samples from two consecutive seasons, with different maturity index, were used. Results show that temperature and malaxation time exert a positive influence in olive yield, with optimal values ranging from 20.1 to 32.2 °C and from 73.3 to 90 min. Oil quality decreased slightly as temperature and time of malaxation were increased. Top quality oils were obtained below 30 °C and shorter mixing time. The oil content in photosynthetic pigments increased with temperature and mixing time, while total polyphenols increased with temperature but decreased with mixing time.

Technological Factors Affecting Sterols in Australian Olive Oils

AbstractSterols are important lipids related to the quality of olive oil and broadly used for checking its genuineness. Recent analyses have identified that some Australian olive oils would not meet international standards for total content of sterols or for certain individual components. Several research works indicate that there are some significant correlations between cultural and processing practices and sterols content and composition. In this work the horticultural and processing practices that may have an impact on the sterol content and profile of the most important Australian varieties were analysed. The information generated with this study aims to solve a legislation problem as well as maximising the nutritional and health benefits of Australian olive oils. The evaluation was undertaken using three different varieties and the processing practices evaluated were: irrigation, fruit size, maturity, malaxing time, malaxing temperature and delays between harvest and process. The total content of sterols and their composition in olive oil is strongly influenced by genetic factors and year. Processing practices particularly affect triterpene dialcohols and stigmasterol while horticultural practices and fruit characteristics tend to affect more significantly other sterols such as β‐sitosterol, sitostanol, Δ5‐avenasterol and Δ7‐avenasterol.

The Activity of Healthy Olive Microbiota during Virgin Olive Oil Extraction Influences Oil Chemical Composition

The activity of olive microbiota during the oil extraction process could be a critical point for virgin olive oil quality. With the aim to evaluate the role of microbiological activity during the virgin olive oil extraction process, just before oil extraction freshly collected healthy olive fruits were immersed in contaminated water from an olive mill washing tank. The oils extracted were then compared with control samples from the same batch of hand-picked olives. The presence of lactic and enteric bacteria, fungi and Pseudomonas on the surface of olives was proved to be much higher in washed than in control olives, with increments in cfu/g between 2 and 3 orders of magnitude. The biogenesis of volatile compounds and the extraction of olive polyphenols and pigments were significantly influenced by the microbiological profile of olives even without any previous storage. In most cases the effect of olive microbiota on oil characteristics was greater than the effect exerted by malaxation time and temperature. Oils from microbiologically contaminated olives showed lower amounts of C5 volatiles and higher levels of C6 volatiles from the lipoxygenase pathway and some fermentation products. On the other hand, a decrease of chlorophylls, pheophytins, xanthophylls and the ratio chlorophyll/pheophytin was observed in these oils. Likewise, the microbiological activity during oil extraction led to significantly lower amounts of polyphenols, in particular of oleuropein derivatives. These differences in olive oil chemical composition were reflected in oil sensory characteristics by the decrease of the green and bitter attributes and by the modification of the oil color chromatic ordinates.

Hydrophilic antioxidants of virgin olive oil. Part 2: Biosynthesis and biotransformation of phenolic compounds in virgin olive oil as affected by agronomic and processing factors

The biosynthesis of the phenolic fraction of olive fruits during ripening and the transformations occurring in this moiety during virgin olive oil (VOO) extraction are discussed in this paper. The influence of agronomical factors that can significantly affect the phenolic profile of VOO is also discussed. Particularly, it is worth emphasizing the role of genetic factors, cultivation and climatic conditions such as water availability, atmospheric temperature, altitude, health status of the fruits, alternate bearing in the olive, and some processing factors such as crushing, malaxation time and temperature or volume of water added during milling. Among these parameters, special attention has been paid to genetic factors due to the high variability observed among Olea europaea genotypes for all recorded traits. In this context, interesting experimental results have been obtained with cultivated and wild olive trees, and also with segregating populations resulting from olive breeding programs. To the authors' knowledge, reviews evaluating the influence of the main factors that contribute to the profile of hydrophilic phenols have not been previously published. The discussion concerning olive breeding programs is a major and novel aspect to be emphasized considering recent trends to obtain new olive cultivars that confer better organoleptic properties and better quality to VOO.

Optimization of the Abencor system to extract olive oil from irrigated orchards

AbstractStudying the composition of olive oil requires cold‐press olive oil extraction. One of the most common laboratorial mills is the Abencor system. However, its operation protocol was formulated decades ago for Spanish olive varieties from traditionally rain‐fed orchards. We modified this protocol for use with “Barnea” and “Picual” olives from irrigated orchards that are characterized by high water content. Independent effects of malaxation time, temperature, water addition and talc addition on extraction efficiency, and major quality indices of virgin olive oil were studied. Overall, addition of talc to the fruit paste was the most significant treatment in terms of yield and quality of the oil although its effect was cultivar dependent. Improved oil yield was particularly significant for “Picual.” Extended malaxation time was also effective in improving oil extractability. Addition of talc generally improved oil‐quality parameters, while water addition had the opposite effect. Yet, quality parameters remained within the extra virgin level. Temperature increments reduced oil quality. The need to adapt a modified protocol for use with fruits from irrigated orchards that will facilitate critical comparison of results obtained from different agronomic theses and different laboratories is highlighted. It is recommended that each laboratory develops an appropriate protocol for the operation of the Abencor system in accordance to the characteristics of the olive fruit they are working with.Practical applications: Abencor system serves as the major laboratorial mill world‐wide. Those mills allow the researchers to characterize olive oil in accordance to the treatments received by the trees. This cannot be done in commercial mills. The system operation protocol was established decades ago for fruits from rain‐fed orchards. In the past decade there was a rapid increase in the use of irrigation in olive orchards and therefore it is crucial to optimize the operation protocol for fruit with relatively high water content. In the current work we have evaluated the influence of a series of technological parameters (i.e., talc and water addition, malaxation time, and temperature) on the extraction efficiency and quality indices of olive oil. This allowed us to present a modified protocol for the Abencor system operation suitable for olive fruit of irrigated orchards that will facilitate a reliable representation of the influence of different treatments on the yield and characteristics of the olive oil.

Influence of olive paste preparation conditions on virgin olive oil triterpenic compounds at laboratory-scale

The influence of olive paste preparation conditions on the triterpenic content of virgin olive oils from Arbequina and Picual cultivars was investigated. For this purpose, three sieve diameters of the hammer mill (4, 5, and 6 mm), two malaxation temperatures (20 and 30 °C), and two malaxation times (20 and 40 min) were tested. Results obtained showed that for Arbequina oils, a finer crushing level resulted in higher maslinic acid and erythrodiol content. Increasing malaxing temperature and time lead to a rise in both oleanolic and maslinic acid concentration, whereas erythrodiol content increased only for the longer malaxation time. For Picual oils, higher concentrations of oleanolic acid, maslinic acid, and uvaol were obtained by prolonging the paste malaxation time. A finer crushing level resulted also in an increase of maslinic acid content. These findings suggest that virgin olive oil triterpenic composition can be improved by regulating olive paste preparation conditions.

Effect of Malaxation Conditions on Phenol and Volatile Profiles in Olive Paste and the Corresponding Virgin Olive Oils (Olea europaea L. Cv. Cornicabra)

Malaxation of olive paste must be considered to be 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. A combined study of the effect of kneading temperature and time on the minor composition of olive paste and its corresponding virgin olive oil, processed in an experimental oil mill (Pieralisi, Fattoria) with a working capacity of 200 kg/h, is reported. A large drop in the oleuropein content in the olive paste with respect to its initial content in the olive fruit (between 92 and 96%) was observed, which suggested its almost total degradation during the crushing operation. The major phenolic compound found in the olive paste during kneading was the dialdehydic form of elenolic acid linked to hydroxytyrosol (3,4-DHPEA-EDA, always higher than 60% of the total phenols). This greatly decreased during malaxation (from 5505 to 2317 mg/kg, on average). The content of phenolic compounds in virgin olive oil was much more affected by the malaxation temperature than the kneading time. For instance, the 3,4-DHPEA-EDA content increased by 220-630% in the two batches when the temperature was increased from 20 to 40 degrees C. A reduction in the C6 aldehydes was found in virgin olive oil as the malaxation temperature increased, especially in E-2-hexenal (30% reduction). In contrast, C6 aldehydes in the oils from the oil mill plant significantly increased as the malaxation time increased from 30 to 90 min, chiefly E-2-hexenal (about a 70% increase).

The effect of citric acid on the phenolic contents of olive oil

Abstract Response surface methodology was used to optimise the combined effects of malaxation time (t) and aqueous citric acid solution (CA) added at the beginning of the malaxation step on total polyphenols (TP) and o-diphenols (OD) content and the antiradical power (ARP) of the olive oil extracted from the Italian olive fruits of Coratina cultivar. Different tests were performed according to a 32 full factorial design, varying t from 30 to 90 min and the CA from 5 to 15 ml/kgpaste. Overall optimal conditions identified by a numerical optimisation for the three responses were found to be at t = 30 min and CA = 13.79 ml/kgpaste under which the model predicted TP = 604.52 μgCAE/goil, OD = 80.44 μgCAE/goil and ARP = 28.73 μgDPPH/μlextract. There were also linear correlations between TP (R2 = 0.8176) and OD (R2 = 0.8633) values of olive oil and waste water. The results of this study demonstrate that considerably short malaxation time and relatively small amounts of citric acid were required to enhance the quality of olive oil. The outcome of our study will therefore be of great value for the commercial production of olive oil with high level of polyphenols and o-diphenols.

OLIVE PASTE CONSISTENCY AS A CONTROL PARAMETER FOR OIL EXTRACTION: A PRELIMINARY APPROACH

Malaxation is a critical step of olive oil extraction process as it can largely affect the extraction yield along with product quality. At present, malaxation control is based upon accumulated empirical results and the experience of the operators. There are evidences that this method rarely point out the olive-paste state suitable for oil extraction. The paper reports the results of a laboratory investigation aimed to verify the feasibility of using the olive paste consistency variation during malaxation as a parameter representing the right state for oil extraction. Olive pastes consistency evaluation was performed with a rotational rheometer. Oil extraction yield was evaluated by means of an extractability index (EI) determined by laboratory centrifugation of the paste. The effect of different malaxation time and pastes humidity was investigated. Both malaxation time and humidity increments involve significant decrements of paste consistency and a simultaneous increase of EI. A good linear correlation among paste consistency and EI has been found, i.e. a large proportion of EI variance, about 90%, can be explained in terms of paste consistency variation during malaxation. The availability of a measurable parameter representing the paste state suitable for oil extraction could allow to implement a “closed-loop” control system for extraction yield maximization.

Optimisation of olive oil extraction by means of enzyme processing aids using response surface methodology

The aim of the present work was to optimise the oil extraction process of the Italian olive fruits of Coratina cultivar using a previously selected enzyme formulation. To this purpose, the combined effects of the malaxation time ( t) and the concentration of the enzyme formulation ( C E), added at the beginning of the malaxation step, were investigated by a 3 2 full factorial design combined with response surface methodology, selecting the concentration of total polyphenols (TP) and o-diphenols (OD), the oil extraction yield ( Y) and the antiradical power (ARP) as the response variables. The model enabled us to identify the optimum operating conditions ( t = 91.64 min and C E = 25.00 mL/kg paste), under which it predicted TP = 844.30 μg CAE/g oil; OD = 120.80 μg CAE/g oil; ARP = 24.93 μg DPPH/μL extract and Y = 15.72 g oil/100 g paste. These results, which were confirmed by additional tests performed within the selected ranges of variables, suggest that the use of the proposed enzyme treatment could enhance quantity and quality levels of the product.

Effect of Processing Conditions, Prestorage Treatment, and Storage Conditions on the Phenol Content and Antioxidant Activity of Olive Mill Waste

The impact of two- and three-phase processing systems and malaxation conditions on phenol content (both total and individual phenols) and antioxidant capacity of laboratory-generated olive mill waste (OMW) was assessed. Two-phase olive processing generated a waste with higher phenol content and antioxidant capacity. Using the two-phase system, both malaxation time and temperature affected the phenol content and antioxidant capacity. The effects of different prestorage drying treatments on phenol content and antioxidant capacity were also compared. Air drying and drying at 60 degrees C resulted in a substantial decrease in the phenol content and antioxidant capacity. Drying at 105 degrees C and freeze-drying produced less degradation. The phenol content and antioxidant capacity of OMW stored at 4 degrees C and of OMW preserved by 40% w/w ethanol and 1% w/w acetic acid and stored at 4 degrees C were monitored for 30 days and compared with those of OMW stored at room temperature. None of these storage conditions could prevent the rapid decrease in phenolic concentrations and antioxidant capacity, which happened within the first 24 h.

High-power ultrasound in olive paste pretreatment. Effect on process yield and virgin olive oil characteristics

The effect of high-power ultrasound on olive paste, on laboratory thermo-mixing operations for virgin olive oil extraction, has been studied. Direct sonication by an ultrasound probe horn (105 W cm −2 and 24 kHz) and indirect sonication with an ultrasound-cleaning bath (150 W and 25 kHz) were applied and their effects compared with the conventional thermal treatment. A quick-heating of olive paste, from ambient (12–20 °C) to optimal temperature conditions (28–30 °C), and an oil extractability improvement were observed when applying sonication. Better extractability was obtained by direct sonication for high moisture olives (>50%) whereas indirect sonication gave greater extractability for low moisture olive fruits (<50%). Optimal application of ultrasound was achieved with direct sonication for 4 min at the beginning of paste malaxation and with indirect sonication during the malaxation time. Effect of high-power ultrasound on oil quality parameters and nutritional and sensory characteristics were studied. Changes in quality parameters (free acidity value, peroxide value, K270 and K232) were not found, however significant effects on the levels of bitterness, polyphenols, tocopherols (vitamin E), chlorophyll and carotenoids were observed. Oils from sonicated pastes showed lower bitterness and higher content of tocopherols, chlorophylls and carotenoids. Related to sensory characteristics, off-flavour volatiles were not detected in oils from sonication treatments. Total peak areas of volatiles and the ratio hexanal/ E-2-hexenal, as determined by SPME analysis, were lower than non-sonicated reference oils; sensory evaluation by panel test showed higher intensity of positive attributes and lesser of negative characteristics than those untreated.

Partition of phenolic compounds during the virgin olive oil industrial extraction process

Phenolics have been considered an important group of natural antioxidants. The type and quantity of phenolics vary in olive matrices (leaves, fruit, stones, seeds, and paste). However, the relationships linking the products from the olive oil extraction process are poorly studied. This manuscript deals with the partition of phenolic compounds during olive oil production season at three times. Samples were taken during malaxation to determine the phenolic content in the olive paste at 0, 15, and 45 min. The wet pomace and oil phases were analyzed and the phenolics quantified in terms of kilogram of olive paste. Malaxation time had an important effect on the alcohols and secoiridoids. Hydroxytyrosol and tyrosol decreased, and their hydrophilic character was proved through their presence in the wet pomace and wastewater. Oleuropein and ligstroside degradation results in the formation of secoiridoid derivatives, mainly the dialdehydic form of elenolic acid linked to hydroxytyrosol (3,4-DHPEA-EDA). A molar transfer index (MTI) was established between the 3,4-DHPEA-EDA in the olive paste and olive oil (as the liquid phase) and wet pomace (as the solid phase). An increasing trend was observed for the molar transference to virgin olive oil with the advance of the crop season.

Changes in Volatile and Phenolic Compounds with Malaxation Time and Temperature during Virgin Olive Oil Production

Virgin olive oils produced at wide ranges of malaxation temperatures (15, 30, 45, and 60 degrees C) and times (30, 60, 90, and 120 min) in a complete factorial experimental design were discriminated with stepwise linear discriminant analysis (SLDA) revealing differences with processing conditions. Virgin olive oils produced at 15 and 60 degrees C for 30 min showed the most significant (p < 0.01) differences. Discrimination was based upon volatile and phenolic compounds detected in olive oils, peroxide value (PV), free fatty acids (FFA), ultraviolet (UV) absorbances, and oil yield. There were different discriminating variables for processing conditions illustrating the dependence of virgin olive oil quality on malaxation time and temperature. Volatile compounds were the dominant discriminating variables. Common oxidation indicators of olive oil (PV, K232, and K270) were not among the variables that significantly (p < 0.01) changed with malaxation time and temperature. Variables that discriminated both malaxation time and temperature were hexanal, 3,4-dihydroxyphenyl ethyl alcohol-decarboxymethyl elenolic acid dialdehyde (3,4-DHPEA-DEDA) and FFA, whereas 1-penten-3-ol, E-2-hexenal, octane, tyrosol, and vanillic acid significantly (p < 0.01) changed with temperature only and Z-2-penten-1-ol, (+)-acetoxypinoresinol, and oil yield changed with time only. Virgin olive oil quality was significantly influenced by malaxation temperature, whereas oil yield discriminated malaxation time. This study demonstrates the two modes of hexanal formation: enzymatic and nonenzymatic during virgin olive oil extraction.

Varietal and processing effects on the volatile profile of Australian olive oils

The volatile profile of virgin olive oils was established using SPME and gas chromatography(-mass spectrometry). The major volatile in approximately 50% of the oils was E-hex-2-enal in contrast with European oils. The minor contribution of C5 compounds to the volatile profiles also contrasted with data on European oils. Hierarchical Cluster Analysis (HCA) implicates variety as the single-most important factor in determining volatile profile whilst malaxation time and temperature exerted a minor secondary effect on the volatile profile.

Effect of olive paste kneading process time on the overall quality of virgin olive oil

AbstractThe influence of the olive paste malaxation time on the composition and the industrial output of oil was investigated. To this purpose, three Italian olive varieties (Leccino, Dritta, Caroleo) were processed with a centrifugal system for six malaxation periods (0, 15, 30, 45, 60 and 75 min). The concentrations of the majority of the oil constituents changed during the malaxation. However, these changes were not significant for all of them: the contents of β‐carotene, the major xanthophylls, chlorophylls a and b, pheophytins a and b in the oils increased progressively with increasing malaxing times, whereas the contents of simple and hydrolysable phenols (secoiridoid derivatives), o‐diphenols and total phenols decreased. A significant increase in total volatiles and green volatiles of the lipoxygenase cascade (C6 aldehydes, C6 alcohols, C5 alcohols and C5 carbonyls) was detected. An opposite trend was observed for the green C6 esters. As a result, the global analytical quality, flavour, aroma and shelf‐life of the oils were negatively affected. The oil yield increased substantially up to 45 min of paste malaxation times. Beyond 60 min, the yields tended to decrease.

Influence of malaxation time of olive paste on oil extraction yields and chemical and organoleptic characteristics of virgin olive oil obtained by a centrifugal decanter at water saving

Experimental tests were carried out to ascertain the influence of malaxation time of olive paste on extraction yields and qualitative characteristics of virgin olive oils obtained by a centrifugal decanter at water saving. Results show that malaxation time has to be no less than 45 minutes to have a satisfactory oil extraction yield. Furthermore, it was ascertained that the malaxation time, protracted up to 90 minutes, does not have influence upon qualitative and organoleptic characteristics of oils. Only the total phenols content of oils changed significantly when the malaxation time of olive paste increased from 15 to 90 minutes. However, in this research has been demonstrated that in some cases the total phenols content of oils increased during the first 30-45 minutes of malaxation and after it diminished. This is due to the variation of total phenols content of vegetable water that in the first time increased and after diminished very quickly. Because of the partition equilibrium law, the total phenols content of oil changed in the same way. Finally, results show that the composition of volatile substances of head-space of oils did not change increasing the malaxation time of olive paste obtained from good quality olive fruits.

Volatile profile of olive oils.

The volatile components of olive oil have been studied from several perspectives: qualitative and quantitative description of the volatile profile; relating specific compounds to sensory perceptions; influence of processing variables such as malaxation time, temperature and mill types; and the biogenesis of volatiles. Of these, current and future research are focussed on a fundamental understanding of the biogenesis of olive volatiles and the effect of processing variables. Most studies have emphasised the C-6 and C-5 volatile compounds and in European oils E-2-hexenal is the major volatile, which preliminary data suggest may not be the case in Australian oils.

Influence of malaxation temperature and time on the quality of virgin olive oils

To study the influence of operative conditions adopted during the malaxation of pastes on the quality of resulting oils, we compared sensory characteristics, secoiridoid compounds and the volatile composition of oils extracted from homogeneous batches of olive fruits from Coratina and Frantoio cultivars by using different malaxation times and temperatures. Malaxation time, and especially temperature, negatively affected the intensity of sensory attributes and the content of secoiridoid compounds, modified the composition of metabolites arising from lipoxygenase (LOX) pathways, reducing volatile compounds displaying pleasant sensations and increasing those giving less attractive perceptions, and also elevated the production of 2-methyl butanal and 3-methyl butanal through amino acid conversion. Low temperatures and times, ranging between 30 and 45 min, according to the rheology of the olive pastes, were the optimal operative conditions for the malaxation.