In the following phase, called malaxation, the oil particles combine into bigger droplets, preparing the paste for the next phase — oil separation. The paste goes in a horizontal centrifuge, or decanter, which divides the oil from the pomace and the vegetation water. It will then pass through a second centrifuge, which dries it further, ensuring a better preservation of the product.
Guide to tasting. How to choose olive oil. Our oils. The amount of water to be added is decided by the foreman, depending on the olive cultivar and the physical characteristics of the harvested olives, with best results varying from The addition of water increases yield but also results in an increase of the amount of olive mill wastewater OMW Thus, a relatively new centrifugation process has been implemented in modern olive mills to avoid contamination.
It is the so-called two-phase decanter that does not need the addition of water. The new decanters, which hardly consume water — only L per kg paste if olives are very dry - do not show significant differences compared with three-phase decanters regarding quality parameters, purity criteria and a general sensory assessment. The only exception is the bitterness perception due to a noticeably higher amount of phenols as consequence of the absence of water during the centrifugation process.
Irrespective of the process used for oil extraction pressure, percolation or centrifugation , a final centrifugation of the VOO is needed to remove water and small solids from the oil. This process is carried out in vertical centrifuges that rotate at high speed rpm. Warm water is added to clean the oil of fine solids. The technician can adjust the ring size to adjust the phase separation point and hence the oil-to-water ratio at the exit.
Temperature and throughput are the other variables to be controlled. A low temperature can cause oil losses with the vegetable water, while an excessive temperature will produce an oil lacking in pleasant flavor. Oil will be insufficiently cleaned if not enough water is added. The objective of this step is to obtain cleaned oil with less than 0.
The whole process produces VOO, which is stored in large storage tanks that protect the oil from oxidation, and by-products. Although VOO does not have to be filtered prior to bottling, some consumers do not purchase bottles that show some sediment at the bottom despite the fact that filtered oils are less stable because some of the water-soluble components mostly phenols are removed. Diatomaceous earth is the commonly used filter aid. Glass is the ideal olive oil container as it is recyclable, impermeable to oxygen, allows airtight closure, does not transmit anything into the oil, and colored glass blocks light.
The oil is usually bottled with nitrogen to extend the shelf life. OMW is a dark red, acidic pH 4. The pollution impact of OMW, together with the potential economic interest of some of its constituents mostly phenols , has increased the interest in olive mill wastewater management. Olive pomace from a two-phase decanter has to be heated to a high temperature, due to the moisture content, and it increases the cost and also the risk of generating polycyclic aromatic hydrocarbons PAH.
The de-oiled pomace can be used as agricultural fertilizer due to its high content of organic matter and mineral elements N, P, K. Another alternative is the use of the pulp for animal feed and the stone fragments as fuel or in the manufacture of furfural or active carbon. Introduction The first olive oil producer was primitive man who employed a stone mortar to squeeze fallen olives and noticed that oil was released ca.
Olive Harvesting Olive picking is an important operation that affects virgin olive oil VOO quality since its sensory quality depends on the health and ripeness of the harvested olives.
Olive Batch Cleaning The current harvesting process does not prevent the accidental collection of foreign materials with the olives. Olive Crushing Cleaned and washed olives are then put on a moving belt to the processing zone of the olive mill. Olive Paste Malaxation Metal crushers can cause emulsions that lower yield, but the mixing or malaxation operation diminishes this effect by causing the droplets produced by crushing the olives to coalesce, thereby increasing the percentage of available oil.
Liquid-Solid Separation The main constituents of olive paste are liquids - olive oil and olive mill wastewater OMW - and solids such as small pieces of kernel and tissues.
Liquid-Liquid Separation Irrespective of the process used for oil extraction pressure, percolation or centrifugation , a final centrifugation of the VOO is needed to remove water and small solids from the oil. Virgin Olive Oil Storage The whole process produces VOO, which is stored in large storage tanks that protect the oil from oxidation, and by-products.
Virgin Olive Oil Filtration Although VOO does not have to be filtered prior to bottling, some consumers do not purchase bottles that show some sediment at the bottom despite the fact that filtered oils are less stable because some of the water-soluble components mostly phenols are removed. Virgin Olive Oil Bottling Glass is the ideal olive oil container as it is recyclable, impermeable to oxygen, allows airtight closure, does not transmit anything into the oil, and colored glass blocks light.
Advantages and disadvantages of the olive mill process. Chemical and sensory variables affected by the processes Process Advantages Disadvantages Harvesting by shakers Low-cost harvesting. Better harvesting for olives and trees. If the amount of olives delivered at the olive mill is higher than olive mill capacity, olives will have to be stored days before processing.
Washing Cleans olives. Removes earth, mud, leaves, twigs etc. Protects machinery against mineral materials. Avoids undesirable sensory attributes. Loss of olive oil in case of overripe olives. Need for a water recycling system. Crushing by metal crushers Low cost.
High hourly working load. There are several kinds of crushers at various speeds. Can produce emulsions. Lower amount of volatiles than old granite crushers.
Mixing Essential process. Automatic control of time and temperature. Can work with inert atmosphere N 2. Some olives need the addition of adjuvants micronized mineral talc. Low investment. The most significant changes were observed for the antioxidant capacity with a drop of The phenolic compound content decreased by A decrease in the content of most phenolic compounds was also observed, which could explain at least in part the loss of antioxidant capacity.
This may be due to the loss of hydroxytyrosol, and the decrease of secoiridoid compounds, since they are compounds with a high antioxidant capacity.
Making an individual analysis of the phenolic compounds during storage, it is worth highlighting the total disappearance of hydroxytyrosol. On the contrary, tyrosol, flavones and cinnamic acid have a slight increase in their content. The effect of filtration on the characteristics of the olive oil samples was evaluated. For this purpose, the characteristics of filtered and unfiltered samples were compared. The quality parameters, sensory data, and phenolic and volatile compound content in the filtered and unfiltered oil samples are presented in Tables 1 — 3.
After oil filtration, slight but significant differences were observed. The acidity and K value decreased slightly and the peroxide index increased by In contrast, the photosynthetic pigment content was reduced during the filtration process.
The chlorophyll concentration decreased by This means that the cellulose acetate filter collects a very important fraction of photosynthetic pigments. These results are consistent with those reported by Gordillo et al. Although the quality parameters underwent some changes, the category of the olive oil was not changed by the filtration process.
The antioxidant capacity was also similar in both cases. The results of the volatile compounds are presented in Table 2 , and are represented in Figure S2 A. The volatile compounds were analyzed separately to detect any differences between the unfiltered and filtered samples. Overall, no major differences were observed between the two samples, except for some compounds.
E Hexenal, Z hexenol, and Z hexenyl acetate were found in greater proportion in the unfiltered sample; in contrast, Z pentenol, 3-pentanone, and E pentenal were detected in smaller proportion in the unfiltered sample.
The amount of six-carbon-atom volatile compounds decreased after filtration; however, the amount of five-carbon-atom volatile compounds increased after the filtration process. Although the observed differences are minor, they still reveal a slight trend. These results are similar to those previously reported in the literature by Bottino et al. The results obtained from the analysis of phenolic compounds are shown in Table 3 , and are represented in Figure S2 B.
The total amount of phenolic compounds was similar in both filtered and unfiltered samples. Certain similarities exist in both samples, except for some particular compounds. Larger amounts of luteolin and p -coumaric acid were detected in the unfiltered sample, results similar to those obtained by Bakhouche et al.
On the other hand, oleacin and 3, 4-DHPEA-EA were found in smaller proportion in the unfiltered sample, although they are not significant differences. All other phenolic compounds presented no differences in the filtered and unfiltered samples. Also, the type of filter used in the filtration process can be affected the content of phenolic compounds, according to results obtained by Bakhouche et al.
The use of centrifugation, storage in order to decant and filtration in an industrial olive mill have the function of to clean and to clarify olive oils.
The olive oil category was not changed after the centrifugation, storage and filtration processes with slight changes in the fruitiness, bitterness and pungency. However, centrifugation, storage and filtration produced some significant changes found in the quality parameters and minor composition. A relevant result was how the content of phenolic compounds was affected by centrifugation. A reduction in the concentration of these compounds was observed after the vertical centrifugation process.
This is probably the result of the transfer of hydrophilic phenols from the oil to the water phase. Centrifugation led to a It should be noted that a significant decrease of A small number of differences were detected after oil filtration, with no differences in the sensory characteristics.
The total amount of phenolic compounds and volatile compounds from the LOX pathway was similar in both filtered and unfiltered samples; furthermore, the antioxidant capacity exhibited a similar trend to the phenolic compound content. On the contrary, the photosynthetic pigment content decreased after the filtration process.
From these results, it is concluded that the water addition in the vertical centrifugation and the time of storage of olive oils should be reduced in order to avoid the decrease of the antioxidant capacity and phenolics compounds.
Figure S1. Comparison of the volatile A and phenolic B compound content in oil before and after centrifugation. Data at the decanter exit and centrifuge exit. The error bars show the standard deviation. Figure S2. Comparison of the volatile A and phenolic B compound content in unfiltered and filtered oil. Data at the unfiltered and filtered oils. Supplementary Materials. Vidal et al. This is an open access article distributed under the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Article of the Year Award: Outstanding research contributions of , as selected by our Chief Editors. Read the winning articles. Journal overview. Special Issues. Guest Editor: Nabil Ben Youssef. Received 17 Aug Accepted 23 Jan Published 18 Feb Abstract Centrifugation, storage, and filtration of olive oil were evaluated in an oil mill to determine their effect on the final quality of virgin olive oil.
Introduction Virgin olive oil VOO is a fat known worldwide for its beneficial properties for human health. Materials and Methods 2. Raw Material Olive fruits Olea europaea L. Analysis of Olive Oil Quality Parameters The free acidity, peroxide index, and extinction coefficients K and K were determined according to the European Union standard method [ 26 ].
Analysis of Volatile Compounds The volatile compounds were quantified by following the method previously described by Vidal et al. Determination of the Antioxidant Potential The antioxidant potential was determined according to the method described by Vidal et al. Sensory Analysis A panel formed by highly experienced people carried out the quantitative descriptive sensory analysis of the EVOO. Statistical Analysis The results were processed with the StatGraphics Centurion software, version Results and Discussion Olives were characterized by a MI of 1.
Table 1. Quality parameters and sensory characteristics for the oil samples before and after vertical centrifugation, storage, and filtration. Table 2. Table 3. References M. Parkinson and S. Tsimidou and D. Altieri, F. Genovese, A.
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