Türkiye kökenli pirina yağından sıvı-sıvı ekstraksiyonu ile serbest yağ asitlerinin giderilmesi üzerinde bir inceleme

Abstract

- Ill - ÖZET Bu çalışmada, yüksek asitli bitkisel yağlardan pirina yağının yemeklik olarak değerlendirilmesi amacı ile, uygulan ması gereken rafinasyon işlemlerinin ilk aşaması olan serbest yağ asitlerinin giderilmesi üzerind,e çalışılmıştır. Bu konu üzerinde yapılan literatür incelemesine dayanarak, düşük bir nötr yağ kaybı ile asit giderme işlemini gerçekleştirmek ve aynı işlem ile doğrudan doğruya yüksek oranda serbest yağ asitleri içeren bir yan ürün elde etmek amacı ile, pirina ya ğının iki farklı çözücü sistemi ile sıvı-sıvı ekstraksiyonu incelenmiştir. 1- Pirina yağının heksandaki çözeltisinin (misella'nın) çeşitli konsantrasyondaki sulu etil alkol çözeltileri ile ekstraksiyonu, 2- Pirina yağının % 90'lık metanol çözeltisi ile ekstrak siyonu. Misellanın etil alkol ile eks t raks iyonunda, önce piri na yağının serbest asit içeriği, kısmi gliserid içeriği, mi sellanın bileşimi, sulu etil alkol çözeltilerinin bileşimi gibi çeşitli faktörlerin bu işleme etkisi incelenmiştir. Bu deney serisi sonuçlarının değerlendirilmesi ile, düşük bir nötr yağ kaybı ile serbest yağ asitlerinin giderilmesi için misellanın % 70 veya % 80flik etil alkol ile sıvı-sıvı ekst- raksiyonunun uygun olduğu, ancak bu çözücülerin önce heksan ile doyurulması gerektiği anlaşılmıştır. Daha sonra, bir pirina yağı örneği misellasma, hek- sanla doyurulmuş % 70 ve 80flik etil alkol çözeltileri ile çok kademeli doğru ve ters akım ekstraksiyonları uygulanmış ve özellikle ekstrakte edilebilen yağ asitleri miktarının teo rik olarak hesaplanabilen aynı değere genel olarak çok iyi uyduğu saptanmıştır. Buna dayanarak, herhangi bir pirina yağındaki serbest yağ asitlerini istenen oranda gidermek için, gerekli olan çö zücü miktarını ve kademe sayısını ters akım ekstraksiyonu için belirlemek mümkün olmuştur. Bu açıdan yapılan değerlendirmede çözücü olarak % 80'lik etil alkolün ekstraksiyon için daha uy gun olduğu ortaya çıkmıştır. Çalışmanın ikinci kısmında, farklı pirina yağı örnekle rinin % 90'lık metanol çözeltisi ile sıvı-sıvı ekstraksiyonu incelenmiştir.-IV - Bu konu üzerinde yapılan ön deneylerde, birçok haller de pirina yağının % 90flık metanol ile kuvvetli bir emülsiyon oluşturduğu, ancak % 90'lık metanol çözeltisine adi tuz ilave si ile bu emülsiyonun önlendiği ortaya çıkmıştır. Serbest asit içeriği % 35 ile % 60 arasında değişen üç pirina yağı örneği ile aynı koşullarda % 90'lık metanol ile yapılan ters akım ekstr aks iyonu sonunda, herbir örnekte bulu nan serbest asitlerin hemen hemen aynı oranda giderildiği ve bu işlem sırasında trigliserid kaybının pratik olarak yok de necek kadar az olduğu saptanmıştır. Yine bu deneylerin sonunda, pirina yağından % 90'lık metanol ile çekilen ekstrakt fazlarında, serbest yağ asitleri ile metanolün esterleşmesi neticesinde, çok az da olsa yağ asitlerinin metil esterlerinin oluştuğu ve ortamda bulunan tuzun bu reaksiyonu hızlandırdığı anlaşılmıştır. Sonuç olarak, gerek pirina yağı misellasını % 80'lik etil alkol ile ve gerek pirina yağını doğrudan doğruya % 90'- lık metanol ile ekstrakte ederek, düşük bir trigliserid kaybı ile serbest yağ asitlerini gidermenin mümkün olduğu ve nihai rafinasyon için uygun vasıfta ön rafinasyonu bir yağın elde edilebileceği anlaşılmıştır. Ayrıca söz konusu işlemlerde ekstrakt olarak ele geçen ve ortalama olarak % 84-86 oranında serbest asit içeren ürünün teknik oleik asit olarak değerlen dirilebileceği ortaya çıkmıştır. Türkiye'de zeytin tarımı ve zeytin yağı üretiminin po tansiyeli dikkate alınırsa, bu sanayi branşının bugüne kadar çok iyi değerlendirilemeyen bir yan ürünü olan pirina yağın dan hem yemeklik yağ üretimi ve hem de endüstriyel ürünler arasında önemli bir yer olan teknik oleik asit ürpt-imi imkan larına bu çalışmada belli bir açıklık getirilmiştir.

- V- SUMMARY An investigation on the deacidilication of Turkish sulphur olive oil by liquid- liquid extraction In this study, the removal of free fatty acids from the sulphur olive oil with a low refining loss and the recovery of fatty acids as a by-product were investigated. Sulphur olive oil is obtained from the pressed olive cakes by solvent extraction. Even though it originates from the same fruit as the olive oil, which may partly consumed without being refined, most of the sulphur olive oil cannot be neutralized by the classical sodium hydroxide method, as this way of refining is not normally applied to oils containing more than 10 % free fatty acids. The high free fatty acid content of the sulphur olive oil is mainly due to the rapid enzymatic hydrolysis of the tryglicerides during the storage time passed between the pressing and the extraction of the cakes. As a result of this unavoidable change, the free fatty acid content of the oil may increase up to 70 % percent. Sulphur olive oil, therefore, may be considered somehow as a high potential fatty acids source because it may contain most of its component fatty acids readily in a free state. For this reason, the main object of this study being the deacidification of the sulphur olive oil with a low refining loss, but the, recovery of pure grade fatty acids as a by product is also simultaneously considered. Based on the literature survey, two solvent systems were chosen for the removal of free fatty acids with a low loss of neutral oil by liquid-liquid extraction: 1- Extraction of the solution oc the sulphur olive oil in hexane (miscella) with aqueous ethanol solutions, 2- Extraction of the sulphur olive oil with aqueous 90 % methanol solution. At first, in order to determine the effect of different working parameters on the extraction, a series of single stage extraction experiments were carried out. In order to investi gate the effect of free fatty acid content variation of the oil in the system, instead of using directly sulphur olive-VI - oil, synthetically prepared mixtures of olive oil and oleic acid were used and hexane-miscella from these mixtures were extracted with aqueous ethanol solutions at room temperature. In a complementary series of experiments, a sulphur olive oil-miscella was extracted under similar conditions and results thus obtained, especially with 96 % aqueous ethanol, were different from those of the olive oil-oleic acid mixtures, Similarly, when the same sulphur olive oil sample was extracted after 8 months of ageing, results were also different xf rom those of the fresh oil. The difference in these results was mainly due to the impurity content of the sulphur olive oil. This was concluded clearly from the experiments carried out later on the synthetical oil which contained similar free fatty acid content, but with differing partial glycerides content. These experiments proved that the partial glycerides present in the oil, increased the solubility of both free acids and tryglicerides in 96 % aqueous ethanol. However, when the water content of alcohol was increased, the effect of the impurities on the extraction was decreased. In practice, from oils with differing amounts of partial glycerides, nearly equal amounts of free fatty acids were extracted using 80 % aqueous ethanol. Even though the amount of extracted neutral oil was increased slightly under these conditions, the investigation of the extracts by thin layer chromatography showed that only minor amounts of tryglicerides were present in the extract obtained with 80 % aqueous ethanol. Similarly, when the extracts obtained from the sulphur olive oil, using 80 % or more dilute ethanol solutions, were subjected to an analysis by thin layer chromatography, it was found that these extracts also contained impurities, such as partial glycerides, unsaponif iable matter, oxyacids, the main component being the free fatty acids. In practical terms no tryglicerides were lost from the original oil. As a result of these experiments it is concluded that to ensure the deacidification with a low neutral oil loss, it is appropriate to extract the miscella with 70 % or 80 % aqueous ethanol. It was also noted from these experiments that the solvents must be saturated with hexahe before extraction.- VII - Changing oil: hexane ratio in miscella between 1:2 to 2:1 (by weight) did not have any significant effect on the extraction results. Later a sulphur olive oil (with 36,8 % acidity) miscella was subjected to a laboratory scale cross-current multistage extraction with hexane saturated 70% aqueous ethanol. It was observed that the extraction factor related to free acids was constant for each extraction stage. Therefore, the extraction factor determined for the first stage may be used to calculate the extracted free fatty acid percentage for cross-current and countercurrent multistage extraction according to equations 1 and 2 (p. 48) (67). This approach was used to calculate the extracted fatty acid percentages of the multistage cross-current extraction with 70 % and 80 % aqueous ethanol using equation 1. Results thus obtained were in close agreement with the experimental data. For the countercurrent multistage experiments `Batch Simulation of Continuous Processes` was used and the experimen tal results were also in agreement with the calculated values using equation 2. Based on the above results, it is possible to determine the amount of solvent and the number of stages required for countercurrent extraction to remove the desired amount of free fatty acids from a given sulphur olive oil, using 70 % or 80 % aqueous ethanol. Comparison of the results for these two solvents from this point of view showed that 80 % aqueous ethanol was more suitable. In this way, even though it was possible to predict the amount of fatty acids that would be extracted from a given sulphur olive oil in various extraction conditions, it was not possible to predict the amount c- neutral oil applying equations 1 and 2. However, generally the percentage of extracted neutral oil being so small compared with the amount of free fatty acids, it would be, therefore, possible to calculate the yield and composition of the raffinate, and as well as of the extract which would be obtained from a sulphur olive oil- of given composition. In fact, results calculated in this way were found to be in close agreement with the experimental data.-VIII - In the second part of this study, the extraction of different sulphur olive oil samples with 90 % aqueous methanol was investigated. At first the literature survey on the phase diagram data of the sulphur olive oil/free fatty acids/90 % methanol system was done(47). It has been thus noted that the impurity content of the raw oil has a notable effect on the phase diagram. Therefore, it was expected that this phase diagram would vary in accordance with the composition of each individual sulphur olive oil. For this reason, the investiga tion was oriented to study the extraction of different sulphur olive oil samples with 90 % aqueous methanol. In the early stage of the experiments, by the extraction of samples with the highest free fatty acid content, the occurence of a strong emulsion was observed. However, the addition of common salt to the solvent prevented absolutely this emulsion. As base for the orientation of the further experiments, `Batch Simulation of Continuous Processes` was applied for the counter current extraction of 3 different oil samples, with differing free fatty acid content, under similar conditions. As a result of these experiments, the equilibrium distribution diagram (on the solvent free basis) for the sulphur olive oil/free fatty acids/90 % aqueous methanol system was developed, and for each of the oil samples a different equilibrium cujrve was obtained. It was concluded, therefore, that the phase diagram of this system is affected by the individual composition of each sulphur olive oil sample. On the other hand, these experiments showed that an esterif ication reaction between free acids and methanol in the extract phases occurred. It was also observed that the salt present in the medium, increased the rate of this reaction. As an another result of the countercurrent extractions of the sulphur olive oil samples with free acid contents varying from 35 % to 60 % under similar conditions it was concluded that the removal of free acids from each of the samples amounted in similar percentages. At the end of this experiments, the thin layer chromatographic analysis of extracts confirmed that the apparent neutral oil losses in-IX these deacidif ication processes were mainly due to partial glycerides, unsaponifiable matter and other impurity content of the oil. The real triglycerides loss was just minimal. At the last stage of this study, countercurrent extraction experiments for sulphur olive oil samples with similar free fatty acid contents (practically 36 %), using 80 % aqueous ethanol and 90 % aqueous methanol were compared. In the first experiment, solution of 1 part oil and 0,68 part hexane was extracted with 7 parts of hexane saturated 80 % aqueous ethanol in 5 stages. At the end of this extraction, 60,17 parts of a raffinate with 4,0 % free fatty acid content and 39,83 parts of an extract with 86,4 % free fatty acid content were obtained. In the second series of extraction, 6,5 parts of 90 % aqueous methanol (containing 0,2 g NaCl/lt) was used for 1 part of oil in 5 stages and 60,75 parts of a raffinate with 4,40 % free fatty acid content and 39,25 parts of an extract with 83,7 % free fatty acid content were obtained. It was concluded from this comparison that there was no significant difference in the amounts and compositions of the products for both of the solvent systems. As a result of this study, it is showed that the removal of free fatty acids from the high acidity sulphur olive oil can be performed with a low refining factor (1,10-1,12) and a prerefined oil and fatty acids of technical grade can be obtained.