Pamuk tohumu yağının yeni bir yöntemle yönlendirilmiş interesterleşmesi

Abstract

Yağlar, kullanım alam olarak önemli bir yere sahiptir. Bu nedenle yağ ve yağ asitleri reaksiyonlanda önem kazanmaktadır. Bu çalışmada trigliserid yağlarda, yönlendirilmiş interesterleşme reak siyonu incelenmiştir. înteres teri eşme reaksiyonu bir yağın veya yağ asıti esterinin alkoller, yağ asitleri veya diğer esterlerle yeni bir ester vermek üzere yağ asidi gruplarının yer değiştirmesiyle o- luşan bir reaksiyondur. Bu çalışmada yağ olarak rafine edilmiş pamuk yağı kullanılmış tır. Pamuk yağı aynı iyod değerine sahip diğer yağlar içerisinde, doymuş yağ asiti içeriği bakımından daha zengin olduğu için seçil miştir, interesterleşme reaksiyonu inert bir ortamda sodyum metok- sit katalizörü varlığında gerçekleştirilmiştir. İnteresterleşme reaksiyonu yürütülürken, katı yağ fraksiyonla rının reaksiyon ortamında oluşturulan düşük temperatürdeki bir yüzey üzerinde toplanması ve bu şekilde interesterleşme reaksiyonunun yön lendirilmesi amaçlanmıştır. Soğutma çubuğu kullanılarak ve zaman za man katı yağ fraksiyonlarının uzaklaştır! İmasıyla, reaksiyon sonunda elde edilen katı ve sıvı yağların iyod değerleri tespit edilmiştir. Aynı koşullarda katı yağ fraksiyonlarını uzaklaştırmadan reaksiyon tekrarlanmıştır. Buradan elde edilen sonuçlara göre ortamdan katı yağ fraksiyonlarının uzaklaştırılmasının reaksiyon üzerinde etkili olduğu tespit edilmiştir.

Fats and oils are water-insoluble substance of plant or animal origin.. The word fat is ordinarily used to refer to triglycerides structually, a triglyceride is the condensation product of one mole cule of glycerol with three molecules of fatty acids to yield three molecules of water and one molecule of triglyceride. When the three fatty acids are the same, the product is a simple triglyceride; when they are different, it is a mixed triglyceride. Monoglycerides and diglycerides contain only one or two fatty acids, respectively, and consequently have two or one free hydroxy! groups. The naturally occuring fatty acids are in general normal mono basic aliphatic compounds, consisting of a single carboxyl group at tached to the end of a straight hydrocarbon chain with some excepti ons, most fatty acids found in nature contain an even number of car bon atoms. The individual acids differ from one another primarily in the number of carbon atoms in their chains, and the number and position of the ethylenic linkages or. double bonds between the carbon atoms. Those fatty acids in which all carbon atoms in the chain con tain 2 hydrogen atoms and thus contain no double bonds are tened saturated. The fatty acids which contain double bonds are tened unsaturated. The degree of unsaturation of an oil depends upon the average number of double bonds in fatty acids. The more common fatty acids are usually referred to by a trivial name such as lauric, palmitic, or oleic. The chemical reactions of fats and fatty acids that are impor tant. Because they are employed in the manufacture of commercial products. Unlike most edible materials, fats and oils suffer rela tively little spoilage or, deterioration from bacterial action. Most of the damage incurred by fats in storage is the result of at mospheric oxidation. For this reason, particular attention will be given to the reaction occuring between fats and the oxygen in the air. The term "interesterification" refers to that class of reacti ons in which a fat or other material composed of fatty acid esters is caused to react with fatty acids, alcohols or other esters with the interchange of fatty acid groups, to produce a new esters. Thus the reaction of an ester with an acid is called "acidolysis" the reaction of an ester with an alcohol is called "alcoholysis" and the reaction of one ester with another is "ester interchange" or "transesteri f ication". înteresterifi cation can change the composition and properties of a fat, simply by changing the arrangement of the different fatty acid radicals in the triglyceride molecules. Of the many possible arrangements, the one corresponding with completely random distribu tion of the fatty acid radicals is always approached when a given fat is interesterified by the processes previously known, in comp letely molten condition. In contrast, the method of directed inter- esterif i cation at temperatures low enough to cause fractional crystal lization. In the study we use transesteri f i cation reaction. The reaction between two esters to produce two other esters was described by Friedel and Crafts in 1865, but has nat been used as much as alcoholy sis. The same general principles apply, as to reversibility of the reaction and means for driving the reaction to completion. Without a catalyst, a reaction time of several hours at temperatures above 250°C is required to bring two typical esters to equilibrium. Acid, alkaline or metal catalysts are used. Tin compounds, especially stannous hydroxide have been mentioned frequently as catalysts. ? More effective at lower temperatures are the acid catalysts such as sulfu ric acid and sulfonic acids; and especially the alkaline catalysts such as sodium alkoxide. With an alkaline catalyst, ester-ester in terchange can be carried out at temperatures as low as 0°C. Acid value of triglycerides must be less than 1%. Because the free fatty acids in glycerides can destroy the alkaline catalyst. It is essential that no water be present to form soap and the ca-. talyst be rapidly dispersed through the reaction mixture immediately after it is added. The process of directed interesterification as developed by Eckey is far more versatile than random rearrangement; By conducting rearrangement and at the same time continuously removing the trisa- turated glycerides that are formed (by crystallization); it is pos sible to concentrate the saturated acids in a fat largely in to a trisaturated glyceride fraction. In this study we use cottonseed oil as a triglyceride in the reactions. Cottonseed oil a by product of the growing of cotton, is one of the most important edible oils in the world cottonseed oil is used in the preparation of shortenings and margarines and as a coo king and salad oil. Cnnte cottonseed oil, derived largely from the seeds of the plants. Gassypium hirtusutum (American) or Go'ssypium barbodense (Egyption), has a strong characteristic flavor and odor and a dark, reddish brown color from the presence of highly colored material extracted from the seed. The whole seed contains 15-24% vi oil and the kernel about 30-38%, most of the oil is obtained by pres sing, but solvent extraction methods are becoming increasingly impor tant. The free fatty acid, content and general quality of cottonseed oil depend to a considerable extent upon the weather prevailing during the time that the cotton stands in the field after coming to mataruty Cottonseed oil contains more saturated fatty acids than most oils of an equivalent iodine number. Hence its titer is high and the itself will become partially solidified upon storage at temperatures below 10°C to 15.5°C. Cloud and Pour points at refined cottonseed oil by the ASTM method are about 0.5°C to 3°C and -3.80C to -1.1°C respectively. Characteristics and approximate compositions of cottonseed oils are shown Table (1) and (2). Table-1 Characteristics of refined cottonseed oil. Specific gravity at 25°C 0.916-0.918 Refractive index at 25<>c 1.468-1.472 Iodine number 99-103 Saponification ntanber 189-198 Free fatty acids (as oleic), % not over 0.25 Table-2 Fatty acid composition of cottonseed oil. Fatty acids, wt. % Range of values Myristic acid 0.5-1.5 Palmitic acid,.. 20-23 Stearic acid 1-3 Oleic acid 23-35 Linoleic acid 42-54 Arachidic acid 0.2-1.5 In this study solid fat fractions seperated by crystallization. The principle of seperation by progressive freezing is based on the phase change liquid/solid. A binary or a multi component liquid mixture is crystallized on a cooled surface. The cooled surfaces are in most cases tubes. In order to control the seperation process it is necessary to control the dominant parameters of the process. Besides the physical properties of the material the growth rate of the crystal layer is the dominant parameter influencing the purity and the main parameter influencing the yield of product. The growth rate itself is vii influenced by several parameters such as cooling rate of the surface, physical properties of the subtances, volume flow rate and flow regi me, feed concentration and temperature. If parameters like volume flow conditions, feed conditions of temperature and concentration are constant, the growth rate is directly proportional to the cooling rate of the crystal layer. The growth rate of the layer is rather different compared to the growth rates of a single crystal. The cumulative growth rate in one dimension of a group öf single crystals will add up to the layer growth rate. There is a linear relation between cooling rate of the cooled surface and the growth rate of the crystal layer Vw. Starting from this relation it is possible to define a factor, which describes irregularities in the growth rate occurring in industrial crystalliza tion processes. These irregularities have an important, mostly nega tive, influence on the purity of the product. Among other reasons the metastable zone of the fluid and unknown impurities in ppm con centration ranges are their explanations. The irregularities of the growth rate can be qualified by a growth rate deviation here defined to: v. w,real du = ! w, ideal The so called ideal growth rate of the crystal layer Vw ideal can be a calculated one, or can be found by several reproducible experiments. The actually measured growth rate of crystal layer Vw>real includes all possible irregularities. The growth rate deviation dv defined in that way has in most cases a value greater than one, because ir regularities normally lead to a higher growth rates. For example irregularities in growth can lead to more liquid inclusions in the crystal layer and therefore to a larger volume but less purity of the crystal layer. In this study collection of the solidified fat fraction on a surface of low temperature held in the reaction mediim tlurinq the interestification reaction was aimied. The reaction would be directed by this way. In order to prevent the reversion of the reaction, the portions collected on the cold surface were taken in definite periods. Reac tion was also carried out without cold surface and the effect of re moval of solidified fat fractions from the medium on the properties of solid and liquid fats was investigated. In the case of using cold surface the iodine value of the solid fat portion obtained from the reaction by removal of solid fat fraction time by time was found as 95.6 and iodine value of liquid fat portion was found as 105.4. Under the same conditions iodine value of solid portion was found as 103.1 without removal of solid fat fractions. This shows that removal of solid fat fractions from the medium during the reactions effected the reaction. Vlll However this effect was limited because cold surface area was not large enough to collect the obtained solid portion. It was conc luded that a more effective seperation of the solid and liquid fat fractions could be achieved by enlarging the cold surface area and design of a more convenient experimental apparatus by further studies.