The edible oils and fats, whether of vegetable or of animal origin, structurally are triglycerides of fatty acids particularly higher fatty acids. Vegetable oils, mostly rich in unsaturated fats (coconut oil with less than 10 percent unsaturated oil is the exception) while animal fats are generally found to contain bigger proportions of saturated fats (perhaps butterfat possesses the lowest saturated fat contents but around 62%). All the fats and oils, irrespective of their saturation or un-saturation and carbon chain length of their fatty acid part of configuration, are soluble in ethers and might be extracted from their natural sources via solvent extraction. The solvent extraction technique has been employed not only to recover fats and oils from the sources in manufacturing plants but also to determine their percent of contents in source samples in laboratories. The experimental determination of any ingredient, soluble in a volatile organic solvent like hexane or ether, in the sample employs the solvent extraction technique called soxhlet method.
The solvent extraction is a time consuming process applicable to very well ground or powdered samples. The easily grind-able material samples of oilseeds and oilcakes are quite suitable to soxhlet method for fat determination. But difficulty grind-able material samples of particularly animal origin, like meat, don’t exactly suit to soxhlet method to accurately estimate its fat content. The quick and accurate fat determination in the difficultly grind-able material samples has been a challenge for laboratory technocrats which was partly met out by NIR (near infrared) technique but almost completely and effectively met out by DEXA (dual energy X-ray absorptiometry) technology. The DEXA technology involves X-rays and normally used in X-ray inspection systems for diagnosis of osteoporosis and other conditions related to bone loss in the body. The same technology has been successfully employed for quick and reliable determination of fat contents of the meat samples in laboratories. Both the old classical and the latest advanced methods, the soxhlet and the DEXA, are nowadays used in the laboratories for fat content determination. The brief details of system operation of both the methods are as follow:
The separation of a constituent soluble in a particular solvent, say fat or oil in petroleum ether, from a solid sample may be conveniently achieved by extraction or selective dissolution with the specific solvent usually organic in nature in which solubility of other substances present in sample is negligible, extraction of solutes, contained by a solid sample material, is a slow activity and demands a process of regular solvent-solute interaction with arrival of solvent and departure of solution. The specialty of soxhlet apparatus is that it utilises heating of solvent contained in an accurately weighed flask (weight W1) yielding solvent vapour that rises up to a reflux condenser through the extractor, a wide inner tube provided with solvent vapour passage and solution siphoning facilities and holds the porous tough filter paper thimble that contains an accurately weighted ground samples (say M). The solvent vapour, via vapour passage tube fitted in the extractor, reaches the condenser where it gets condensed to liquid state again and falls down to inner tube of the extractor where thimble containing the accurately weighed ground sample is placed.
A fraction of sample portion (constituent) specifically soluble in the solvent begins to get dissolved in the condensed liquid falling drop-wise from the condenser unit to extractor unit of soxhlet apparatus. When extractor the tube gets filled to the brim with solution it is siphoned back to a flask. In this way the extractor gets emptied and the flask regains its vaporised portion along with the dissolved fraction of solute separated from the sample. These steps go on till the entire solute material contained in the sample gets separated by solvent extraction process and reaches the flask. The solvent is recollected from the flask by the means of condensation. The dried flask containing the extracted solute is accurately weighed; say this weight is W2. The percent contents of soluble matter in solvent in the sample is calculated as Mx100 / (W2-W1) Suppose 9.5018 grams of ground peanut kernel samples, are poured in a tare thimble, is subjected to soxhlet extraction using petroleum ether as solvent. If the initial weight of empty flask and final weight of flask containing extracted oil are 70.0253 grams and 74.6432 grams respectively, then M=9.5018 grams, W1=70.0253 grams and W2=74.6432 grams. Therefore percent oil content in given peanut sample is 9.5018×100/(74.6432-70.0253) = 48.60 percent.
The X-rays – a kind of electromagnetic radiation of 1017-1018 Hertz order frequency and around 10-10 meters order wavelength – are generally utilised in hospitals for bone density scanning and diagnosis of bone loss conditions of body including osteoporosis. The security scanning at airports, railways, hotels etc is also based on X-ray inspection technology. Known as DEXA (dual energy X-ray absorptiometry) technology. It is nowadays popular in the food industry too for its use in determination of fat contents of a food sample, particularly in the case the sample can’t be well ground into powder state. The soxhlet solvent extraction method has limitation in that complete extraction of solute from finely powdered samples only is possible. It can’t be employed for difficultly breakable samples, like meat, which can’t be brought to fine powder state. The X-ray inspection technology does not need disintegration of sample. As the X-rays pass through the human body; in the same way they penetrate food sample, particularly the meat. The X-ray scan of meat sample provides details of contents of all chemicals present except the fat. This value called as percentage of CL (Chemical lean) leads to estimation of fat contents in meat sample as 100 minus fat.
In DEXA technology an X-ray generator also called X-ray tube is employed to generate low energy or low frequency-high wavelength X-rays. The products or packs are passed through the X-ray beam before reaching the detector. A certain amount of energy depending upon thickness, density and chemical configuration of product, is absorbed when the X-ray beam passes through it. The detector receives the residual energy when the product, after passing through the X-ray beam, reaches it. A measurement of the difference in absorption between the product and a foreign body is the basis of detection of foreign body via X-ray inspection. In this way the X-ray inspection system has three fundamental components, X-ray generator and detector and computer. The X-ray generator or X-ray tube consists of a glass envelope, a tungsten filament cathode, a copper anode and a tungsten target. When the cathode is heated to incandescence by electrical current, the electrons are emitted which are accelerated to target the mounted inside the copper anode by application of high voltage between anode and the cathode. As the electrons strike against the target, they get rapidly decelerated emitting X-rays, the electromagnetic radiation.
The X-ray detector is just like a camera to visible light that means a device of capturing X-ray energy to form an image via its conversion to an electrical signal through the diode. The signal is received by a computer. In other words the X-ray inspection system is a scanning device. After passing through a constantly moving product, the X-ray’s energy is absorbed by it. The detector detects the difference in absorption between product and foreign body building an image made up of pixels. The X-ray energy absorbed by each pixel creates a value on a grayscale, from black zero to white 255. The on board computer provides the numerical value that represents the crude fat content of the food product sample. However Chemical Lean (CL) term is used in meat transactions, which stands for anything except fat. That means if fat contents in meat sample is 12 percent, the CL value for sample would be 100-12 = 88 percent.
* The author is a freelance writer.