Determination of Fat in Food

The methods used for determination of fat or oil in food are often based on extraction with either ethyl ether or petroleum ether and gravimetric determination of the extraction residue. These methods may provide unreliable or incorrect results, particularly with food of animal origin. As shown in Table 14.20, where a corned beef sample was analyzed, the amount and composition of fatty acids in the fat residue were influenced greatly by the analytical methods used. In addition to the accessible free lipids, the emulsifiers present and the changes induced by autoxidation affect the amount of extractable lipids and the lipid-to-nonlipid ratio in the residue. The use of a standard method still does not eliminate the disadvantages shown by analytical methods of fat analysis. Therefore, in questionable cases, quantitative determination of fatty acids and/or glycerol is recommended. 

Analytical method Fat content (%) Fatty acid composition (g/lOOg)  

Dried sample is extracted with ethyl ether 7.9 3.98 2.06 0.05 0.08 

Sample is homogenized in 95% ethanol and then extracted with ether 15.8 4.0 2.60 0.77 0.32 

Sample is hydrolyzed with cone. HCl (at 100 °C for 1 h), methanol added and then extracted with carbon tetrachloride 13.9 2.45 1.68 0.34 0.21 

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When the analyte is already present in a particulate form that is easily separated from its matrix, then a particulate gravimetric analysis may be feasible. Examples include the determination of dissolved solids and the determination of fat in foods. 

Capillary gas chromatography is an alternative method to measure trans fats as FAMEs (AOAC 996.06 and AOCS Ce lf-96), particularly for lower concentrations (-0.5%). GC official method AOAC 996.06 (AOAC, 2001) is appropriate for the determination of fat in food products, while AOCS Ce lf-96 (AOCS, 1996) is applicable to the determination of cis and trans fatty acids in hydrogenated and re-... 

Piezoelectric measurements have also been made on-line with supercritical extraction by using an FI interface such as that of Fig. 7.18C, which allowed the determination of fat in foods using the procedure described in Section 7.6.2 [120]. 

Senorans F], Luna P. Sample preparation techniques for the determination of fats in food. In Pawlyszin J, editor. Comprehensive sampling and sample preparation. Amsterdam Elsevier 2012. p. 203—11. 

Very few methods have appeared in the literature with respect to the extraction, cleanup, and subsequent determination of corticosteroids in food samples (Table 29.17). Milk analysis usually requires a pretreatment step for fat elimination (527). Centrifugation for 20 min at about 7000 g at 4 C is the usually applied procedure for making the fat floating on the top of the sample. Tissue analysis also requires a pretreatment step for matrix break-up that can be accomplished by means of a mincing and/or a homogenizing apparatus. 

Table X. Determination of Fat in Snack Foods Comparison of SFE vs. Soxhlet Extraction...

Lipase-catalyzed hydrolysis of the vitamin esters in food samples in SCCO2 has been investigated as a pretreatment step in the analytical determination of vitamins in food samples (216, 217). Lipase-catalyzed transesterification of oils with methanol have been used for the determination of total fat content in lipid-containing samples such as oilseeds and meat samples (218, 219) and for the determination of fatty or resin acid content of tall oil products (220). Esterification of fatty acids with methanol in SCCO2 has been reported for total fatty acid analysis of soapstock (221). 

It is also possible to use broad-line NMR to determine the amount of fat in foods without solvent extraction. This technique has been applied, for instance, in the chocolate industry (Bruker Reports,... 

Gurr, M.I. Determination of the amounts and types of fats in foods. In Role offats in food and nutrition, Gurr, M.I. (Ed.) p. 43—57, Elsevier Applied Science London, 1984 pp. 43—57. 

B. G. Osborne, Determination of fat in a variety of cereal foods using NIR spectroscopy. 7n I. S. Crease, A. M. C. Davies, eds, 68-71. Analytical applications of spectroscopy. Royal Society of Chemists, London, 1988. 

G. S. Ranhotra, J. A. Gehoth, J. L. Vetter. Determination of fat in bakery products by three different techniques. Cereal Foods World 41 620-622, 1996. 

S. K. Henderson and A. F. Wickroski, In Application of High Pressure Liquid Chromatographic Methods for Determination of Fat Soluble Vitamins A, D, E, and iCin Foods and Pharmaceuticals, Symposium Proceedings Association of Vitamin Chemists Chicago, III. 1978, pp. 48-61. 

Feller, F.J. and King, J.W. 1996. Determination of fat content in foods by analytical SFE. Semin. Food Anal. 1 145-162. 

SL Reynolds. The use of HPLC in the determination of fat-soluble vitamins in a variety of milk-based food products. Proc Inst Food Sci Technol UK 18 43-50, 1985. 

JN Thompson, L Plouffe. Determination of cholecalciferol in meat and fat from livestock fed normal and excessive quantities of vitamin D. Food Chem 46 313-318, 1993. 

The GPC has been effectively applied for quantitative determination of OPPs in the Food and Drug Administration s Total Diet Study. Fats in spiked samples were removed with methylene chloride-hexane (1 1). This procedure was used to analyze fatty foods for OPPs. This procedure also worked well in removing a large portion of the coextractive materials from nonfatty foods (73). 

Localized NMR spectroscopy, which is often called as MRS in comparison with MRI, is not so familiar technique in food science, because a specific pulse sequence such as ISIS and a facility which can precisely follow the pulse sequence without any contamination from other position is needed for localization of position. The localized NMR is usually used together with NMR imaging. The study of solid/liquid ratios, fat structure and polymorphism and the kinetics of fat crystallization was reviewed [24], The potential of applications in food process development and control was offered. The localized spectra of sausages in areas of 0.3 mm X 0.05 mm (thickness of sample =1.5 mm) were obtained by the spin echo 2DFT method [113], in which the difference in the tissue structure was discussed with relation to the process and original materials. McCarthy et al. determined mobility of water in foams by using a localized spectroscopy [114]. T2 relaxation time varies in the foam as function of diameter and its variation was analyzed by the classic 2-state fast exchange model. 

Procedure. A System 2250 was used to perform the SFE of fat from processed snack foods. Unlike other SFE procedures described in this paper, the fat extract was not collected for any subsequent analysis. Since gravimetric determination of weight loss in the sample was used for determination of fat, a large amount of CQj was passed through each sample in a very short period of time. Parameters used are summarized in Table IX. 

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