Extraction of Fat in Meats, Dairy and Egg Products

A wide range of methods for the estimation of the fat content of foods has been developed and modified over the years. These methods are primarily based on the extraction of fats in non-polar organic solvents such as petroleum ether, diethyl ether, chloroform and dichloromethane. Meat, meat products, dairy products, and egg products are all of prime importance to the food analyst. 

The current methods used for the determination of fat in meat and meat products include tedious Soxhlet and Soxtec extractions (AOAC method 991.36) - which suffer from being time, energy and solvent consuming techniques - and an automated method that uses microwaves to dry the sample before extracting the dried sample with solvent while agitating it mechanically [17, 18]. All these methods have in common the requirement that the sample must be dry because efficient permeation of the solvent is hindered by residual moisture, hence decreasing the abihty to dissolve the fat. 

Dairy products represent a different challenge as the extraction of fat is characterised by the formation of fat-protein emulsion and, in the case of cheese samples for example, is plagued by severe interference from casein. Conventional chemistry would prescribe the concurrent use of heat and aqueous alkali solutions (e.g., KOH or NH4OH) to dissolve the protein and to free the fal which can then be separated, collected, washed and dried. Not surprisingly current AOAC methods are based upon such principles. Generally, the samples are heated in presence of alkali solution in solvents such as diethyl ether and petroleum ether. Ethanol is also used to minimise the formation of emulsion, to further assist in breaking up fat-protein interactions, and to precipitate the proteins. 

Finally, egg products present a similar problem with respect to the difficulty in achieving a complete dissolution of the sample. Here, an overall treatment 

We have reported on atmospheric pressure MAP methods, using focused microwave irradiation for the extraction of fat from meat, dairy and egg products [19, 20]. These methods are characterised by efficiency, ease of use, and speed, in addition to offer significant economic and environmental advantages e.g., disposal of solvents). In these methods, we adhered to conventional chemistry principles applied in current methods but simply substituted the usual heating and extraction steps by a microwave treatment one while the materials are immersed into solvents that are transparent to microwaves relative to the sample in order to impart most, if not all, of the microwave energy to the sample. 

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