Abstract
Dairy fat is one of the most complex natural fats because of its fatty acid (FA) composition. Ruminant dairy fat contains more than 400 different FA varying in carbon chain length, and degree, position and configuration of unsaturation. The following article reviews the different methods available to analyze FA (both total and free) in milk and dairy products. The most widely used methodology for separating and analyzing dairy FA is gas chromatography, coupled to a flame ionization detector (CG-FID). Alternatively, gas chromatography coupled to a mass spectrometer (GC-MS) is also used. After lipid extraction, total FA (TFA) are commonly converted into their methyl esters (fatty acid methyl esters, FAME) prior to chromatographic analysis. In contrast, free FA (FFA) can be analyzed after conversion to FAME or directly as FFA after extraction from the product. One of the key questions when analyzing FAME from TFA is the selection of a proper column for separating them, which depends mainly on the objective of the analysis. Quantification is best achieved by the internal standard method. Recently, near-infrared spectroscopy (NIRS), Raman spectroscopy (RS) and nuclear magnetic resonance (NMR) have been reported as promising techniques to analyze FA in milk and dairy products.
Highlights
Milk is an emulsion in which lipids are structured in milk fat globules (MFG)
If the purpose of our analysis is to study the fatty acid (FA) composition of different lipid classes, a lipid fractionation procedure has to be undertaken
Underivatized free fatty acids (FFA) strongly interact with column phases, which can lead to irreversible adsorption
Summary
Milk is an emulsion in which lipids are structured in milk fat globules (MFG). MFG contain nonpolar lipids in the interior, mainly triacylglycerols (TAG), and cholesteryl esters and other minor lipids, covered by a membrane containing amphipathic lipids and proteins. Heat treatments and dairy product processes look to disrupt MFG structure but have little effect on lipid content and composition [1]. Because TAG account for about 98% of the total fat, they have a major and direct effect on the properties of milk fat, for example hydrophobicity, density and melting characteristics. Taking the data of all fractions together, they were able to detect 430 different FA in a butter sample They include FA varying in carbon chain length from 4 to 26 carbons (both even and odd, in a straight or branched chain), degree of unsaturation, presenting many geometrical isomers, with double bonds in cis and trans configuration, etc. The physicochemical properties and sensory and nutritional quality of milk and dairy fat are largely determined by its FA composition [7]. The FFA content in milk is very low (Table 1), but can be important in some dairy products. Some FFA have been shown to have antimicrobial activity [12]
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