Lipids: Fatty Acid and Amp

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The measurement of parameters such as oil and fat content help define product quality for many agricultural and food products. These values are widely used to determine energy content and to calculate the proportions of other food components. In addition oil and fat content significantly affect the texture, perceived quality and the flavour of products. (Whitney, Rolfes, Crowe, Cameron- Smith, & Walsh, 2011). An accurate and precise quantitative and qualitative analysis of lipids in food is important for accurate nutritional labelling, determination of wether food meets standard identity, and to ensure that the product meets manufacturing specifications (Nielsen, 2010). AOAC International (2007) state “the sample preparation for the lipid analysis depends on the type of food and the nature of the lipids in the food. “ Several preparatory steps are common in lipid analysis. They act to aid extraction by removal of water, reduction of particle size, or separation of the lipid from bound proteins or carbohydrates (Min &Ellefson, 2010). To analyse lipids it is necessary to first isolate them quantitatively from nonlipid components. Extraction of lipids from source materials, such as food, animal and plant tissues or microorganisms, should be carried out in a manner that avoids changes in the lipids or leads to formations of artefacts (Christie, 1993). It might be necessary to deactivate enzymes that might hydrolyse lipids via heat treatment. (Vain, & Nairn, & Reid, 1991). Precaution must be taken to minimise oxidation of lipids, especially those with polyunsaturated fatty acids. Use of antioxidants might prove beneficial when dealing with extractions of lipids with highly unsaturated fatty acids (Carapace &Garcia, 2000). Carapace et al, (2000) state the accuracy of direct solvent extraction methods greatly depends on the solubility of the lipids in the solvent used and the ability to separate the lipids from complexes with other macromolecules. The lipid content in food determined by extraction with one solvent may be quite different from the content determined with another solvent of different polarity. Fisheries and Aquaculture department (1986) concluded that solvent extraction techniques are commonly used for the determination of fat content. However they tend to be slow, cumbersome, and require highly skilled personnel. In addition, many of the often-hazardous chemicals used are becoming increasingly unacceptable according to international environmental standards. Despite these issues, solvent extraction continues to be used as a reference measurement for quality control. Nielsen (1994) acknowledged the validity of the fat analysis of a food depends on sampling and the preservation of the sample before analysis. An ideal sample should be as close as possible to its intrinsic properties to the material from which it was taken. Pomeranz and Meloan (1994) states “ a sample is considered satisfactory if the properties under investigation correspond to those of the bulk material within the limits of the test. “ Min and Ellefson (2010) note organic solvent methods, which include Goldfish a continuous method, Soxhlet as a semicontinuous method and Folch as a discontinuous method are commonly used to determine the total lipid content of food. They also note the major uses of these methods include extracting the fat prior to GC analysis, quality control of formulated products, determination of fat content in product development, verifying when fat content is <0.5g per serving, so nutrient content claim can be made and defat samples prior to fibre analysis.

The Association of Analytical Chemists (AOAC) as the standard method for crude fat analysis recognizes Soxhlet. The underlying process is that of fat extracted through repeated washing, with an organic solvent under reflux in special glassware. Extraction efficiencies for different compound classes are highly dependent on the properties...
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