Approach to fat analysis of foods

Behind the nutritional labelling of food fat hides a problem of definition of fat, as well as an analytical problem. Although triacylglycerols are the prevailing structure of the food lipids in most cases, there are exceptions, too. Analytes called ether extract, crude fat, total fat and total lipids have been interpreted to food fat in nutritional labelling and food databases. However, the techniques traditionally used for fat determination in foods may vary considerably in their ability to recover the various lipid components. Diversity in the lipid composition of various foods and the effects of processing and storage on the diversity and availability of the fat make the correct nutritional labelling of fat problematic. The traditional methods, where the total fat content is determined by extracting the fat with an appropriate fat solvent or a solvent mixture, give good technical measures. The use of this extracted fat-soluble material as the nutritional concept of fat may be misleading. We have suggested (Hyvönen et al., 1993, J. Food Comp. Anal., 6, 24–40) the use of the concept of net fat in nutritional food labelling. This definition of fat includes all the unchanged fatty acids from the various food lipids converted to triacylglycerols. In energy calculations 1 g of net fat corresponds to 9 kcal or 38 kJ. This concept reduces the energy values of foods because it eliminates the lipid components, which are not real fats, from the calculation.