Determination of fat in butter. A review

Fat in butter may be determined using direct or indirect methods. Indirect (that is, fat-by-difference) methods analyse the non-fat portion of the butter and subtract this from 100/ to calculate the fat content, whereas direct methods measure fat directly. Although indirect methods have been accepted globally for both routine and reference testing, the lack of a direct method has long been recognized and a project on a direct method for the determination of fat in butter was initiated by International Dairy Federation (TDF) group of experts F301 in 1996. As a first step in this project, the literature was to be reviewed resulting in this paper. An overview of both direct and indirect methods is given so that these method principles may be compared. Essentially two different groups of methods have been employed to determine fat by difference. One group of methods is based on the principle of physically separating the total non-fat portion from the fat followed by the volumetric determination of the total non-fat portion. The other, gravimetric, group of methods separately determines the moisture and the solids-not-fat (SNF) portions of the butter. The moisture may be removed by placing a dish containing the butter in an oven, on a hot plate or above a non-sooting flame. The weight loss of the butter through a particular heating process is defined as moisture. The fat is then removed from the dried butter using a suitable solvent and the retained SNF portion is dried and weighed. For the direct determination of fat in butter, a number of test principles have been reported. These include: refractometric and weighing methods, which measure a change in refractive index, or specific gravity, of a solvent with a change in the concentration of fat; saponification methods, which measure free fatty acids released by alkaline hydrolysis; filtration methods, which employ filtration techniques to separate the fat from the butter after which the fat is determined gravimetrically; gravimetric centrifugation methods, which separate the fat from the butter by washing out the non-fat components by employing centrifugal force; volumetric centrifugation methods, which, after isolation of the fat, measure the fat volumetrically by reading a calibrated scale; spectroscopic methods employing infra-red absorption or reflectance; and, finally, solvent extraction methods, which extract the fat from either the "wet" or dried butter sample. These last methods may be preceded by an acid or alkaline digestion. Triglycerides are the main constituents of butterfat. However, butter may also contain small amounts of other neutral lipids as well as phospholipids and free fatty acids. The levels of these components are variable and their recoveries vary with different methods. For this reason, any direct fat method should be compared with IDF Standard 80 as this method is currently widely accepted as a reference method.