Espectrofotometria

Extraction and Measurement of Total Lipids
Lipids are soluble in organic solvents, but sparingly soluble or insoluble in water. The existing procedures for the extraction of lipids from sourcematerial usually involve selective solvent extraction and the starting material may be subjected to drying prior to extraction. Solubility of lipids is an important criterion for their extraction fromsource material and depends heavily on the type of lipid present, and the proportion of nonpolar (principally triacylglycerols) and polar lipids (mainly phospholipids and glycolipids) in the sample;therefore, several solvent systems might be considered, depending on the type of sample and its components. Incomplete removal of lipids via cold pressing can be employed, such as is in practice for theextraction of oil from flaxseed or screw-pressing of seeds like canola, prior to solvent extraction. The solvents of choice are usually hexane, in the case of Soxhlet (AOAC, 1995; see Basic Protocol 1)and Goldfisch methods (see Alternate Protocol 1), chloroform/methanol or chloroform/methanol/water, in the case of the Folch Method (Folch et al., 1957; see Basic Protocol 2) or its modified Bligh andDyer Procedure (Bligh and Dyer, 1959; see Alternate Protocol 2), and n-propanol/water for high-amylose containing starchy foods (see Basic Protocol 3). In addition, to release lipids from sourcematerial, such as those in starch, fish meal, or milk, it might be necessary to treat the sample with an acid prior to lipid extraction (see Basic Protocol 4). In the case of milk, addition of ammoniumhydroxide is necessary to dissolve casein prior to lipid extraction, which will release the lipids from its surrounding matrix (e.g., from the film surrounding the fat globules in milk). Furthermore, incertain cases, it is necessary to predry the sample in order to allow efficient and complete extraction of lipids. Particle size reduction is another factor that may improve lipid extraction...