Fat analysis
Analysis of fat sources is performed as an attempt to determine fat composition, quality, and feeding value. Common measures of fat quality include color, fatty acid profile, free fatty acid content, degree of unsaturation, saponification value, and impurities including moisture, insolubles, and unsaponifiables (MIU). These measurements are generally used to determine fat composition and to ensure the quality specifications are met ( Table 1 ), but provide no information about feeding value (Shurson et al., 2015). The feeding value is assessed by measures of fat oxidation, but no single analysis adequately determines fat oxidation because of the different compounds produced during fat oxidation. The use of a combination of analysis of peroxide value, thiobarbituric acid reactive substances, and anisidine value that measures compounds at different stages of oxidation is recommended to provide an accurate assessment of fat oxidation and rancidification (Kerr et al., 2015; Shurson et al., 2015).
Measures of fat quality
- Color: ranging from 1 (light) to 45 (dark)
- Fatty acid profile: relative amount of individual fatty acids
- Free fatty acid content: amount of fatty acids not bound to a chain
- Total fatty acid content: amount of free fatty acids and fatty acids bound to a chain
- Degree of unsaturation: iodine value, expressed as grams of iodine absorbed by 100 g of fat. The greater the iodine value, the greater the degree of unsaturation.
- Saponification value: estimate of fatty acid chain length, pressed as the amount of caustic soda needed to turn 1 g of fat into soap. The greater the saponification value, the lower the chain length.
- Moisture:amount of moisture
- Insolubles: amount of materials that have no energy value, such as dirt, fiber, or hair
- Unsaponifiables: amount of compounds that do not degrade upon mixing in alkaline solution, such as sterols, pigments, or vitamins
Measures of fat oxidation
- Peroxide value (PV): estimate of peroxides and hydroperoxides produced during the initiation of fat oxidation
- Thiobarbituric acid reactive substances (TBARS): estimate of malondialdehyde produced during propagation of fat oxidation
- Anisidine value (AnV): estimate of aldehydes produced during propagation of fat oxidation
