CategoryAnimal Science - Swine Nutrition
Date Full Report Received08/09/2012
Date Abstract Report Received08/09/2012
Funded ByNational Pork Board
BACKGROUND: A better understanding of methods to assess quality and feeding value of feed fats and oils is needed because of variability in composition and quality. Commonly used lipid quality measures such as moisture-insolubles-unsaponables, titer and free fatty acid content are used to insure that the lipid products meet trading specifications. However, these measures provide limited information regarding the feeding value of feed fats and oils and provide essentially no information regarding the degree of degradation, called peroxidation, of a given lipid source. Methods specific for evaluating lipid peroxidative stability can be divided into indicative and predictive tests. Indicative tests are used to measure the presence of peroxidation products in lipids and include: peroxide value (PV), thiobarbituric acid reactive substances (TBARS), p-anisidine value (AnV), conjugated dienes, hexanal value, 2, 4-decadienal (DDE), and 4-hydroxynonenal (HNE). Predictive tests measure the stability or susceptibility of lipids to peroxidation and include active oxygen method (AOM) and oxygen stability index (OSI). In predictive tests, the lipid is subjected to specific conditions that accelerate peroxidation and a peroxidation endpoint is defined to determine the degree of peroxidation damage. However, assessment of the degree of lipid peroxidation is complex because the process consists of three phases: (1) an initiation phase which involves the formation of free lipid radicals and hydroperoxides as primary reaction products, (2) a propagation phase where the hydroperoxides formed are decomposed into secondary peroxidation products, and (3) a termination phase involving the formation of tertiary peroxidation products.
LIPID PEROXIDATION: In the current study, analysis of the slowly and rapidly peroxidized lipids compared to the original lipids showed that a high PV accurately indicated a high degree of lipid peroxidation, but a moderate or low PV may be misleading. This is due to the unstable characteristics of hydroperoxides as indicated by the unchanged PV of rapidly peroxidized corn and canola oil compared to their original, unoxidized state. Additional tests which measured secondary peroxidation products (AnV, TBARS, hexanal, HNE and DDE) showed peroxidation differences between the lipid treatments, but similar to PV analysis, these tests also may not provide irrefutable information regarding the amount of peroxidation because secondary peroxidation products are extremely volitile. For the predictive tests, AOM stability accurately reflected the increased lipid peroxidation caused by the slow and rapid peroxidation treatments as indicated by the increased AOM stability value in corn and canola oil, but not in poultry fat and tallow, which indicates a potential disadvantage of the AOM stability test. The OSI assay successfully showed the increased lipid peroxidation caused by slow or rapid peroxidation treatments in all lipids, but it too may have disadvantages similar to AnV, TBARS, hexanal, HNE and DDE, because the OSI assay directly depends on quantification of the volatile secondary peroxidation products. Thus, relative to peroxidation assays utilized in the current study, no individual indicative or predictive test appears to provide a complete assessment of the degree of lipid peroxidation. Therefore, to accurately analyze the amount of lipid damage caused by peroxidation, it may be advantageous to determine the degree of lipid peroxidation at several time points during the peroxidation process using more than one test.