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Evaluation of Common Analysis Methods for Oxidation in Rendered Protein Meals Used to Produce Pet Foods
A significant amount of rendered protein meal is used in pet food to meet the pets’ dietary protein and fat needs. These protein meals contain approximately 15-20% fat, which can oxidize and lead to unusable material. Peroxide value (PV) is a common method used to evaluate oxidation in commercial proteins, but it has been criticized as inconsistent and imprecise. Therefore, our objectives were to evaluate alternative methods to measure fat quality in rendered protein meals and to compare the results among different animal sources and rendering plants. It was hypothesized that PV was an inconsistent and unrepresentative method of analysis for measuring fat stability for rendered protein meals. In this experiment, samples of five chicken byproduct meals (CBPM) from each of three locations, and five beef meat and bone meals (BMBM) from each of two locations were evaluated. Samples were analyzed for proximate constituents, anisidine value (AV), thiobarbituric acid reactive substances (TBARS), PV via titration by two laboratories and PV via rapid method (SafTest; peroxysafe). Fat content differed among plants (P < 0.0001; BMBM = 8.44 vs. 11.87% and CBPM = 13.24 vs. 15.11 vs. 16.59%) and when aggregated into protein meal type, the ash concentration was greater for BMBM and protein concentration greater for CBPM (P < 0.0001). Again, for compiled least square means between the protein meal types, the peroxide values for the BMBM and CBPM were 10.42 and 58.08 meq/kg, respectively from laboratory 1; 4.65 and 3.01 meq/kg, respectively from laboratory 2; and 11.52 and 42.96 meq/kg, respectively from the rapid method test. There was a direct correlation (R = 0.98) between PV titration results from laboratory 1 data and the rapid method, but not with titration results from laboratory 2 (R = 0.46). This variation among labs is consistent with the anecdotal field evidence and our hypothesis. As expected, the PV from laboratory 1 did not correlate to the AV (R = 0.61); a measure of secondary oxidation products. Oxidation indicated by TBARS differed among both protein meal and plant (P < 0.0001). Our data corroborate the inconsistencies noted from commercial quality control laboratories. Combined with the results from the AV and TBARS, there is a clear need for further research to create a more accurate and precise analytical method for fat oxidation in rendered protein meals.
Keywords: oxidation, rendered protein meal, pet food