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The Effect of Extrusion and Elevated Storage Temperatures on Vitamin Retention in Pet Food
Little research has been published in recent years regarding the magnitude of vitamin losses through extrusion manufacturing and storage of pet food. The matrixes of pet diets have changed dramatically within the past twenty years since vitamin degradation was last published. Therefore the objective of our research was to determine the effects of processing conditions and dietary protein content on vitamin retention (vitamin A, vitamin D3, vitamin E, folic acid and thiamine) during extrusion and drying and the subsequent effect during storage at elevated temperatures. Three diets differing in protein (21.7, 25, and 30% CP; Low, Medium, and High, respectively) were produced. Diets were extruded at 350 and 450 rpm screw speed on a Wenger X-20 single screw extruder (Wenger Mfg, Sabetha, KS) and dried at 104°C for 6 min at each pass or 127°C for 10 min at each pass in a Wenger (Wenger Mfg, Sabetha, KS) triple pass dryer. Samples from each treatment were analyzed immediately following production. Without current established criterion for accelerated shelf life studies of pet food, conditions by industry laboratories were practiced using 50°C and 75% relative humidity for 3, 6, 12, and 18 weeks before vitamin analysis. Retention of all vitamins evaluated in this study was not affected (P > 0.05) by extruder screw speed or dryer conditions. As time in storage (50°C) increased through 3, 6, 12 and 18 weeks vitamin A (P < 0.05; 153,708, 95,542, 62,491, 21,713, and 6,689 IU/kg, respectively), vitamin D3 (P < 0.05; 6,956, 4,652, 3,572, 1,824, and 1,421 IU/kg, respectively), vitamin E (P < 0.05; 855, 970, 834, 837, and 803 mg/kg, respectively), folic acid (P < 0.05; 1.75, 1.81, 2.37, 1.45, and 0.98 mg/kg, respectively), and thiamine (P < 0.05; 22.9, 19.7, 16.1, 7.4, and 3.3 mg/kg, respectively) concentrations decreased. These results suggest that the processing parameters in this study had little effect on vitamin losses; but, elevated temperature during storage for 18 weeks could reduce vitamin content from initial by 95.65, 79.57, 6.08, 44.00, and 85.86% for vitamin A, vitamin D3, vitamin E, folic acid and thiamine, respectively. Vitamin fortification of extruded pet diets must take into account these changes to avoid deficiency diseases.
Keywords: Vitamin stability, Effects of Thermal Processing, Vitamin retention