PSVIII-6 Effect of Pellet Die Thickness and Conditioning Temperature During the Pelleting Process on Phytase Stability

Abstract

Abstract This experiment evaluated the effects of pellet die thickness and conditioning temperature on microbial phytase stability. Treatments were arranged as a 2 × 3 factorial of die thickness (5.6 and 8.0 length:diameter [L:D]) and conditioning temperature (74, 79, and 85°C). Phytase was added to a corn-soybean meal-based diet. The diet was steam conditioned (245 × 1397 mm Wenger twin staff pre-conditioner, Model 150) and pelleted (CPM Model 1012-2) with a 4 × 22.2 mm (5.6 L:D) or 4 × 31.8 mm (8.0 L:D) pellet die. Conditioner retention time was set at 30 s and production rate was set at 15 kg/min. All treatments were replicated over 3 days. Conditioned mash and pellet samples were collected and immediately placed in an experimental counter-flow cooler for 15 min. Samples were analyzed for phytase activity and pellet durability index (PDI). Conditioning temperature, hot pellet temperature (HPT), and production rate were recorded throughout each processing run. Data were analyzed using PROC GLIMMIX in SAS (v. 9.4), with pelleting run as the experimental unit and day as the blocking factor. There was no evidence (P >0.14) for any die thickness × conditioning temperature interactions. Pelleting with the 8.0 L:D die increased (P < 0.01) HPT (83.2 and 84.2°C) and PDI (81.9 and 89.7%). Increasing conditioning temperature from 74 to 85°C increased (linear, P< 0.03) HPT (80.1, 83.6, and 87.5°C , respectively) and PDI (84.3, 84.9, and 88.2%, respectively) and decreased (linear, P< 0.01) phytase stability from 97.1 to 35.8% in conditioned mash and from 60.8 to 25.9% in cooled pellets. There was no difference (P >0.72) in stability due to die thickness. Results of this experiment demonstrated phytase stability decreased linearly as temperature rose above 74°C. Although the thicker pellet die increased HPT and PDI, the rise in HPT was not great enough to reduce phytase stability.