Stability of four commercial phytase products under increasing thermal conditioning temperatures

Phytase is a feed-grade enzyme frequently added to swine diets to help improve the digestibility of phytate phosphorus. However, like any enzyme, it may be subject to heat damage when exposed to thermal processing. Therefore the objective of this experiment was to determine the stability of 4 commercial phytase products exposed to increasing thermal conditioning temperatures in the pelleting process. The 4 commercial products used were: Quantum Blue G (AB Vista, Plantation, FL); Ronozyme Hi Phos GT (DSM Nutritional Products, Parsippany, NJ); Axtra Phy TPT (Dupont, Wilmington, DE), and Microtech 5000 Plus (Guangdong Vtr Bio-Tech Co., Ltd., Guangdong, China). The phytase products were mixed as part of a corn-soybean meal-based swine diet at a concentration recommended by the manufacturer to provide a 0.12% aP release. Diets were exposed to each of 4 thermal conditioning temperatures (65, 75, 85, and 95°C) and the entire process repeated on 4 consecutive days to create 4 replicates. Samples were taken while feed exited the conditioner and before entering the pellet die. Samples were cooled to room temperature before being stored in plastic bags until analysis. Phytase stability was measured as the residual phytase activity (% of initial) at each conditioning temperature. There were no product × temperature interactions observed for conditioning temperature, conditioner throughput, or residual phytase activity. As target temperature increased, conditioner throughput decreased (linear; P < 0.001) and phytase activity decreased (linear; P < 0.001) for each product. Residual phytase activity decreased as conditioning temperature increased from 65 to 95°C at a rate of -1.9% for every 1°C increase in conditioning temperature. There was a significant phytase product (P < 0.001) main effect which was mainly driven by Microtech 5000 Plus having decreased (P < 0.05) phytase activity when compared to all other products at 65, 75, and 85°C. However at 95°C Axtra Phy TPT had greater (P < 0.05) residual phytase activity compared with Microtech 5000 Plus, with Quantum Blue G and Ronozyme Hi Phos intermediate. Increasing target conditioning temperatures decreased phytase stability regardless of product. In addition, Microtech 5000 Plus had decreased residual phytase activity (% of initial) when compared to all other products at 65, 75, and 85°C.