The effect of the level of mixer-added water and mash conditioning temperature on parameters monitored during pelleting and phytase and xylanase thermostability

Exogenous enzymes have been used in broiler and swine rations to improve nutrient utilization and reduce feed costs, both of which improved the efficiencies of live production. Feed manufacturers have also utilized practices, such as warm mash conditioning temperatures (CT) and the addition of moisture at the mixer or mash conditioning chamber, to maintain adequate physical feed quality. While the impact of warm conditioning practices on enzyme thermostability had been well described, the impact of mixer-added water (MAW) on enzyme thermostability was scarcely investigated in previous literature. The present experiment intended to investigate the interaction of three mash CT and three levels of MAW on the thermostability of a phytase and xylanase mixer-added enzyme within a swine gestation diet in a 3 × 3 factorial randomized complete block design. The mash CT included 80, 86, and 92 °C and the levels of MAW included 0, 10, and 20 g/kg. Parameters monitored during the pelleting process included pellet durability index (PDI), pellet mill energy consumption (PMEC), and the change in temperature between hot pellets and conditioned mash (Δ T). Conditioning mash at 92 °C resulted in a 22.5 percentage-point reduction in phytase recovery in conditioned mash and a 70.1 percentage-point reduction in phytase recovery in pellets when compared to diets pelleted at 80 °C (P < 0.01). The xylanase, however, was not affected by mash CT. Phytase and xylanase recovery in pellets was not affected by the level of MAW. As PDI and PMEC increased, phytase recovery in pellets relative to unconditioned mash decreased (P < 0.01). As Δ T increased, phytase recovery in pellets relative to unconditioned mash increased (P < 0.01). Xylanase denaturation was poorly described by the parameters monitored during pelleting, likely because it was minimally denatured during pelleting. A robust multiple regression model was generated to predict phytase activity in pellets relative to unconditioned mash (R² = 0.95; P < 0.01) when the controlled factors and monitored parameters were combined in a predictive model. In conclusion, the primary site of enzyme denaturation in a pilot scale pellet mill was the pellet mill die and MAW did not affect enzyme recovery.