The effects of pelleting process parameters and phytase source on the in-feed stability of phytase

Abstract

Three experiments were conducted to determine the effect of various pelleting parameters and phytase sources on phytase stability during pelleting. In experiment 1, treatments were arranged in a 4 × 3 × 2 factorial with phytase source (A, B, C, and D), conditioning temperature (82, 88, and 93 °C), and conditioner retention time (30 and 60 s). In experiment 2, treatments were arranged for one phytase source as a 2 × 3 factorial of steam pressure (1.7 and 3 bar) and conditioning temperature (77, 82, and 88 °C). In experiment 3, treatments were arranged for one phytase source as a 2 × 3 factorial of die thickness (lengh:diameter [L:D] 5.6 and 8.0) and conditioning temperature (74, 79, and 85 °C). Treatment diets for all three experiments were mixed using a horizontal counterpoise mixer. Phytase premix was added to the mixer via a hand-add port after being hand mixed for 3 min with 2.3 kg of ground corn. Diets were steam conditioned and pelleted using a 30-horsepower pellet mill. Initial mash, conditioned mash, and pellet samples were collected for analysis of phytase level, moisture content, and pellet durability (PDI). Conditioning temperature, hot pellet temperature (HPT), and production rate were also recorded for each treatment, and each treatment was replicated 3 times. For Exp. 1, there was a source × conditioning temperature interaction for phytase stability. At conditioning temperatures of 82 and 88 °C, phytase A had greater stability compared to all other phytase sources. At 93 °C, phytase A stability was not different than phytase C, but greater than phytase B and D. At 82 °C conditioning temperature, phytase stability of phytase B was less than that of the other phytase sources and not different than the stability of phytase C or D at 88 and 93 °C. For all 3 experiments, phytase stability decreased and PDI and HPT increased with increasing conditioning temperature. Even at the lowest conditioning temperature of 74 °C (Exp. 3), maximum phytase stability averaged 63 % in pellets. There was no evidence that conditioner retention time or die L:D affected phytase stability and increasing steam pressure tended to improve phytase recovery by 18 % in pellets. There is a complex matrix of pelleting factors that influence phytase stability with most of the factors affecting HPT and enzyme recovery accordingly, perhaps making HPT the best determinant for phytase stability.