Degradation of Phytates in Distillers’ Grains and Corn Gluten Feed by Aspergillus niger Phytase

Abstract

Distillers' dried grains with solubles (DDGS) and corn gluten feed (CGF) are major coproducts of ethanol production from corn dry grind and wet milling facilities, respectively. These coproducts contain important nutrients and high levels of phytates. The phytates in these products cannot be digested by nonruminant animals; consequently, large quantities of phytate phosphorus (P) are deposited into the soil with the animal wastes which potentially could cause P pollution in soil and underground water resources. To reduce phytates in DDGS and CGF, a phytase from Aspergillus niger, PhyA, was investigated regarding its capability to catalyze the hydrolysis of phytates in light steep water (LSW) and whole stillage (WS). LSW and WS streams are the intermediate streams in the production of CGF and DDGS, respectively, and contribute to most of the P in these streams. Enzyme loadings with activity of 0.1, 1, 2, and 4 FTU/g substrate and temperatures of 35 and 45 degrees C were investigated regarding their influences on the degree of hydrolysis. The analysis of the hydrolyzate suggested to a sequentially degradation of phytates to lower order myo-inositol phosphate isomers. Approximately 90% phytate P of LSW and 66% phytate P of WS were released, suggesting myo-inositol monophosphate as the end product. The maximum amount of released P was 4.52 +/- 0.03 mg/g LSW and 0.86 +/- 0.01 mg/g WS.