Distribution of inositol phosphates in animal feed grains and excreta: distinctions among isomers and phosphate oxygen isotope compositions
Background and Aims
Phytate (myo-IP6) is a common form of organic phosphorus in the environment. Little information is available, however, about the distribution of phytate and its degradation products. In this research, we aimed to identify the compositions of phytate in different natural P sources as well as to explore a reliable method to measure their isotope signatures so that the link between original phytate and P outputs in the environment could be established.
A variety of feed ingredients for selected ruminant and non-ruminant animals and their excreta were analyzed using HPIC (high-performance ion chromatography) and their oxygen isotope (δ18OPA-Pi) signatures were identified using IRMS (isotope ratio mass spectrometry) method.
The HPIC results show that IP6 was dominant in all grains, followed by IP5 and several IP4 isomers, and an insignificant amount of IP3. Similarly, IP6 and IP5 were also detected in all animal feeds and several excreta. More importantly, the distribution of different IPx species in a grain type was essentially the same. The δ18OPA values of phytate in grains varied from 20.5 to 24.2 ‰, while the δ18OPi values of inorganic P in the same grains were heavier by 0.4-3.2‰. Similarly, the δ18OPA values of phytate in animal feeds and excreta were within the ranges of grain phytate.
Overall, combination of results from IRMS and HPIC analyses provided important information on the distribution of IPx species in various sources and their distinct oxygen isotope ratios pointed towards the possibility of connecting the original phytate sources to degradation products in the environment.
KeywordsPhytate Inositol phosphate isomers Animal feeds Animal excreta Phosphate oxygen isotopes
This research was supported by an NSF grant (EAR 1654642). We offer our immense thanks to Bill Brown for facilitating and collecting samples for analyses, and to whom we would like to dedicate this paper as a tribute to his professionalism and dedication to agricultural research. We are grateful to BASF for supplying A. niger phytase for this research.
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