Interactions of phytate and myo-inositol phosphate esters (IP1-5) including IP5 isomers with dietary protein and iron and inhibition of pepsin

Phytic acid (IP6) and myo-inositol phosphate esters (IP1-5), including IP5 isomers prepared chemically and enzymatically with bacterial and fungal phytases, were examined for their effects on protein aggregation of soy protein and beta-casein, interaction with Fe3+, and pepsin activity. The results indicated that the aggregating capabilities of IP esters (IP1-6) on the 2 proteins decreased dramatically from IP6 to IP5 and became negligible with IP1-4. Among the IP5 isomers tested, InsP(5)(1,2,3,4,5) produced by 6-phytase was slightly less powerful in aggregating protein than InsP(5)(1,2,4,5,6) produced by 3-phytase (P = 0.001). For protein hydrolysis, IP esters of IP3-4 still showed inhibition of pepsin though to a lesser extent than IP5-6. The in vitro data with IP1-5 generated with microbial 3- and 6-phytases indicate that, for complete alleviation of pepsin inhibition, IP6 needs to be broken down to IP1-2. In contrast to the aggregation with protein, the reactivity of IP1-6 toward Fe3+ decreased proportionally from IP6 to IP3. Based on the radical decrease in turbidity of IP6-protein complex observed, as a result of IP6 dephosphorylation to IP5, a novel qualitative and semi-quantitative phytase plate assay was established using IP6-protein complex incorporated into an agarose petri-dish as substrate. Phytase activity was shown as the development of clear halos on the agarose plate with time. This simple phytase plate assay method can be used at animal farms, control laboratories, and even for the screening of engineered phytase variants. The current study, thus, stresses the importance of the efficient hydrolysis of IP6 at lower pH range to alleviate the negative effect of phytic acid and its degradation products on protein and Fe3+ digestion.