Phytate hydrolysis in pigs fed a barley-rapeseed meal diet treated with Aspergillus niger phytase or steeped with whey

The degradation of phytate (myo-inositol hexaphosphate) in a barley-rapeseed meal (80:20) diet due to supplemented Aspergillus niger phytase and steeping (soaking at 40 °C for 3 h with feed to water ratio 1 kg:1 L) with whey was studied in eight growing pigs (initial weight 27.8 kg). Phytate and its hydrolysis products (inositol penta-, tetra- and triphosphates, abbreviated IP5, IP4 and IP3) in diets and feces were determined using ion-pair high-performance liquid chromatography (HPLC). Different isomeric forms of inositol tetra- and pentaphosphates were studied utilizing high-performance ion chromatography (HPIC). Supplementing the diet with microbial phytase resulted in a 47% reduction in the amount of fecal phytate. Whey steeping of the diet reduced fecal phytate by 35%. Further reduction of the amount of fecal phytate (64%) was demonstrated in pigs fed the diet both steeped with whey and supplemented with microbial phytase, compared with pigs fed the untreated diet. Identification of IP4 and IP5 isomers in fecal samples showed which kind of phytase enzyme was active during phytate hydrolysis in the digestive tract. From these data, it was concluded that pigs fed the basal or whey steeped diet, without supplemented microbial phytase, had higher relative fecal amounts of DL-Ins(1,2,3,4,5)P5, compared with pigs fed the microbial phytase supplemented diets. Adding microbial phytase to the diet increased the relative amount of DL-Ins(1,2,4,5,6)P5 in feces. With whey steeping of the diet, the relative amount of DL-Ins(1,2,3,4)P4 isomer in feces was increased and the relative amount of DL-Ins(1,2,5,6)P4 isomer was decreased. Key words: Inositol phosphates, steeping, Aspergillus niger phytase, pig