Phytate analysis and phytase application in Jatropha curcas kernel meal for use in aquaculture feeds
Phytate is the main phosphate storage molecule in plants. Phytate phosphorus is not available to monogastric animals, in addition, phytate may reduce the digestibility of proteins and minerals. Studies on different photometrical methods for phytate analysis as well as phytase application in vitro and in vivo for Jatropha curcas kernel meal (JKM) have been conducted with the following outcomes: 1) several frequently-used methods for phytate analysis involving the Wade-reagent as a photo indicator severely overestimate the true phytate content of JKM, predominantly because of oxalate, and should not be used despite their comparative convenience; 2) in vitro incubation of JKM with 2000 U kg-1 phytase at pH 4.5 completely eliminates phytate, as well as other inositol phosphates (IPs), from the meal. Incubation at the same pH without phytase addition also led to complete phytate eradication from the meal, but left significant amounts of IP5 and IP4 (0.43% and 0.47%, respectively); 3) feeding Nile tilapia (Oreochromis niloticus) with a phytase containing JKM-based diet leads to a significant reduction of about 56% of phytate, 31% of IP5 and 100% of IP4 in the feces compared to a control diet. This is associated with significantly lower P-, Ca- and Zn-content in the feces and therefore presumably better assimilation of these minerals. Though significant reductions were observed, considerable amounts of IPs were still found in feces despite phytase addition. To achieve maximum availability of minerals from JKM, phytase pre-incubation seems a necessary step.