Effect of toasting on phytic acid, protein and pH in a plant-based diet and its ingesta in fed catfish

Feed accounts for up to 70% of production costs in aquaculture, hence reducing this cost is needed for rural development. Plant ingredients commonly used in feed contain phytic acid that forms indigestible complexes with nutrients thus reducing their use for fish growth. Toasting feed material is widely practiced to reduce antinutrients but its effect on phytic acid remains unclear. In the study, phytic acid, crude protein (CP) and pH in plant-based diets from untoasted and toasted ingredients and their ingesta along the gut were analysed using complex-metric titration, Kjeldahl method and micro pH meter, respectively. Phytic acid in the diet from untoasted and toasted ingredients differed (p ≤ 0.002) while CP and pH did not (p ≥0.06 and p ≤ 0.40, respectively). The content of phytic acid in the diet doubled along the gut, CP halved and pH was 5.30 - 7.78. Diet from untoasted ingredients was not eaten thus no ingesta was analysed. Results showed that toasting plant ingredients had no effect on phytic, CP and pH implying that replacing animal protein with plant protein depends on proper pre-treatment of phytic acid.