Combined effects of sodium chloride, citric acid, and autoclave conditions on apparent in vivo digestibility of rapeseed meal and macrophyte meal determined in common carp Cyprinus carpio

Abstract

Rapeseed meal (RM) and macrophyte meal (MM; made from Egeria densa) were autoclaved (120 °C) for 10 or 60 min, either before or after NaCl (Na) or citric acid (Cit) supplementation in order to increase their nutritive values as fish feed ingredients. Effects of these supplements and treatments were evaluated by measuring the in vivo apparent digestibility of crude protein (CP), organic matter, dry matter, and the net absorption of selected minerals using common carp Cyprinus carpio. The results showed that supplemental Na increased digestibility of CP, organic matter, and dry matter, and the absorption of P in RM, which is low in Na. Supplemental Cit increased the absorption of P and other minerals in both RM and MM. The timing of autoclaving was important for RM when Cit was added in order to increase the digestibility of CP, organic matter, and dry matter, and the absorption of Ca and Fe. The duration of autoclaving was also important for RM when Cit was added in order not to lower the digestibility of CP, organic matter, or dry matter. These results indicate that optimum autoclave timing and duration can vary depending on the combination of ingredients and supplements.