In vivo and In vitro digestibility of different novel canola protein concentrates developed by solid state fermentation technique in Rainbow Trout Oncorhynchus mykiss

The need to reduce fishmeal use and improve feed efficiency in salmonid nutrition has created a major challenge of developing novel feed ingredients for aquafeeds. One sustainable approach to deal with this challenge is producing renewable concentrated proteins using plant proteins. Canola meal is the second most grown plant protein source after soybean meal and accounts for about 13% of the world production of protein meals (253.27 mt) in 2010-2011. Solid state fermentation is an environmentally friendly bio-processing method for producing concentrated plant proteins. The aim of the current study was to investigate in vivo and in vitro apparent digestibility (AD) of canola protein concentrates produced using solid state fermentation technology in rainbow trout.

The fermented canola protein concentrates produced by Neurospora sitophila (10⁷ spore/g; FCPC) and Rhizopus microsporus var. oligosporus (10⁶ and 10⁷ spore/g; FCPC1 and FCPC2, respectively) were included in experimental diets (consisting 30% of each ingredient and 70% basal diet). Rainbow trout (initial weight, 29.5±2.8 g) were held in a recirculation system (3 tanks per treatment, 30 fish per 120-l tank). Culture conditions (T, 17±0.3°C; pH, 7.0±0.15; DO, 7.7±0.16 mg O2/l; photoperiod, 12L:12D) were regulated based on the optimum ranges reported for salmonids with a daily water exchange rate of 10%. To measure AD the experimental diets were fed to satiation for 9 days. Faeces were then collected over a 7 day period in a Guelph system and freeze dried. After anesthetizing the fish with clove oil (100 ppm), the pyloric caeca (15 fish per treatment) were collected, homogenized with distilled water (1:5 w/v) and then centrifuged (13000 ×g, 20 min at 4°C) for enzyme extraction at -80°C. In vivo ADs of dry matter (92.05%), crude protein (87.03%) and gross energy (88.47%) of FCPC2 were significantly (P<0.05) higher than those of FCPC1 (74.45, 72.37 and 71.74%) and FCPC (77.86, 73.22 and 75.15%), respectively.

In vivo ADs of sulfur amino acids (methionine and cysteine) (92.55%) and lysine (94.65%) of FCPC2 were significantly (P<0.05) higher than other concentrates. In vitro ADs of dry matter (68.16%), crude protein (70.46%) and gross energy (65.24%) of FCPC were significantly (P<0.05) higher than those of FCPC1 (49.93, 54.34 and 51.0%). There were significant (P<0.05) regressions (R²=82.4-85.5) between in vivo and in vitro ADs for dry matter, crude protein and gross energy. Differences among ADs may be related to the metabolism rate of fungi leading to over bio-processing of nutrients and the production of unknown compounds competing with amino acids during intestinal absorption and interfering with their absorption.