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By means of activity-guided fractionation using taste dilution analysis, liquid chromatography−tandem mass spectrometry (LC−MS/MS), liquid chromatography−time-of-flight mass spectrometry, one-/two-dimensional nuclear magnetic resonance spectroscopy, LC−MS/MS quantitation, dose-over-threshold considerations, and sensory spiking experiments, kaempferol 3-O-(2‴-O-sinapoyl-β-sophoroside), exhibiting a bitter taste above the low threshold concentration of 3.4 μmol/L, was found for the first time as the key molecule contributing to the unpleasant bitter taste of rapeseed (canola) protein isolates. This finding opens new avenues for a biorefinery approach targeting an off-taste removal.

The potential of rapeseed protein concentrate as fish meal alternative in diets for rainbow trout (initial average weight 37.8 ± 1.4 g) was evaluated. Nine experimental tanks of a freshwater flow-through system were stocked with 12 fish each. Triplicate groups of fish received isonitrogenous (47.9 ± 0.5% CP) and isoenergetic (22.4 ± 0.2 kJ g -1 ) experimental diets with 0, 66 and 100% of fish meal substituted with rapeseed protein concentrate (71.2% CP), thereby providing 0, 29 and 43% of dietary protein. As the amino acid profile of rapeseed protein concentrate was comparable to fish meal, there was no need to supplement experimental diets with synthetic amino acids. At the end of the 84 days of feeding period, fish growth performance, feed intake and feed efficiencies were not compromised, when 100% of fish meal in the control diet was replaced with rapeseed protein concentrate, revealing a SGR of 1.19 or 1.10, a FCR of 1.09 or 1.18 and a feed intake of 78.5 or 74.7 g in fish fed on the control diet or fed the diet devoid of fish meal, respectively. Intestinal morphology did not reveal any histological abnormalities in all dietary groups. Blood parameters including haematocrit and haemoglobin as well as glucose, triglycerides and total protein in the plasma were not different between treatment groups. Thus, the rapeseed protein concentrate tested here has great potential as an alternative to fish meal in rainbow trout diets.

The potential of rapeseed protein concentrate as fish meal alternative in diets for wels catfish (initial average weight 86.5 ± 1.9 g) was evaluated. Sixteen fish were stocked into each of 12 experimental tanks being part of a freshwater recirculation system. Fish were organized in triplicate groups and received isonitrogenous (603 ± 3 g CP kg )1 ) and isocaloric (23.0 ± 0.3 kJ g )1 ) experimental diets with 0%, 25%, 50% and 75% of fish meal replaced with rapeseed protein concentrate (710 g CP kg )1 ). At the end of the 63-day feeding period, weight gain, standard growth rate, feed intake, feed conversion ratio and protein efficiency showed no significant difference between control group and fish fed on diets with 25% reduced fish meal content by inclusion of rapeseed protein concentrate. Higher dietary fish meal replacement negatively affected diet quality and palatability resulting in reduced feed intake, feed efficiencies and fish performance. However, blood serum values of triglycerides, glucose and protein were not significantly different between treatment groups, still indicating a favourable nutrient supply from all experimental diets. KEY WORDS

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