News last update:6 Aug 2012

Bacterial protein influences feed quality

Margareth Øverland and colleagues from the Aquaculture Protein Centre of the Norwegian University of Life Sciences in Ås looked at the effects of adding bacterial protein on dog food and salmon feed quality after different extrusion conditions.

The results demonstrate that low amounts of Bacterial protein meal (BPM) and its homogenate (HOM) influenced the technical quality of extruded diets for dogs and salmon. The effect of BPM and HOM was different in dog food with higher starch content compared to the salmon feed with lower starch content, and was dependent on extrusion conditions.

Experimental set up
BPM shows great potential as a raw ingredient in fish feed, and it has characteristics that can make us less reliant on fish meal in the production of feed for the aquaculture industry. The effect of BPM and its HOM on length, expansion, density, sinking rate, fat leakage, durability, and breaking force of extruded dog food and salmon feed exposed to mild and moderate processing conditions was evaluated.

The treatment consisted of a control diet and four test diets where high-quality (low temperature dried; LT) fish meal was partly replaced with either 25 or 50 g BPM or HOM per kg. The differences in processing characteristics were obtained by a combination of conditioner and extruder adjustments. Fat was added to the extruded diets by vacuum coating.

Results in dog food
In the dog diets, the inclusion of BPM and HOM resulted in shorter pellets with increased diametric expansion, and reduced dust percentage, sinking rate and breaking force, with the effect being in general greatest with the highest concentration.
In general, moderate feed processing resulted in increased pellet length and expansion while sinking rate and fat leakage decreased in both the BPM and HOM diets.
Neither BPM nor HOM affected fat leakage, but fat leakage decreased by moderate processing.

Results in salmon diets
In the salmon diets, dietary BPM and HOM increased density and breaking force, but decreased durability and had no effect on sinking rate or fat leakage of the extruded salmon pellets.
A significant interaction between feed processing and bacterial protein source was found for pellet length and diameter. Moderate feed processing increased pellet length in the BPM diets but reduced pellet length and increased pellet expansion in the HOM diet. Moderate processing decreased durability and sinking rate of the pellets.

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