Lactic acid fermentation eliminates indigestible carbohydrates and antinutritional factors in soybean meal for Atlantic salmon (Salmo salar)

This study investigated how lactic acid fermentation of extracted (de-oiled) soybean white flakes (WF) affected the nutritional value of the WF when fed to Atlantic salmon. WF and fermented WF (FWF) were compared with a commercial extracted (SBM) and a commercial biotechnologically processed (BPSBM) soybean meal. Lactic acid fermentation eliminated sucrose, reduced the level of raffinose, and lowered trypsin inhibitor activity in the FWF. Eight extruded diets were produced in which the soy products substituted LT-fish meal (FM) on a crude protein (CP) basis: No soy (LT-FM); 20% SBM; 20% WF; 20% FWF; 20% BPSBM; 40% WF; 40% FWF; and 40% BPSBM. Each diet was fed to triplicate groups of 188 g salmon maintained in 8.4 °C seawater for 68 days. The groups fed 40% FWF consumed slightly less feed than the other groups. The groups fed LT-FM and 20% BPSBM grew fastest, while those fed 40% WF and 40% FWF grew slowest and at similar rates. All soy products reduced the digestibility of lipid, but this effect was less severe when feeding the diets with FWF and BPSBM. Soybean meal-induced pathological changes in the intestine were less pronounced in fish fed FWF and BPSBM than in fish fed WF and SBM. The similar growth in the groups fed 40% WF and 40% FWF was attributed to higher digestibility of lipid and energy when feeding FWF. The intestinal microflora of the salmon appeared to utilise soy oligosaccharides, and also some pectin and mannan. To conclude, lactic acid fermentation improved the nutritional value of WF by partly eliminating feed allergen(s) and soy factor(s) that restrict the absorption of lipid by Atlantic salmon.