Potential of solid-state fermentation to enhance the nutritional value of oilseed cakes for poultry

The objective of this study was to evaluate the potential of solid-state fermentation (SSF) to enhance the nutritional value of oilseed cakes (OC) for poultry. To this end, firstly, we characterized the main nutrients and antinutritional factors in non-fermented OC and fermented OC, as well as in fermented and extracted OC, from where enzymatic extracts were recovered. The fermented and extracted OC represented the fermented residue obtained after SSF and extracted with distilled water. Secondly, we assessed the in vitro digestibility of dry matter (DM), organic matter (OM) and crude protein (CP) from these products using a poultry in vitro digestion model. The in vitro procedure used a two-stage sequential protocol simulating gastric digestion (proventriculus and gizzard - using pepsin in hydrochloric acid) and small intestinal digestion with pancreatin solution. Additionally, raw OC were supplemented with enzymatic concentrated extracts generated during SSF and their effect on nutrient digestibility was also evaluated. Solid-state fermentation exhibited a potential to reduce fiber fractions (except for lignin), decrease certain antinutritional factors, and enhance CP and mineral content in OC mixtures. However, this process concurrently diminished protein availability, through lower amino acid content, lower soluble protein, higher protein dispersibility and lower available lysine in the fermented product. The aqueous extractions led to the obtainment of a concentrated protein fraction with highly undigestible fibre. The likely effect of SSF on tannins and erucic acid content in OC should be further investigated, as SSF may not effectively reduce these antinutritional factors in the substrate, negatively affecting the overall nutritional quality of the final product. Solid-state fermented mixtures significantly increased the DM (by 12%), OM (by 8%), and CP (by 11%) in vitro digestibility coefficients compared with non-fermented. Enzymatic supplementation did not statistically modify digestibility parameters. This study demonstrated that SSF is an effective approach to obtain value-added products. However, it is crucial to ensure its effect on protein quality and amino acid availability is given special attention if applied to animal feed.