Optimization of solid state fermentation of dried distillers grains with solubles ( DDGS ) and its effect on performance and nutrient digestibility in European sea bass

To increase the nutritional value of coproducts from corn ethanol fermentation, distiller’s dried grains with solubles (DDGS) was used as a substrate for solid state fermentation (SSF). Firstly, the optimization of solid state fermentation condition of DDGS was carried out using different fungi: Aspergillus ibericus, A. niger, and A. uvarum; that were chosen based on its capacity to segregate exo-enzymes and good growth rates under SSF conditions. All the fungi performed well, although A. ibericus proved to be more efficient in upgrading the protein and exoenzymes (cellulase and xylanase) content of fermented DDGS, being chosen to perform SSF of DDGS, at a pilot scale, to produce an upgrading value fermented DDGS (SSF-DDGS). The efficacy of both DDGS and SSFDDGS as feed ingredients were then tested in a digestibility and growth trials with European seabass (Dicentrarchus labrax) juvenile. FCUP Optimization of solid state fermentation of DDGS and its effect on performance and nutrient digestibility in European sea bass 3 The digestibility trial was conducted to evaluate the apparent digestibility coefficients (ADC) of nutrients and energy of both ingredients, unfermented DDGS and fermented DDGS (SSF-DDGS), and the digestive enzymes activity. Digestibility was determined based on the substitution of 30% of a reference diet (47% CP; 15%CL) by each test ingredient. Compared to the unfermented DDGS, SSF-DDGS had higher ADC of protein (92.4 vs 98.3%), lipids (87.9 vs 98.3%) and energy (71.7 vs 89.6%) while dry matter and organic matter digestibility were not affected. Digestive lipases, trypsin and chymotrypsin activities were significantly higher with the DDGS or SSF-DDGS based diets that with the reference diet. Amylase activity has significantly higher for DDGS diet when compared with SSF-DDGS diet. The growth trial was conducted to evaluate the effect of dietary inclusion of DDGS or SSF-DDGS. Five experimental diets were formulated to be isoproteic (45% crude protein) and isolipidic (18% crude fat), including 20% of fishmeal. Test diets were formulated similarly to the control diet, but replacing the mixture of plant protein (soybean meal + wheat meal) of control diet by 10 or 20% of DDGS or SSF-DDGS. Final body weight, weight gain, and daily growth index were significantly lower in 20% DDGS or SSF-DDGS diets than in the control diet, while no differences were observed for feed intake and feed or protein utilization. Comparing the effect of fermented versus unfermented DDGS; the inclusion of 10% SSF-DDGS promoted higher weight gain and daily growth index that 10% DDGS diets, but did not affect feed intake and feed utilization. Protein efficiency ratio has also lower in 20% DDGS or SSF-DDGS than with the 10%SSF-DDGS diet. Overall, it’s concluded that SSF with A. ibericus is a suitable technique to upgrading the nutrient content and added exo-enzymes to DDGS, increasing significantly its digestibility. Moreover, the dietary replacement of 10% of soybean meal + wheat meal by DDGS is feasible, if the DDGS is previously submitted to the SSF. Otherwise, its incorporation will negatively affect growth performance of European sea bass juveniles. Therefore, it can be concluded that SSF-DDGS as a higher nutritional value than the unfermented DDGS, which increase its potential as a feedstuff for European sea bass.