Olive pomace is characterized by its low nutritional value and high phenolic content, which hinders its direct use as animal feed, fertilizer, or as a substrate in bioprocesses such as solid-state fermentation (SSF). A possible strategy for bioprocessing olive pomace by SSF is the mixture of olive mill wastes with other wastes produced in the same region, such as winery wastes. This may improve the production of bioactive compounds like enzymes and antioxidant phenolics. A simplex-centroid design was used to evaluate the use of olive mill and winery wastes alone or in combination as a substrate for SSF with Aspergillus niger and Aspergillus ibericus. Synergistic effects of combinations of crude olive pomace (COP), exhausted olive pomace (EOP), vine trimming shoots (VTS), and exhausted grape marc (EGM) were observed in the production of xylanases, cellulases, β-glucosidases, and in the variation in total phenolics and antioxidant activity of SFF extracts. A multiple response optimization was carried out, leading to the following optimal mixture of substrates: for A. niger, 23% (w/w) COP, 30% EGM, 33% VTS, 14% EOP; for A. ibericus, 30% EGM, 36% VTS, 34% EOP. The scale-up to tray bioreactor with optimal substrate made it possible to achieve the maximum xylanase, cellulase, and β-glucosidase production of 189.1 ± 26.7, 56.3 ± 2.1 and 10.9 ± 0.8 U/g, respectively. The antioxidant activity of fermented wastes was also improved 2.2-fold as compared with unfermented wastes. Thus, a combination of olive mill and winery wastes in SSF is a potential strategy to increase their value and to develop a circular strategy in these industries.

Agricultural, forestry, and food industries produce large amounts of lignocellulosic wastes every year. Land disposal of these residues without proper treatment leads to environmental pollution and negative health effects. The recent advances in valorization of agro-industrial wastes by the production of lignocellulolytic enzymes under solid-state fermentation (SSF) are reviewed. SSF is a promising technology to produce lignocellulolytic enzymes. However, the large-scale feasibility is the main challenge of SSF being the control of operational parameters and adequate reactor design the first locks. The current and future trends of SSF bioreactors for lignocellulolytic enzyme production are summarized. SSF allows the production of lignocellulolytic enzymes with high stability at different temperatures and pH, improving their applicability in different industrial settings.

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In a previous study, it was shown that dietary supplementation with a carbohydrases and antioxidant-enriched extract (BSG-extract) produced by solid-state fermentation of brewer’s spent grain (BSG) improved nutrients digestibility, feed, and protein utilization of European seabass juveniles. This work aims to investigate the effect of this BSG-extract on liver and intestine oxidative status and muscle lipid peroxidation (LPO) of European seabass. A plant-based diet (55.4% plant feedstuffs; PF) was used as a control. Four test diets were formulated by supplementing the control diet with the BSG-extract (0.4 or 0.8% diet), added directly to the diet (BSG4 and BSG8 diets), or used to pre-treat the PF mixture of the control diet (PreBSG4 and PreBSG8 diets). European seabass juveniles (IBW 22 ± 1  g) were fed the experimental diets for 66 days until apparent satiety. In fish fed BSG-extract diets, compared to the control diet, intestinal LPO was reduced up to 29-40% ( p < 0.05 ); GPX, GR, and G6PD activities were increased compared to the control ( p < 0.05 ). In the liver, LPO was similar among diets, but except for catalase and G6PD, fish fed BSG-extract diets had higher antioxidant enzyme activities than the control ( p < 0.05 ). Except for the liver SOD activity, hepatic and intestinal antioxidant capacity was not affected by the dietary BSG-extract incorporation mode ( p > 0.05 ). After 72 h of storage at 4°C, muscle LPO was higher than at time 0 h. Compared to the control, BSG-extract reduced muscle LPO levels up to 30% at time 0 h in fish fed diets BSG4, BSG8, and PreBSG8 ( p < 0.008 ). Results indicate that dietary supplementation with BSG-extract increased the antioxidant level of diets, improved the intestine antioxidant capacity, and decreased LPO in European seabass juveniles’ muscle.

Solid-state fermentation (SSF) is a process that can use agroindustry solid residues as substrate for microbial growth. During SSF, value-added products and fermented biomass are generated contributing for the reutilization of otherwise pollutant agroindustry wastes. By SSF, fungi can hydrolyze anti-nutritional factors of plantbased residues, as the lignocellulosic matrix, and produce enzymes, phenolic compounds and other bioactive compounds, making this a high interest bioprocess for the aquafeed industry. The present study optimized (simplex centroid design) the mixture of winery and olive mill wastes to produce lignocellulolytic enzymes and to extract phenolic compounds through SSF by Aspergillus niger. The substrate mixture that maximized the production of lignocellulolytic enzymes, antioxidant and phenolic compounds was 0.44 g exhausted olive pomace/gds; 0.3 g exhausted grape marc/gds; 0.15 g vine-shoot trimmings and 0.1 g crude olive pomace/gds. The crude extract will be applied as additive in meagre (Argyrosomus regius) diets, to improve the feed utilization efficiency of low-fish meal-based diets, contributing to the sustainability of aquafeeds.

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This study aimed to evaluate the effects of dietary inclusion of plant feedstuff mixture (PFM) pre-treated by solid-state fermentation (SSF) on the physiological responses of European seabass. For that purpose, two diets were formulated to contain: 20% inclusion level of non-fermented plant ingredients mixture (20Mix) and 20Mix fermented by A. niger in SSF conditions (20Mix-SSF). Seabass juveniles (initial body weight: 20.9 ± 3.3 g) were fed the experimental diets, reared at two different temperatures (21 and 26 °C) and subjected to weekly salinity oscillations for six weeks. Growth performance, digestive enzyme activities, humoral immune parameters, and oxidative stress indicators were evaluated. A reduction in weight gain, feed intake, and thermal growth coefficient was observed in fish fed the fermented diet (20Mix-SSF). Salinity oscillation led to an increase in weight gain, feed efficiency, daily growth index, and thermal growth coefficient, regardless of dietary treatment. Higher rearing temperatures also increased daily growth index. No dietary effect was observed on digestive enzymes activities, whereas rearing temperature and salinity oscillation modulated digestive enzyme activities. Oxidative stress responses were significantly affected by experimental diets, temperature, and salinity conditions. Catalase and glutathione peroxidase activities showed an interactive effect. Fish reared at 21 °C showed higher enzymatic activity when fed the 20Mix-SSF. Conversely, fish reared at 26 °C showed higher GPx activity when fed the 20Mix diet. Fish reared at 26 °C showed reduced peroxidase and lysozyme activities, while salinity fluctuation led to increased lysozyme activity and decreased ACH50 activity. ACH50 activity increased in fish fed the 20Mix-SSF. Overall, the dietary inclusion of PFM fermented by A. niger was unable to mitigate the impact of environmental stress on physiological performance in European seabass. In fact, fermented feed caused an inhibition of growth performances and an alteration of some physiological stress indicators.