A standard diet for zebrafish, based on their specific nutritional requirements, is of primary importance to improve experimental outcomes with this model organism and optimize its large-scale production. However, the main basic nutritional requirements of zebrafish are yet to be determined. This study aimed at contributing to fill this gap by evaluating the dietary protein requirement of zebrafish juvenile. Ten isoenergetic fishmeal-based diets with increasing protein levels (15%-60%) were formulated, and each diet was assigned to duplicated groups of zebrafish (53.6 mg/17.8 mm initial mean body weight/fork length), fed to apparent satiation during 8 weeks. Weight gain, protein retention, and feed efficiency significantly increased in fish fed diets with increasing protein levels up to 35%-40% and then stabilized. Based on dose-response models, the dietary protein requirement of zebrafish juvenile was estimated at 37.6% and 44.8% for maximum weight gain and maximum protein retention, respectively (with a crude protein-to-energy ratio of about 22.5 g/MJ), corresponding to a protein intake of 14 mg/g average body weight/day. Feed intake increased linearly when fish were fed diets with decreasing protein levels below the estimated requirement, suggesting that zebrafish would regulate feed intake primarily to meet protein needs. On the other hand, the efficiency of protein utilization and retention linearly decreased when fish were fed diets with increasing protein levels above the estimated requirement, indicating that the excess of dietary protein would be deaminated, contributing to increased ammonia excretion. The whole-body composition of fish was affected by the dietary protein level, with fish fed diets with higher protein levels having higher water and protein contents and lower energy content. Considering that zebrafish juveniles are often reared with diets containing excessive amounts of protein, we suggest that the estimated protein requirement should be taken into account to formulate a more suitable, cost-effective, and less pollutant diet for this species.

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A B S T R A C TThe macroalgae aquaculture industry has grown up in the last years, and new applications for macroalgae should be considered. In this work, sequential biological treatments as solid-state fermentation (SSF) by Aspergillus ibericus and enzymatic hydrolysis (EH) were applied to washed and unwashed Ulva rigida. SSF of unwashed macroalgae showed higher xylanase (359.8 U/g), cellulase (73.07 U/g) and β-glucosidase (14.9 U/g) activities per dry mass of macroalgae. After SSF, two strategies to carry out EH were assayed. The best process was SSF followed by EH by simply adding a buffer. The non-starch polysaccharides content was reduced by 93.2%, achieving a glucan conversion of 98%. In addition, the antioxidant activity was improved 2.8-fold and the protein concentration of macroalgae extracts increased from 16.9% to 29.8% (w/w). These biological treatments allowed to increase macroalgae value as feedstuff with potential for use in aquafeeds. 2015). Even thought, macroalgae are usually dried to be preserved, SSF

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.

Brewer’s spent grain (BSG) is the largest by-product originated from the brewery industry with a high potential for producing carbohydrases by solid-state fermentation. This work aimed to test the efficacy of a carbohydrases-rich extract produced from solid-state fermentation of BSG, to enhance the digestibility of a plant-based diet for European seabass (Dicentrarchus labrax). First, BSG was fermented with A. ibericus to obtain an aqueous lyophilized extract (SSF-BSG extract) and incorporated in a plant-based diet at increasing levels (0—control; 0.1%, 0.2%, and 0.4%). Another diet incorporating a commercial carbohydrases-complex (0.04%; Natugrain; BASF) was formulated. Then, all diets were tested in in vitro and in vivo digestibility assays. In vitro assays, simulating stomach and intestine digestion in European seabass, assessed dietary phosphorus, phytate phosphorus, carbohydrates, and protein hydrolysis, as well as interactive effects between fish enzymes and dietary SSF-BSG extract. After, an in vivo assay was carried out with European seabass juveniles fed selected diets (0—control; 0.1%, and 0.4%). In vitro digestibility assays showed that pentoses release increased 45% with 0.4% SSF-BSG extract and 25% with Natugrain supplemented diets, while amino acids release was not affected. A negative interaction between endogenous fish enzymes and SSF-BSG extract was observed in both diets. The in vivo digestibility assay corroborated in vitro data. Accordingly, the dietary supplementation with 0.4% SSF-BSG increased the digestibility of dry matter, starch, cellulose, glucans, and energy and did not affect protein digestibility. The present work showed the high potential of BSG to produce an added-value functional supplement with high carbohydrases activity and its potential contribution to the circular economy by improving the nutritional value of low-cost and sustainable ingredients that can be included in aquafeeds.

Oilseed cakes have potential for new applications as substrates for solid-state fermentation (SSF), to increase their nutritional value by increasing its polyunsaturated fatty acids (PUFAs) or protein content. In this sense, it was performed a screening of oilseed cakes to be used as substrates for the production of PUFAs by Mortierella alpina Peyronel MUM 9412. Of all by-products tested, linseed cake (LSC) was the oilseed cake that achieved the highest production of total PUFAs: 153.09 ± 2.25 mg/g. Overall, the PUFAs and protein contents of fermented LSC increased 33% and 11%, respectively. Further, supplementation of the rapeseed cake with linseed oil, prior to the SSF, proved to increase the PUFAs production in about 26%. This study demonstrated the potential of SSF for improving linseed and linseed cakes nutritional composition and the positive effect of linseed oil as inductor to improve the PUFAs production by M. alpina.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the infectious agent that has caused the current coronavirus disease (COVID) pandemic. Viral infection relies on the viral S (spike) protein/cellular receptor ACE2 interaction.