Valorization of Brewer’s Spent Grain Using Biological Treatments and its Application in Feeds for European Seabass (Dicentrarchus labrax)

Abstract

Brewer’s spent grain (BSG) is the main brewery industry by-product, with potential applications in the feed and food industries due to its carbohydrate composition. In addition, the lignocellulosic nature of BSG makes it an adequate substrate for carbohydrases production. In this work, solid-state fermentation (SSF) of BSG was performed with Aspergillus ibericus, a non-mycotoxin producer fungus with a high capacity to hydrolyze the lignocellulosic matrix of the agro-industrial by-products. SSF was performed at different scales to produce a crude extract rich in cellulase and xylanase. The potential of the crude extract was tested in two different applications: -(1) - the enzymatic hydrolysis of the fermented BSG and (2) - as a supplement in aquafeeds. SSF of BSG increased the protein content from 25% to 29% (w/w), while the fiber content was reduced to 43%, and cellulose and hemicellulose contents were markedly reduced to around 15%. The scale-up of SSF from 10 g of dry BSG in flasks to 50 g or 400 g in tray-type bioreactors increased 55% and 25% production of cellulase and xylanase, up to 323 and 1073 U g−1 BSG, respectively. The optimum temperature and pH of maximal activities were found to be 55°C and pH 4.4 for xylanase and 50°C and pH 3.9 for cellulase, cellulase being more thermostable than xylanase when exposed at temperatures from 45°C to 60°C. A Box–Behnken factorial design was applied to optimize the hydrolysis of the fermented BSG by crude extract. The crude extract load was a significant factor in sugars release, highlighting the role of hydrolytic enzymes, while the load of fermented BSG, and addition of a commercial β-glucosidase were responsible for the highest phenolic compounds and antioxidant activity release. The lyophilized crude extract (12,400 and 1050 U g−1 lyophilized extract of xylanase and cellulase, respectively) was also tested as an enzyme supplement in aquafeed for European seabass (Dicentrarchus labrax) juveniles. The dietary supplementation with the crude extract significantly improved feed and protein utilization. The processing of BSG using biological treatments, such as SSF with A. ibericus, led to the production of a nutritionally enriched BSG and a crude extract with highly efficient carbohydrases capable of hydrolyzing lignocellulosic substrates, such as BSG, and with the potential to be used as feed enzymes with remarkable results in improving feed utilization of an important aquaculture fish species.

Brewers’ Spent Grain: An Unprecedented Opportunity to Develop Sustainable Plant-Based Nutrition Ingredients Addressing Global Malnutrition Challenges

“…To compare, the composition of BSG alongside unmalted barley and some common cereal and legume sources is shown in Figure ; though it should be noted that this is a comparison between a byproduct whose nutritional value has been enhanced by processing and unprocessed cereal and legume raw materials. As most of the starch present in the barley grains is removed during the brewing process, the dietary fiber content of BSG can range from 40 to 50%, ,− significantly higher than that of unmalted barley, wheat, and oat (9–20%) ,− and legume sources including pea (14–21%), , soy bean (21–25%), , and faba bean (11–28%) ,, The main fiber constituent in BSG is hemicellulose which comprises 20–40% of the total composition. , The hemicellulose fraction of BSG primarily consists of arabinoxylan, a dietary fiber which has been linked with potential health benefits such as prebiotic activity, improved glycemic control, and antioxidant activity. ,− Cellulose and lignin are the other abundant polysaccharides in BSG, whose contents can range from 16 to 29%, ,, and 12 to 28%, respectively. ,− β-glucan is also present in low levels, normally in the range of ∼1% w/w …”

Potential of Red, Green and Brown Seaweeds as Substrates for Solid State Fermentation to Increase Their Nutritional Value and to Produce Enzymes

“…According to Fernandes et al [ 17 ], the SSF of unwashed U. rigida with A. ibericus led to a higher total polysaccharide reduction, along with higher cellulase and xylanase production. The same correlation between polysaccharide reduction and enzyme production was also observed using other substrates in SSF, such as brewer’s spent grain [ 63 ], or soybean and rapeseed cakes [ 56 ].…”

“…During SSF, the filamentous fungi partially degrade the substrate’s structural matrix through the production of carbohydrate-degrading enzymes [ 63 ]. The carbohydrate content before and after the seaweeds’ SSF is shown in Figure 2 .…”

Enhancing Antioxidants Extraction from Agro-Industrial By-Products by Enzymatic Treatment

“…The enzymatic treatment was performed according to the method described by Fernandes et al [ 16 ] with some modifications. Experiments were carried out in 100 mL Erlenmeyer flasks with 1 g of untreated agro-industrial by-products (COP, EOP, BSG and VTS) and 30 mL of sodium acetate buffer (0.1 mol L −1 , pH 4.6) was added.…”