Solid-state fermented brewer's spent grain enzymatic extract increases in vitro and in vivo feed digestibility in European seabass

Abstract

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.

Figure 1

Flow chart of the experimental design.

Figure 2

Total phosphorus (a) and phytate phosphorus (b) release (mg g⁻¹ of diet) from control (filled black square) and BSG0.4 (filled black triangle) diets under the simulated conditions of European seabass digestive tract. Stomach and intestinal digestion are represented in dark and light grey, respectively. Values are presented as the mean of the cumulative values ± standard deviation.

Figure 3

Pentoses release (µg g⁻¹ of diet) from BSG0.4 diet with inactivate fish enzymes (filled black square), inactive BSG 0.4 diet with active fish enzymes (filled black triangle) and both inactive BSG 0.4 diet and fish enzymes (filled black cirle), under the simulated conditions of European seabass digestive tract. Stomach and intestinal digestion are represented in dark and light grey, respectively. Values are presented as the mean of the cumulative values ± standard deviation.

Figure 4

Pentoses release (mg g⁻¹ of diet) from the different experimental diets under the simulated conditions of the European seabass digestive tract with active (continuous line) and inactive fish enzymes (dashed line). The slope of linear fitting provides the rate of release of pentoses per hour (mg g⁻¹ of diet h⁻¹). Stomach and intestinal digestions are represented in dark and light grey, respectively. Values expressed as mean ± standard deviation. Asterisks indicate significant differences between active and inactive fish enzymes (p < 0.05).

Figure 5

Amino acids release (mg g⁻¹ of diet) from the different experimental diets under the simulated conditions of the European seabass digestive tract with active (continuous line) and inactive fish enzymes (dashed line). The slope of linear fitting provides the rate of release of amino acids per hour (mg g⁻¹ of diet h⁻¹). Stomach and intestinal digestions are represented in dark and light grey, respectively. Values expressed as mean ± standard deviation. Asterisks indicate significant differences between active and inactive fish enzymes (p < 0.05).