By-products from the food sector with a high load of organic matter present both a waste-handling problem related to expenses and to the environment, yet also an opportunity. This study aims to increase the value of stale bread and brewers spent grain (BSG) by re-introducing these residues to the food production chain by converting them to new protein-enriched products using the edible filamentous fungi Neurospora intermedia and Rhizopusoryzae. After 6 days of solid state fermentation (at 35°C, with a95% relative humidity and moisture content of 40% in the substrate) on stale bread, a nutrient-rich fungal-fermented product was produced. The total protein content, as analyzed by total amino acids, increased from 16.5% in stale sourdough bread to 21.1% (on dry weight basis) in the final product with an improved relative ratio of essential amino acids. An increase in dietary fiber, minerals (Cu, Fe, Zn) and vitamin E, as well as an addition of vitamin D2 (0.89 µg/g dry weight sample) was obtained compared with untreated stale bread. Furthermore, addition of BSG to the sourdough bread with the aim to improve textural changes after fermentation showed promising outcomes. Cultivation of N. intermedia or R. oryzae on stale sourdough bread mixed with 6.5% or 11.8% BSG, respectively, resulted in fungal-fermented products with similar textural properties to a commercial soybean burger. Bioconversion of stale bread and BSG by fungal solid state fermentation to produce a nutrient-enriched food product was confirmed to be a successful way to minimize food waste and protein shortage.

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From stale bread and brewers spent grain to a new food source using edible filamentous fungi.

Valorization of brewer’s spent grain using fungi solid-state fermentation to enhance nutritional value

Brewers' spent grain (BSG) is the most abundant by-product of brewing. Due to its microbiological instability and high perishability, fresh BSG is currently disposed of as low-cost cattle feed. However, BSG is an appealing source of nutrients to obtain products with high added value through microbial-based transformation. As such, BSG could become a potential source of income for the brewery itself. While recent studies have covered the relevance of BSG chemical composition in detail, this review aims to underline the importance of microorganisms from the stabilization/contamination of fresh BSG to its biotechnological exploitation. Indeed, the evaluation of BSG-associated microorganisms, which include yeast, fungi, and bacteria, can allow their safe use and the best methods for their exploitation. This bibliographical examination is particularly focused on the role of microorganisms in BSG exploitation to (1) produce enzymes and metabolites of industrial interest, (2) supplement human and animal diets, and (3) improve soil fertility. Emerging safety issues in the use of BSG as a food and feed additive is also considered, particularly considering the presence of mycotoxins.Key points• Microorganisms are used to enhance brewers' spent grain nutritional value.• Knowledge of brewers' spent grain microbiota allows the reduction of health risks. Graphical abstract.

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The role of microorganisms on biotransformation of brewers' spent grain.

In this study a valuable fermented brewer’s spent grain (BSG) was obtained by solid state fermentation (SSF) with Rhizopus sp. and assessed for feed and food applications. SSF conditions were optimized by factorial design and response surface methodology (RSM) to maximize the value of the resulting BSG biomass. Two Rhizopus sp. strains were tested as inoculum (one wild and one mutant strain) and time and temperature were analyzed. Measured response variables included, among others, protein content, soluble protein, degree of hydrolysis, antioxidant activity, total phenolic content and antibacterial activity. Both strains led to the highest protein concentration (31.7 ± 7.6%) and soluble protein (47.4 ± 3.8 mg/g DM) when BSG was fermented at 30 °C for 9 days. The biomass obtained presented a modified amino acid profile resulting in an essential amino acid index (EAAI) of 1.58 compared to FAO human nutrition standard, with antioxidant capacity (59.7 ± 7.7% DPPH reduction) and 11 times higher total polyphenol content (2.7 ± 0.1 mg GAE/g DM). Hereby, results demonstrate that SSF of BSG results in a significant increase of highly appreciated characteristics for feed or food applications, which could lead to a promising valorization alternative.

Solid State Fermentation of Brewer’s Spent Grain Using Rhizopus sp. to Enhance Nutritional Value

Food byproducts derived from industrial processing present high potential to be reused as ingredients for human nutrition. However, even though food byproducts are often reprocessed and studied, few studies report the inclusion of such byproducts on new food products and assess the new product acceptability. Therefore, on our work guava peels and cashew bagasse were subjected to solid-state fermentation for protein enrichment through single-cell protein and then included on cereal bars for human nutrition. The solid-state fermentation of fruit byproducts was carried out at 30 °C, with 70% equilibrium humidity, 0.9 water activity, and initial Saccharomyces cerevisiae yeast concentration of 3% for the cashew bagasse and 5% for the guava peels. The protein-enriched byproducts were included on three different formulations of cereal bars, and physicochemical, instrumental texture, and sensorial analysis was performed. Multivariate analysis was used to investigate the results. Solid-state fermentation resulted in increased 11 times the protein content of both byproducts. Instrumental texture revealed that high dietary fiber content increases hardness and cohesiveness. All cereal bars presented average scores of 7/10 for sensorial attributes and average 4/5 for purchase intention. During the storage period the cereal bars presented increases in the textural parameters when compared to the control bars. However, all samples revealed compositional stability during the 28-day test period. The overall results suggest that the addition of protein-enriched byproducts is an alternative to add nutritional and economic value to cereal bars.

Solid-state fermentation for single-cell protein enrichment of guava and cashew by-products and inclusion on cereal bars

Brewery spent grain represents approximately 85 % of total by-products generated in a brewery. Consisting of carbohydrates, fiber, minerals and low amounts of protein, the use of brewery spent grain is limited to the feeding of ruminants; however, its potential use should be investigated. The reuse of this by-product using microorganisms by solid-state fermentation process as the case of protein enrichment by single-cell protein incorporation is an alternative to ensure sustainability and generate commercially interesting products. In this context, the aim of this study was to grow Rhizopus oligosporus in brewery spent grain under different initial moisture contents and nitrogen sources to increase the protein content of the fermented material. After 7 days of fermentation, increase of 2–4 times in the crude protein and soluble protein content was verified, respectively, compared to unfermented brewery spent grain. The kinetics of protein enrichment demonstrated the possibility of application of this technique, which can be a great alternative for use in diets for animals.

Protein enrichment of brewery spent grain from Rhizopus oligosporus by solid-state fermentation

The aim of this work was to obtain Brazil-soluble Brazil nut extract on a pilot scale, to determine the physical-chemical, microbiological, sensory and rheological characteristics of the products obtained and to determine the microbiological, physical-chemical and physical stability of the extract in presence and absence light and preservatives. This is a quantitative study, carried out in the laboratory. Extracts were characterized in terms of physicochemical (proximate composition, mineral profile, pH, titratable acidity, color), rheological (apparent viscosity, flow index, consistency coefficient), microbiological (yeast and molds, Salmonella sp., coliforms at 35oC and at 45oC and coagulase positive Staphylococcus), and sensory (odor, color, taste, global impression, buying intention) parameters. Furthermore, the effect of the addition of preservatives (500 mg/L citric acid, 0.15% w:v sodium benzoate and 0.1% w:v potassium sorbate) and of the exposure to light on the physicochemical (pH, titratable acidity), physical (color variation) and microbiological stabilities throughout storage were assessed. The extracts had high energy content, due to its high protein and fat contents, besides being a valuable source of selenium. The extracts were characterized as non-Newtonian pseudoplastic fluids, and were well accepted in sensory analysis, with up to 60% of the consumers indicating willingness to buy the product. The presence of preservatives at least doubled the shelf-life of the products, from 9 to up to 21 days. The incidence of light had no effect in the stability of the extracts.

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Marianny Silva Canedo

Papers

Protein enrichment of brewery spent grain from Rhizopus oligosporus by solid-state fermentation

Processing, characterization and stability of Brazil nut (Bertholletia excelsa) extract