The Potential of Brewer’s Spent Grain in the Circular Bioeconomy: State of the Art and Future Perspectives

Impacts of industrial food wastes on nutritional value of mealworm (Tenebrio molitor) and its gut microbiota community shift

The extensive investigation into the capacity of mealworms to digest diverse food by-products, as well as plastic wastes, has been a focal point in recent years. The transition from traditional diet sources like brans to food wastes has the potential to impact the physiological properties of mealworms. This study explored the utilization of various industrial food wastes such as okara, barley spent grain (BSG), sesame oil meal (SOM), and spent coffee grounds (SCG) as feed alternatives, and reports on their survival rate, biomass variations, and nutritional composition. In additional, the shift in their gut microbiota was also assessed. Among the range of industrial food wastes, mealworms exhibited the most robust growth performance when nourished with BSG. This particular group showed a survival rate of 98.33 % and a biomass increase of 23.06 %. In contrast, mealworms fed with SCG demonstrated the lowest survival rate and experienced a significant reduction in biomass. Although the groups fed with okara and SCG displayed moderate growth performance, both exhibited protein levels comparable to those observed in the oatmeal-fed group (used as the positive control). Notably, the inclusion of BSG in the mealworm diet exhibited the potential to enrich their omega-3 fatty acid content, suggesting potential benefits for applications as animal feed or even human consumption. Furthermore, an analysis of the gut microbiome was conducted to investigate the associations between specific diets and the composition of mealworm gut microbiota. In summary, food wastes such as BSG may be repurposed as feed substrates for mealworms before converting them into an alternative source of protein.

The effect of L-cysteine on starch and protein degradation during barley germination

OBJECTIVES

In order to investigate the impact of L-cysteine (L-Cys) on starch and protein degradation during barley germination. The amylase activities, degradation of macromolecules during germination were determined in this study.

METHODS

Barley was germinated in petri dish for 0 to 5 days with different levels of L-Cys (0 mM, 2.5 mM, 5 mM, 10 mM).

RESULTS

L-Cys addition increased the total limit dextrinase (LD) activities and decreased the LD inhibitor activities during whole germination stage. The activities of α-amylase, β-amylase and free LD were increased with the addition of 2.5, 5 mM L-Cys at germination days 1 to 4. Due to higher amylase in malt with the addition of L-Cys, the non-fermentable sugars were reduced and the glucose, maltotriose were improved. Furthermore, the protein degradation analysis showed that low molecular weight protein increased and middle molecular weight protein decreased obviously in wort from the malt germinated with L-Cys, demonstrating that the L-Cys promote the protein degradation. Lastly, the filtration performance of malt with the addition of L-Cys during malting was better than the control.

CONCLUSION

In conclusion, L-Cys can promote the degradation of storage material (starch, protein) during barley germination, leading to a better green malt quality.

Food circular economy and safety considerations in waste management of urban manufacturing side streams

In food circular economy, the utilization of food manufacturing side streams (FMSS) offers significant potential instead of being discarded. However, reincorporating FMSS into the food value chain raises food safety concerns due to potential food hazards. This perspective explores food safety risks associated with circular management of FMSS by using a 'Quad-Modal hazard dynamic' approach with case studies. Future research and advancements in food safety control strategies are also discussed.

Prebiotic potential of spent brewery grain - In vitro study

Spent brewery grain (SBG) is a by-product of the brewery industry. The study aimed to investigate the prebiotic potential of SBG. The chemical composition and fermentation capacity of SBG were checked. The gut microbiota response to SBG was assessed in two in vitro models (batch fermentation and dynamic system). Substances with prebiotic properties, including arabinoxylans (16.7 g/100 g) and polyphenols (49.1 mg/100 g), were identified in SBG. Suitable growth and fermentation by probiotic bacteria were observed. The modulatory effect of gut microbiota depends on the in vitro system used. In batch fermentation, there was no stimulation of Bifidobacterium or lactic acid bacteria (LAB), but short-chain fatty acid (SCFA) and branched short-chain fatty acids (BCFA) synthesis increased. In dynamic, SBG exhibited a moderate bifidogenic effect, promoting Akkermansia and LAB growth while reducing Bacteroides and Escherichia-Shigella. SCFA stabilisation and reduction of BCFA content were noted. Moderate prebiotic effects were observed.

Soy whey and brewer's spent grain hydrolysates wholly replace conventional medium for microalgae growth: Process performance and economic considerations

To enhance circularity in heterotrophic microalgal bioprocesses, this study completely substituted glucose and Bold's basal medium (BBM) with brewer's spent grain (BSG) and soy whey (SW) hydrolysates. Mild acid hydrolysis conditions of BSG (0.2 M H2SO4, 130 °C, 36 min) and SW (0.1 M HCl, 95 °C, 30 min) were optimised for glucose release, and their hydrolysates were optimally mixed (15 % SW-85 % BSG) to obtain a medium that best supported Auxenochlorella protothecoides growth. Maximum biomass production (Xmax) and productivity (PXmax) obtained in the hydrolysate medium containing 50.75 g/L endogenous glucose (Xmax: 22.17 g/L; PXmax: 7.06 g/L/day) were comparable to that in BBM containing 50.44 g/L exogenous glucose (Xmax: 20.02 g/L; PXmax: 6.34 g/L/day). Moreover, estimated hydrolysate medium production costs were within an order of magnitude to BBM. Overall, the integrated approach of tailored hydrolytic treatments and complementary side-streams presents a promising technical and economic feasibility, with applications extending beyond A. protothecoides.

Recent advances in microbial high-value utilization of brewer's spent grain

Mitigating the adverse impacts of agricultural and industrial by-products on human populations and the environment is essential. It is crucial to continually explore methods to upgrade and reengineer these by-products. Brewer's Spent Grain (BSG), the primary by-product of the beer brewing process, constitutes approximately 85% of these by-products. Its high moisture content and rich nutritional profile make BSG a promising candidate for microbial utilization. Consequently, valorizing high-yield, low-cost BSG through microbial fermentation adds significant value. This paper provides a comprehensive overview of two valorization pathways for BSG via microbial processing, tailored to the desired end products: utilizing fermented BSG as a nutritional supplement in human or animal diets, or cultivating edible fungi using BSG as a substrate. The review also explores the microbial fermentation of BSG to produce valuable metabolites, laying a theoretical foundation for its high-value utilization.

Unlocking the Potential of Brewers' Spent Grain: A Sustainable Model to Use Beer for Better Outcome in Chronic Kidney Disease

The rising global incidence of chronic inflammatory diseases calls for innovative and sustainable medical solutions. Brewers' spent grain (BSG), a byproduct of beer production, presents a unique opportunity in this regard. This review explores the multifaceted health benefits of BSG, with a focus on managing chronic kidney disease (CKD). BSG is identified as a potent prebiotic with potential as a therapeutic agent in CKD. We emphasize the role of gut dysbiosis in CKD and discuss how BSG could help mitigate metabolic derangements resulting from dysbiosis and CKD. Fermentation of BSG further enhances its positive impact on gut health. Incorporating fermented BSG as a key component in preventive health care could promote a more sustainable and healthier future. By optimizing the use of this typically discarded byproduct, we can align proactive health-care strategies with responsible resource management, benefiting both people and the environment.

Exploiting Agri-Food Waste as Feed for Tenebrio molitor Larvae Rearing: A Review

The agri-food industry generates substantial amounts of waste, including by-products and residues. The increasing demand for sustainable and eco-friendly practices in the agri-food sector has sparked an interest in finding alternative uses for such waste materials. One promising approach is the utilization of waste from the agri-food industry as feed for the rearing of mealworms (Tenebrio molitor). Since agri-food waste is rich in proteins, carbohydrates, lipids, and vitamins, as well as other bioactive compounds, all of which are essential for insect growth and development, incorporating such waste into the diet of mealworms promotes sustainable insect production, reducing the economic and environmental problems associated with waste disposal. This practice can also be beneficial for the rearing of mealworms since their nutritional value can also be enhanced. To this end, various waste materials, such as fruit and vegetable peels, spent grains, and food processing residues, have been investigated as potential feed sources, leading to increased mass production, lower cost, and enhanced nutritional value. This review aims to highlight the potential of agri-food waste as a feed source for mealworms, as well as their potential to enhance their nutritional value. Furthermore, the potential applications of mealworms reared on agri-food waste are highlighted, including their potential as a sustainable protein source for human consumption and as feed ingredients in the livestock and aquaculture sectors.

Microbial community assembly and chemical dynamics of raw brewers' spent grain during inoculated and spontaneous solid-state fermentation

Solid-state fermentation (SSF) carried out by microbial bioinoculants is an environmentally friendly technology for the sustainable recovery and valorization of agri-food wastes. Particularly, mesophilic SSF processes allows the production of bio-organic fertilizers enriched with beneficial soil microorganisms. However, the establishment of microbial consortia and the interaction with native waste microbiota still require thoughtful investigations. Here, raw brewers' spent grain (BSG), the main waste from the brewing industry, was subjected to two mesophilic SSF processes (maximum temperature of 35 °C) carried out by a multi-kingdom microbial bioinoculant and the BSG spontaneous microbiota. After 90 days, both SSF processes led to stable organic soil amendments, as indicated by the C:N ratio (10.00 ± 1.4), pH (6.66 ± 0.09), and DOC (8.45 ± 1.2 mg/g) values. Additionally, the fermented BSG showed a high nitrogen content (42.2 ± 3.4 mg/Kg) and biostimulating activities towardLepidium sativumseeds. The monitoring of microbial communities by high-throughput sequencing of 16S and ITS rRNA indicated that BSG samples were enriched in microbial genera with interesting agronomic applications (i.e.,Devosia, Paenibacillum, Trichoderma, Mucor, etc.). Microbial cross-kingdom network analyses suggested that the microbial assembly of BSG was significantly influenced by the bioinoculant, despite the inoculated microbial genera being able to persist in BSG samples only the first week of SSF. This suggests that the study of microbial interactions between exogenous microbial inoculants and waste resident microbiota is required to optimize SSF processes aimed at the recovery and valorization of unprocessed wastes.

Synthesis of Poly-Lactic Acid by Ring Open Polymerization from Beer Spent Grain for Drug Delivery

Poly-lactic acid (PLA) is a synthetic polymer that has gained popularity as a scaffold due to well-established manufacturing processes, predictable biomaterial properties, and sustained therapeutic release rates. However, its drawbacks include weak mechanical parameters and reduced medicinal delivery efficacy after PLA degradation. The development of synthetic polymers that can release antibiotics and other medicines remains a top research priority. This study proposes a novel approach to produce PLA by converting Brewer's spent grain (BSG) into lactic acid by bacterial fermentation followed by lactide ring polymerization with a metal catalyst. The elution properties of the PLA polymer are evaluated using modified Kirby-Bauer assays involving the antimicrobial chemotherapeutical, trimethoprim (TMP). Molded PLA polymer disks are impregnated with a known killing concentration of TMP, and the PLA is evaluated as a drug vehicle against TMP-sensitive Escherichia coli. This approach provides a practical means of assessing the polymer's ability to release antimicrobials, which could be beneficial in exploring new drug-eluting synthetic polymer strategies. Overall, this study highlights the potential of using BSG waste materials to produce valuable biomaterials of medical value with the promise of expanded versatility of synthetic PLA polymers in the field of drug-impregnated tissue grafts.

Microbial alchemy: upcycling of brewery spent grains into high-value products through fermentation

Spent grains are one of the lignocellulosic biomasses available in abundance, discarded by breweries as waste. The brewing process generates around 25-30% of waste in different forms and spent grains alone account for 80-85% of that waste, resulting in a significant global waste volume. Despite containing essential nutrients, i.e., carbohydrates, fibers, proteins, fatty acids, lipids, minerals, and vitamins, efficient and economically viable valorization of these grains is lacking. Microbial fermentation enables the valorization of spent grain biomass into numerous commercially valuable products used in energy, food, healthcare, and biomaterials. However, the process still needs more investigation to overcome challenges, such as transportation, cost-effective pretreatment, and fermentation strategy. to lower the product cost and to achieve market feasibility and customer affordability. This review summarizes the potential of spent grains valorization via microbial fermentation and associated challenges.

Sequential Extraction and Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy Monitoring in the Biorefining of Brewer's Spent Grain

The brewing industry plays a significant role in producing a substantial annual volume of by-products, which contributes to the global accumulation of food waste. The primary by-product generated is brewer's spent grain (BSG), a lignocellulosic biomass rich in proteins, fiber, and moisture content. Leveraging biorefining and valorization techniques for BSG represents a promising strategy to enhance sustainability, resilience, and circularity within the brewing chain. To date, most studies have focused on extracting proteins from BSG. Yet, it is crucial to note that the fiber part of BSG also holds considerable potential for biorefining processes. This study introduces a novel sequential extraction method designed to integrally recover the major components of BSG. Notably, it introduces a reactive extraction approach that enables the simultaneous extraction and tuneable functionalization of the hemicellulose component. Additionally, the study assesses the utility of the attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy as a user-friendly tool to monitor and evaluate the effectiveness of the fractionation process. This spectroscopic technique can provide valuable insights into the changes and composition of BSG throughout the extraction process.

A specific H2/CO2 consumption molar ratio of 3 as a signature for the chain elongation of carboxylates from brewer's spent grain acidogenesis

Brewer's spent grain (BSG) is an undervalorized organic feedstock residue composed of fermentable macromolecules, such as proteins, starch, and residual soluble carbohydrates. It also contains at least 50% (as dry weight) of lignocellulose. Methane-arrested anaerobic digestion is one of the promising microbial technologies to valorize such complex organic feedstock into value-added metabolic intermediates, such as ethanol, H₂, and short-chain carboxylates (SCC). Under specific fermentation conditions, these intermediates can be microbially transformed into medium-chain carboxylates through a chain elongation pathway. Medium-chain carboxylates are of great interest as they can be used as bio-based pesticides, food additives, or components of drug formulations. They can also be easily upgraded by classical organic chemistry into bio-based fuels and chemicals. This study investigates the production potential of medium-chain carboxylates driven by a mixed microbial culture in the presence of BSG as an organic substrate. Because the conversion of complex organic feedstock to medium-chain carboxylates is limited by the electron donor content, we assessed the supplementation of H₂ in the headspace to improve the chain elongation yield and increase the production of medium-chain carboxylates. The supply of CO₂ as a carbon source was tested as well. The additions of H₂ alone, CO₂ alone, and both H₂ and CO₂ were compared. The exogenous supply of H₂ alone allowed CO₂ produced during acidogenesis to be consumed and nearly doubled the medium-chain carboxylate production yield. The exogenous supply of CO₂ alone inhibited the whole fermentation. The supplementation of both H₂ and CO₂ allowed a second elongation phase when the organic feedstock was exhausted, which increased the medium-chain carboxylate production by 285% compared to the N₂ reference condition. Carbon- and electron-equivalent balances, and the stoichiometric ratio of 3 observed for the consumed H₂/CO₂, suggest an H₂- and CO₂-driven second elongation phase, converting SCC to medium-chain carboxylates without an organic electron donor. The thermodynamic assessment confirmed the feasibility of such elongation.

Spent Grain: A Functional Ingredient for Food Applications

Spent grain is the solid fraction remaining after wort removal. It is nutritionally rich, composed of fibers—mainly hemicellulose, cellulose, and lignin—proteins, lipids, vitamins, and minerals, and must be managed properly. Spent grain is a by-product with high moisture, high protein and high fiber content and is susceptible to microbial contamination; thus, a suitable, cost-effective, and environmentally friendly valorization method of processing it is required. This by-product is used as a raw material in the production of many other food products—bakery products, pasta, cookies, muffins, wafers, snacks, yogurt or plant-based yogurt alternatives, Frankfurter sausages or fruit beverages—due to its nutritional values. The circular economy is built on waste reduction and the reuse of by-products, which find opportunities in the regeneration and recycling of waste materials and energy that become inputs in other processes and food products. Waste disposal in the food industry has become a major issue in recent years when attempting to maintain hygiene standards and avoid soil, air and water contamination. Fortifying food products with spent grain follows the precepts of the circular bio-economy and industrial symbiosis of strengthening sustainable development. The purpose of this review is to update information on the addition of spent grain to various foods and the influence of spent grain on these foods.

Functional Bread Produced in a Circular Economy Perspective: The Use of Brewers' Spent Grain

Brewers' spent grain (BSG) is the main by-product of the brewing industry, corresponding to ~85% of its solid residues. The attention of food technologists towards BSG is due to its content in nutraceutical compounds and its suitability to be dried, ground, and used for bakery products. This work was aimed to investigate the use of BSG as a functional ingredient in bread-making. BSGs were characterised for formulation (three mixtures of malted barley and unmalted durum (Da), soft (Ri), or emmer (Em) wheats) and origin (two cereal cultivation places). The breads enriched with two different percentages of each BSG flour and gluten were analysed to evaluate the effects of replacements on their overall quality and functional characteristics. Principal Component Analysis homogeneously grouped BSGs by type and origin and breads into three sets: the control bread, with high values of crumb development, a specific volume, a minimum and maximum height, and cohesiveness; Em breads, with high values of IDF, TPC, crispiness, porosity, fibrousness, and wheat smell; and the group of Ri and Da breads, which have high values of overall smell intensity, toasty smell, pore size, crust thickness, overall quality, a darker crumb colour, and intermediate TPC. Based on these results, Em breads had the highest concentrations of nutraceuticals but the lowest overall quality. Ri and Da breads were the best choice (intermediate phenolic and fibre contents and overall quality comparable to that of control bread). Practical applications: the transformation of breweries into biorefineries capable of turning BSG into high-value, low-perishable ingredients; the extensive use of BSGs to increase the production of food commodities; and the study of food formulations marketable with health claims.

Improvement of the Nutraceutical Profile of Brewer's Spent Grain after Treatment with Trametes versicolor

Brewer's spent grain (BSG) is an important secondary raw material that provides a readily available natural source of nutraceuticals. It finds its largest application as animal feed and part of the human diet, while the future perspective predicts an application in the production of value-added products. In order to investigate a sustainable BSG treatment method, two BSG samples (BSG1 and BSG2) were evaluated as substrates for the production of hydrolytic (xylanase, β-glucosidase and cellulase) and lignolytic enzymes (laccase, manganese peroxidase and lignin peroxidase) by solid-state fermentation (SSF) with Trametes versicolor while improving BSG nutritional value. The biological treatment was successful for the production of all hydrolytic enzymes and laccase and manganese peroxidase, while it was unsuccessful for the production of lignin peroxidase. Because the two BSGs were chemically different, the Trametes versicolor enzymes were synthesized at different fermentation times and had different activities. Consequently, the chemical composition of the two BSG samples at the end of fermentation was also different. The biological treatment had a positive effect on the increase in protein content, ash content, polyphenolic compounds, and sugars in BSG1. In BSG2, there was a decrease in the content of reducing sugars. Cellulose, hemicellulose, and lignin were degraded in BSG1, whereas only cellulose was degraded in BSG2, and the content of hemicellulose and lignin increased. The fat content decreased in both samples. The safety-related correctness analysis showed that the biologically treated sample did not contain any harmful components and was therefore safe for use in nutritionally enriched animal feed.