applied sciences Review Brewer’s Spent Grains: Possibilities of Valorization, a Review Ancut, a Chetrariu and Adriana Dabija * Faculty of Food Engineering, Stefan cel Mare University of Suceava, 720229 Suceava, Romania; ancuta.chetrariu@fia.usv.ro * Correspondence: adriana.dabija@fia.usv.ro; Tel.: +40-748-845-567 Received: 3 August 2020; Accepted: 12 August 2020; Published: 13 August 2020 Abstract: This review was based on updated research on how to use brewer’s spent grains (BSG). The use of BSG was considered both in food, as an ingredient or using value-added components derived from brewer’s spent grain, or in non-food products such as pharmaceuticals, cosmetics, construction, or food packaging. BSG is a valuable source of individual components due to its high nutritional value and low cost that is worth exploiting more to reduce food waste but also to improve human health and the environment. From the bioeconomy point of view, biological resources are transformed into bioenergetically viable and economically valuable products. The pretreatment stage of BSG biomass plays an important role in the efficiency of the extraction process and the yield obtained. The pretreatments presented in this review are both conventional and modern extraction methods, such as solvent extractions or microwave-assisted extractions, ultrasonic-assisted extractions, etc. Keywords: brewer’s spent grain; bioeconomy; valuable compounds 1. Introduction While global hunger still plays an important role affecting millions of people, there is an overproduction of food in developed countries. High production of food includes a big amount of waste. Around 90 million tons of food waste per year are produced, which causes serious environmental problems [1], but the waste reduction has become of interest to researchers, thus alternative uses can be found [2]. Food waste can be an important source of carbohydrates, proteins, lipids, and complex nutraceuticals. The bioeconomy addresses the possibilities of transforming renewable biological resources into economically and bioenergetically viable products [3]. In industries around the world, there is a need to expand the basic resources for the production of fuel, chemicals, energy, and materials, but the pretreatment of biomass is the main impediment to the development of the bioeconomy [4]. Waste reduction has a positive impact on the environment (soil, water, atmosphere) and contributes to climate change mitigation [5]. Zero hunger, responsible food consumption, and production belong to the 17 global sustainability goals of the United Nations, which represents a global action by 2030 and defines sustainable development in the three dimensions: economic, social, and environmental [3]. Product Lifecycle Assessment (LCA) is an environmental management technique adopted by the main food industry companies regarding the environmental impact of the product and the flow of materials, energy, and waste [3]. In 2018, 1.94 billion hectolitres of beer were produced globally [6]. An hL of beer results in 20 kg of wet brewers spent grain (BSG) [7,8], which means that 2018 resulted in 38.8 million tons of wet BSG. BSG consists of layers of peel, pericarp, and seeds with residual amounts of endosperm and aleurone from barley used as raw material (Figure1). BSG has 80% moisture, sweet taste, malt smell, and can be considered lignocellulosic material [9–11]; it is characterized by large amounts of fiber (up to Appl. Sci. 2020, 10, 5619; doi:10.3390/app10165619 www.mdpi.com/journal/applsci Appl.Appl. Sci. Sci. 20202020,, 1010,, x 5619 FOR PEER REVIEW 22 of of 17 17 to 70%), including cellulose, hemicellulose, and lignin, and protein content of 25–30% [3,12,13]. BSG is70%), a little including used by-product cellulose, hemicellulose,due to its high andmoisture lignin, content, and protein which content makes of it 25–30%difficult [ 3to,12 transport,13]. BSG and is a storelittle usedand by-productmakes it an due unstable to its high product moisture conducive content, to which microbial makes growth it difficult [8]. to Recycling transport and storereuse and of foodmakes waste it an unstableand by-products product conducive benefits toboth microbial the beer growth industry [8]. Recyclingand the andenvironment. reuse of food EUROSTAT waste and estimatesby-products approximately benefits both 90 the million beer industry tons of food and theis wasted environment. in the EU/year, EUROSTAT which estimates means 179 approximately kg/person [14].90 million EU norms tons of encourage food is wasted the inextraction the EU/year, of valu whichable means components 179 kg/person (functional [14]. EU foods, norms adjuvants, encourage pharmaceuticalthe extraction of preparations) valuable components from food (functionalindustry by-products. foods, adjuvants, Until recently, pharmaceutical food waste preparations) was of no interest,from food being industry used by-products. only for animal Until feed recently, or composting, food waste was but ofcurrent no interest, trends—and being used because only forit representsanimal feed a orcheap composting, and valuable but current raw trends—andmaterial—have because brought it represents food waste a cheap to andthe valuableattentionraw of researchers.material—have Waste brought is a valuable food waste resource to the attentionthat we do of researchers.not yet know Waste how is to a valuableuse intelligently, resource and that convertingwe do not yetit from know problem how to to use resource intelligently, needs to and be convertingmore of an interest it from problemto us. By-products to resource and needs waste to canbe morebecome of an a interestsustainable to us. alternative By-products source and wasteto reduce can becomemalnutrition a sustainable and hunger alternative in developing source to countriesreduce malnutrition [15]. There andis a hungergrowing in interest developing in find countriesing natural [15]. resources There is awith growing antioxidant interest activity in finding to effectivelynatural resources replace with synthetic antioxidant antioxidants activity with to eff toectivelyxic and replace carcinogenic synthetic effects antioxidants [16]. Oxidative with toxic stress and occurscarcinogenic as an imbalance effects [16 ].between Oxidative the stressnumber occurs of oxidants as an imbalance and the antioxidant between the defense number mechanism, of oxidants and and regularthe antioxidant consumption defense of mechanism,cereals and by-products and regular consumptionhelps prevent of many cereals chronic and by-products diseases associated helps prevent with oxidativemany chronic stress. diseases Since associatedBSG is derived with oxidative from food stress. materials, Since BSG it can is derived be incorporated from food into materials, food itdiets can (bread,be incorporated snacks, muffins, into food pasta, diets etc.) (bread, [17]. snacks, The purpose muffins, of pasta,this review etc.) [ 17is to]. Theupdate purpose information of this reviewon BSG, is healthto update roles, information and methods on BSG,of extraction health roles, of valuable and methods components. of extraction of valuable components. FigureFigure 1. 1. BarleyBarley structure. structure. 2.2. BSG: BSG: A A Valuable Valuable By-Product By-Product BSGBSG has has a a complex chemical chemical composition, composition, which which varies varies according according to to variety variety of of barley barley used, used, harvestingharvesting andand malting malting time, time, and and mixing mixing time [8time]. Due [8]. to theDue high to moisturethe high of themoisture BSG (approximately of the BSG (approximately80%), shelf life is 80%), 7–10 shelf days. life Preservation is 7–10 days. can Preservation be done with can acids be (lacticdone with acid, acids benzoic (lactic acid, acid, formic benzoic acid, acid,or acetic formic acid), acid, which or acetic is contrary acid), to which the desire is contra of consumersry to the of desire the most of consumers natural food, of orthe can most be used natural in a food,mixture or ofcan benzoate-propionate-sorbate be used in a mixture of benzoate-propionate-sorbate in concentrations 0.2–0.3% (vin/v), concentrations which can extend 0.2–0.3% its validity (v/v), whichby 4–5 can days extend [8]. Drying its validity is considered by 4–5 days the most[8]. Drying effective is methodconsidered of preservationthe most effective of BSG. method A drying of preservationmethod can beof usedBSG. in A two drying stages—pressing method can be and used drying—bringing in two stages—pressing moisture to and 10% drying—bringing [9]. According to moisturestudies by to Lynch 10% [9]. et al.According (2016), other to studies preservation by Lync/dryingh et al. methods(2016), other that canpreservation/drying be used are: methods that can be used are: drying in the oven is considered the most suitable but must be carried out at temperatures below •• drying60 ◦C, within the the oven disadvantage is considered of athe high most energy suitable consumption; but must be carried out at temperatures below 60drying °C, with by overheated the disadvantage steam in of a thina high layer energy brings consumption; the advantage of less consumption and improved • • dryingdrying ebyffi ciency;overheated steam in a thin layer brings the advantage of less consumption and improvedautoclaving drying at 121 efficiency;◦C for one hour has the disadvantage of solubilization of polysaccharides and •• autoclavingphenolic compounds; at 121 °C for one hour has the disadvantage of solubilization of polysaccharides