Brewers' spent grain : generation, characteristics and potential applications

Brewer's spent grain (BSG) is the most abundant by-product generated from the beer-brewing process, representing approximately 85% of the total by-products obtained. This material is basically constituted by the barley grain husks obtained as solid residue after the wort production. Since BSG is rich in sugars and proteins, the main and quickest alternative for elimination of this industrial by-product has been as animal feed. However, BSG is a raw material of interest for application in different areas because of its low cost, large availability throughout the year and valuable chemical composition. In the last decade, many efforts have been directed towards the reuse of BSG, taking into account the incentive that has been given to recycle the wastes and by-products generated by industrial activities. Currently, many interesting and advantageous methods for application of BSG in foods, in energy production and in chemical and biotechnological processes have been reported. The present study presents and discusses the most recent perspectives for BSG application in such areas.

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Brewer's spent grain: a valuable feedstock for industrial applications

Brewers' spent grain (BSG) is the most abundant by-product generated in the beer-brewing process. This material consists of the barley grain husks obtained as solid residue after the production of wort. BSG is rich in fibre and protein and, to date, the main use for the elimination of this by-product has been as an animal feed. However, because of its nutritional content, BSG is of interest for application and fortification of human food products, particularly in view of its low cost and availability in large amounts. In addition, the importance of BSG as an ingredient and potential source of health-promoting bioactive components is beginning to be recognised. The investigation of alternative uses of BSG is pertinent, not only from the perspective of the brewer who can benefit from valorisation of this by-product, but also from an environmental perspective as the recycling and re-use of industrial wastes and by-products has become increasingly important. This review presents the current knowledge on BSG, covering its production, composition and methods for the release of valuable components, and focuses on the potential health benefits attributed to its constituents and the use of this brewer by-product in food applications. Copyright © 2016 The Institute of Brewing & Distilling

https://onlinelibrary.wiley.com/doi/pdf/10.1002/jib.363

Brewers' spent grain: a review with an emphasis on food and health

Yarrowia lipolytica is a fungus that degrades hydrophobic substrates very efficiently. The fungus displays several important characteristics that have encouraged researchers to study various basic biological and biotechnological applications in detail. Although the organism has been used as model system for studying dimorphism, salt tolerance, heterologous protein expression, and lipid accumulation, there are no recent reviews on the environmental and industrial applications of this organism. Included here are applications in bioremediation of environments contaminated with aliphatic and aromatic compounds, organic pollutants, 2,4,6-trinitrotoluene, and metals. A variety of industrially important recent processes for the synthesis of β-hydroxy butyrate, l-dopa, and emulsifiers have also been reviewed. Production of unique inherent enzymes (inulinases, α-mannosidases), novel applications of esterases and lipases, and the use of the fungus for heterologous expression of biotechnologically relevant products have also been highlighted. The review while entailing a general overview focuses critically on some of the recent advances on the applications of this yeast. The examples cited here demonstrate the use of wild-type, mutant as well as genetically manipulated strains of Y. lipolytica for the development of different products, processes, and technologies. This also throws light on how a single organism can be versatile with respect to its metabolic abilities and how it can be exploited for a variety of purposes. This review will thus form a base for future developments in this field.

Environmental and industrial applications of Yarrowia lipolytica

This chapter discusses proteolysis process in cheese during ripening. Proteolysis contributes to: (1) The development of cheese texture: via hydrolysis of the protein matrix of cheese; via a decrease in aw through changes to water binding by the new carboxylic acid and amino groups liberated on hydrolysis of peptide bonds. These groups are ionized at the pH of cheese and thus bind water; indirectly via an increase in pH caused by the liberation of ammonia from amino acids produced by proteolysis. (2) Flavor and perhaps the off-flavor of cheese, directly by the production of short peptides and amino acids, some of which have flavors; indirectly by the liberation of amino acids, which act as substrates for a range of catabolic reactions, which generate important volatile flavor compounds; by facilitating the release of sapid compounds from the cheese matrix during mastication. Proteolysis in cheese during ripening is catalyzed by proteinases and peptidases from six sources: (1) the coagulant—the enzymes involved depend on the type of coagulant used. (2) the milk—a number of indigenous proteinases are present in milk, the most important of which is plasmin, which is produced from an inactive precursor, plasminogen. (3) starter lactic acid bacteria (LAB) contain a cell envelope-associated proteinase, which contributes to ripening principally by hydrolyzing intermediate-sized and short peptides produced from the caseins by the action of chymosin or plasmin. The other three sources are nonstarter lactic acid bacteria (NSEAB), secondary starter ( Propionibacterium freudenreichii subsp, shermanii in Swiss-type cheese), and exogenous proteinases and peptidases.

Proteolysis in Cheese during Ripening

Brewer's spent grains (BSG), the voluminous residue after mashing, contains on dry weight basis about 40-50 % polysaccharides. For the recovery of soluble carbohydrates from BSG different physical, thermal and enzymatic treatments were used to solubilize the polysaccharides in BSG. Heating by microwave radiation to 160 °C in the presence of 0.1 M HCl released 35 % of the material in the form of reducing sugar, indicating that about 80 % of the polysaccharides were hydrolyzed. Nevertheless, 0.1 M acetic acid will even solubilize 30 % of the material as oligosaccharides on a prolonged incubation when pretreating the spent grains by extrusion cooking. A combination of the enzymes Ceremix Plus MG and CelluPract AL 70 achieved an almost 25 % release of saccharides after 4 hrs of incubation at 50 °C. A combination of extrusion cooking and enzymatic hydrolysis seems to be a very promising procedure.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/elsc.200301831

Pretreatment and Hydrolysis of Brewer's Spent Grains

Development of a microbial bioassay for chlorinated and brominated hydrocarbons

Bacterial cell surface layers (S-layers) which show a crystalline structure, defined pores, and a regular arrangement of functional groups can be used for production of isoporous ultrafiltration membranes and as a matrix for immobilization of macromolecules. S-layer-carrying cell wall fragments from thermophilic Bacillaceae possess an extremely thin peptidoglycan-containing layer with pores larger than those in the S-layer lattice. Thus, they can directly be used for biotechnological applications, when an S-layer protein pool is stored in the rigid cell wall layer which is released during cell wall preparation, forming an inner S-layer. In the present study, a synthetic medium for Bacillus stearothermophilus PV 72 was developed by applying the pulse and shift technique with the aim to produce cell wall fragments with before-mentioned properties by varying the growth conditions in continuous culture. The organism was grown at 57 degrees C in a bioreactor with 1 L working volume equipped with exhaust gas analysis and connected to a PC-based process control system. Biomass concentration was 2.2 g/L out of 8 g/L glucose at a dilution rate of 0.3 h(-1), giving a biomass productivity of 0.66 g/L h. Although the organism was grown under different conditions, no change in peptidoglycan composition, extent of peptidoglycan crosslinking, and content of secondary cell wall polymers was observed. The amount of S-layer protein pool stored in the rigid cell wall layer and the autolytic activity depended mainly on the specific growth rate. Cell wall fragments with properties required for ultrafiltration membrane production could be produced by parameter settings in continuous culture.

A synthetic medium for continuous culture of the S‐layer carrying Bacillus stearothermophilus PV 72 and studies on the influence of growth conditions on cell wall properties

Cells of an Actinomycete-like bacterium, strain GJ70, with the ability to degrade several haloalkanes were used as a biological component in a discontinuous microbial bioassay for the detection of 1,3-dichloropropene and 1,2-dibromoethane in water. The cells were entrapped in different matrices such as calcium alginate, carrageenan, chitosan, polyacrylamide-hydrazide and chitosan-carboxy-methyl cellulose; the specific dehalogenating activity of the immobilized cells was highest with the two last matrices. By the addition of small beads of immobilized cells to a stirred sample solution and by the use of an ion selective electrode (ISE) for the quantification of enzymatically released halogen ions, the concentration of halogenated hydrocarbons could be estimated by determining the change of electrode potential within a period of 5 min. The detection limits for 1,3-dichloropropene and 1,2-dibromoethane were below 100 μg/l and 25 μg/l, respectively; the relative standard deviation was < 10%. In addition, several chlorinated and brominated hydrocarbons were converted by the bacterial cells at a reduced rate e.g. 1,2-dibromopropane, 1-bromoethane, 1,5-dichloropentane, etc. Moreover, temperatures of between 20 and 40°C did not affect the enzymatic activity of the cells, and a pH of between at 5 and 9 had little influence. Several organic substances and non-metabolizable compounds did not affect the conversion, whereas some heavy metal ions acted as inhibitors.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/abio.370170204

Characteristics of a microbial assay for the detection of halogenated hydrocarbons using cells of an Actinomycete-like organism as a biological component

When Brevibacterium linens ATCC 9172 was grown in shake flasks, it produced a cell-associated lipase with a specific activity of 152 to 188 U g−1 cells depending on the composition of the growth medium. There was no growth in media containing tributyrine as the sole carbon source. The cell-associated lipase had maximum activity at pH 8.0 and 37 °C and was strongly inhibited by 3,4-dichloroisocoumarin, an inhibitor specific for serine esterases. Cell-associated activity was released from the cells by treatment with lysozyme. The kinetics of lipase formation was closely related to the amount of biomass formed during growth.

Werner A. Hampel

Papers

Pretreatment and Hydrolysis of Brewer's Spent Grains

Development of a microbial bioassay for chlorinated and brominated hydrocarbons

A synthetic medium for continuous culture of the S‐layer carrying Bacillus stearothermophilus PV 72 and studies on the influence of growth conditions on cell wall properties

Characteristics of a microbial assay for the detection of halogenated hydrocarbons using cells of an Actinomycete-like organism as a biological component

Formation of lipolytic enzymes by Brevibacterium linens