Characterisation of protein‐rich isolates and antioxidative phenolic extracts from pale and black brewers' spent grain

Protein‐enriched isolates and co‐product fractions were obtained from sheared, pale and black brewers' spent grain (BSG) using sequential aqueous and alkaline (110 mm NaOH) extraction, followed by isoelectric precipitation at pH 3.8. A recovery of 59% of the original pale BSG protein and 15% of the black BSG protein was obtained for the final isolates. Gel permeation HPLC (GP‐HPLC) revealed that 59% of the extracted pale BSG protein and only 6% of black BSG protein had a molecular mass >10 kDa. Glutamine/glutamate and proline were the most abundant amino acids present in both isolates. Analysis of four co‐product fractions obtained during fractionation from both pale and black BSG revealed the presence of phenolics, with higher concentrations in the black BSG extracts. These fractions possessed antioxidant and free radical scavenging activity when tested using the ferric reducing ability of plasma (0.16 ± 0.01 to 4.33 ± 0.11 mg Trolox equivalents g^?1 BSG dry weight) and diphenylpicrylhydrazyl (12.85 ± 1.16% to 59.50 ± 3.47% DPPH?_sc) assays, respectively. The protein‐enriched isolates and the phenolic‐rich extracts may find use as value‐added ingredients for incorporation into conventional and functional foods.     

Characterisation of melanoidins derived from Brewers' spent grain: new insights into their structure and antioxidant activity

Melanoidins, formed at the final stages of Maillard reaction (MR), present important physiological activities, but their structure and reaction pathways are largely unknown in real food systems. In the present work, these bioactive compounds derived from Brewers' spent grain (BSG) with different roasting degrees were analysed. Results showed that BSG could be considered a more important source of bioavailable antioxidants than what it was reported in previous studies. During MR development, proteinic structures are partially lost while a carbohydrate skeleton is formed. The crystallinity is reduced and the structure sets into a conformation with a peak centred at 20° (2θ), stable with the increasing thermal treatment. While MR continues the development of browning compounds increases, the antioxidant activity rises and phenolic compounds are bind to the melanoidin structure (P ≤ 0.05). Moreover, FTIR analysis showed a dominance of α-glyosidic linkage and the presence of furanose rings in the melanoidins structure.     

Study on utilizing solid food industry waste with brewers' spent grain and potato pulp as possible peroxidase sources

This study found that extracts containing ionically bound proteins, isolated from potato pulp and brewers' spent grain, were characterized by high peroxidase activities. The kinetic parameters, namely K_m and V_max values, were typical for plant peroxidases. Seven peroxidase isoenzymes in potato pulp and two isoenzymes in brewers' spent grain were obtained from their respective ionically bound fractions. Peroxidases from both potato pulp and brewers' spent grain displayed high storage stability, over a 90‐day‐long storage period, if stored at ?20°C with glycerol added to a concentration of 50% or as unsupplemented extracts at 4°C. Peroxidase activity was present in the covalently bound fraction of potato pulp, whereas it was absent in the respective fraction of brewers' spent grain. Covalently bound peroxidases from potato pulp displayed high activity, but low stability. Peroxidases extracted from brewers' spent grain and potato pulp, followed the ping‐pong mechanism and the sequence mechanism, respectively.

Practical applications

Plant peroxidases are widely applicable in various fields of biotechnology and diagnostics. These enzymes are used for biosensor and glucometer construction and in conjugation with antibodies for the purpose of enzyme immunoassays. Using waste products as a peroxidase source provides a cost‐friendly alternative to commercially available horseradish peroxidase and gives an opportunity to recycle waste from the food industry—processed plant biomass. Here, the properties of peroxidases from food waste products, namely potato pulp and brewers' spent grain are analyzed. The extracts were characterized by high storage stability and high enzymatic activity, which are two key traits necessary for the practical use of enzyme preparations.     

Recent advances in biotechnological valorization of brewers' spent grain

Brewers'' spent grain (BSG) is the most abundant by-product of beer-brewing. BSG is rich in nutrients such as protein, fiber, minerals, and vitamins, and therefore it is conventionally used as low-cost animal feed. On the other hand, alternative utilization of BSG has gained increased attention during recent years due to technological progress in its processing and the emergence of the concept of circular economy. The valorization of BSG through biotechnological approaches is environmentally friendly and sustainable. This review was focused on recent advancements in the conversion of BSG into value-added products, including bioenergy (ethanol, butanol, hydrogen, biodiesel, and biogas), organic acids, enzymes, xylitol, oligosaccharides, and single cell protein, via biotechnological approaches. In addition, the potential applications of BSG as immobilization matrices in bioprocesses have been reviewed.     

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

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     

啤酒糟中细菌的分离鉴定及其在啤酒糟发酵中的应用

该研究采用传统培养分离法从啤酒糟中分离细菌,通过形态观察及分子生物学技术对其进行菌种鉴定,选择其中3株细菌发酵啤酒糟,并与常规发酵真菌黑曲霉（Aspergillus niger）和出芽短梗霉（Aureobasidium pullulans）对比,以期获得对啤酒糟降解效果较好的细菌。结果表明,从啤酒糟中共分离得到6株细菌（编号为B1～B6）,经鉴定,分别为蜡样芽孢杆菌（Bacillus cereus）、梭状菌属（Clostridium sp.）、解淀粉芽孢杆菌（Bacillus amyloliquefaciens）、贝莱斯芽孢杆菌（Bacillus velezensis）、暹罗芽孢杆菌（Bacillus siamensis）、枯草芽孢杆菌（Bacillus subtilis）。其中解淀粉芽孢杆菌B3对啤酒糟的降解效果最好,且优于常规真菌,其发酵啤酒糟的蛋白质、总还原糖、阿魏酰低聚糖含量、木聚糖酶酶活、羧甲基纤维素酶酶活均最高,分别为25.26%、3.92%、10.01μmol/L、803.59 U及38.16 U。     

超滤法处理麦草亚铵法黑液的研究

研究了采用超滤技术处理麦草亚铵法黑液过程的规律,给出了超滤膜的选择、温度、操作压力、体积浓缩倍数等操作参数对超滤过程的影响。研究表明：截留分子量为PES100的超滤膜较适合于分离麦草亚铵法黑液,并具有较好的抗污染性;在操作压力0．20MPa、温度为25℃下进行超滤,随着体积浓缩倍数的增加,灰分的透过率增加,透过率在50％以上,木质素的截留率缓慢下降,维持在80％以上。     

Antioxidant capacity,arabinoxylans content and in vitro glycaemic index of cereal-based snacks incorporated with brewer's spent grain

Extruded snacks and breadsticks were formulated with increasing levels of brewer's spent grain (BSG). The phenolic content increased by 4 and 7 fold with BSG addition in extrudates (40 g/100 g) and in breadsticks (35 g/100 g), respectively. Consequently, antioxidant capacity (DPPH, FRAP) also increased despite a recorded loss of phenolic compounds in extruded snacks. Arabinoxylans content increased up to 20 and 25 g of BSG addition/100 g of formulated extruded snacks and breadsticks, respectively. Further addition of BSG did not improve the content of arabinoxylans due to the possible formation of polysaccharide–protein complexes. Medium GI breadsticks were obtained with 35 g of BSG incorporation/100 g formulation. Phenolic content, arabinoxylans content and antioxidant capacity increased in the final products with BSG addition while the glycaemic response decreased. BSG can be incorporated as an ingredient in the formulation of extruded snacks and breadsticks generating products richer in antioxidants and fibre and with low GI.     

Quantitative determination of fluorine in spent grain and brewery yeast

Previously published studies have shown that fluorine could present a health risk for humans. In this context, legislative regulations define the fluorine limits in many commodities, including brewery by‐products, such as spent grain and brewery yeast used as a feed. A method for the determination of fluorine in these by‐products using gas chromatography with flame ionization detection is therefore proposed. The first step is based on extraction of fluorine with 1 mol/L hydrochloric acid solution simulating acidic stomach surroundings. Then, fluorine is derivatized by trimethylchlorosilane to form trimethylfluorosilane (TMFS), which is subsequently extracted in liquid–liquid mode. TMFS is then analysed by gas chromatography–flame ionization detection; n‐pentane is used as an internal standard for fluorine quantification. The recovery of the method was >96%. The results also showed a high correlation coefficient (R > 0.999) in the calibration range studied (0–2000 mg/kg). The precision of the method, expressed as the relative standard deviation, was 13%. The limit of quantification was 0.02 mg/kg. This method was used for pilot screening of fluorine in 16 grain and 12 yeast samples. The resulting concentrations of fluorine ranged between 1.5 and 20.0 mg/kg, levels far below the legislative limits. Copyright © 2015 The Institute of Brewing & Distilling     

Lactic acid fermentation of brewer's spent grain hydrolysate by Lactobacillus rhamnosus with yeast extract addition and pH control

Lactic acid (LA) is a versatile chemical with a wide range of applications in food, pharmaceutical, cosmetic, textile and polymer industries. Brewer's spent grain (BSG) is the most abundant brewing by‐product. In this study BSG hydrolysates were used for LA fermentation by Lactobacillus rhamnosus ATCC 7469. The aim of this study was to evaluate the effects of pH control during fermentation, reducing sugar content and yeast extract content in BSG hydrolysate on LA fermentation parameters. The pH control greatly increased reducing sugar utilization, l ‐(+)‐LA content, yield and volumetric productivity. The highest l ‐(+)‐LA yield and volumetric productivity were achieved with the reducing sugar content of 54 g/L. Yeast extract addition significantly increased reducing sugar utilization, l ‐(+)‐LA content, L. rhamnosus cell viability, l ‐(+)‐LA yield and volumetric productivity. The highest l ‐(+)‐LA content (39.38 g/L), L. rhamnosus cell viability (9.67 log CFU/mL), l ‐(+)‐LA yield (91.29%) and volumetric productivity (1.69 g/L/h) were achieved with the reducing sugar content of 54 g/L and yeast extract content of 50 g/L. Copyright © 2017 The Institute of Brewing & Distilling     

Utilization of brewer's spent grain in the production of Frankfurters

The effects of dried and ground brewer's spent grain (BSG) on dietary fibre content and some quality characteristics of beef Frankfurters were investigated. BSG preparations of fine (<212 μm), medium (212–425 μm) and coarse (425–850 μm) particle sizes were used in the production of Frankfurters. The total dietary fibre (TDF) content of the Frankfurters supplemented with BSG of different particle sizes increased significantly ( P  < 0.05) as the level of addition was increased. The mean TBA (2-thiobarbituric acid), colour and texture values except springiness had significant differences ( P  < 0.05) among the treatments. The overall acceptability scores for the control and the Frankfurters with BSG were 7.57 and 5.47–7.02 on a nine-point scale, respectively. Cluster analysis was also carried out to divide the measured parameters into clusters according to their similarities and to find out the correlations among them. It can be concluded that BSG can be added to Frankfurters to increase their fibre content without deleteriously affecting their sensory parameters.     

Profiling brewers' spent grain for composition and microbial ecology at the site of production

Brewers' spent grain (BSG) is a readily available, high volume low cost byproduct of brewing and is a potentially valuable resource for industrial exploitation. The variation in BSG composition and the implications for microbiological spoilage by a resident microflora might affect the potential to use BSG as a reliable food-grade industrial feedstock for value-added downstream processing. Fresh samples of BSG from a range of 10 breweries have been analysed for their microbial and chemical composition. The results show that a resident microflora of mainly thermophilic aerobic bacteria (<10⁷ g^-1 fresh weight) persists on BSG. This population is susceptible to rapid change but at the point of production BSG can be considered microbiologically stable. Chemically, BSG is rich in polysaccharides, protein and lignin. Residual starch can contribute up to 13% of the dry weight and BSG from lager malts has higher protein content than that from ale. In general, at the point of production, BSG is a relatively uniform chemical feedstock available for industrial upgrading. Differences between breweries should not present problems when considering BSG for industrial exploitation but susceptibility to microbial colonisation is identified as a potential problem area which might restrict its successful exploitation.     

Acid hydrolysis and fermentation of brewer's spent grain to produce xylitol

The hemicellulosic fraction of brewer's spent grain (BSG) was hydrolysed with diluted acid under different conditions of liquid/solid ratio (8–12 g g⁻¹), sulfuric acid concentration (100–140 mg g⁻¹ dry matter) and reaction time (17–37 min) in order to produce a liquor with a large amount of xylose and good fermentability to produce xylitol. Results showed that all the evaluated reaction conditions were able to hydrolyse xylan and arabinan with efficiencies higher than 85.8 and 95.7% respectively, and even under the mildest reaction condition a considerable amount (92.7%) of the hemicellulosic fraction could be extracted. The hydrolysates presented different fermentabilities when used as fermentation media for xylitol production by Candida guilliermondii yeast, owing to the differences in their composition. Based on statistical analysis, the best condition for BSG acid hydrolysis was the use of a liquid/solid ratio of 8 g g⁻¹, 100 mg H₂SO₄ g⁻¹ dry matter and a reaction time of 17 min. Under this condition a high extraction efficiency of hemicellulosic sugars (92.7%) and good fermentation results (Y_P/S = 0.70 g g⁻¹ and Q_P = 0.45 g dm⁻³ h⁻¹) were attained. Copyright © 2005 Society of Chemical Industry     

Optimising separation process of protein and polysaccharide from spent brewer’s yeast by ultrafiltration

The aim of this study was to optimise the ultrafiltration process for the separation of polysaccharide and protein from spent brewer’s yeast. Influence of concentration (1.5–4.5%), pH (4.0–8.0) and operating pressure (10–20 psi) on the yield of protein and polysaccharide was assessed using response surface methodology. The optimum separation conditions were found to be concentration 2.7%, pH 5.0 and operation pressure 14.0 psi. Under these conditions, the experimental yields of protein and polysaccharide were 95.03% and 94.65%, respectively, which were agreed closely to the predicted value. The polysaccharide was composed of glucose, sucrose and trehalose in a ratio of 1.12:0.83:2.36. The results indicated that ultrafiltration technology could be an effective and advisable technique for the separation of protein and polysaccharide.     

啤酒糟在国内外食品加工中的利用现状

啤酒糟是啤酒酿造的最主要副产物,含有丰富的蛋白质和非淀粉多糖.随着啤酒原料中小麦芽使用量的增加(≥40％),啤酒糟中膳食纤维和蛋白质的含量明显增加.目前啤酒糟主要用作饲料或工业原料出售,但在食品加工中的应用研究较少.本文通过概述啤酒糟的营养、加工处理方法及其在国内外食品加工领域中的研究利用情况,为高蛋白膳食纤维啤酒糟食品的进一步开发提供了参考.     

The hydroxycinnamic acid content of barley and brewers’ spent grain (BSG) and the potential to incorporate phenolic extracts of BSG as antioxidants into fruit beverages

The hydroxycinnamic acid (HA) content of starting barley for brewers’ spent grains (BSG), whole BSG and phenolic extracts from BSG was measured using high performance liquid chromatography (HPLC) and correlated with antioxidant potential. The effect of BSG phenolic extracts on antioxidant activity of fruit beverages was also assessed (using the total phenolic content (TPC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays). The concentration of HA present in barley extract and BSG was in the order of ferulic acid (FA), p-coumaric acid (p-CA) derivatives, FA derivatives, p-CA, caffeic acid (CA) and CA derivatives. Results suggested that brewing and roasting decreased the HA content. Antioxidant activity was significantly (P < 0.05) correlated with caffeic acid (R² = 0.8309) and total HA (R² = 0.3942) concentrations. Addition of extracts to fruit beverages resulted in a significant (P < 0.05) increase in antioxidant activity of cranberry juice, measured by the FRAP assay. In vitro digestion significantly (P < 0.05) reduced TPC, DPPH and FRAP activity of the fruit beverages.