Assessment of endogenous antioxidative compounds and antioxidant activities of lager beers

BACKGROUND: Flavour stability is increasingly becoming the limiting factor in the shelf life of beer. Increasing the antioxidant activity of beer itself could suppress the rate of oxidative reaction and improve the flavour stability of beer. This report describes the levels of phenolic compounds, melanoidins and sulfur dioxide, and antioxidant activities of 40 lager beers. The relationships between antioxidative compounds and antioxidant activity were elucidated by multivariate analysis techniques. RESULTS: The results showed that the total phenolic content and the melanoidins content correlated well (P < 0.05) with antioxidant activity, while there was no significant correlation (P > 0.05) between total sulfur dioxide content and antioxidant activity. Satisfactory discrimination among beer samples with significantly different antioxidant activity was achieved by principal component analysis. Results from stepwise linear regression further demonstrated that different antioxidative components responsible for antioxidant activity were dependent on the assay used. The phenolic compound group is by far the most antioxidative compounds in beer and total phenolic content, melanoidins and sulfur dioxide together made a 22–68% contribution to the antioxidant activities of beers. CONCLUSION: Therefore, it might be an efficient means for brewers to increase total phenolic content during brewing for improvement in flavour stability of the final beer. © 2012 Society of Chemical Industry     

Antioxidant activity,polyphenols, caffeine and melanoidins in soluble coffee: The influence of processing conditions and raw material

The production of soluble coffee starts with the selection of beans and is followed by roasting, grinding, extraction and drying. Lyophilised soluble coffees extracted by various methods from light, medium and dark-roasted arabica and robusta beans were evaluated for antioxidant activity (AA) using ABTS, Folin, DPPH and FRAP techniques. Caffeine, chlorogenic acid (5-CQA) and melanoidin content was also quantified. The data were analysed by principal component analysis. The AA values derived from the various methods used were correlated. Roasting resulted in the degradation of 5-CQA and formation of melanoidins, while AA was largely unaffected by roasting. The extraction of soluble coffee more prominently affected the AA of light-roasted coffee, mainly because it favoured the extraction of 5-CQA. The larger caffeine content in robusta coffee resulted in greater AA. All of soluble coffee products studied possessed antioxidant potential, which was conferred by their concentrations of phenolic compounds, caffeine and melanoidins.     

Relationship between the chemical composition and the biological activities of food melanoidins

The relationship between the chemical composition and the biological activities of food melanoidin-rich fractions was investigated. Melanoidin-rich fractions were extracted using ultrafiltration (a 10 kDa cut-off) from coffee, barley coffee, dark beer, and traditional balsamic vinegar. All the food melanoidin-rich fractions were formed mainly of carbohydrates, phenolic compounds, and proteins. In dark beer, barley coffee, and traditional balsamic vinegar melanoidins, glucose was the most abundant sugar incorporated into melanoidins. Coffee melanoidins contained the largest amount of phenolic groups, followed by traditional balsamic vinegar melanoidins. The radical scavenging, Fe²⁺-chelating, and heme binding abilities of food melanoidins were investigated under gastric conditions. The melanoidinrich fraction extracted from coffee was the most active, showing the highest radical scavenging, Fe²⁺-chelating, and heme binding activities, compared to barley coffee, dark beer, and traditional balsamic vinegar. The radical scavenging and Fe²⁺-chelating abilities were assigned to the phenolic groups present in food melanoidins.     

Bioactivities of low-grade green coffee and spent coffee in different in vitro model systems

Methanolic extracts of low-grade green coffee beans (LCB) and spent coffee were analysed for radical-scavenging activity (α,α-diphenyl-β-picrylhydrazyl radical) and oxygen radical absorbance capacity (ORAC). The extracts were also evaluated for anti-tumour (P388 cell assay), anti-inflammatory (J774A.1 cell assay) and anti-allergenic (RBL-2H3 cell line) activities in vitro. LCB extract was found to exhibit a radical-scavenging activity of 92.0% followed by spent Arabica (86.9%) and spent Robusta (82.0%) at a concentration of 50 ppm. The antioxidant activity of LCB extract, measured as Trolox equivalents (4416 μM/g) was significantly (p < 0.05) higher than that of the spent coffee extracts. However, extracts of spent coffee exhibited significantly (p < 0.05) more anti-tumour activity than the LCB extract in terms of cell viability. This could be due to the possible role of brown pigments (melanoidins and phenolic polymers), formed during roasting, which may protect cells from oxidative damage in the biological system. However, both the extracts of LCB and spent coffee showed limited anti-inflammatory and anti-allergic activities. The presence of phenolics and chlorogenic acids in appreciable quantities along with brown pigments makes these coffee by-products a source for natural antioxidants.     

Roasting process affects differently the bioactive compounds and the antioxidant activity of arabica and robusta coffees

The influence of different roasting degrees on the content of bioactive compounds and the antioxidant activity (AA) of arabica and robusta coffees was evaluated. AA was estimated by Folin–Ciocalteau, FRAP and ABTS methods. The results were analyzed by principal components analysis. While the levels of 5-CQA (5-caffeoylquinic acid), trigonelline, furfural and HMF (hydroxymethylfurfural) decreased with the degree of roasting, the level of melanoidins increased. Changes in the levels of the bioactive compounds were more intense that those observed for AA. PC 1 (principal component 1) was mainly correlated with the levels of, furfural, HMF, 5-CQA, trigonelline, and melanoidins. PC2 was mainly correlated with AA and caffeine content. Different compounds contribute to the AA of the coffee and the final result for AA is dependent on the balance of the compounds formed and degraded during the roasting process.     

Investigation on the extractability of melanoidins in portioned espresso coffee

Coffee melanoidins have attracted interest as a result of its potential health benefits. This investigation aims to elucidate the extraction behavior of melanoidins and their populations during the preparation of portioned espresso coffee and its relationship with the antioxidant activity of the coffee brew. Filter-paper pods, FAP capsule, and clone capsule containing light roasted coffee have been investigated. An accumulative fractionation approach has applied to model the extraction kinetics of melanoidins, melanoidin populations, browning, chlorogenic acids (CGA), and antioxidant activity. Melanoidins were very efficiently extracted in clone capsules since less than 9 s was necessary to extract the 50% of the melanoidin content as compared with pods and FAP capsules, and the kinetic of extraction is slower than CGA. The extraction profile of melanoidins and browning fitted better with the antioxidant capacity than CGA and total solids profile. Melanoidin populations were obtained according to ethanol solubility. Total melanoidin content and the ratio between melanoidin populations did not change during extraction volume for espresso coffee. Melanoidin populations soluble at 75% ethanol showed the highest antioxidant activity. However, melanoidins with higher antioxidant activity are extracted at higher volumes. This investigation could make possible the adjustment of the technological requirements of espresso coffeemakers to produce an espresso coffee with high levels of beneficial compounds.     

Antioxidant activity of coffee brews

The total antioxidant activity of coffee beverages was measured with stabilized radical EPR spectroscopy. Depending on which stabilized radical is used, Fremy's salt (potassium nitrosodisulphonate) or 2,2,6,6-tetramethyl-1-piperidin-1-oxyl (TEMPO) values can differ significantly. For the determination of antioxidant activity of Maillard reaction products in coffee, TEMPO appears to be the better radical marker. Thus the contribution of both main antioxidant active compounds (polyphenols, melanoidins) whose ratio varies with roasting conditions could be estimated. During storage experiments of coffees brews changes in antioxidant action are found to be time dependent. The content of chlorogenic acids increased significantly at higher storage temperatures, probably caused by a release from polymer structures. Additional antioxidant capacity of coffee melanoidins seems to be strongly influenced by atmospheric oxygen. The higher roasted sample is less vulnerable than medium or light roasted coffee. Investigations with model systems showed that among all coffee constituents the carbohydrates are mainly responsible for the formation of oxygen scavenging substances.     

Selection of the Solvent and Extraction Conditions for Maximum Recovery of Antioxidant Phenolic Compounds from Coffee Silverskin

The extraction of antioxidant phenolic compounds from coffee silverskin (CS) was studied. Firstly, the effect of different solvents (methanol, ethanol, acetone, and distilled water) on the production of antioxidant extracts was evaluated. All the extracts showed antioxidant activity (FRAP and DPPH assays), but those obtained with methanol and ethanol had significantly higher (p?<?0.05) DPPH inhibition than the remaining ones. Due to the lower toxicity, ethanol was selected as extraction solvent, and further experiments were performed in order to define the solvent concentration, solvent/solid ratio, and time to maximize the extraction results. The best condition to produce an extract with high content of phenolic compounds (13 mg gallic acid equivalents/g CS) and antioxidant activity [DPPH?=?18.24 μmol Trolox equivalents/g CS and FRAP?=?0.83 mmol Fe(II)/g CS] was achieved when using 60 % ethanol in a ratio of 35 ml/g CS, during 30 min at 60–65 °C.     

Spent coffee as a rich source of antioxidative compounds

Antioxidant activities and major antioxidants were investigated in the methanolic extracts of roasted and spent coffee to evaluate the feasibility of spent coffee as a source of functional ingredients. Phenolic compounds, such as gallic acid, protocatechuic acid, and chlorogenic acid, and nitrogenous compounds, including trigonelline and caffeine, were identified. Caffeine was the most abundant compound, followed by chlorogenic acid. Despite the significant reduction of antioxidants, 2,2,-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was retained in more than 95% of roasted coffee. The retentions of superoxide dismutase (SOD)-like activity and ferric reducing antioxidant power (FRAP) were 65–90 and 46–60%, respectively. Gallic acid had a positive correlation with SOD-like activity, whereas protocatechuic acid positively correlated with FRAP, suggesting that the major compounds contributing to each antioxidant activity are different. These results show that spent coffee can be used as an antioxidant source for functional foods and cosmetic products to improve antioxidant properties.     

High antioxidant activity of coffee silverskin extracts obtained by the treatment of coffee silverskin with subcritical water

Coffee silverskin (CS) is a thin tegument of the outer layer of green coffee beans and a major by-product of the roasting process to produce roasted coffee beans. CS extracts obtained by the treatment of CS with subcritical water at 25-270°C were investigated for their antioxidant activity using hydrophilic oxygen radical absorption capacity (H-ORAC) and DPPH radical scavenging capacity assays. The antioxidant activity increased with increasing the extraction temperature and the highest activity was observed with the extracts obtained at 270°C. The H-ORAC and DPPH values of the extracts were 2629±193 and 379±36μmol TE/g of CS extract, respectively. High correlation (R=0.999) was observed between H-ORAC and DPPH values for the CS extracts. High correlation of the antioxidant activity was also observed with protein and phenolic contents in the extracts. The CS extracts could be useful as a good source of antioxidative materials.     

Influence of extraction process on antioxidant capacity of spent coffee

Spent coffee that is produced in tons by restaurants and cafeterias, and consumers at domestic levels, could be a good opportunity to have an important source of natural antioxidants. The main aim of this work was to study the influence of several process factors on the antioxidant capacity extraction from spent coffee. Total phenolic compounds, radical scavenging activity (ABTS and DPPH) and browned compounds (Abs 420 nm) of spent coffee extracts obtained with continuous (Soxhlet 1 h and 3 h) and discontinuous methods (solid–liquid extraction and filter coffeemaker), several solvents (water, ethanol, methanol and their mixtures), successive extractions, and water with different pHs (4.5, 7.0 and 9.5) were carried out. Spent coffee extracts with the highest antioxidant capacity were obtained after one extraction with neutral water (pH 7.0) in a filter coffeemaker (24 g spent coffee per 400 mL water). Furthermore, spent coffee defatting and extract lyophilization allowed us to obtain spent coffee extracts powder with high antioxidant capacity that can be used as an ingredient or additive in food industry with potential preservation and functional properties.     

Antioxidant activity and antimicrobial properties of phenolic extracts from acerola (Malpighia emarginata DC) fruit

The antioxidant activity and antimicrobial property of phenolic extracts from acerola (Malpighia emarginata DC) fruit were assessed. The contribution of ascorbic acid and phenolic compounds in the total antioxidant capacity of the extracts was also evaluated. The extracts showed high total phenolic values and possessed high antioxidant activity as expressed by 2,2′‐diphenylpicrylhydrazyl (DPPH) and oxygen radical absorbance capacity assays (ORAC). The ascorbic acid content ranged from 405 to 1744 mg/100 g of fruit on a fresh weight basis. The antioxidant capacity of the phenolic fractions was in the following order: anthocyanins<phenolic acids<flavonoids. The phenolic fractions contributed 7.1–36.5% of the antioxidant activity expressed by ORAC, whereas the contribution of ascorbic accounted for 18–39% of the total activity. Selected extracts from the flavonoids fraction showed some activity against Staphylococcus aureus.     

Identification of H₂O₂ as a major antimicrobial component in coffee

Coffee shows distinct antimicrobial activity against several bacterial genera. The present study investigated molecular mechanisms and active ingredients mediating the antimicrobial effect of coffee. Depending on concentration, roasted, but not raw coffee brew inhibited the growth of Escherichia coli and Listeria innocua. Several coffee ingredients with known antibacterial properties were tested for their contribution to the observed effect. In natural concentration, caffeine, ferulic acid and a mixture of all test compounds showed very weak, but significant activity, whereas trigonelline, 5-(hydroxymethyl)furfural, chlorogenic acid, nicotinic acid, caffeic acid, and methylglyoxal were not active. Antimicrobial activity, however, was completely abolished by addition of catalase indicating that H(2)O(2) is a major antimicrobial coffee component. In accordance with this assumption, bacterial counts during 16 h of incubation were inversely related to the H(2)O(2) concentration in the incubation solution. Pure H(2)O(2) showed slightly weaker activity. The H(2)O(2) dependent antimicrobial activity of coffee could be mimicked by a reaction mixture of d-ribose and l-lysine (30 min 120 °C) indicating that H(2)O(2) is generated in the coffee brew by Maillard reaction products. Identification of H(2)O(2) as major antimicrobial coffee component is important to evaluate the application of coffee or coffee extracts as natural preservatives.     

Functional properties of melanoidins: In vitro antioxidant,antimicrobial and antihypertensive activities

Melanoidins formed at the last stage of the Maillard reaction have been pointed out to possess certain functional properties such as antioxidant, antimicrobial and antihypertensive activities. In order to gain more insights on these functional properties different soluble melanoidins and melanoidin fractions isolated from several amino acid–glucose model systems has been analysed In the case of antioxidant and antimicrobial properties, low molecular weight compounds bounded to melanoidins (BMC fraction) exerts antioxidant and antimicrobial activities usually higher than those of the pure melanoidins to whom they are linked. Contrary, in the case of antihypertensive activity it has been found that the main activity is related to the melanoidin core, not to BMC fraction. In addition it has been found no correlation, except for ABTS assay, among colour and antioxidant, antimicrobial or antihypertensive activity, supporting the idea that melanoidin chromophores are not responsible for these actions.     

Honey melanoidins: Analysis of the compositions of the high molecular weight melanoidins exhibiting radical-scavenging activity

Size-exclusion chromatography (SEC) and activity-guided fractionation of honeys allowed the isolation of high molecular weight brown compounds, ranging in size from 66 to 235 kDa that exhibited peroxyl radical-scavenging activity. Their concentrations, antioxidant activity and degree of browning increased after heat-treatment of honeys, suggesting that they represent melanoidins. Chemical analysis of melanoidins demonstrated the presence of proteins, polyphenols and oligosaccharides. Heat-treatment caused an increased incorporation of phenolics into high molecular weight melanoidins and drastically decreased the protein content in these fractions with a concomitant appearance of high molecular weight protein–polyphenol complexes of reduced solubility. LC–ESI–MS demonstrated the presence of oligosaccharide moieties, supporting the postulated origin of melanoidins. The changes in the phenolic content of melanoidins from heated honeys were strongly correlated with their oxygen radical absorbance capacity (ORAC) values (R = 0.75, p < 0.0001), indicating that polyphenols contribute to the antioxidant activity of melanoidins. In summary, honey melanoidins are multi-component polymers consisting of protein–polyphenol–oligosaccharide complexes. A direct interaction between polyphenols and melanoidins resulted in a loss or gain of function for melanoidin antioxidant activity.     

Optimisation,characterisation and quantification of phenolic compounds in olive cake

The phenolic compounds in extracts from pressed olive cake were investigated. Free phenolic compounds were extracted from olive cake using methanol. To liberate bound phenolic compounds, the olive cake was subjected to basic and acidic hydrolysis followed by methanol extraction. The individual phenolic compounds and antioxidant activity of the extracts were determined. The highest total phenolic content and antioxidant activity were obtained using methanol extraction for 12 h at 70 °C. The RP-HPLC profiles for full-fat and defatted olive cake showed that protocatechuic acid, hydroxybenzoic acid, sinapic acid, p-coumaric acid, rutin and hesperidin were the predominant free phenolic compounds. Meanwhile, syringic acid, sinapic acid, caffeic acid and protocatechuic acid were the predominant bound phenolic acids. A positive correlation was observed between total phenolic content and antioxidant activity. The results indicated that most of the phenolic compounds in olive products were present in their free forms (75–90% of total phenolic content), while bound phenolic compounds were only a small proportion (10–25%) of total phenolic content.     

Recovery of Phenolic Antioxidants and Functional Compounds from Coffee Industry By-Products

The recovery process of the phenolic compounds from the coffee industry by-products and their antioxidant activity were investigated in this work. The coffee by-products (coffee pulp, husk, silver skin, and spent coffee) were obtained from coffee processing industry. The phenolic conserves were extracted using solvent mixture of isoproponal and water. The yield of the conserve was highest in case of silver skin (25%) followed by spent waste (19%) and cherry husk (17%) when pretreated with viscozyme. The conserve enclosed chlorogenic acid as major component when analyzed with high-performance liquid chromatography. The bioactive conserves prepared from coffee by-products possessed 65%–70% antioxidant activity. Apart from these, the coffee by-products encompassed total dietary fiber of 40%–80%. Whereas the soluble and insoluble fiber proportion of the coffee by-product ranged between 16–35% and 18–64%, respectively. The antioxidant activity of coffee by-product fiber ranged from 1.5 to 2.0 mmol trolox/100 g and is analogous to that of widespread fruits and fresh vegetables. The hydration properties such as water holding capacity of each by-product was strictly related to the amount of insoluble fiber and to the granulometry. This is the first report on the isolation of bioactive and functional compounds from coffee by-products and can be a source of new value-added products such as phenolic antioxidant adjunct for food processing.     

Biological Properties of Melanoidins: A Review

Melanoidins are brown, high molecular weight products of Maillard reaction, which takes place during thermal processing of food. They are formed in a multistage reaction between reducing sugars and compounds possessing free amino groups and found in roasted coffee, bakery products, cooked meat, beer, honey, sweet wine, processed tomatoes, and fiber. Nowadays, melanoidins have attracted a lot of attention, not only as a functional food ingredient, but also as a potential pro-healthy dietary supplement. In this field, their antioxidant, antimicrobial, anticancer, and detoxifying activity have been described. Based on recent research developments, an overview of the biological properties of melanoidins with implications for human health is presented.     

An investigation into green coffee press cake as a renewable source of bioactive compounds

The residual biomass of coffee, obtained after the oil extraction from coffee beans, called coffee beans residual press cake, has been attracted interest as a source of compounds with antioxidant capacity. This study investigated the effects of ethanolic and methanol-acetone extracts of green coffee beans (GCB) and its residual press cake (GCC) on the phenolic composition and antioxidant capacity. Antioxidant capacity was assayed through five different methods (total phenolic compounds, •DPPH, ABTS, FRAP and β-carotene bleaching assay), and the phenolic profile of the samples through High Performance Liquid Cromatography. GCB and GCC enclosed chlorogenic (55.16 and 64.96 mg g⁻¹, respectively) and caffeic (25.07 and 44.37 mg g⁻¹, respectively) acids as the major components, and the cake presented higher antioxidant capacity than the actual green bean. Antioxidant capacity was higher for GCC extracted with methanol and acetone. This study on the evaluation of the effects of the type of solvent on the bioactive compounds from GCB and GCC showed that this by-product can be a source of new value-added products, such as phenolic antioxidant adjuncts for food or pharmaceutic processing.     

Spent espresso coffee grounds as a source of anti-proliferative and antioxidant compounds

Disposal of spent espresso coffee grounds (SCG) is costly and leads to the loss of bioactive compounds that could be fractionated, in several applications. This work aimed to investigate phenolic profile, tocopherols, and antioxidant and anti-proliferative activities of SCGs ethanolic extracts from coffee powders differing in coffee provenience and composition (arabica/robusta). Tyrosol, detected for the first time in SCGs, was the most abundant phenolic measured (121–1084 mg/kg in the extract), along with 4-hydroxybenzoic acid and vanillin (885–1813 and 340–1103 mg/kg, respectively). Extract derived from 100% robusta from Guatemala (S7-R) showed the highest α- to β-tocopherol ratio of 1.2 and the highest antioxidant potential as evidenced by RACI and GAS values of −0.43 and 0.20, respectively. Moreover, S7-R showed a promising anti-proliferative activity toward human lung carcinoma cells (A549), with IC₅₀ value of 61.2 μg/mL comparable to that given by the positive control vinblastine (IC₅₀ value of 67.3 μg/mL).