Modelling the kinetics of tea and coffee infusion

Data from infusion experiments with tea and coffee are commonly fitted to an equation derived by Spiro from a lumped parameter mass transfer model. However, this equation is generally modified by adding an intercept term in order to achieve acceptable fits to data. Spiro has since reported a Fick's second law analysis using a ‘long‐time approximation’ which yields the same form as the modified fit equation, including the non‐zero intercept term. This successfully predicts the high initial rates of mass transfer due to high initial concentration gradients at the surface of the solid. In this paper the value of the intercept is evaluated for both tea leaf (infinite slab) and coffee particle (sphere) geometries under combined boundary conditions of non‐zero interfacial mass transfer resistance and finite volume of extracting solution. Predicted intercepts are similar to experimental values reported in the literature; however, the analysis suggests that fits to data should ignore ‘early’ points where the solution concentration is less than 35% of its final value. This may not be the case with some literature values and this limits the conclusions that may be drawn from them. Solute diffusivities calculated from the observed rate constant using this model differ slightly from those obtained using the original Spiro method. © 2002 Society of Chemical Industry     

New aspects on the chemistry of tea and coffee. II

Zusammenfassung Als Fortsetzung der Übersicht aus den Jahren 1982/1983 werden nunmehr neuere Veröffentlichungen aus den Jahren 1983/1984 zur Chemie und Technologie von Tee (Blatt, grün und schwarz) und Kaffee (roh, geröstet und instantlöslich) referiert, besonders über die Veränderung der Zusammensetzung während der Herstellung und Lagerung und der Einfluß der Zusammensetzung auf die Qualität der Getränke (155 Referenzen).

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New aspects on the chemistry of tea and coffee. II

Summary As a continuation of the previous review for 1982/83, recent publications (1983/1984) on the chemistry and technology of tea (leaf, green and black) and coffee (raw, roasted and instant), with particular reference to composition and changes during manufacture, and the effects of composition on the quality of the beverage are now reviewed (155 references).

     

Availability of aluminium from tea and coffee

 The amount of aluminium in different kinds of tea and ground coffee was analysed, the transfer of aluminium into the infusion was determined and aluminium intake via tea and coffee was calculated within the framework of our investigations. Aluminium concentrations amounted to (in μg/g dry matter): black tea, 899; flavoured black tea, 763; peppermint tea, 477; mountain herbal tea, 419; fruit tea, 292; ground coffee, 19. About 30% of the aluminium stored in black tea’s dry matter was transferred into the infusion, which contained 4.2 mg Al/l. In contrast, the availability of aluminium from peppermint and fruit tea as well as from ground coffee was very low (about 5%). The calculated aluminium intake via tea and coffee was 0.2 to 0.3 mg/day and contributed about 5% to the total aluminium intake. Only black tea infusions are a significant source of aluminium intake via beverages. Received: 9 January 1997     

New aspects on the chemistry of tea and coffee. III

Summary The previous review for 1983/1984 is now continued with references to recent publications (1984/1985) and as before covers the chemistry and technology of tea (leaf, green and black) and coffee (raw, roasted and instant soluble), with particular reference to composition and changes during manufacture, extraction and storage. The effects of composition on the quality of the beverage, with mention of particular physiological properties, are included (210 references).

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Neue Gesichtspunkte zur Chemie von Tee und Kaffee. III

Zusammenfassung Die vorausgegangenen Übersichtsberichte für 1983 und 1984 werden mit diesem Beitrag der 1984/85 erschienenen Publikationen fortgesetzt, und er berichtet wieder über die Chemie und Technologie des Tees (Blätter, grün und schwarz) und des Kaffees (roh, geröstet und sofort löslich) mit besonderer Berücksichtigung der Zusammensetzung und der Veränderung während der Herstellung, Extraktion und Lagerung. Der Einflu der Zusammensfazung auf die Qualität des Getränkes mit Erwähnung physiologischer Eigenschaften sind eingeschlossen (211 Literaturzitate).

     

无锡小排骨

由于饮茶的人群数量呈现上升之势,茶吧已经开始遍布美国,但咖啡在美国市场仍然保持霸主地位.     

An investigation of coffee roasting using high performance gel filtration chromatography

Changes in the molecular weight distribution of components in green coffee during roasting were investigated using high performance gel filtration chromatography (HPGFC) with TSK-PW 4000 columns. The chromatographic separation of sample extracts obtained from green and roasted coffees, after different degrees of roasting, was monitored by refractive index (RI) detection and UV detection at 280, 325 and 420 nm. The chromatograms obtained with RI detection showed significant differences in molecular weight profiles. UV detection showed similar patterns at 280 and 325 nm, suggesting that phenolic compounds were probably bound to proteins. The formation of pigments was clearly demonstrated when chromatography was carried out with detection at 420 nm and the coloured material was found to be distributed throughout the molecular weight range studied. The use of HPGFC provided a more rapid analysis compared with traditional gel filtration and proved to be useful in monitoring changes in molecular weight which occur during coffee roasting.     

HPLC determination of caffeine in tea,chocolate products and carbonated beverages

Different brands of mate and black tea, chocolate products and carbonated beverages available on the Brazilian market were analysed for caffeine by high-performance liquid chromatography with a UV-vis detector at 254 nm. The column was a reverse phase C18 and the mobile phase consisted of methanol–water (30:70, v/v), acetonitrile–water (10:90, v/v) and methanol–water (25:75, v/v) for tea, chocolate products and soft drinks respectively. Caffeine content ranged from 1.05 to 15.83 mg per cup in mate tea, from 32.21 to 36.23 mg per cup in black tea, from 0.14 to 0.95 mg g⁻¹ in chocolate products from 2.73 to 7.49 mg per can in guaraná-type soft drinks and from 19.81 to 45.89 mg per can in cola soft drinks. These data indicate that the levels of caffeine in Brazilian teas, chocolates and soft drinks are within the ranges reported for similar products in other countries. © 1999 Society of Chemical Industry     

Determination of acrylamide in coffee and chocolate by pressurised fluid extraction and liquid chromatography-tandem mass spectrometry

A selective and sensitive procedure has been developed and validated for the determination of acrylamide in difficult matrices, such as coffee and chocolate. The proposed method includes pressurised fluid extraction (PFE) with acetonitrile, florisil® clean-up purification inside the PFE extraction cell and detection by liquid chromatography (LC) coupled to atmospheric pressure ionisation in positive mode tandem mass spectrometry (APCI-MS-MS). Comparison of ionisation sources (atmospheric pressure chemical ionisation (APCI), atmospheric pressure photoionization (APPI) and the combined APCI/APPI) and clean-up procedures were carried out to improve the analytical signal. The main parameters affecting the performance of the different ionisation sources were previously optimised using statistical design of experiments (DOE). PFE parameters were also optimised by DOE. For quantitation, an isotope dilution approach was used. The limit of quantification (LOQ) of the method was 1 µg kg^-1 for coffee and 0.6 µg kg^-1 for chocolate. Recoveries ranged between 81-105% in coffee and 87-102% in chocolate. The accuracy was evaluated using a coffee reference test material FAPAS T3008. Using the optimised method, 20 coffee and 15 chocolate samples collected from Valencian (Spain) supermarkets, were investigated for acrylamide, yielding median levels of 146 µg kg^-1 in coffee and 102 µg kg^-1 in chocolate.     

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.     

Recycling coffee grounds and tea leaf wastes to improve the yield and mineral content of grains of paddy rice

BACKGROUND: Coffee grounds and tea leaf wastes exhibit strong affinity for metals such as Fe and Zn. The objective of this experiment was to evaluate the effect of top‐dressing application of Fe‐ and Zn‐enriched coffee grounds and tea leaf wastes at the panicle initiation stage on the mineral content of rice grains and the yield of paddy rice. RESULTS: The Fe and Zn contents of brown rice grains increased significantly on application of both coffee and tea waste materials. The concentration of Mn was increased by top‐dressing application of coffee waste material only. For Cu, no significant (P < 0.05) differences were found between the control and ferrous sulfate/zinc sulfate treatment. The application of coffee and tea waste materials led to a significant (P < 0.05) increase in the number of grains per panicle, which was reflected in increases in the total number of grains per hill and in grain yield. CONCLUSION: The top‐dressing application of these materials is an excellent method to recycle coffee grounds and tea wastes from coffee shops. Use of these novel materials would not only reduce the waste going to landfill but would also benefit the mineral nutrition of rice consumers at low cost by increasing Fe and Zn levels of rice grains as well as grain yield. Copyright © 2011 Society of Chemical Industry     

An impression of coffee carbohydrates

Coffee is one of the most popular beverages in the world. It is consumed for its refreshing and stimulating properties. Carbohydrates are the major constituents of coffee beans and serve various functions like binding of aroma, stabilization of foam, formation of sedimentation, and increased viscosity of the extract. The principal low molecular weight carbohydrate is sucrose and no evidence of other simple oligosaccharides has been found. Polysaccharide fraction from green coffee is dominated by arabinogalactan, galactomannan, and cellulose. The polysaccharide content is reduced during roasting due to degradation to low molecular weight carbohydrates (viz., mono and oligosaccharide) and become more extractable. Various methods that can be employed to extract the carbohydrate from roasted coffee are sequential extraction, acid hydroloysis, hot water extraction, enzymatic extraction etc. Carbohydrates from coffee can be quantitatively determined by liquid chromatography, high performance anion exchange chromatography, size exclusion chromatography, and high performance liquid chromatography. Besides improving the organoleptic quality of the coffee beverage, carbohydrates also possess various biological activities such as lowering colon cancer risk. Besides their sheer mass, a variety of evidences testify to the important contribution that the polysaccharide content makes to the character of the final brew. Although a number of chemical and enzymatic methods have been devised to isolate and quantify the carbohydrates of R&G coffee, till date hot water extraction is the only method which can be accepted as a most feasible process and hence, there is wide scope of further research for the efficient and economically viable technology for extraction of carbohydrates from coffee.     

Linking sensory characteristics to emotions: An example using dark chocolate

The conceptual profile of an unbranded product arises via three sources of influence: (i) category effect – how consumers conceptualise the product category: (ii) sensory effect – how the sensory characteristics of a particular product differentiate it from other products in the category: (iii) liking effect – the disposition of consumers to the category and how much they like a particular product. Assuming that category effects (conceptualisation and disposition) are constant across the set of products, it is anticipated that the conceptual differences apparent across the set of unbranded products would be driven, at least in part, by sensory differences. This study describes the application of best–worst scaling to conceptual profiling of unbranded dark chocolates and outlines novel data modelling procedures used to explore sensory/conceptual relationships.     

胶囊式咖啡概述及其安全性分析

本文介绍了胶囊式咖啡的产生和发展过程, 并通过与现磨及速溶咖啡的比较阐述了胶囊式咖啡风味独特、品质持久、方便快捷的特性。同时对胶囊式咖啡包装材料中的铝、塑化剂、胶囊中咖啡粉的潜在安全性进行了分析, 并对胶囊式咖啡产品的研发、改进提出合理的发展方向。