Correlation between cup quality and chemical attributes of Brazilian coffee

Brazilian arabica coffee is classified for trading according to the quality of the beverage obtained after roasting and brewing. In the present study, Brazilian green and roasted coffee beans were investigated for possible correlations between cup quality and the levels of sucrose, caffeine, trigonelline and chlorogenic acids, determined by HPLC analysis. Trigonelline and 3,4-dicaffeoylquinic acid levels in green and roasted coffee correlated strongly with high quality. To a lesser extent, caffeine levels were also associated with good quality. On the other hand, the amount of defective beans, the levels of caffeoylquinic acids (predominantly 5-caffeoyilquinic acid), feruloylquinic acids, and their oxidation products were associated with poor cup quality and with the Rio-off-flavor. The fact that similar correlations between cup quality and chemical attributes were observed in green and light roasted samples – the latter used for coffee cup classification – indicates that chemical analysis of green beans may be used as an additional tool for coffee quality evaluation.     

Formation of aliphatic acids by carbohydrate degradation during roasting of coffee

 A major fraction of the acidity generated on coffee roasting can be attributed to formation of the four aliphatic acids formic, acetic, glycolic and lactic. Addition of sucrose, glucose or fructose to green coffee beans gave, compared to untreated beans, significant increases in the yields of the four acids on subsequent roasting. In addition, model studies using these three carbohydrates confirmed sucrose as the principal green bean precursor of the acids. Arabinose, erythrose and 1,6-anhydroglucose were identified as reaction products of sucrose thermal degradation and also subsequently served as precursors for acid formation. Isotopic labelling experiments indicated that known degradation pathways could be used to explain the formation of the four aliphatic acids from sucrose. Received: 7 January 2000     

Evaluation of green coffee beans quality using near infrared spectroscopy: A quantitative approach

Characterisation of coffee quality based on bean quality assessment is associated with the relative amount of defective beans among non-defective beans. It is therefore important to develop a methodology capable of identifying the presence of defective beans that enables a fast assessment of coffee grade and that can become an analytical tool to standardise coffee quality. In this work, a methodology for quality assessment of green coffee based on near infrared spectroscopy (NIRS) is proposed. NIRS is a green chemistry, low cost, fast response technique without the need of sample processing. The applicability of NIRS was evaluated for Arabica and Robusta varieties from different geographical locations. Partial least squares regression was used to relate the NIR spectrum to the mass fraction of defective and non-defective beans. Relative errors around 5% show that NIRS can be a valuable analytical tool to be used by coffee roasters, enabling a simple and quantitative evaluation of green coffee quality in a fast way.     

Physicochemical characteristics of green coffee: comparison of graded and defective beans

ABSTRACT:  Defective (triage) coffee beans are beans rejected after separating the graded ones according to the size and color. These coffee beans represent about 15% to 20% of coffee production in India but are not utilized for beverages since these affect the quality of coffee brew. In the present study, physical characteristics such as bean density, brightness, titratable acidity, pH, moisture, and total soluble solids and also chemical composition, namely, caffeine, chlorogenic acids, lipids, sucrose, total polyphenols, and proteins, were evaluated in defective as well as in graded green coffee beans. The physical parameters such as weight, density, and brightness of defective coffee beans were low compared to the graded beans, which is due to the presence of immature, broken, bleached, and black beans. Caffeine content was low in triage beans compared to graded beans. Chlorogenic acids, one of the composition in coffee responsible for antioxidant activity, was found to be intact (marginally high in some cases) in defective coffee beans. Hence, triage coffee beans can be evaluated as a source of antioxidant or radical scavenging conserve for food systems.     

Effect of shading on yield, sugar content, phenolic acids and antioxidant property of coffee beans (Coffea Arabica L. cv. Catimor) harvested from north-eastern Thailand

BACKGROUND: Environmental conditions, including shading, generally influence the physical and chemical qualities of coffee beans. The present study assessed the changes in some phenolic compounds, antioxidant activity and agronomic characters of coffee beans (Coffea arabica L. cv. Catimor) as affected by different shading conditions including full sun, three artificial shading conditions using a saran covering (50% shade, 60% shade, and 70% shade) and lychee shade. RESULTS: Bean weight and bean size increased significantly (P < 0.05) when the shade level was progressively increased. The coffee beans grown under lychee shade exhibited superior bean yield, 1000‐bean weight, total phenolic content and antioxidant activity compared to all other beans. Chlorogenic acid was the most predominant phenolic acid in all samples studied, being the highest in the beans grown under lychee shade, followed by 60% shade, 70% shade, 50% shade and full sun, respectively. In contrast, bean grown under full sun had the highest amount of vanillic acid and caffeic acid. CONCLUSIONS: Antioxidant activity was highly positively associated with chlorogenic acid content. The content of total sugar (fructose, glucose and sucrose) was found highest in coffee beans grown in 60% shade, with fructose the predominant sugar. Under climatic conditions similar to this experiment, it is advisable that growers provide shade to the coffee crop to reduce heat from direct sunlight and promote yield as well as obtain good quality coffee beans. Copyright © 2012 Society of Chemical Industry     

Fruit thinning and shade improve bean characteristics and beverage quality of coffee (Coffea arabica L.) under optimal conditions

Under two contrasting light regimes (full sun and 45% shade) and the optimal coffee‐growing conditions of the central valley of Costa Rica, production pattern, bean characteristics and beverage quality were assessed over two production cycles on dwarf coffee (Coffea arabica L. cv. Costa Rica 95) trees with varying fruit loads (quarter, half and full loads) imposed by manual fruit thinning. Shade decreased coffee tree productivity by 18% but reduced alternate bearing. Shade positively affected bean size and composition as well as beverage quality by delaying berry flesh ripening by up to 1 month. Higher sucrose, chlorogenic acid and trigonelline contents in sun‐grown beans pointed towards incomplete bean maturation and explained the higher bitterness and astringency of the coffee beverage. Higher fruit loads reduced bean size owing to carbohydrate competition among berries during bean filling. These results have important implications in terms of agricultural management (shade, fruit thinning, tree pruning) to help farmers increase coffee plantation sustainability, produce coffee beans of larger size and higher quality and ultimately improve their revenues, especially during times of world overproduction. Copyright © 2005 Society of Chemical Industry     

Extraction of coffee diterpenes and coffee oil using supercritical carbon dioxide

Commercial green and roasted coffee beans were used to maximize oil extraction and conditions were studied to obtain the highest and lowest diterpene levels on green and roasted coffee oil, respectively. Thus, operational temperatures (60–90 °C) and pressure (235–380 bar) were optimized for coffee oil extraction. Oil content levels and diterpene oil concentration were compared to the results obtained with the extraction with Soxhlet apparatus, using hexane as solvent. In general, an inverse correlation was observed between the amount of extracted oil and diterpene concentration levels. As a result, different oil contents with different diterpene concentrations could be obtained. The HPLC analysis of cafestol and kahweol in the oil extracted from green coffee beans at 70 °C/253 bar resulted in the highest concentration (453.3 mg 100 g⁻¹), which was 48% lower than in the oil extracted with hexane while in the oil extracted from roasted coffee beans at 70 °C/371 bar, resulted in 71.2% reduction of diterpenes.     

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.     

Evaluation of microstructural properties of coffee beans by synchrotron X-ray microtomography: a methodological approach

Synchrotron radiation microtomography was used as a nondestructive imaging technique to investigate the microstructural properties of green and roasted coffee beans. After image acquisition, 2D images have been reconstructed and 3D images of the beans have been then obtained. Qualitative and quantitative analysis of the images allow to fully characterize the morphological and structural features of the coffee beans. Roasting causes meaningful changes in the microstructure of the coffee bean tissue with the development in the entire bean of a porous structure with pores of different shape and size depending on the zone of the bean and cracks occurring mainly in the more external regions and between parenchyma and mucilage. The highly contrasted X-ray images have been analyzed to determine the pore size and its distribution in different regions of the coffee beans by selecting Volume-of-Interest (VoI). The use of phase-contrast hard X-rays imaging techniques represents an interesting tool of investigation of the internal structure, morphology, as well as the quality of whole coffee beans. Moreover, the high potentiality of 3D X-ray imaging and the approach used in this study could be applied in understanding the effects of roasting process conditions on the evolution of microstructural properties of the bean that may affect the stability as well the grinding and brewing performances. PRACTICAL APPLICATION: Synchrotron radiation microtomography is an elegant nondestructive imaging technique to investigate the microstructural properties of porous cellular matrices like the green and roasted coffee beans. The quantitative analysis of the resulting 2D and 3D images allows a more comprehensive and objective characterization of the sample under investigation as a whole or of extracted Volumes-of-Interest in the bean. This imaging technique could have a major role in understanding the effects of roasting process conditions on the microstructural properties of the bean.     

Effect of packaging materials and storage time on changes of colour,phenolic content,chlorogenic acid and antioxidant activity in arabica green coffee beans (Coffea arabica L. cv. Catimor)

The conditions and storage time of green coffee beans are very important for the commercial quality of coffee. This includes factors such as light, humidity and temperature in the warehouse and also the packaging material used. The aim of this study was to evaluate the effects of type of packaging materials namely high density polyethylene (HDPE) bag and jute sack on moisture content, colour, phenolic contents, chlorogenic acids content and antioxidant activity of Arabica green coffee bean during 15 months of storage. The results show that HDPE bag can preserve the moisture content, colour and chlorogenic acid in green coffee beans (GCB) better than a jute sack during storage. No significant difference of phenolics content in green coffee beans was observed during 4 months of storage in both types of packaging. During initial 10 months of storage the antioxidant activity of GCB stored in HDPE showed higher values than that of GCB stored in jute sack. However, after 1 year of storage, the phenolics content and antioxidant activity in GCB in a jute sack were higher than in HDPE bag. The fluctuation of moisture content could lead to stress condition of green coffee bean and contributing to forming of bioactive compounds. This finding was observed and need further investigation.     

Conducting starter culture-controlled fermentations of coffee beans during on-farm wet processing: Growth,metabolic analyses and sensorial effects

In this study, the potential use of Pichia fermentans YC5.2 as a starter culture to conduct controlled coffee bean fermentations during on-farm wet processing was investigated. Inoculated fermentations were conducted with or without the addition of 2% (w/v) sucrose, and the resultant microbial growth and metabolism, bean chemistry and beverage quality were compared with spontaneous (control) fermentation. In both inoculated treatments, P. fermentans prevailed over indigenous microbiota and a restricted microbial composition was observed at the end of fermentation process. The inoculation also increased the production of specific volatile aroma compounds (e.g., ethanol, acetaldehyde, ethyl acetate and isoamyl acetate) and decreased the production of lactic acid during the fermentation process. Sucrose supplementation did not significantly interfere with the growth and frequency of P. fermentans YC5.2 inoculum but maintained high levels of wild bacteria population and lactic acid production similar to the spontaneous process. In roasted beans, the content of sugars and organic acids were statistically (p < 0.05) similar for all the treatments. However, the inoculated fermentations were shown to influence the volatile fraction of roasted coffee beans by increasing the concentration of yeast-derived metabolites compared to control. Sensory analysis of coffee beverages demonstrated that the use of the YC5.2 strain was favorable for the production of high-quality coffees with distinctive characteristics, e.g., intense perception of ‘vanilla’ taste and ‘floral’ aromas. In conclusion, the use of P. fermentans YC5.2 in coffee processing was shown to be a viable alternative to control the fermentation step and to ensure consistent quality of finished products.     

Volatile compounds as potential defective coffee beans’ markers

Although Brazil is the largest raw coffee producer and exporter in the world, a large amount of its Arabica coffee production is considered inappropriate for exportation. This by-product of coffee industry is called PVA due to the presence of black (P), green (V) and sour (A) defective beans, which are known to contribute considerably for cup quality decrease. Data on the volatile composition of Brazilian defective coffee beans are scarce. In this study, we evaluated the volatile composition of defective coffee beans (two lots) compared to good quality beans from the respective lots. Potential defective beans’ markers were identified. In the raw samples, 2-methylpyrazine and 2-furylmethanol acetate were identified only in black-immature beans and butyrolactone only in sour beans, while benzaldehyde and 2,3,5,6-tetramethylpyrazine showed to be potential markers of defective beans in general. In the roasted PVA beans, pyrazine, 2,3-butanediol meso, 2-methyl-5-(1-propenyl)pyrazine, hexanoic acid, 4-ethyl-guayacol and isopropyl p-cresol sulfide also showed to be potential defective coffee beans’ markers.     

Effect of the roasting process on glass transition and phase transition of Colombian Arabic coffee beans

This paper presents results of the analysis of organic coffee beans cultivated in Departamento del Cauca - Colombia. Beans studied are of the Coffea Arabica species cultivated in mountain soils of altitude close to 1500 m. Samples from green and roasted beans were characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and X-ray diffractometry (XRD). We intend to relate the features of the heating spectra with the transformation experimented by the coffee. Glass transition and phase transitions were examined. DSC and TGA spectra show that the green coffee experiments a high and fast decomposition after 200 ^°C until 289 ^°C with a remarkable transformation in a close range around 210 ^°C. XRD shows significant changes for green and roasted beans associated to the amount of caffeine hydrates and caffeine anhydrous. Fit of XRD curves by Lorentzian shows a considerable increase of the active crystalline phase at 2θ equal to 20.4⁰ for the roasted coffee. The results obtained from this study contribute to the insight associated with the final quality of coffee dependent on roasting methods. Better quality of coffee requires a refined and very controlled roasting process around of 218 ^°C with a slow thermal treatment since the room temperature until the 200 ^°C.     

Strontium and oxygen isotope fingerprinting of green coffee beans and its potential to proof authenticity of coffee

Multicollector inductively coupled plasma mass spectrometry (MC-ICP-MS) and Isotope Ratio Mass Spectrometry (IRMS) were applied to combine strontium and oxygen isotope abundance ratios of green coffees from 20 geographical origins in order to evaluate the suitability of these parameters as indicators of geographical origin, which is an important parameter of coffee quality. Results show that both isotopic systems of green coffee beans show a relation to environmental factors that influence processes occurring during the growth of the coffee bean. The final results allowed discrimination of local provenances investigated in this study by principal component analysis (PCA) and exhibit the potential to proof authenticity of world coffees. A good discrimination was obtained especially for coffee of South America region and coffees originating from islands.     

Hydrocolloids from coffee: physicochemical and functional properties of an arabinogalactan–protein fraction from green beans

The arabinogalactan–protein (AGP) fraction of green coffee beans accounts for 15% of the dry bean. A procedure was developed to solubilise most of the AGP content of the beans so that its properties as a hydrocolloid could be investigated. An AGP fraction was partially purified from green arabica coffee beans, its rheological properties characterised and compared to those of some commercially important hydrocolloids, particularly acacia gum. The coffee AGP fraction dissolved readily in water to give colourless clear solutions. The polymer was a polyelectrolyte with a high molecular weight (M_w 3.78×10⁶), characterised by a narrow polydispersity index (M_w/M_n 1.3). The intrinsic viscosity was close to that of acacia gum ([η]=0.23 dL g⁻¹), but a 1 wt% solution of coffee AGP was three times more viscous than acacia gum at the same concentration. Coffee AGP showed Newtonian flow for concentrations below 6 wt%, but above this concentration the flow behaviour entered a shear-thinning regime. The coffee AGP fraction possessed interesting foaming properties providing that the biopolymer concentration was high enough to initially stabilize the interface that is created. The high molecular weight of coffee AGP combined with its globular structure conferred upon it a high ability to retain water within a foam thin film. However, the structure of the interfacial film was less effective than that of acacia gum to entrap efficiently the gas into the foam. In summary, coffee AGP shows some interesting rheological features which suggest that coffee beans could be used as an alternative source of the class of surface-active polymers which find many commercial applications.     

Critical roasting level determines bioactive content and antioxidant activity of Robusta coffee beans

Food Science and Biotechnology - Indonesian Lampung Robusta coffee green beans were roasted at eight roasting levels (green bean, early yellow, brown, 1st crack done, very light, light, medium, and...     

Physicochemical characteristics of Ethiopian Coffea arabica cv. Heirloom coffee extracts with various roasting conditions

This study aimed to investigate the physicochemical characteristics of Ethiopian Coffea arabica cv. Heirloom coffee extracts with various roasting conditions. Green coffee beans were roasted at four different conditions (Light-medium, Medium, Moderately dark, and Very dark) and used to extract espresso and drip coffee. Moisture content in coffee beans was decreased as the roasting degree increased. The contents of crude fat and ash were lower in the Light-medium roasted coffee beans than in green coffee beans but increased as the roasting degree increased. The values of lightness (L^*), redness (a^*), yellowness (b^*), and browning index of coffee extracts were decreased as the roasting degree increased. Total dissolved solids in espresso coffee were increased with increasing roasting degree but decreased in drip coffee. In both the extracts, the contents of reducing sugar, titratable acidity, organic acids, and chlorogenic acid were decreased, but that of caffeine was increased with the roasting degree increased.Supplementary InformationThe online version contains supplementary material available at 10.1007/s10068-020-00865-w.     

Behaviour and reduction of ochratoxin A in green coffee beans in response to various processing methods

 As a consequence of unfavourable harvests, processing conditions or unsuitable transport and storage conditions, unprocessed food and food products may contain ochratoxin A (OTA). This substance has also been found on green coffee beans imported by the coffee roasting industry. The German Coffee Association has initiated a program to check whether existing technologies for the quality control, selection and/or treatment of green coffee beans are appropriate for the reduction of the levels of this mycotoxin. The results showed that all types of processing evaluated, especially decaffeination with solvents, reduced OTA levels significantly. An earlier study has shown that coffee roasting and extraction (in the case of soluble coffee) led to a reduction in the levels of OTA. Received: 28 July 1998 / Revised version: 16 November 1998     

Overview on the mechanisms of coffee germination and fermentation and their significance for coffee and coffee beverage quality

Quality of coffee is a complex trait and is influenced by physical and sensory parameters. A complex succession of transformations during the processing of seeds to roasted coffee will inevitably influence the in-cup attributes of coffee. Germination and fermentation of the beans are two bioprocesses that take place during post-harvest treatment, and may lead to significant modifications of coffee attributes. The aim of this review is to address the current knowledge of dynamics of these two processes and their significance for bean modifications and coffee quality. The first part of this review gives an overview of coffee germination and its influence on coffee chemistry and quality. The germination process initiates while these non-orthodox seeds are still inside the cherry. This process is asynchronous and the evolution of germination depends on how the beans are processed. A range of metabolic reactions takes place during germination and can influence the carbohydrate, protein, and lipid composition of the beans. The second part of this review focuses on the microbiota associated with the beans during post-harvesting, exploring its effects on coffee quality and safety. The microbiota associated with the coffee cherries and beans comprise several bacterial, yeast, and fungal species and affects the processing from cherries to coffee beans. Indigenous bacteria and yeasts play a role in the degradation of pulp/mucilage, and their metabolism can affect the sensory attributes of coffee. On the other hand, the fungal population occurring during post-harvest and storage negatively affects coffee quality, especially regarding spoilage, off-tastes, and mycotoxin production.     

Structure expansion of green coffee beans using instantaneous controlled pressure drop process

Since 1988, when the first experiments with the Instantaneous Controlled Pressure Drop (DIC) process were performed, a lot of investigations have been carried out concerning the structure expansion, processing kinetics (drying, extraction and sterilization) and the improvement of the functional and organoleptic properties of fresh and dried foods. In this study, two DIC technologies were used to expand the structure of green coffee beans. Two varieties of commercial Arabica coffee beans of different agricultural and geographical origins (Brazilian and Ethiopian) were inspected. The effect of initial moisture content (7–40% dry basis), type of heating in the DIC process (steam and microwaves), processing parameters like pressure (0.4–0.7 MPa) and heating time (20–200 s) on bean expansion were investigated. The expansion was evaluated as the ratio of the tapped density of raw beans to that of the treated material. The hydration capacity of the beans was also studied. The Response Surface Methodology was employed to optimize the processing parameters. After the steam DIC treatment, the maximum expansion ratio of the Brazilian beans (e = 1.74) was higher than that of the Ethiopian beans (e = 1.59). For Brazilian beans, the steam DIC treatment resulted in a higher value of expansion ratio than the MW DIC treatment (e = 1.39). Concerning hydration capacity, the steam DIC treatment gave values of 78.6% and 48.2% d.b. for the Ethiopian and Brazilian beans, respectively. It means almost two-fold increase in the hydration capacity using DIC treatment. The steam DIC treatment increased and accelerated in twice the weight loss of beans during roasting.

Industrial relevance

Preliminary experiments have shown that the structure expansion of green coffee beans significantly reduced the roasting time, amended the bean suitability to grinding and improved the kinetics and yield of caffeine and active compounds extraction. The industrial DIC processes can be distinguished by high quality of final products, energy saving and positive environmental impact. Due to the fragile structure of coffee beans, a batch process should be applied. Industrial plant can be designed as a tower plant with several compartments separated by guillotine valves where the material falls down by gravity force or a carrousel or a linear plant with filling, DIC treatment and discharging operations. The ABCAR DIC Process Company (La Rochelle, France) develops plants with a capacity of 50 kg/h to 8 ton/h of dry coffee beans. Despite the promising experimental results concerning microwave DIC technology, the industrial applications are so far limited to the steam DIC treatment due to technical reasons.