The mycobiota of coffee beans and its influence on the coffee beverage

The quality of coffee beverage is influenced by several factors, including the species or botanical variety of the beans, agricultural practices, harvesting, drying and storage techniques and also the preparation of the beverage. Apart from these, there is the input of microbial contamination during the processing of the beans. Numerous studies have demonstrated that fungi are important contaminants of coffee beans, especially just after harvesting and drying. However, the relationship between fungal contamination and the sensorial characteristics of the beverage has yet to be described. The aim of this research was to analyze the mycobiota of coffee beans collected from different stages of the coffee production chain and to correlate these data with the sensorial characteristics of the final beverage. Fungal infection of 22 coffee bean samples from the southwest of São Paulo state was analyzed. Samples were collected from the tree (mature cherries), from the ground, from the patio (mature, immature and dried floaters or overripe cherries from the tree) and from storage facilities. In general, coffee samples from this region showed high fungal infection and contamination was higher than 70% in about 45% of the samples. A high diversity of fungi was isolated from all the coffee samples analyzed and the most common were Penicillium brevicompactum, Aspergillus section Nigri, Penicillium sp. nov. (closely related to Penicillium crustosum) and Fusarium sp. Both P. brevicompactum and Penicillium sp. nov. were found at all processing stages, including in the cherries, showing that these fungi are naturally found in the coffee beans from this region. Floater coffee and coffee from the ground showed negative sensorial evaluation with attributes such as moldy, dirty and fermented and presented a high contamination by Aspergillus section Nigri and Aspergillus westerdijikiae.     

Reprint of “The mycobiota of coffee beans and its influence on the coffee beverage”

The quality of coffee beverage is influenced by several factors, including the species or botanical variety of the beans, agricultural practices, harvesting, drying and storage techniques and also the preparation of the beverage. Apart from these, there is the input of microbial contamination during the processing of the beans. Numerous studies have demonstrated that fungi are important contaminants of coffee beans, especially just after harvesting and drying. However, the relationship between fungal contamination and the sensorial characteristics of the beverage has yet to be described. The aim of this research was to analyze the mycobiota of coffee beans collected from different stages of the coffee production chain and to correlate these data with the sensorial characteristics of the final beverage. Fungal infection of 22 coffee bean samples from the southwest of São Paulo state was analyzed. Samples were collected from the tree (mature cherries), from the ground, from the patio (mature, immature and dried floaters or overripe cherries from the tree) and from storage facilities. In general, coffee samples from this region showed high fungal infection and contamination was higher than 70% in about 45% of the samples. A high diversity of fungi was isolated from all the coffee samples analyzed and the most common were Penicillium brevicompactum, Aspergillus section Nigri, Penicillium sp. nov. (closely related to Penicillium crustosum) and Fusarium sp. Both P. brevicompactum and Penicillium sp. nov. were found at all processing stages, including in the cherries, showing that these fungi are naturally found in the coffee beans from this region. Floater coffee and coffee from the ground showed negative sensorial evaluation with attributes such as moldy, dirty and fermented and presented a high contamination by Aspergillus section Nigri and Aspergillus westerdijikiae.     

Amino acid profiles in unripe Arabica coffee fruits processed using wet and dry methods

The quality of natural coffee produced in Brazil is quite variable. Fruits at different stages of maturation can be found on the same plant, and unripe fruits are naturally present during the harvest. The pulping of ripe fruits can be effectively used to improve the quality of the coffee, as the ripe fruits will be separated from the unripe fruits; however, the presence of a portion of unripe fruit (with lower quality) in the processing is unavoidable. The wet processing of immature coffee fruit appears to be a potential way of improving its quality. According to the coffee processing used post-harvest, changes were observed in the levels of free amino acids in immature coffee beans. Among the amino acids present, asparagine is the primary amino acid found in unripe coffee beans. Asparagine produces acrylamide, a potentially harmful substance generated during the course of the Maillard reaction. In this study, amino acids in immature coffee beans were analysed using reversed-phase chromatography and ultraviolet detection after the derivatisation with phenylisothiocyanate. The amino acid profiles of the immature coffee beans demonstrated that asparagine is present at more significant levels when immature coffee fruits were processed via dry processing, as compared to wet processing.     

Microbial ecology and starter culture technology in coffee processing

Coffee has been for decades the most commercialized food product and most widely consumed beverage in the world, with over 600 billion cups served per year. Before coffee cherries can be traded and processed into a final industrial product, they have to undergo postharvest processing on farms, which have a direct impact on the cost and quality of a coffee. Three different methods can be used for transforming the coffee cherries into beans, known as wet, dry, and semi-dry methods. In all these processing methods, a spontaneous fermentation is carried out in order to eliminate any mucilage still stuck to the beans and helps improve beverage flavor by microbial metabolites. The microorganisms responsible for the fermentation (e.g., yeasts and lactic acid bacteria) can play a number of roles, such as degradation of mucilage (pectinolytic activity), inhibition of mycotoxin-producing fungi growth, and production of flavor-active components. The use of starter cultures (mainly yeast strains) has emerged in recent years as a promising alternative to control the fermentation process and to promote quality development of coffee product. However, scarce information is still available about the effects of controlled starter cultures in coffee fermentation performance and bean quality, making it impossible to use this technology in actual field conditions. A broader knowledge about the ecology, biochemistry, and molecular biology could facilitate the understanding and application of starter cultures for coffee fermentation process. This review provides a comprehensive coverage of these issues, while pointing out new directions for exploiting starter cultures in coffee processing.     

Research on the origin, and on the impact of post-harvest handling and manufacturing on the presence of ochratoxin A in coffee

The major risk factors and processing steps that can lead to contamination of green coffee with ochratoxin A (OTA) have been identified. Surveys of the green coffee production chain indicate that Aspergillus ochraceus and A. carbonarius are the most potent OTA producers on coffee. Both have been successfully grown in vitro on green coffee and coffee cherries, respectively, producing high amounts of OTA (5-13 mg kg -1 ). The so-called dry processing of coffee, which is cherry drying, was identified as one of the steps during which OTA formation can take place, particularly under humid tropical conditions. Cherries contain sufficient amounts of water to support mould growth and OTA formation during the initial 3-5 days of drying on the outer part of the cherries. Not surprisingly, after dehulling, husks can be highly contaminated with OTA, as also indicated by its enhanced concentration in soluble coffees adulterated with husks and parchment. A minimum water activity of 0.80 (about 14% MC) is required for in vitro OTA production on green coffee, a fact that does not rule out the possibility of OTA contamination due to improper transportation and storage of green coffee. However, this appears not to be a major route for OTA contamination of coffee. OTA contamination can clearly be minimized by following good agricultural practice and a subsequent post-harvest handling consisting of appropriate techniques for drying, grading, transportation and storage of green coffee; these procedures are well established.     

Influence of environmental factors,wet processing and their interactions on the biochemical composition of green Arabica coffee beans

Although cultivation of Arabica coffee trees at high elevation is known to favourably affect the final quality of the beverage, quantitative data describing the influence of climatic conditions on the chemical composition of the seed are still lacking. Similarly, post-harvest treatments of the beans are known to affect the generation of flavour, but the chemical transformations that occur during wet processing are poorly understood. To better characterise the effects of the environment, wet processing and their possible interactions, we quantified the changes in the main chemical components of the coffee seed (lipids, chlorogenic acids, sugars and caffeine) caused by wet processing, and analysed how these changes were affected by the variations induced by the environment before harvest. Using 16 experimental plots in Reunion Island displaying broad climatic variations, we showed that chlorogenic acids and fatty acids in the seed were controlled by the mean air temperature during seed development. By contrast, total lipid, total soluble sugar, total polysaccharide and total chlorogenic acid contents were not influenced by climate. Glucose content was positively affected by altitude, while sorbitol content after wet processing depended directly on the glucose content in fresh seeds.     

Inactivation of A. ochraceus spores and detoxification of ochratoxin A in coffee beans by gamma irradiation

Ochratoxin A (OTA) produced in food by Aspergillus ochraceus is known to cause adverse health effects. Among the plantation products, green coffee beans are prone to fungal attack and get contaminated with OTA frequently. A fungal strain isolated from green coffee beans was characterized by morphological analyses as well as internal transcribed spacer (ITS) and 5.8S rDNA sequencing, turned out to be A. ochraceus, however, nontoxigenic. Hence, additional strains of A. ochraceus were procured and characterized for toxin production. Presterilized green coffee beans were spiked with a toxigenic strain and treated with gamma radiation. Minimum inhibitory dose (MID) of gamma radiation for 10(4) and 10(8) spores of A. ochraceus strain per 10 g of green coffee beans was found to be approximately 1 and approximately 2.5 kGy, respectively. The radiation treatment (10 kGy) almost degraded the preformed or in vitro added OTA (50 ppb) in coffee beans. OTA degradation was found to be enhanced with increase in moisture content. Cytotoxicity in terms of cell viability was found to be reduced significantly for radiation treated OTA in MTT [3-(4,5-dimethylthiazole-2yl)-2,5-diphenyl tetrazolium bromide] assay as well as flow cytometric analysis when studied using human intestinal epithelial (Int-407) cells. Similar finding was also observed with E. coli MG1655 cells. Thus the inclusion of gamma radiation treatment in the postharvest processing chain of green coffee beans could help in eliminating toxigenic fungi as well as destroying preformed OTA without affecting the sensory attributes. PRACTICAL APPLICATION: In general, mycotoxins including ochratoxin A (OTA) are highly stable to detoxifying agents. Green coffee beans are prone to fungal attack and could get frequently contaminated with the OTA due to improper drying or rehydration during storage. Gamma radiation processing of green coffee beans was found to eliminate the A. ochraceus spores as well as inactivate OTA without affecting its sensory attributes. Thus inclusion of gamma radiation in the postharvest processing chain of green coffee beans would be very useful for consumer safety and coffee trade.     

Influence of processing on the content of sugars in green Arabica coffee beans

Quantitative analyses of low molecular sugars in green coffees (Coffea arabica L. var. Acaià) that were processed in parallel either by the traditional wet or the traditional dry method, revealed a close correlation between the kind of post-harvest treatment and the contents of fructose and glucose. While in washed coffee beans (wet processing) only low amounts of these both hexoses were present, those in unwashed coffees (dry processing) were significantly higher. Model-processing experiments in the laboratory confirmed these findings. Moreover, a comparison with the untreated controls revealed that the low levels of both sugars are the consequence of a decrease in the case of wet processing, whereas they remained unchanged or even increased in the case of dry processing. Further minor sugars are also affected by post-harvest treatment. The amounts of galactose, arabinose and mannose show a similar arrangement as those for glucose and fructose, although their overall concentration is about 100-fold lower. Sucrose, the major low molecular sugar in green coffee beans, is not significantly affected by coffee processing. The influence of an active seed metabolism on the observed alterations of the sugar concentrations is discussed.     

Analysis of free amino acids in green coffee beans

To investigate amino acid changes in green coffee beans in the post-harvest period, amino acid concentrations were determined in green beans and after modelled drying, fermentation and storage. After the drying at alternating temperatures up to maximally 40°C, considerable changes in the concentrations of individual amino acids were identified. At the beginning of the storage period, significant changes in concentration were found to a minor extent. Under the condition of drying, it was mainly the concentration of glutamic acid that changed considerably. There was an increase in all the samples by 500 mg/kg dry matter on average, which corresponds to an increase of about 50% of the original value. In contrast, the concentration of aspartic acid in most of the samples decreased clearly due to drying. For the predominant part of the coffee samples, there was a significant increase in the hydrophobic amino acids Val, Phe, Ile and Leu. Changes of the quantities of other amino acids were non-uniform and only insignificant. Constant drying at 80°C for most of the amino acids brought about only minor concentration changes compared to those values obtained at 40°C. Modelled fermentation had no significant effect on the concentrations of the individual amino acids. After a 4-week storage of dried beans, amino acid concentrations did not change further. It is very possible that different post-harvest treatment parameters may influence the amount of aroma precursor compounds in the coffee beans.     

Evaluation of sensory attributes of coffee brews from robusta coffee roasted under different conditions

Robusta coffee beans with a different initial moisture of 5, 7.5 and 10% were convectively roasted at 230 °C, microwaved at 700 W, and roasted by the coupled convective-microwave method. Sensory attributes of brews prepared from these coffee samples were evaluated. Final temperature of microwaved coffee beans was lower than that of the beans processed by the two other methods, which resulted in a higher content of volatile aroma compounds and a lesser degree of charring of their surface. Lower initial humidity of coffee beans shortened the time of roasting. However, the aroma developed upon roasting of the moistest beans was the most intense and pleasant. Modification of roasting conditions increased shifting of the overall acceptability of coffee infusions by 2 points in a 10-point hedonic scale, which implies that, if roasting conditions are adequate to the type of coffee, its sensory characteristics can be improved. Thus, optimization of roasting parameters can increase the share of robusta in well-accepted commercial coffee blends, a convenient fact because of the significant difference in price between the latter and arabica coffee.     

The source of ochratoxin A in Brazilian coffee and its formation in relation to processing methods

A total of 408 Brazilian coffee samples was examined during the 1999 and 2000 coffee harvest seasons for the presence of ochratoxin A (OA) and fungi with the potential to produce it. Samples came from four regions: Alta Paulista (western area of S?o Paulo State), Sorocabana (southwest S?o Paulo State), Alta Mogiana (northeast S?o Paulo State) and Cerrado Mineiro (western area of Minas Gerais State). Cherries and beans were examined at different stages: immature, mature and overripe cherries from trees, overripe cherries from the ground and beans during drying and storage on the farm. For mycological studies, the cherries and beans were surface disinfected with chlorine, plated on Dichloran 18% Glycerol Agar at 25 degrees C for 5-7 days and analysed for the presence of Aspergillus ochraceus and closely related species, A. carbonarius and A. niger. More than 800 isolates of fungi belonging to these species were identified and studied for the ability to produce OA using the agar plug technique and thin layer chromatography (TLC). A. niger was the species found most commonly (63% of isolates of these three species), but only 3% of them produced OA. A. ochraceus also occurred commonly (31% of isolates), and 75% of those studied were capable of OA production, a much higher percentage than reported elsewhere. A. carbonarius was found (6% of isolates) only in Alta Paulista, the hottest region studied, and only from beans in the drying yard or in storage. However, 77% of the A. carbonarius isolates were capable of producing OA. Average infection rates for cherries taken from trees were very low, but were higher in fruit taken from the ground, from the drying yard and from storage, indicating infection by toxigenic species after harvest. The average OA content in 135 samples of mature cherries from trees, overripe from trees, overripe from the ground, drying yard and storage was 0.1, <0.2, 1.6, 2.1 and 3.3 microg/kg, respectively. Although individual OA levels varied widely, only 9 of the 135 samples analysed exceeded 5 microg/kg OA, with one sample of poor quality dried coffee in excess of 100 microg/kg OA. The causes of high contamination were investigated on the farms concerned and several critical points were found, relating both to local climatic conditions and the drying processes used.     

不同初加工工艺对云南阿拉比卡咖啡品质的影响

为了挖掘优质的云南精品咖啡,以云南普文南岛河卡蒂姆系列品种、成熟全红果为试材,探索带果胶非浸泡式发酵(鲜果发酵和水洗干发酵、日晒、黑蜜、干红蜜)和浸泡式发酵(三重水洗发酵、全水洗)等六种不同初加工工艺对生豆粗蛋白质、粗脂肪、咖啡因等内含物质及密度的影响,并采用模糊数学法对熟豆感官风味进行统计学分析。感官评审结果表明:采用黑蜜加工处理和日晒加工处理的咖啡感官品质最佳,综合评分为5.49和5.44,评定为"优";采用三重水洗发酵处理的咖啡豆感官品质最差,综合评分为3.37,评定为"中";干红蜜加工处理的咖啡感官品质综合评分为3.85,评定为"良好";鲜果发酵和水洗干发酵、全水洗发酵加工感官品质综合评分为3.72,3.70,评定为"良"。理化检测结果:带果胶非浸泡式发酵的四种加工方式所得咖啡生豆的粗蛋白质、粗脂肪、咖啡因含量高于两种浸泡式发酵加工所得咖啡生豆;不同的初加工工艺对咖啡生豆密度的影响差异不显著。     

Influence of coffee/water ratio on the final quality of espresso coffee

Espresso coffee is a polyphasic beverage in which the physico‐chemical and sensory characteristics obviously depend on both the selection of ground roasted coffee and the technical conditions of the percolation process. The aim of this work was to evaluate the influence of the coffee/water ratio on the physico‐chemical and sensory quality of espresso coffee. Furthermore, the influence of botanical varieties (Arabica and Robusta) and the type of roast (conventional and torrefacto) on the selection of coffee/water ratio was studied. The relationship between pH and the perception of acidity intensity is discussed in relation to the influence of the coffee/water ratio, type of coffee and roast. The optimisation of other technical parameters in previous studies seemed to minimise the influence of an increase in the coffee/water ratio on the extraction of soluble and solid compounds. In fact, only some sensory attributes, such as bitterness, astringency and burnt, acrid and earthy/musty flavours were proposed as relevant to the selection of 6.5 g 40 mL^?1 or 7.5 g 40 mL^?1 in conventional roasted coffees (Arabica 100% and Robusta blend), and 6.5 g 40 mL^?1 in torrefacto roasted coffees. On the other hand, the addition of sugar during the roasting process in torrefacto roast coffees seemed to contribute to a higher generation of acids, melanoidins and other compounds by the Maillard reaction or caramelisation, which led us to select the lowest coffee/water ratio. Copyright © 2006 Society of Chemical Industry     

Acetaldehyde as a possible indicator of spoilage in green Kona (Hawaiian) coffee

Kona coffee cherries were demucilaged by either mechanical, enzymic or chemical methods, by the action of bacterial pure cultures, or by natural fermentation. Thirteen volatile components were detected by gas chromatography in all samples of green coffee tested, and these included methanethiol, acetaldehyde, dimethyl sulphide, propionaldehyde, acetone, isobutyraldehyde, butyraldehyde, ethanol, and isovaleraldehyde. Probably, methanol and/or methyl ethyl ketone also were present among the volatile components detected. The relative concentrations of several volatile components did not vary appreciably among the different lots of coffee demucilaged experimentally. However, acetaldehyde concentration increased as the duration of natural fermentation was prolonged, being markedly higher in grossly over-fermented (spoiled) coffee beans. All samples of coffee demucilaged experimentally had similar cup-testing quality (Kona grade No. 1), indicating that none of the demucilaging methods enhanced or diminished coffee flavour or aroma. Over-fermented beans, however, were poor in cup-testing quality.     

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.     

Application of artificial neural networks in the geographical identification of coffee samples

The recognition of the characteristics of coffee associated with a given agricultural system and aimed at adding value and attending the consumers’ demands stimulates the production of types of coffee properly described. The objective of this study was to explore and to explain the physicochemical characteristics and sensory attributes of the coffee grown in Parana State (Southern Brazil) based on an integrated approach of the terrior and the application of artificial neural network. Physicochemical variables of green coffee beans and roasted coffee beans were determined, as well as sensory attributes of the beverage. One hundred and seventy-two coffee samples were analyzed for moisture, proteins, chlorogenic acids, tannins, total acidity, total lipids, caffeine, total and reducing sugars and minerals. These properties were tabulated and presented to artificial neural network multilayer perceptron to be identified as the region and the city of planting. The artificial neural network classified correctly and tested 100% of the samples grown by region. For the database containing information by city, the automatic mode of the software Statistica 9.0 was used. The neural network showed 99% accuracy in training and 100% accuracy in the stage of testing and validation.     

Storage of green coffee in hermetic packaging injected with CO2

The objective of this study was to evaluate the physical, chemical, and sensory qualities of green coffee beans (Coffea arabica L.) during storage in different types of packaging. Coffee was stored from October 2008 to September 2009 in a warehouse of the Agriculture Society Ltda. (SAAG) in Santana da Vargem, southern Minas Gerais State, Brazil. The treatments in the factorial design consisted of two types of packaging (hermetic big bags with the injection of up to 60% CO₂ in a controlled atmosphere; similar bags but without the injection of CO₂ in a modified atmosphere) and three sampling positions in the bags (high, medium, and low). At 3-month intervals during a 12-month period, grains were analyzed to determine their water content, color, electrical conductivity, potassium lixiviation, and content of sugars. Sensory analysis was also conducted at these sampling times. The storage of green coffee beans in hermetic big bags on a commercial scale under modified and controlled atmospheric conditions is viable over a 12-month period. The coffee packed in big bags maintained its quality and exhibited an intensification of the green coloration of the grains during storage. Sensory analysis of coffee beans stored in a controlled atmosphere showed that the medium sampling position yielded the best ratings. The results of this analysis demonstrated that this storage technique can potentially increase the effectiveness of methods used to preserve the sensory quality of coffee beans.     

Post-harvest practices linked with ochratoxin A contamination of coffee in three provinces of Cordillera Administrative Region,Philippines

One of the emerging concerns in the Cordillera Administrative Region, Philippines is ochratoxin A (OTA) contamination in coffee. During 2015 to 2016, a total of 51 Arabica (Coffea arabica) coffee samples from Benguet province and 71 Robusta (Coffea canephora var. Robusta) coffee samples from the provinces of Ifugao and Kalinga were analysed for OTA contamination. The OTA-producing fungal contaminants during drying and storage of Arabica and Robusta coffee were Aspergillus niger and Aspergillus ochraceus. Ochratoxin A was more commonly detected in Robusta coffee (36.6%) than in Arabica coffee (21.6%). Among the contaminated samples, Robusta coffee cherries in the drying yard had the highest mean OTA level (120.2 μg kg^?1, n = 10) while roasted Robusta coffee beans had the lowest mean level (4.8 μg kg^?1, n = 9). The onset of contamination of Arabica coffee occurred during storage, with a mean OTA level of 46.7 μg kg^?1 (n = 9). Roasted coffee had lower OTA content although five samples had levels >5.0 μg kg^?1. Pearson Chi-square analysis (χ²) and Fisher’s exact test revealed that several post-harvest practices involving non-removal of the husk or hull and mixing of defective coffee were significantly associated with the occurrence of OTA during drying and storage (p < 0.05). No significant associations, however, were identified during roasting. This study suggests that the post-harvest practices in Cordillera Administrative Region should focus on the removal of defective coffee in all stages of post-harvest and rapid reduction of moisture content particularly during drying.     

Peroxyl radical-scavenging activity of coffee brews

The ORAC_FL assay was used in non-automated mode to evaluate the specific peroxyl radical scavenging properties of the aqueous soluble components of green and roasted Arabica and Robusta coffee samples. A relationship between ORAC_FL and the concentration of CQAs (caffeoyl quinic acids) was found for the extracts from green coffee beans. Aqueous extracts from roasted coffee beans possessed equal or stronger scavenging power than that obtained for the green coffee beans extracts and the scavenging activity depended on the variety of coffee and the roasting conditions. Brews from Robusta coffee beans showed the highest ORAC_FL. The best scavenging properties for the brews from Arabica coffee beans were detected in samples prepared from coffee beans roasted under light conditions. The data indicate that, during roasting, a complex network of reactions takes place leading to the formation of a wide number of compounds possessing specific scavenging properties. Under mild roasting conditions, caffeoyl quinic acids appear to be the main components responsible for the free radical scavenging power of coffee brews. In contrast, Maillard reaction products may be the principal components with free radical scavenging activity in more severely (medium and dark) roasted coffees.