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.     

Construction of COD simulation model for activated sludge process by fuzzy neural network

Fuzzy neural network (FNN) was applied to construct a simulation model for estimating the effluent chemical oxygen demand (COD) value of an activated sludge process in a "U" plant, in which most of process variables were measured once an hour. The constructed FNN model could simulate periodic changes in COD with high accuracy. Comparing the simulation result obtained using the FNN model with that obtained using the multiple regression analysis (MRA) model, it was found that the FNN model had 3.7 times higher accuracy than the MRA model. The FNN models corresponding to each of the four seasons were also constructed. Analyzing the fuzzy rules acquired from the FNN models after learning, the operational characteristic of this plant could be elucidated. Construction of the simulation model for another plant "A", in which process variables were measured once a day, was also carried out. This FNN model also had a relatively high accuracy.     

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.     

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.     

EFFECT OF STORAGE CONDITIONS ON THE SENSORY QUALITY OF GROUND ARABICA COFFEE

The objective of this study was to determine how long ground coffee beans could be stored at room and freezing temperatures before sensory changes could be detected, and to identify specific attribute changes associated with this storage. Ground beans were stored for 0 (fresh), 1, 2 and 3 weeks at room and freezing temperatures. Coffee was prepared from each of these treatments and difference testing was performed. Paired comparison tests were conducted on the fresh, 1‐ and 2‐week‐stored coffee grounds to examine the attributes of coffee aroma, flavor, bitterness and overall preference. At room temperature storage, results indicated significant (P < 0.05) differences in the coffee prepared from fresh versus the 2‐week‐stored ground beans. Coffee made from freshly ground beans had a stronger coffee aroma, less bitterness and was more preferred compared with the beans stored for 1 or 2 weeks (P < 0.05). At freezer storage, differences were detected between coffee prepared from coffee grounds stored for 1 or 2 weeks. Coffee prepared from grounds stored for 2 weeks had a stronger coffee aroma and was more bitter compared with the other storage times (P < 0.05).     

Optimization of roasting conditions according to antioxidant activity and sensory quality of coffee brews

Response surface methodology (RSM) was used to determine the optimal roasting temperature and roasting time of coffee beans used for preparing brews with high antioxidant activity and sensory quality. Green coffee beans (Coffea arabica L. cv. Colombia Organic Tamata) were roasted at temperatures ranging from 140 to 220°C for 2–10 min and were then brewed with dripping hot water. The effects of the roasting conditions on the browning index, antioxidant activity, color, aroma, taste, and overall acceptability of the coffee brewed from the bean were investigated using a second-order central composite design. The quality indicators except the taste were significantly affected by roasting temperature and time, tending to increase and then decrease with increasing roasting temperature and time. Superimposed contour plots indicated that the optimal roasting temperature was 182°C and optimal roasting time was 7 min.     

Optimization of the roasting of robusta coffee (C. canephora conillon) using acceptability tests and RSM

With the objective of optimizing the roasting of robusta coffee (Coffea canephora Conillon), a two factor central composite design (11 samples) was used to optimise the settings for roasting time and the initial internal temperature of the roaster drum on response variables of acceptance with 25 consuming assessors, for the sensory attributes of beverage aroma, flavour and colour. Predictive models were also obtained for the instumental measurement of the colour of the beans and ground coffee. The optimum range for roasting was shown to be a time of 22–28 min at a temperature of 225–230°C, corresponding to the degree of roasting characterized by the following range of colour of roasted robusta beans: L* between 37.05 and 40.69, a* between 2.29 and 4.15 and b* between 2.70 and 6.29.     

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.     

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.     

Sensory profile of Italian Espresso brewed Arabica Specialty Coffee under three roasting profiles with chemical and safety insight on roasted beans

Specialty coffee (SC) has been showing an increasing interest from the consumers which appreciate its traceability and the peculiar flavours from each single origin. Additionally, the processes to which coffee fruits underwent to get green coffee characterise the beans in terms of macromolecules acting as substrates during the roasting. This work evaluates via sensory analysed eight SC, roasted at light, medium, and dark level, submitted to Italian espresso extraction, to assess how different roasting levels exalt the expected cup profile obtained by the suppliers via cupping in origin countries. Finally, roasted beans were characterised for physico-chemical features (pH, titratable acidity, caffeine, melanoidins, polyphenols and acrylamide). Sensory analysis demonstrated that the intermediate roasting level and espresso extraction match better attributes from in-origin cupping. Melanoidins (mmol g⁻¹ coffee d.b.) was able to discriminate among roasting levels (light 0.12 ± 0.01; medium 0.13 ± 0.003; dark 0.14 ± 0.01; α = 0.05). Acrylamide analyses ensured compliance with the food safety standards (light 301.9 ± 37.2 ppb; medium 126.1±19ppb; dark 107.9 ± 22.5ppb). Physico-chemical features were able to cluster samples from different origins within the same roasting level (α = 0.05). Results showed correlations (α = 0.01) between sensory analysis and physico-chemical values: direct for caffeine and astringency, reverse for perceived acidity in relation to astringency, roasted, dried fruits and nutty notes.     

咖啡精油超临界CO2萃取工艺优化及理化特性分析

以云南保山小粒咖啡豆为对象,根据国家标准,测定生、熟咖啡豆的营养成分,在单因素实验的基础上,以响应面优化超临界CO₂萃取咖啡精油的工艺参数;测定生、熟咖啡精油理化指标,并通过气相色谱-氢火焰离子化检测器（GC-FID）分析生、熟咖啡精油的脂肪酸组成。结果表明:经烘焙处理后,熟咖啡豆中水分、水浸出物、咖啡因、总糖、粗纤维和粗脂肪含量与生咖啡豆中的存在显著差异（P<0.05）;超临界CO₂萃取生咖啡精油的最佳工艺条件为萃取压力25 MPa,萃取温度54 ℃,萃取时间150 min,在此条件下咖啡精油萃取得率为13.98%。烘焙处理前后,咖啡精油各常规理化指标无显著差异,且均符合国家标准要求。通过GC-FID分别检测到15和16种脂肪酸,其中亚油酸、棕榈酸、硬脂酸和油酸等为主要脂肪酸,烘焙对咖啡豆脂肪酸组成影响不明显,但各脂肪酸的含量存在一定差异。烘焙对咖啡豆及咖啡精油的各项指标均有一定程度的影响,为云南地区咖啡产业发展提供科学依据。     

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。     

A DAIRY-BASED ESPRESSO BEVERAGE MANUFACTURED USING THREE DIFFERENT COFFEE BEAN ROASTS

The objective of this study was to evaluate the effects of coffee bean roast on the acceptability of a dairy‐based espresso drink. Espresso coffee was made from freshly ground coffee beans with light‐medium roast, between roast (between medium and dark) and dark French roast in order to show the influence of roasting on flavor. Samples were prepared by blending skim milk, soft‐serve ice cream mix, ice and fresh espresso extracts. No significant differences (P < 0.05) were detected in total solids and fat content among treatments. Viscosity for the light‐medium roasted beverage was significantly (P < 0.05) higher than the others. The beverage pH increased with increased darkening of roast. The beverage made with the light‐medium roasted coffee had significantly (P < 0.05) higher preference scores for coffee flavor and overall flavor than beverages made with the between and French roasts. The between and French roasted treatments were shown to have a more intense coffee flavor by trained sensory panelists. Consumers in this study preferred a less intense coffee flavor.     

Use of methylpyrazine ratios to monitor the coffee roasting

The formation of methylpyrazines has been determined in roasted coffee beans (Arabica and Robusta). The determination of different methylpyrazines was studied by the coupled steam distillation-microdistillator as extraction method and gas chromatography using a capillary column and a thermionic detector.

The pyrazine; 2-methyl-; 2,3-dimethyl-; 2,5-dimethyl-; 2,6-dimethyl-; trimethyl- and tetramethyl pyrazine were detected in coffee beans. The principal compound was 2-methylpyrazine. The concentration of the latter pyrazine was more than 2000 μg/100 g of coffee beans depending on the time, the temperature of roasting and the origin of the beans. The correlation of the methylpyrazine quantity with the sensory analysis of the beans has shown the possibility of monitoring the roasting process of coffee beans.     

Discrimination between immature and mature green coffees by attenuated total reflectance and diffuse reflectance Fourier transform infrared spectroscopy

The objective of this work was to evaluate the potential of Fourier transform infrared spectroscopy (FTIR) in the characterization and discrimination between immature and mature or ripe coffee beans. Arabica coffee beans were submitted to FTIR analysis by reflectance readings employing attenuated total reflectance (ATR) and diffuse reflectance (DR) accessories. The obtained spectra were similar, but in general higher absorbance values were observed for nondefective beans in comparison to immature ones. Multivariate statistical analysis (principal component analysis, PCA, and agglomerative hierarchical clustering, AHC) was performed in order to verify the possibility of discrimination between immature and mature coffee samples. A clear separation between immature and mature coffees was observed based on AHC and PCA analyses of the normalized spectra obtained by employing both ATR and DR accessories. Linear discriminant analysis was employed for developing classification models, with recognition and prediction abilities of 100%. Such results showed that FTIR analysis presents potential for the development of a simple routine methodology for separation of immature and mature coffee beans. Practical Application: The ultimate goal of this research is to be able to propose improvements in the way immature coffee beans are separated from graded mature beans in coffee facilities (cooperatives and other coffee producer's associations). The results obtained herein point toward FTIR as a potential tool for the aimed improvements.     

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.