Influence of roasting and brew preparation on the ochratoxin A content in coffee infusion

A study of the effect of coffee processing in the ochratoxin A (OTA) level has been carried out from the green beans to the drinking form. The analysis of OTA has been carried out by an in-house validated HPLC method with fluorescence detection. The limits of detection were 0.04 µg/kg for green and roasted coffee, and 0.01 µg/L for coffee brew. Thirty-six green coffee samples of different origin (Colombia, Costa Rica, Brazil, Vietnam, India and Uganda) were analysed. The highest concentrations of OTA were found in Vietnamese samples - Robusta species treated by dry processing - (range 0.64-8.05 µg/kg), that also showed the highest percentage of defective beans (7.6%). These contaminated samples were roasted in a process that controlled loss of weight and color, as in the industry. A mean reduction of 66.5% was obtained, but the reduction seems to be heterogeneous. Coffee brew was prepared by the three brewing processes more utilized in Europe: moka, auto-drip and espresso. A reduction of the OTA level has been attained, being greater when using a espresso coffee maker (49.8%) than when using auto-drip (14.5%) or moka brewing (32.1%). Therefore, the method of coffee brew preparation plays a key role in the final OTA human exposure.     

Influence of roasting and different brewing processes on the ochratoxin A content in coffee determined by high-performance liquid chromatography-fluorescence detection (HPLC-FLD)

A rapid and reliable procedure has been developed for the determination of ochratoxin A (OTA) in green and roasted coffee. The method consists of extraction of the sample with methanol-5% aqueous sodium hydrogen carbonate/1% PEG8000 (20:80), followed by immunoaffinity column (IAC) clean-up and, finally, high-performance liquid chromatography (HPLC) determination with fluorimetric detection. Mean recoveries for green and roasted coffee spiked at different levels ranging from 94 and 105% were obtained. The limit of determination (S/N = 3) was 0.032 ng g(-1) and the precision (within-laboratory relative standard deviation) was 6%. The method described has been used to assess the influence of roasting and different brewing processes on OTA content in commercial lots of green and roasted coffee. The results provided evidence that roasting led to a significant drop on OTA levels (65-100%). Also, the way coffee is prepared affects the OTA content: brewing using a Moka Express (Italian coffee) led to a significant reduction of OTA concentration (50-75%) since hot water stays in contact with coffee for a short time. On the contrary, Turkish coffee-making (infusion for about 10 min) cause poor reduction in OTA.     

Production of ochratoxin A by Aspergillus carbonarius on coffee cherries

Robusta coffee cherries collected before and during sun drying from two coffee farms in Thailand were examined for moulds producing ochratoxin A (OA). Aspergillus ochraceus was only detected in one sample, whereas Aspergillus carbonarius was isolated from 7 out of 14 samples. On gamma-irradiated coffee cherries, each of the six tested A. carbonarius strains produced OA. More than 4800 microg kg(-1) of toxin were detected under optimal conditions (25 degrees C, a(w) 0.99). OA production was strongly reduced (230 microg kg(-1)) at an a(w) of 0.94.     

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...     

A numerical approach for the analysis of the coffee roasting process

A numerical model of the coffee roasting process under operating conditions is proposed. This numerical tool is able to simulate the behaviour of all the components of a batch roaster as well as the roasting process of the coffee beans within the drum. The model evaluates the heat and mass transfer between a hot air flow and the coffee beans during the roasting process on the basis of the physical properties of the coffee and the operation of the roasting machine. Different submodels are included in the modelling in order to address particular thermo-physical processes, such as the evaporation of coffee moisture and the heat released or absorbed by the beans due to the roasting reactions.     

Effect of the roasting method on the content of 5-hydroxytryptamides of carboxylic acids in roasted coffee beans

Coffee beans of Coffea liberica (robusta) variety were roasted using convection and microwave heating. For roasting we used green coffee beans of 7.5% moisture content, and beans wetted to 10% moisture content and dried to 5% moisture content. The content of 5-hydroxytryptamides of carboxylic acids C-5-HT (determined by TLC) as the index of substances irritating alimentary canal was investigated in the roasted beans, depending on the bean treatment before roasting and applied roasting method. Analytical results show that predrying of the coffee beans caused 15-30% loss of C-5-HT, depending on the applied drying conditions. The content of C-5-HT in the roasted beans depended on the roasting method and preliminary treatment of the beans prior to roasting. A higher C-5-HT loss occurred in the case of beans subjected to two-stage processing, predrying and roasting. Convection roasting caused higher degradation of C-5-HT than microwave roasting.     

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.     

Effect of temperature and relative humidity during transportation on green coffee bean moisture content and ochratoxin A production

Changes in temperature, relative humidity, and moisture content of green coffee beans were monitored during transportation of coffee from Brazil to Italy. Six containers (three conventional and three prototype) were stowed in three different places (hold, first floor, and deck) on the ship. Each prototype was located next to a conventional container. The moisture content of the coffee in the container located on the first floor was less affected by environmental variations (0.7%) than that in the hold and on the deck. Coffee located in the hold showed the highest variation in moisture content (3%); in addition, the container showed visible condensation. Coffee transported on the deck showed an intermediary variation in moisture (2%), and there was no visible condensation. The variation in coffee moisture content of the prototype containers was similar to that of the conventional ones, especially in the top layers of coffee bags (2 to 3%), while the increase in water activity was 0.70. This suggests that diffusion of moisture occurs very slowly inside the cargo and that there are thus sufficient time and conditions for fungal growth. The regions of the container near the wall and ceiling are susceptible to condensation since they are close to the headspace with its high relative humidity. Ochratoxin A production occurred in coffee located at the top of the container on the deck and in the wet bags from the hold (those found to be wet on opening the containers at the final destination).     

Impact of the roasting degree of coffee on the in vitro radical scavenging capacity and content of acrylamide

Due to the recognized toxicity of acrylamide, intensive efforts have been made to reduce the concentration of this undesired Maillard by-product in food. This work reports the results obtained from a series of experiments aimed at determining the concentration of acrylamide and the in vitro radical scavenging capacity in the same roasted and ground coffee samples, as it is well established that a significant part of the antioxidant activity in coffee is linked to the melanoidins, which are also considered as Maillard reaction products (MRPs). The radical scavenging capacity was measured using electroparamagnetic resonance (EPR). Coffee samples from the Robusta and Arabica varieties were roasted at 236 °C over different time periods to obtain very light, light, medium and dark roast. Color analyses were performed on all samples. Increasing the roasting degree led to a decrease in acrylamide concentration as well as radical scavenging capacity. The results of this work indicate that any mitigation efforts must also take into account the potential loss of desired food constituents and consequently changes to the risk/benefit characteristics of foods.     

Effect of operating conditions on ochratoxin A extraction from roasted coffee

Operating conditions affect ochratoxin A (OTA) extraction from roasted coffee. The OTA content found in the beverage can thus be greater than that found in the roasted coffee used to prepare it. Three extraction parameters were studied for roasted coffee: type of extraction solvent (alkaline, neutral, acid), temperature (ambient temperature/23°C, 60°C and 85°C), and extraction time (5, 20, 30, 40, 50, 60 and 80 min). The alkaline solvent used in the method recommended by the European Union extracted OTA better, but a maximum content was obtained at 60°C after 50 min. At least a 100% improvement in extraction was obtained when compared with the European Union usual quantification method that is carried out at ambient temperature. It turned out that the OTA extraction parameters for roasted coffee, as defined by that method, were not optimum and needed to be modified. These results were verified in double-extraction experiments showing that OTA is not completely extracted by this method. Confirmation was obtained by comparison of extraction methods on several commercial samples of roasted coffee.     

Studies on the sample weight for ochratoxin A determination in raw coffee

Ochratoxin A is a mycotoxin that may cause damage to the kidneys and the immune system in man. Foods are examined for this contaminant by the laboratories responsible for official food control. At present, there are no specific provisions for the sampling and examination of ochratoxin A in foods. Therefore, recourse is made to the provisions for aflatoxins. They prescribe the processing of samples with a weight of up to 30 kg. The examination of raw coffee for ochratoxin A in conjunction with the German Food Monitoring Programme of 2000 was undertaken with various sample weights (5, 10 and 30 kg) in order to identify the influence of the sample weight on the result. Overall, the sample weight did not have an effect on the detection and level of the ochratoxin A content in the samples of raw coffee examined.     

焙炒条件对咖啡风味影响的研究

以云南产的两种咖啡豆为分析对象．研究了焙烤过程中咖啡抽提液一些成分的变化以及对咖啡香气的影响。利用高效液相色谱对在焙烤过程中葫芦巴碱、绿原酸、烟酸、咖啡因含量的变化进行分析，并对绿原酸／咖啡因比率与色度值的相关关系建立了相应的模型。     

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.     

A study of the effect of roasting on the chlorogenic acid composition of coffee using HPLC

A method, based on HPLC, described in our previous publication for the analysis of chlorogenic acids in instant coffee, was used in a study of the effect of roasting on the chlorogenic acid composition of Arabica and Robusta coffee. The degradation of seven chlorogenic acids was followed during roasting. Losses of about 60% were observed when mild roasting conditions were used and almost 100% after severe roasting. Considerable differences in degradation rates of individual isomers were observed so that the composition of chlorogenic acids changed throughout the roasting process. Thus the degree of roasting may have a direct influence on the final product flavour as the individual isomers have different sensory properties.     

The effect of roasting method on headspace composition of robusta coffee bean aroma

Robusta coffee beans were roasted by three methods, i.e. convectively at 230 °C, by microwaves at 700 W, and by the coupled convective–microwave (CMR) method (the simultaneous convective heating at 230 °C and microwaving at 700 W) for 590, 670, and 370 s, respectively. The ultimate temperature of roasted beans was 238, 207, and 228 °C, respectively. Volatile compounds were determined in the headspace by GC-SPME both in samples of roasted coffee and in green beans to find effects of roasting methods on their formation and retention. Eighty-two and 148 odorants were identified in green and roasted coffee, respectively. The highest contents of the latter were found in coffee roasted by the coupled method because both the relatively short time of roasting and moderately high final temperature of beans favored retention of volatile aroma compounds. Because of these reasons, the contents of odorants were the lowest in convectively roasted coffee.     

A study of the contamination by ochratoxin A of green and roasted coffee beans

A study was performed to evaluate the contamination by ochratoxin A in coffee beans. Twenty-nine samples of green coffee were collected from large lots of material by representative sampling. The analyses of green coffee samples showed a significantly high contamination percentage (58%) ranging from 0.2 to 15 micrograms/kg. Naturally and artificially contaminated samples were roasted at different operation times (5-6 min) to verify the percentage of destruction of the mycotoxin. The percentage ranged from 48% to 87% and from 90% to 100% in artificially and naturally contaminated samples respectively. The beverages prepared from artificially contaminated coffee using the most common types of coffee makers showed no residues of ochratoxin A.     

Two-dimensional thin-layer chromatographic method for the analysis of ochratoxin A in green coffee

A low-cost thin-layer chromatographic method has been developed for the presumptive measurement of ochratoxin A (OTA) at 5 microg/kg in green coffee beans. The analytical method consisted of extracting OTA by shaking the beans with a mixture of methanol and aqueous sodium bicarbonate solution, which was then purified by liquid-liquid partition into toluene. OTA was separated by normal-phase two-dimensional thin-layer chromatography and detected by visual estimation of fluorescence intensity under a UV lamp at 365 nm. The chromatography solvents were toluene-methanol-formic acid (8:2:0.03) for the first development and petroleum ether-ethyl acetate-formic acid (8:10:1) for the second dimension development. This method was tested with uncontaminated green coffee bean samples spiked with an OTA standard at four different concentrations (5, 10, 20, and 30 microg/kg). The method is rapid, simple, and very easy to implement in coffee-producing countries. It is highly selective and does not involve the use of chlorinated solvents in the sample extraction step. This inexpensive method has been applied to different types of green coffee samples from various countries (Zimbabwe, Brazil, India, Uganda, Colombia, and Indonesia) and different manufacturers, and no OTA below the detection limit of 5 microg/kg was detected in any samples analyzed.     

Effect of roasting conditions on carbon dioxide degassing behavior in coffee

CO₂ is one of the major gases formed during coffee roasting, which has important implications on coffee's quality and packaging requirements. In this study, the residual CO₂ content and CO₂ degassing behavior of an Arabica coffee processed using a fluidized bed roaster, as affected by the roasting temperature–time conditions, were investigated. The results showed that positive correlations existed between the degree of roast (expressed as lightness value) and residual CO₂, implying that lightness could be used as an indicator of initial CO₂ content in roasted coffee. At the same degree of roast, coffee roasted with high-temperature–short-time process had significantly higher CO₂ degassing rate than those with low-temperature–long-time process. Moreover, the CO₂ releasing rate increased with the degree of roast. The degassing rate of CO₂ in ground coffee was highly dependent on the grind size and roasting temperature, but less dependent on the degree of roast. The different degassing behaviors observed between roasted coffee samples were explained on the basis of chemical composition and microstructural differences.     

Study of ochratoxin A-producing strains in coffee processing

Ochratoxin A (OTA) is the main mycotoxin that has been detected in coffee. The occurrence of OTA in coffee beans can be because of environmental conditions and/or processing conditions. Three coffee processes were evaluated (wet, mechanical and dry processes), at different stages from harvesting to storage, and fungi producing OTA were enumerated and identified. The frequency of potential OTA‐producing fungi and their ability to produce OTA was also studied. By direct plating, the levels of contamination found in the coffee processes were 80, 72 and 92%, respectively, for parchment and dry cherry coffee and 20, 34 and 15% for green coffee. Aspergillus ochraceus isolated from the three processes accounted for 6.6, 8.3 and 3.3%, and Aspergillus niger for 15, 13 and 25% of the strains isolated, respectively. The toxigenic potential of five A. ochraceus and two A. niger strains was tested in FDA medium and coffee medium using the HPLC technique. There was no difference between the processes studied in terms of isolation and occurrence of ochratoxigenic fungi.     

Design of a sampling plan to detect ochratoxin A in green coffee

The establishment of maximum limits for ochratoxin A (OTA) in coffee by importing countries requires that coffee-producing countries develop scientifically based sampling plans to assess OTA contents in lots of green coffee before coffee enters the market thus reducing consumer exposure to OTA, minimizing the number of lots rejected, and reducing financial loss for producing countries. A study was carried out to design an official sampling plan to determine OTA in green coffee produced in Brazil. Twenty-five lots of green coffee (type 7 - approximately 160 defects) were sampled according to an experimental protocol where 16 test samples were taken from each lot (total of 16 kg) resulting in a total of 800 OTA analyses. The total, sampling, sample preparation, and analytical variances were 10.75 (CV = 65.6%), 7.80 (CV = 55.8%), 2.84 (CV = 33.7%), and 0.11 (CV = 6.6%), respectively, assuming a regulatory limit of 5 µg kg^-1 OTA and using a 1 kg sample, Romer RAS mill, 25 g sub-samples, and high performance liquid chromatography. The observed OTA distribution among the 16 OTA sample results was compared to several theoretical distributions. The 2 parameter-log normal distribution was selected to model OTA test results for green coffee as it gave the best fit across all 25 lot distributions. Specific computer software was developed using the variance and distribution information to predict the probability of accepting or rejecting coffee lots at specific OTA concentrations. The acceptation probability was used to compute an operating characteristic (OC) curve specific to a sampling plan design. The OC curve was used to predict the rejection of good lots (sellers' or exporters' risk) and the acceptance of bad lots (buyers' or importers' risk).