Discrimination between defective and non-defective Brazilian coffee beans by their volatile profile

The coffee roasted in Brazil is considered to be of low quality, due to the presence of defective coffee beans that depreciate the beverage quality. In view of the fact that coffee flavour is directly related to the volatile compounds produced during roasting, the objective of the present study was to perform a comparative evaluation of the volatile fraction of defective (black, immature, sour) and healthy coffee beans, in order to find possible chemical markers for detection of defective coffee beans in roasted coffee. Volatiles extraction and concentration was performed by solid phase micro-extraction (SPME) of the roasted coffee headspace, using a triple phase (divinylbenzene/carboxen/polydimethylsiloxane) fiber. Analysis of the volatile profiles was performed by GC–MS. The results obtained showed that the proposed methodology was adequate for extraction, concentration and analysis of the coffees volatile profile. Several substances were identified as possible markers for differentiating black, sour and immature beans from healthy coffee beans. Statistical analysis of the data by principal components (PCA) demonstrated that the volatile profile enables the differentiation of healthy and defective coffees. The data were separated into two major groups, one represented by immature and black beans and the other by healthy and sour coffee beans. Such results indicated that black and sour beans can be associated to fermentation of immature and of healthy beans, respectively.     

A comparative study of chemical attributes and levels of amines in defective green and roasted coffee beans

Differences in chemical attributes (proximate composition, water activity, sucrose, acidity and pH levels) and amine levels between defective and healthy coffee beans were studied. Before roasting, significant differences (p < 0.05) were observed for the ash contents of the coffee samples, with the highest values found for black beans. Moisture content was higher for non-defective beans in comparison to defective beans. Non-defective coffee beans had higher lipids contents than both sour and black beans. There were no significant differences (p > 0.05) for protein levels between defective and non-defective beans. After roasting, protein levels remained constant, there was a small decrease in ash contents and a slight increase in oil contents of black and sour beans. Both black and sour beans had higher acidity levels than immature and non-defective beans. Acidity levels decreased after roasting. Water activity levels also decreased with roasting, with slightly higher levels for defective beans in comparison to non-defective ones. Sucrose levels were much higher in non-defective beans, and the lowest values were in black beans, prior to roasting. After roasting, only traces of sucrose were found. Total amine levels were much lower for black beans, in comparison to the other coffee samples. Putrescine was the prevailing amine in all samples. Histamine was only detected in the defective coffee samples. Small amounts of serotonin, cadaverine and tryptamine were found in some of the samples. After roasting to a light degree, only traces of serotonin were detected and no amines were detected after roasting to medium and dark degrees.     

Evaluation of the potential of FTIR and chemometrics for separation between defective and non-defective coffees

The objective of this work was to evaluate the potential of Fourier transform infrared spectroscopy (FTIR) for the discrimination of defective and non-defective coffee beans. Defective (black, immature and sour) and non-defective Arabica coffee beans were submitted to FTIR analysis by transmittance readings employing KBr discs and reflectance readings employing attenuated total reflectance (ATR) and diffuse reflectance (DR) accessories. Multivariate statistical analysis (PCA, clusters) was performed in order to verify the possibility of discrimination between defective and non-defective coffee samples. A clear separation between defective and non-defective coffee beans was observed, based on both PCA and cluster analysis of the reflectance spectra (ATR and DR accessories) and of the first derivatives of the transmittance spectra (KBr discs). Such results indicate that FTIR analysis has the potential for the development of a fast and reliable analytical methodology for the discrimination between defective and non-defective coffee beans.     

Chemical characterisation of non-defective and defective green arabica and robusta coffees by electrospray ionization-mass spectrometry (ESI-MS)

The coffee roasted in Brazil is considered to be of low quality, due to the presence of defective coffee beans that depreciate the beverage quality. These beans, although being separated from the non-defective ones prior to roasting, are still commercialized in the coffee trading market. Thus, it was the aim of this work to verify the feasibility of employing ESI-MS to identify chemical characteristics that will allow the discrimination of Arabica and Robusta species and also of defective and non-defective coffees. Aqueous extracts of green (raw) defective and non-defective coffee beans were analyzed by direct infusion electrospray ionization mass spectrometry (ESI-MS) and this technique provided characteristic fingerprinting mass spectra that not only allowed for discrimination of species but also between defective and non-defective coffee beans. ESI-MS profiles in the positive mode (ESI(+)-MS) provided separation between defective and non-defective coffees within a given species, whereas ESI-MS profiles in the negative mode (ESI(−)-MS) provided separation between Arabica and Robusta coffees.     

Proximate composition and fatty acids profile of green and roasted defective coffee beans

Defective coffee beans are responsible for the depreciation of the quality of roasted coffee consumed in Brazil. The extraction of the oil of defective beans for applications in the food and pharmaceutical sectors is being considered as an alternative use for those beans. The objective of this work was to determine the composition of the fatty acid fraction of the pressed oil and the proximate composition of crude defective beans in order to provide subsidiary information for proposals of alternative uses for these beans. The amounts of oil extracted from the defective beans were smaller than the amounts extracted from healthy mature beans. The fatty acid composition of oils from defective beans was not significantly different than that from healthy mature coffee beans.     

Fungal colonization and biochemical changes in coffee beans undergoing monsooning

Changes in the mycofloral composition and concentrations of proteins, reducing sugars, phenols and tannins in coffee beans were analysed during different weeks of monsooning in Coffea arabica L. (Arabica) and C. canephora Pierre ex Froehner (Robusta). The highest fungal populations occurred during the fourth to seventh week of the monsooning process and the dominant fungal species were Aspergillus niger, Aspergillus tamarii, Aspergillus candidus, Penicillium spp. and Absidia heterospora. The protein and reducing sugar content increased steadily while the tannin content decreased beyond the detectable limit during monsooning. The phenolic content, however, was found to decline in the case of Robusta and increase slightly in Arabica. Throughout the study the monsooned coffee beans had different mycoflora and varied biochemical composition compared to non-monsooned coffee beans.     

About Sr isotopes in coffee ‘Bourbon Pointu’ of the Réunion Island

Demonstration of the regional source of a high-quality product is nowadays essential to protect it from commercial transactions and cheatings. In this study, Sr isotopes are proposed as a tool to identify the regional source of a vegetable, on the basis of a combined geochemical investigation on a Coffea Arabica var. Laurina cultivation plot located on th Réunion Island. The Sr isotopic composition (⁸⁷Sr/⁸⁶Sr) of the produced coffee beans (called Pointed Bourbon) and of their growing environment, including soils, parent rocks, waters and fertilizers are determined. Flux of Sr in coffee beans is mainly dominated by soil solutions that can be influenced by Sr-rich fertilizers. This influence is however low enough to detect the cultivation soils’ Sr isotopic ratio in the vegetable product, even after roasting. It also allows discrimination of coffees produced on varied geological areas. Measurements performed on the same variety of coffee beans produced in New Caledonia strengthen the demonstration.     

Coffee beans microstructural changes induced by cultivation processing: An X-ray microtomographic investigation

The present work reports on the microstructural characterisation of four types of different processed coffee beans, Coffea arabica, Arabica monsooned, Coffea canephora and Robusta monsooned, by means of X-ray microtomography technique (μCT). A three dimensional (3-D) quantitative analysis was carried out on the microstructure the bean samples before and after roasting. The 3-D microstructure information provides a better understanding of the structure of the beans and from an engineering perspective; knowledge about the microstructure can be used to identify the important processing parameters that affect the quality of coffee. With regards to the microstructure, the porosity increase can summarise the overall effects of the roasting process on coffee beans. Results demonstrate the success of μCT for the quantification of the microstructural alterations of the coffee beans induced by their different cultivation processes before and after the roasting process.     

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.     

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 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.     

Protein and starch content of raw,soaked and cooked beans (Phaseolus vulgaris L.)

Organoleptic qualities are an important factor in the market value of legumes, especially in developed countries. Unfortunately, the molecules that have the greatest influence on the texture of beans undergo important transformations during soaking and cooking. Moreover, the extent to which these changes are linear is unknown, making uncertain the use of raw beans in chemical screenings for sensory properties. Results of our experiments show that the amount of protein and amylose present in raw beans provides a good indicator of these substances in cooked beans (correlation coefficients between raw and cooked beans = 0.91, p ? 0.001 and 0.87, p ? 0.01, respectively). The Mg content in the raw seed coat also shows a strong correlation with that found in the cooked seed coat (r = 0.86, p ? 0.01). The correlations found for the other traits are weaker, indicating that the evaluation of raw samples is not predictive of the findings in cooked beans.     

Discrimination between defective and non-defective roasted coffees by diffuse reflectance infrared Fourier transform spectroscopy

The objective of this work was to evaluate the feasibility of employing Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) for discrimination between defective and non-defective coffees after roasting and grinding. Defective (black, immature and sour) and non-defective Arabica coffee beans were submitted to light, medium and dark roasts at 220, 235 and 250 °C. Principal Components Analysis of the DRIFTS spectra (normalized or not) and of the first derivatives of the spectra provided separation of the samples into four groups: non-defective, black, dark sour and light sour, with immature beans scattered among the sour samples. Classification models were developed based on Linear Discriminant Analysis and recognition and prediction abilities of these models ranged from 95 to 100%. Such results indicate that DRIFTS presents potential for the development of a fast and reliable analytical methodology for discrimination between defective and non-defective coffee after roasting and grinding.     

Mass transfer of water and volatile fatty acids in cocoa beans during drying

In order to elucidate the phenomena involved in the remnant acidity of cocoa beans dried artificially, the diffusivities of water, and volatile fatty acids (VFAs: acetic, propionic, butyric and iso-butyric acids) in cocoa beans during drying were evaluated. Experimental drying kinetics of the acids were conduced at 40–60 °C with and without shell. Samples were taken at different drying times for moisture and acids content evaluation. VFAs content was evaluated by GC in a methanolic extract, and moisture content by a vacuum oven. Mass diffusivity was estimated from the fitting of experimental kinetics to a theoretical model that takes into consideration the beans’ shape. Acetic, propionic and butyric acids diffusivities were significantly (p < 0.05) smaller than water diffusivities both with and without shell. VFAs diffusivities were between 1/6 and 1/22 diffusivities values for water. Iso-butyric acid diffusivity was not statistically significant but the value was smaller than for the other VFAs. The diffusivities of VFAs may explain the remnant acidity in artificially dried cocoa beans.     

Coffea arabica beans microstructural changes induced by roasting: An X-ray microtomographic investigation

The present work reports on a microstructural characterization of Coffea arabica beans in the course of roasting by means of X-ray microtomography technique (μCT). In fact, the aim of this study is to demonstrate the capability of μCT as a useful tool for the characterization of microstructure of C. arabica beans at different roasting times: from green to very dark. μCT is a non-invasive technique that has the ability to image low moisture materials by using the differences in X-ray attenuation arising, mainly, from differences in density within the specimen. Green coffee beans were roasted and sampled at the following roasting times; 2, 3, 4 and 5 min. Several parameters such as percentage object volume (POV), density, total volume and pore size distributions were calculated for each roasting time and their variations discussed. The results from this study show how the microstructure of the coffee bean evolves with increasing roasting time, for example, the increase in total pore volume, the increase in porosity and density due to the rupture of bonds in the internal structure of the coffee beans during roasting. μCT has proven to be a suitable technique for microstructural analysis of roasted foods such as coffee bean and provides an accurate analysis of the pores and microstructure during the roasting process.     

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.     

Development of a tensiometric model for surface energy characterization of raw coffee beans

The aim of this work is to investigate surface energy properties of various raw coffee bean species (tensiometric approach) and to develop a tensiometric marker based on contact angle measurements of Fomblin HC/25 drops, a perfluoropolyether phosphate (PFPE), to distinguish different species of raw coffee beans. To create measurable contact angles, raw coffee beans were pre-selected according to the endosperm surface morphology (smooth surface) and affixed to a specifically developed support. The tensiometric method was developed using contact angle method (CA) and calculation models such as Owens, Wendt and Kaelble. Results show the tensiometric properties of raw coffee beans expressed as surface free energy (SFE) and the capability of the marker to distinguish species. This work could create interesting prospects for quality control at the product source, storage conditions, and for industrial process evaluation of roasting and drying.     

Real time monitoring of free radical processes during the roasting of coffee beans using electron paramagnetic resonance spectroscopy

Because of the roles of free radicals in the formation of Maillard reaction products and as markers of oxidation processes in foods, the dynamics of free radical generation during the roasting of coffee beans have been measured, and some exploratory investigations conducted on the extent to which these are influenced by the bean type, and the atmosphere (air vs. N₂), in which the beans were roasted and cooled.     

Genetic and environmental effects on chemical composition related to sensory traits in common beans (Phaseolus vulgaris L.)

The chemical composition determines plant-derived foods’ sensory traits; genetic and environmental effects and their interactions determine chemical composition. Understanding the importance of each factor should help characterise foodstuffs according to the variety and place of cultivation. We studied the effects of variety (five landraces + two checks) and environment (five locations and two years) on some molecules important for beans’ (Phaseolus vulgaris L.) sensory value. The greatest location effects were on protein and starch content and variety effects were due to combinations of traits (mainly sucrose, protein, and malic acid). The variety × location interactions detected in protein, sucrose, citric acid, and malic acid were difficult to associate to the gastronomic success of a particular variety cultivated at a particular location. Our results showed that protected designation of origin (PDO) in beans could be delimited on the basis of chemical composition, derived from the particular environmental characteristics of a region and the genetic characteristics of the varieties admitted.     

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.