Roast Degree Research Articles

Quantitative Lipidomics Reveals the Effects of Roasting Degree on Arabica Coffee Beans Lipid Profiles

Lipids in coffee beans undergo morphological changes and migration during the roasting process, but the impact of roasting intensity on lipid profiles remains unclear. The lipidomics characteristics of coffee beans with different degrees of roasting (unroasted green beans, light roast, medium roast, and dark roast) were compared using ultra performance liquid chromatography-electrospray ionization-tandem mass spectrometry (UPLC-ESI-MS/MS). A total of 571 lipid metabolites were identified, encompassing 25 species of fatty acyls (FA), 142 species of glycerophospholipids (GP) across 12 subclasses, 42 species of sphingolipids (SP) across four subclasses, 360 species of glycerolipids (GL) across ten subclasses, and two species of prenol lipids (PR). GL content was found to be the highest, followed by FA and GP. Through multivariate analysis, 160 lipids were identified that exhibited significant differences among beans with different degrees of roasting. GP content was significantly influenced by the degree of roasting (p<0.05), with diverse dynamic evolution observed through K-means cluster analysis. These findings have important implications for understanding lipid transformation and its effect on the flavor profile during coffee roasting.

Development of an ESP32 Microcontroller-based Colorimeter with an Android App for the Verification of Roasting Degree of Coffee Beans

A lo w-cost and portable colorimeter was developed using an ESP32 microcontroller and a TCS34725 color sensor to monitor the degree of coffee roast, crucial for maintaining flavor consistency and controlling product quality across different batches. The colorimeter detected color recognition resulting in RGB color intensity values, which could be displayed on the device’s TFT LCD touchscreen. Additionally, colorimetric data was transmitted in real-time via WiFi and stored in a MySQL database using an Android app created with the MIT App Inventor platform. The colorimeter was powered by a rechargeable lithium phosphate battery. The consistency of coffee roasting was ensured by self-identifying the standard RGB values of the roasted coffee beans at five degrees (light, light-medium, medium, medium-dark, and dark) with the app. The darker the color of the roasted coffee, the lower the RGB values were gained. The color detection was highly precise, with a relative standard deviation of less than 5%.

Comparison of Ultra-High-Pressure and Conventional Cold Brew Coffee at Different Roasting Degrees: Physicochemical Characteristics and Volatile and Non-Volatile Components

The impact of the roasting degree on ultra-high-pressure cold brew (UHP) coffee remains unclear, although it has been found that UHP technology accelerates the extraction of cold brew (CB) coffee. Therefore, this study investigated the effects of three different degrees of roasting (light, medium, and dark) on the physicochemical characteristics, volatile and non-volatile components, and sensory evaluation of UHP coffee. Orthogonal partial least-squares-discriminant analysis (OPLS-DA) and principal component analysis (PCA) were used to assess the effects of different roasting degrees. The results showed that most physicochemical characteristics, including total dissolved solids (TDSs), extraction yield (EY), total titratable acidity (TTA), total sugars (TSs), and total phenolic content (TPC), of UHP coffee were similar to those of conventional CB coffee regardless of the degree of roasting. However, the majority of physicochemical characteristics, non-volatile components, including the antioxidant capacity (measured based on DPPH and ABTS) and melanoidin, caffeine, trigonelline, and CGA contents increased significantly with an increase in roasting degree. The sensory evaluation revealed that as the roasting degree rose, the nutty flavor, astringency, bitterness, body, and aftertaste intensities increased, while floral, fruity, and sourness attributes decreased. The HS-SPME-GC/MS analysis showed that most volatile components increased from light to dark roasting. Moreover, 15 representative differential compounds, including hazelnut pyrazine, linalool, butane-2,3-dione, and 3-methylbutanal, were identified by calculating the odor-active values (OAVs), indicating that these contributed significantly to the odor. The PCA showed that the distance between the three roasting degree samples in UHP coffee was smaller than that in CB coffee. Overall, the effect of roasting degrees on UHP coffee was less than that on CB coffee, which was consistent with the results of physicochemical characteristics, volatile components, and sensory evaluation.

A machine learning-assisted fluorescent sensor array utilizing silver nanoclusters for coffee discrimination

Coffee is a globally consumed commodity of substantial commercial significance. In this study, we constructed a fluorescent sensor array based on two types of polymer templated silver nanoclusters (AgNCs) for the detection of organic acids and coffees. The nanoclusters exhibited different interactions with organic acids and generated unique fluorescence response patterns. By employing principal component analysis (PCA) and random forest (RF) algorithms, the sensor array exhibited good qualitative and quantitative capabilities for organic acids. Then the sensor array was used to distinguish coffees with different processing methods or roast degrees and the recognition accuracy achieved 100%. It could also successfully identify 40 coffee samples from 12 geographical origins. Moreover, it demonstrated another satisfactory performance for the classification of pure coffee samples with their binary and ternary mixtures or other beverages. In summary, we present a novel method for detecting and identifying multiple coffees, which has considerable potential in applications such as quality control and identification of fake blended coffees.

Investigation of volatile compounds of Liberica coffee beans fermented at varying degrees of roasting

Liberica coffee (Coffea liberica Bull ex Hiern) has gained worldwide popularity, because it has a unique taste and aroma, and it is able to adapt to peatlands and is more tolerant of disease. Previous studies suggested that fermentation with hydrolytic bacteria could improve flavors, mostly determined by volatile compounds by the roasting process. However, studies about the volatile compounds and their roles in the taste and aroma of this coffee are still limited. This study aimed to investigate volatile compounds from fermented Liberica coffee beans roasted at light roast (150-160°C, 2.2 Mbar, 12 mins); medium roast (175-185°C, 2.2 Mbar, 7.30 mins); and dark roast (200-220°C, 2.2 Mbar, 10 mins). Samples were collected from various fermentation times 0, 4, 8, and 12 hrs and dried. Green beans with a moisture content of 12% were roasted in 3 roast stages. In this work, the extraction of volatile coffee compounds was performed using solid phase microextraction (SPME) and subsequently analyzed by gas chromatography-mass spectrometry (GC-MS). To determine the significance of fermentation time and degree of coffee roasting in the area, a two-way univariate analysis of variance (ANOVA) test was used, followed by a Tukey's honest significant difference (HSD) test with a statistical significance level of p&lt;0.05. The results showed that a total of 59 of the 130 volatile compounds had a significant difference at different roasting degrees to the area of compounds with a statistical significance level of p&lt;0.05. Those compounds consisted of 5 aldehydes, 18 furans, 4 ketones, 9 phenols, 13 pyrazines, 5 pyridines and 5 pyrroles.

Profiling flavor characteristics of cold brew coffee with GC-MS, electronic nose and tongue: effect of roasting degrees and freeze-drying.

Roasting is an important process in the formation of coffee flavor characteristics, which determines the quality of coffee and consumer acceptance. However, the influence of roasting degree on the flavor characteristics of cold brew coffee has not been fully described. In the present study, the flavor characteristics of cold brew coffee with different roasting degrees were compared in detail by using chromatographic and electronic sensory approaches, and the flavor changes induced by freeze-drying were investigated. Pyrazine and heterocyclic compounds were the main aroma compounds in coffee, and gradually dominated with the increase of roasting. Pyridine was consistently present in cold brew coffees of different roasting degrees and showed significant gradient of quantity accumulation. Aroma compounds such as pyrazine, linalool and furfuryl acetate were the main contributors to coffee roasting, floral and fruity flavor. Freeze-drying preserved the fruity and floral aromas of medium-roasted cold brew coffee, whereas reducing the bitterness, astringency and acidity properties that are off-putting to consumers. The higher consumer acceptance and enjoyment in medium roast cold brew coffee may be related to its stronger floral and fruity aroma. The aroma profile qualities of freeze-drying processed medium roasted cold brewed coffee were more dominant and more suitable for freeze-drying processing than medium dark roasting. Application of freeze-drying for cold brew coffee will promote the convenience of drinking. The present study provides valuable technical guidance in improving the flavor and quality of cold brew coffee, and also promotes its commercialization process. © 2024 Society of Chemical Industry.

Terahertz Spectroscopic Identification of Roast Degree and Variety of Coffee Beans

In this study, terahertz time-domain spectroscopy (THz-TDS) was proposed to identify coffee of three different varieties and three different roasting degrees of one variety. Principal component analysis (PCA) was applied to extract features from frequency-domain spectral data, and the extracted features were used for classification prediction through linear discrimination (LD), support vector machine (SVM), naive Bayes (NB), and k-nearest neighbors (KNN). The classification effect and misclassification of the model were analyzed via confusion matrix. The coffee varieties, namely Catimor, Typica 1, and Typica 2, under the condition of shallow drying were used for comparative tests. The LD classification model combined with PCA had the best effect of dimension reduction classification, while the speed and accuracy reached 20 ms and 100%, respectively. The LD model was found with the highest speed (25 ms) and accuracy (100%) by comparing the classification results of Typica 1 for three different roasting degrees. The coffee bean quality detection method based on THz-TDS combined with a modeling analysis method had a higher accuracy, faster speed, and simpler operation, and it is expected to become an effective detection method in coffee identification.

E-nose and colorimetric sensor array combining homologous data fusion strategy discriminating the roasting degree of large-leaf yellow tea

Different degrees of roasting result in differences in the quality and flavor of large-leaf yellow tea. The current sensory evaluation and chemical detection methods cannot meet the requirement of online differentiation of LYT roasting degree, so an accurate and comprehensive assessment method needs to be developed urgently. First, the two aroma sensing technologies were compared. Two variable screening methods and three recognition algorithms were employed to build discriminant models. The results showed that the discrimination rate of the colorimetric sensor array (CSA) in the prediction set reached 91.89 %, outperforming that of the E-nose. Subsequently, three fusion strategies were applied to improve the discrimination accuracy. The discrimination rate of the middle fusion strategy resulted in an optimal resolution of 94.59 %. The results obtained from the homologous fusion were able to evaluate the roasting degree comprehensively and accurately, which provides a new method and idea for tea aroma quality.

The Potential of NIR Spectroscopy and Chemometrics to Discriminate Roast Degrees and Predict Volatiles in Coffee.

This study aimed to establish a rapid and practical method for monitoring and predicting volatile compounds during coffee roasting using near-infrared (NIR) spectroscopy coupled with chemometrics. Washed Arabica coffee beans from Ethiopia and Congo were roasted to industry-validated light, medium, and dark degrees. Concurrent analysis of the samples was performed using gas chromatography-mass spectrometry (GC-MS) and NIR spectroscopy, generating datasets for partial least squares (PLS) regression analysis. The results showed that NIR spectroscopy successfully differentiated the differently roasted samples, similar to the discrimination achieved by GC-MS. This finding highlights the potential of NIR spectroscopy as a rapid tool for monitoring and standardizing the degree of coffee roasting in the industry. A PLS regression model was developed using Ethiopian samples to explore the feasibility of NIR spectroscopy to indirectly measure the volatiles that are important in classifying the roast degree. For PLSR, the data underwent autoscaling as a preprocessing step, and the optimal number of latent variables (LVs) was determined through cross-validation, utilizing the root mean squared error (RMSE). The model was further validated using Congo samples and successfully predicted (with R2 values > 0.75 and low error) over 20 volatile compounds, including furans, ketones, phenols, and pyridines. Overall, this study demonstrates the potential of NIR spectroscopy as a practical and rapid method to complement current techniques for monitoring and predicting volatile compounds during the coffee roasting process.

Influence of coffee roasting degree on antioxidant and metabolic parameters: Comprehensive in vitro and in vivo analysis

This study aimed to assess the impact of roasting degree on antioxidant and metabolic parameters in vitro and in vivo. In vitro, we evaluated radical scavenging, lipid peroxidation, and the activity of digestive enzymes (α-glucosidase, α-amylase, and lipase). In vivo, we first examined coffee's effect on carbohydrate and lipid absorption in healthy rats, followed by a chronic evaluation of metabolic disorders and antioxidant markers using a diet-induced obesity model. In vitro results revealed that increased roasting degree reduced the antioxidant capacity of coffee brews. All brews showed lower inhibition of α-glucosidase and α-amylase, and lipase inhibition compared to the positive control (acarbose or orlistat). In vivo, all roasting degrees consistently reduced postprandial glucose levels by 20%. Notably, coffee with a high roasting degree (HRD) decreased serum triglycerides (TG) by ∼44% after a lipid load, while other roasts did not. Chronic administration of unroasted (UN) or HRD coffee significantly reduced weight gain compared to the obese control (∼15% and ∼10%, respectively). Notably, all coffee samples improved lipid metabolism parameters. UN and HRD coffee significantly decreased adipocyte volume by 58% and 48%, respectively, compared to the obese control. Additionally, all groups exhibited less than 30% hepatic lipid droplets independent of roasting degree. HRD treatment notably increased liver catalase (CAT) activity and reduced lipid peroxidation in serum (∼90%), liver (∼59%), and adipose tissue (∼37%) compared to the obese control group. These findings suggest that HRD in coffee may confer certain biological advantages.

The effect of roasting degrees on bioactive compounds levels in Coffea arabica and their associations with glycated hemoglobin levels and kidney function in diabetic rats

The current study aims to assess the content of coffee oil, diterpenes, caffeine, and chlorogenic acid in coffee beans, and to evaluate the effects of roasting degrees on bioactive compound levels in Coffea arabica and their associations with glycated hemoglobin levels and kidney function parameters in streptozotocin-induced diabetic rats. These constituents were quantified using Soxhlet, liquid–liquid extraction (LLE), and high-performance liquid chromatography (HPLC)-diode array detecto (DAD). The outcomes exhibited a positive correlation between levels of coffee oil and diterpenes with a roasting degree. However, it demonstrated a negative correlation between caffeine and chlorogenic acid with a roasting degree. The male rats were categorized into two sections: healthy (nondiabetic) and streptozotocin-induced diabetic groups. Rats have daily administrated 2 ml of coffee extract using an oral gavage subjected to different roasting degrees for 3 weeks. Fasting blood glucose (FBG), urea, and creatinine in serum were assayed at baseline and end of the experiment. The highest significant elevation (Pa = 0.016) in the mean urea and creatinine levels was noted in the diabetic group administrated with dark coffee extract whereas the lowest elevation was in the diabetic group administrated with green coffee extract. In conclusion, our study has shown that coffee roasting degree may have a potential negative effect on kidney function that may accelerate or exacerbate diabetic nephropathy in induced diabetic rats. A noteworthy change in urea levels was observed in diabetic rats treated with dark-roasted coffee, which might be attributed to the decline in antioxidant constituents: chlorogenic acids and diterpenes.

Variables Affecting the Extraction of Antioxidants in Cold and Hot Brew Coffee: A Review.

Coffee beans are a readily available, abundant source of antioxidants used worldwide. With the increasing interest in and consumption of coffee beverages globally, research into the production, preparation, and chemical profile of coffee has also increased in recent years. A wide range of variables such as roasting temperature, coffee grind size, brewing temperature, and brewing duration can have a significant impact on the extractable antioxidant content of coffee products. While there is no single standard method for measuring all of the antioxidants found in coffee, multiple methods which introduce the coffee product to a target molecule or reagent can be used to deduce the overall radical scavenging capacity. In this article, we profile the effect that many of these variables have on the quantifiable concentration of antioxidants found in both cold and hot brew coffee samples. Most protocols for cold brew coffee involve an immersion or steeping method where the coffee grounds are in contact with water at or below room temperature for several hours. Generally, a higher brewing temperature or longer brewing time yielded greater antioxidant activity. Most studies also found that a lower degree of coffee bean roast yielded greater antioxidant activity.

Various roasting characteristics against alteration of antioxidant activity, amino acids content, and flavor of Java Ijen-Raung coffee beans

The coffee roasting keys are temperature and time. Coffee beans have many chemical and physical reactions while the roasting is running. These reactions are characterized by a pattern in the drying and development phases during coffee roasting. This study discussed how roasting affected the characteristics of coffee beans, particularly antioxidant activity and amino acids, and also tried to define the roasting process by describing each roasting phase. The study discussed these characteristics of Java Ijen arabica coffee, which has speciality coffee criteria. The roasting process can increase amino acids and antioxidant activity inside the coffee beans, but the excessive heat and longer duration of roasting can burn the amino acids. Based on this study, the highest antioxidant Activity was found in beans that had been roasted with a total roasting time under 13 minutes, started with charge temperature of 148oC, and released at 190.5oC. The beans that had been roasted with a total duration under 13 minutes, started with charge temperature of 149oC, and released at 184.8oC is the best roasting degree with the highest score on the cup test.

The Determination of Triacylglycerols and Tocopherols Using UHPLC-CAD/FLD Methods for Assessing the Authenticity of Coffee Beans.

The authenticity of coffee beans was addressed in this study using an analytical method with minimal sample preparation to achieve simple oil extraction and through the implementation of cost-effective equipment. For this purpose, methods using UHPLC with CAD and FLD detectors were applied to detect triglycerides and tocopherols in coffee, respectively. The coffee samples included two main varieties: Arabica from Brazil, Colombia, Ethiopia, and Uganda, as well as the Robusta variety from Cambodia, Guatemala, India, and Vietnam. The samples were either in their green state or subjected to different roasting levels. The used methods successfully distinguished the Arabica and Robusta variants targeted in this study based on their tocopherols and TAG profiles, with the latter being particularly effective for discriminating the origins of the Arabica coffee, while tocopherols excelled at differentiating the origin of the Robusta coffee. TAGs and tocopherols were not affected by the type of roasting, from medium to very dark, suggesting it is possible to distinguish between coffee varieties independently from their degree of roasting. The obtained results hold valuable implications for future research regarding coffee fraud and authenticity.

Effect of Brewing Methods on Acrylamide Content and Antioxidant Activity: Studying Eight Different Filter Coffee Preparations.

The aim of this study was to investigate the parameters affecting the extraction of positive molecules such as chlorogenic acids and antioxidants, as well as potentially carcinogenic substances such as acrylamide, in different coffee brewing methods. Three coffee varieties, each assigned a different roasting degree, were used to prepare coffee brews following eight different preparation methods. Acrylamide was quantified using the HPLC-MS/MS instrument, while chlorogenic acids and caffeine were quantified using the HPLC-DAD system. Three spectrophotometric analyses were also performed (DPPH, TFC and TPC) to evaluate antioxidant activity. The results showed that the main brewing parameters, which have the greatest influence on the final content of these compounds, were the volume of water used, more specifically the brewing ratio (coffee to water ratio), the extraction time and the particle size of the coffee powder. In addition, the variables that have the greatest impact on the discrimination of the preparation methods studied are total chlorogenic acid content, TFC, TPC, caffeine and the DPPH assay. For this reason, the recipe and infusion parameters used for each of the extraction systems are the key factors that determine the extraction of coffee components and, consequently, the quality of the cup.

Investigation of the influence of lime content in the charge and its quality on the sintering process of iron ore raw materials

Main objectives of the work was to study the influence of degree of roasting of lime contained in the charge on the sintering process and sinter quality, as well as comparing the impact of changes in the mass fraction of active CaO in the charge by varying degrees of burning lime, and by varying the content of lime in the charge. It is shown that the intensifying effect of lime on the sintering process occurs as a result of a decrease in the content of small classes in the charge. When the lime content in the charge is equal to 3 %, an increase in the degree of lime firing from 5 to 96 % led to an increase in the specific productivity of the plant from 0.96 to 1.87 t/(m 2 · hour). The independence of sintering parameters from the content of active CaO in lime with its constant content in the sinter charge and the decisive role of the content of active CaO in the sinter charge with its constant content in lime are confirmed. A new approach to the production of lime for agglomeration processes is proposed: it should have the lowest cost of the active CaO contained in it.

Roasting conditions and quality coffee: the empirically optimised process

The degree of roast, temperature and duration of the roasting phases of the coffee bean directly affect the sensory characteristics of the coffee cup. Therefore, to achieve the best roasting result, it is important to combine the human factor with special software products. To automate the roasting process, the Artisan roasting recording software was used. Automation of roasting allows better reproduction of the process conditions for different coffee samples. However, roasting is a rather complex and multi-stage process, and its automation does not guarantee the full reproduction and disclosure of the taste and aroma properties of the "perfect cup". Therefore, the qualifications, skills and experience of the roaster play a significant role in achieving and further reproducing the desired flavour profile.

Roasting optimization of peaberry coffee beans from cherry fruits

The aim of this study was to determine the best interaction between roasting time and temperature of peaberry beans from cherry fruits combined with three different degrees of roast in order to archive the best results for sensorial attributes as well as verify changes in physical parameters. The roasting curves showed similarity of temperature profiles, indicating proper conduction of the roasting process. According to the different ways of roasting, significant differences at 5% probability level were observed for the bulk density, moisture content, swelling while shade and weight loss was the same. The optimum roasting condition for peaberry beans was high temperature all the time (T1) in dark color, which obtained higher values for sensorial attributes.

Assessment of various conditions for the simultaneous determination of US EPA and EU priority PAHs in coffee samples and their PAHs consumption risk

The optimal conditions for simultaneous determination of the U.S. Environmental Protection Agency (US EPA) and European Union (EU) priority polycyclic aromatic hydrocarbons (PAHs) in coffee beans and coffee brews were developed. The QuEChERS (quick, easy, cheap, effective, rugged and safe) technology combined with high performance liquid chromatography - temperature-controlled fluorescence detection and gas chromatography - tandem mass spectrometry were used in the investigation. PAHs could be determined in commercially available green coffee beans (possibly caused by environmental contamination), and their PAHs content increased with the degree of roasting. Coffee beans brewed with the coffee machine released more PAHs into their brews than those brewed with the drip bag. The PAHs consumption risk of the brewed coffee samples was not high due to their low PAH level. Nevertheless, the methods of roasting and brewing and the amount of drinking could still be considered to reduce the intake of PAHs.

Volatile Compound Analysis to Authenticate the Geographical Origin of Arabica and Robusta Espresso Coffee

The traceability of the geographical origin of coffee is a challenging issue to protect producers and consumers from the risk of fraud. A total of 162 Arabica from Peru, Colombia and Brazil, and Robusta from India, Vietnam and Uganda, espresso coffee (EC) samples of different degrees of roasting (light, medium and dark) were characterized for physico-chemical features (lipids, solids, and chlorogenic acids) and analyzed via SHS-GC/MS analysis, with the aim of discriminating the samples according to their geographical origin. Linear discriminant analysis (LDA), performed on the data of the chemical classes of the volatile organic compounds (VOCs), was able to correctly identify 97.53% of the tested samples through cross-validation. The dark roasting of the coffee beans implied a higher quantity of volatile compounds in the headspace of the EC, belonging to chemical classes of furans, esters, N-heterocyclic and sulfur compounds, reducing the differences by geographical origin. Light- and medium-roasted Robusta EC showed a major contribution of pyrazines and pyrimidines, while aldehydes, alcohols and ketones were generally more representative in Arabica samples. The quantitative distribution of volatile compounds proved to be a useful tool to discriminate samples by geographical origin.