Untargeted Metabolomic Analysis Using High-Resolution Orbitrap Mass Spectrometry for the Comparison of Volatile and Non-Volatile Compounds in Hot and Cold Brew Coffee

This study investigated the non-volatile and volatile compounds in samples of cold brew (CB) coffee, coffee from a coffee shop (CS), ready-to-drink (RTD) coffee, and brewed coffee from a coffee maker (CM). The volatile compounds were identified using headspace solid-phase microextraction with gas chromatography-mass spectrometry, and the samples were treated with high-performance liquid chromatography for the quantification of caffeine, chlorogenic acid, and trigonelline. The results indicate that RTD coffee had the lowest amounts of non-volatile compounds. A total of 36 volatile compounds were semi-quantified; the contents of most volatile compounds in CS and Folgers samples were higher than those in CB and CM samples. The contents of 25 volatile compounds in the CM sample were higher than those in the CB sample. The consumer and instrumental data show that the bitterness intensity was correlated with pyrazines, pyrroles, and guaiacols, whereas the coffeeID intensity was correlated with phenols. Semi-quantification and principal component analysis results show that the extraction method and temperature could influence the volatile compound profiles.

The cold brew coffee (CBC) trend is increasing globally; nevertheless, there is limited literature on this popular beverage. Many studies have focused on the health benefits of green coffee beans and coffee brewed by conventional hot water methods. Thus, whether cold brew conveys similar benefits is still unclear. This study aimed to investigate the influences of brewing conditions on physicochemical properties using response surface methodology in order to optimize the brewing parameters and compare the resulting CBC with the coffee from the French Press method. Central Composite Design was used to evaluate the effects and optimize the brewing parameters (i.e., water temperature, coffee-to-water ratio (C2WR), coffee mesh size, and extraction time) on total dissolved solids (TDS). Physicochemical properties, antioxidant activity, volatile compounds, and organic acids were compared between CBC and its French Press counterpart. Our results showed that water temperature, C2WR, and coffee mesh size significantly influenced the TDS of CBC. The optimized brewing conditions were water temperature (4 °C), C2WR (1:14), coffee mesh size (0.71 mm), and 24-h extraction time. At similar TDS, caffeine content, volatile compounds, and organic acids were higher in CBC, while other properties showed no significant difference. In conclusion, this study showed that at similar TDS, CBC has characteristics generally similar to hot brew coffee, except for the caffeine and sensory-related compound content. The model for the prediction of TDS from this study may benefit food services or industries for the optimization of brewing conditions to obtain different characteristics of CBC.

Study on ultrasound-assisted extraction of cold brew coffee using physicochemical, flavor, and sensory evaluation

Sensomics and chemometrics approaches of differential brewed and roasted coffee (Coffea arabica) from Ethiopia using biomimetic sensory-based machine perception techniques: Effects of caffeine on bitter taste and the generation of volatiles.

Volatile compounds of coffee brewed under various roasting conditions and by different brewing methods were analyzed. Green coffee beans (Coffea arabica) were roasted at 235 °C for 13 min, 240 °C for 15 min, and 245 °C for 17 min. Roasted coffee beans were ground into particles of three different sizes (710, 500, and 355 μm) and brewed by an espresso coffee machine and the cold brew method. Three types of water (filtered, tap, and bottled) were used for coffee extraction. SPME-GC-MS results indicated that increasing the roasting temperature and time increased the levels of 2,2′-methylene-bis-furan, guaiacol, and 4-ethylguaiacol (p < 0.05) and decreased the levels of furfural (p < 0.05). Grind size was inversely proportional to the measured signal of volatiles by GC-MS (p < 0.05). The measured GC/MS intensities of 2-methylpyrazine, 2,5-dimethylpyrazine, and 2-methoxy-4-vinylphenol were significantly higher in coffee brewed with filtered water (p < 0.05) than tap and bottled water. 2-Methylpyrazine, 1-methylpyrrole, and 2-acetylfuran were the most abundant components in the cold brew. Overall, roasting conditions and extraction methods were determined to be significant factors for volatile compounds in coffee. This is the first study showing the analysis of volatile compounds in coffee according to various types of water and extraction methods, such as espresso and cold brew coffee.

The role of roasting in cold brew coffee chemistry is poorly understood. The brewing temperature influences extraction processes and may have varying effects across the roast spectrum. To understand the relationship between brew temperature and roast temperature, hot and cold brew coffees were prepared from Arabica Columbian coffee beans roasted to light, medium, and dark levels. Chemical and physical parameters were measured to investigate the relationships among degree of roast, water temperature, and key characteristics of resulting coffees. Cold brew coffees showed differential extraction marked by decreased acidity, lower concentration of browned compounds, and fewer TDS indicating that cold water brewing extracts some compounds less effectively than hot water brewing. Compounds in coffee did exhibit sensitivity to degree of roast, with darker roasts resulting in decreased concentrations for both hot and cold brew coffees. Total antioxidant capacity (TAC) was only sensitive to degree of roast in cold brew coffees, while hot brew coffees had a constant TAC for all three roast levels. This indicates that the solid bean matrix and its chemical constituents interact with cold water differently than with hot water. Surface wetting, pore dynamics, and solubility all contribute to the extraction potential during brewing and are all functions of water temperature.

The role of volatile and non-volatile compounds as quality indicators and marker candidates in coffee: A systematic review

The acidity and antioxidant activity of cold brew coffee were investigated using light roast coffees from Brazil, two regions of Ethiopia, Columbia, Myanmar, and Mexico. The concentrations of three caffeoylquinic acid (CQA) isomers were also determined. Cold brew coffee chemistry was compared to that of hot brew coffee prepared with the same grind-to-coffee ratio. The pH values of the cold and hot brew samples were found to be comparable, ranging from 4.85 to 5.13. The hot brew coffees were found to have higher concentrations of total titratable acids, as well as higher antioxidant activity, than that of their cold brew counterparts. It was also noted that both the concentration of total titratable acids and antioxidant activity correlated poorly with total CQA concentration in hot brew coffee. This work suggests that the hot brew method tends to extract more non-deprotonated acids than the cold brew method. These acids may be responsible for the higher antioxidant activities observed in the hot brew coffee samples.

Whether the post-harvest process will greatly influence volatile or non-volatile coffee chemical compounds. Four post-harvest coffee processing techniques, namely natural, honey, fullwash, and wine, were evaluated in this study. This research aims to authenticate the volatile and non-volatile compounds of Robusta Jawa Bogor green bean as a differentiator in natural, fullwash, honey, and wine processing. Using HS-SPME-GC-MS and LC-MS, we identified a total of 128 volatile compounds (113 in natural, 111 in honey, 100 in fullwash, and 126 in wine), as well as 105 non-volatile compounds (77 in natural, 73 in honey, 66 in fullwash, and 93 in wine). The study found volatile compounds like ethyl cinnamate potential marker for honey processing. A potential marker for natural and wine processing is 1- isopropyl-3 methylbenzene. Some potential markers for wine processing are (E)-4-hexen-1-ol, 5-methyl-2-hexanol, diethyl succinate, ketoisophorone, and 4-ethyl-2-methoxyphenol. Non-volatile compounds like 1-naphthoic, [4]-gingerol, and theophylline are non-volatile markers for natural processing. Succinic acid is a non-volatile marker for natural and wine processing. While maleic acid and adenosine are markers for honey processing, adenine is a marker for wine processing. In contrast, fullwash does not have any volatile and non-volatile marker. Due to post-harvest-process variations, the obtained results assist in authenticating the chemical compounds of Robusta Java Bogor green beans.

Coffee brewing is a complex process from roasted coffee bean to beverage, playing an important role in coffee flavor quality. In this study, the effects of hot and cold brewing on the flavor profile of coffee were comprehensively investigated on the basis of chromatographic and sensory approaches. By applying gas chromatography–mass spectrometry and odor activity value calculation, most pyrazines showed higher contribution to the aroma profile of cold brew coffee over hot brew coffee. Using liquid chromatography, 18 differential non-volatiles were identified, most of which possessed lower levels in cold brew coffee than hot brew coffee. The sensory evaluation found higher fruitiness and lower bitterness and astringent notes in cold brew coffee than hot brew coffee, which was attributed by linalool, furfural acetate, and quercetin-3-O-(6″-O-p-coumaroyl) galactoside. This work suggested coffee brewing significantly affected its flavor profile and sensory properties.

Profiling of volatile and non-volatile compounds in stems and leaves of water spinach was performed using gas chromatography-flame ionization detector (GC-FID) and GC/ mass spectrometry (MS) method after derivatization. Antioxidant activity was measured by both 1-diphenyl-2-picrylhydrazyl (DPPH) assay and Folin-Ciocalteu total phenol assay. Partial least squares regression (PLSR) was performed to determine the most important volatile and non-volatile compounds with antioxidant activity in both stem and leaf of water spinach. Phytosterol (26.97 and 19.78%), terpene (5.71 and 7.73%), phenolic compounds (3.87 and 2.66%) and Vit E (2.52 and 2.26%) were found to be major volatile compounds in both stem and leaf of water spinach, respectvely. Among the non-volatile compounds, significant amounts of amino acids (31.48 and 18.83%), sugar and sugar alcohol (32.17 and 18.58%), and fatty acids (7.07 and 26.39%) were found in stem and leaf of water spinach, respectively. DPPH free radical-scavenging effect in stem (92.11%) was higher than that in leaf (84.03%), whereas, electron-reducing capacity was higher in leaf (287.45 μg GAE/mL) than in stem (216.45 μg GAE/mL). Results show that water spinach exerts antioxidant activity via volatile compounds (phytosterol) in stems and nonvolatile compounds (amino acids, acids, sugar alcohols) in leaves.

To develop a process for low-cost and ecologically friendly coffee fermentation, civet gut bacteria were isolated and screened to be used for fermentation. Among 223 isolates from civet feces, two bacteria exhibited strong protease, amylase, lipase, pectinase, and cellulase activities. By analyzing 16S rDNA phylogeny, those bacteria were identified to be Lactiplantibacillus plantarum JT-PN39 (LP) and Paenibacillus motobuensis JT-A29 (PM), where their potency (pure or mixed bacterial culture) for fermenting 5 L of arabica parchment coffee in 48-72 h was further determined. To characterize the role of bacteria in coffee fermentation, growth and pH were also determined. For mixed starter culture conditions, the growth of PM was not detected after 36 h of fermentation due to the low acid conditions generated by LP. Coffee quality was evaluated using a cupping test, and LP-fermented coffee expressed a higher cupping score, with a main fruity and sour flavor, and a dominant caramel-honey-like aroma. Antioxidant and anti-foodborne pathogenic bacteria activity, including total phenolic compounds of PM and LP fermented coffee extracts, was significantly higher than those of ordinary coffee. In addition, LP-fermented coffee expressed the highest antibacterial and antioxidant activities among the fermented coffee. The toxicity test was examined in the murine macrophage RAW 264.7 cell, and all fermented coffee revealed 80-90% cell variability, which means that the fermentation process does not generate any toxicity. In addition, qualifications of non-volatile and volatile compounds in fermented coffee were examined by LC-MS and GC-MS to discriminate the bacterial role during the process by PCA plot. The flavors of fermented coffee, including volatile and non-volatile compounds, were totally different between the non-fermented and fermented conditions. Moreover, the PCA plot showed slightly different flavors among fermentations with different starter cultures. For both the cupping test and biological activities, this study suggests that LP has potential for health benefits in coffee fermentation.

Flavour characterization of twelve species of edible algae

Chemical and sensory evaluation of cold brew coffees using different roasting profiles and brewing methods

Coffee contains different volatile and non-volatile compounds, which are responsible for its characteristic flavor and aroma attributes. The extraction of non-volatile compounds from high-quality and traditional coffee by different methods was evaluated to determine the chemical compounds that discriminate between coffees types. Standard methods of preparing the coffee drink by consumers were evaluated. Method A corresponded to boiling water with coffee, and method B to the strained coffee method. Extraction with different solvents did not distinguish the compounds chosen as markers for coffees. In addition to being non-toxic and low-cost, water was the most suitable solvent, conforming to the principles of green chemistry while enabling direct comparison with sensory analysis. The total dissolved solids, percentage extraction, and non-volatile compounds were quantified to select the most satisfactory extraction method. The TDS value ranged from 1.7 to 3 between methods and coffee types, and the extraction percentage ranged from 25 to 45%. Significant differences in the extracts obtained using methods A and B high-quality versus traditional coffees were detected using the Student’s t-test. Although method A extracted the chemical compounds in more substantial amounts, method B was also efficient in extracting the compounds and was easily executed given its similarity to the usual way of preparing coffee beverages used by consumers. The evaluated non-volatile compounds were identified in both high-quality and traditional coffee samples. In the chosen extraction method (method B), the average concentrations in mg 100 g-1 of the sample found for the compounds were: 5-hydroxymethylfurfural (11±0.5), 3,4-hydroxybenzoic acid (62±4), catechin (58±5), 4-hydroxybenzoic acid (58±2), caffeine (1152±44), chlorogenic acid (598±23), caffeic acid (0.7±0.1), and gallic acid (3±0.2).