1. Introduction
Coffee, valued mainly for its organoleptic-nutritional characteristics, is one of the most consumed foods/drinks in the world. Moreover, coffee is one of the most traded commodities globally [
1]. In 2020, coffee production reached 10.7 million tonnes with a value of approximately USD 102 million. Brazil (34.7%) is among the main producing countries, followed by Vietnam (16.5%), Colombia (7.8%), Indonesia (7.3%), Ethiopia (5.5%), and Peru (3.5%) [
2]. According to the International Coffee Organisation (ICO), more than 169 million 60 kg bags of coffee were produced in 2020, with an increase of 0.3% compared to the previous year. As coffee production and consumption are expected to steadily grow in the coming years, the amount of coffee by-products produced by the coffee industry is also expected to increase [
1,
2].
Hot and cold coffee drinks can be produced from a different variety of beans (i.e., Arabica and Robusta). The two most important species in terms of economics are
Coffea arabica L. (generally referred to as Arabica), which accounts for about 70% of production, and
Coffea canephora (generally referred to as Robusta). Arabica and Robusta coffees differ in terms of ideal pedo-climatic conditions (soil composition, climate, temperature, etc.), physical aspects (size of the green coffee, etc.), chemical composition, and the characteristics of the brew obtained after roasting [
1]. In particular, considering the chemical composition, Robusta coffee contains higher amounts of antioxidant compounds, caffeine, and soluble solids, resulting in increased body and strong flavor and aroma. The caffeine content in seeds ranges from 0.3% to 2.7% and is twice as high in Coffee Robusta as in Coffee Arabica, which contains almost 1.5%. While Arabica coffee offers superior cup quality and aroma, different secondary metabolites (i.e., minor isomers of chlorogenic acids and diterpenes), are not present in
C. Arabica [
1,
2,
3].
There are many coffee preparation techniques, involving the use of different extraction/infusion conditions (i.e., time, temperature, pressure, water/powder ratio, etc.) [
4,
5]. Concerning the coffee brewing methods mostly used in Italy, 87% of the home-brewed coffee beverage is mainly characterized by Moka, and the semi-sweet brewing method [
6]. However, nowadays, coffee preparation with traditional techniques is slowly giving way to faster brewing methods such as pods and capsules. These are small containers containing previously roasted and ground coffee beans that are used in special systems to brew them. The introduction of these new systems resulted in an increase in domestic coffee consumption [
7,
8].
The chemical composition of coffee beverages mainly depends on the processing techniques (i.e., pre-roasting and roasting) of green coffee beans. Moreover, processing methods at the harvesting stage and industrial processes of green coffee, as well as the methods used by consumers to prepare the coffee beverage, contribute to changes in the concentration of certain compounds within the finished product. The study of the chemical composition of coffee also referred to as “coffeeology”, has highlighted more than 1000 different volatile and non-volatile compounds, exhibiting several functional properties, such as antioxidant, anti-inflammatory, antihypertensive and antimicrobial activities, that act both positively and negatively on the consumer’s health [
9,
10].
Considering the physiochemical properties, coffee beans consist of (i) an outer skin (exocarp), which is rich in caffeine, chlorogenic acids, and tannins [
9]; (ii) a middle pulp and a mucilaginous layer (mesocarp), which is a source of carbohydrates, such as glucose, and pectin; (iii) parchment, composed of cellulose, caffeine, and minerals; (iv) silver skin (integument), composed of polysaccharides, such as cellulose, and hemicellulose, as well as proteins and phenolic compounds [
9], and (v) finally, the seeds (endocarp), containing significant concentrations of caffeine, polyphenols, flavonoids and triacylglycerols (TAGs), bioactive compounds with high antioxidant and antimicrobial activities [
10]. The content of bioactive compounds (i.e., antioxidants, biogenic amines, etc.) depends on the coffee species, growing conditions, harvesting techniques, and the processing techniques the bean undergoes (i.e., roasting at high temperatures) [
11,
12,
13]. Among its bioactive compounds, there are biogenic amines (BAs), consisting of basic low-molecular weight compounds derived from microbial and/or thermal decarboxylation of amino acids. These compounds, which can have both undesirable effects on health (e.g., histamine, cadaverine, tyramine, etc.) and positive effects (e.g., serotonin), are considered an indicator of food quality and safety. Studies have reported that the concentration of BA, especially polyamines (spermine, spermidine, and putrescine) changes considerably during the formation of the fruit and the processing phases, especially during the roasting phase of green coffee. Among the most abundant amine is putrescine, followed by spermine, spermidine, and serotonin [
1,
13]. Whereas the BA present in smaller quantities is cadaverine, histamine, and tyramine. Among other bioactive compounds, coffee contains significant amounts of polyphenols, i.e., molecules produced by the secondary metabolism of plants that can have positive effects on human health (i.e., anti-atherosclerotic activity, antioxidant activity, etc.). Among the polyphenols most commonly found in coffee are chlorogenic acid, hydroxycinnamic acid, and their derivatives (i.e., caffeic acid, ferulic acid, etc.), as they are molecules with a high scavenging activity towards free radicals [
14]. The polyphenol content in coffee varies considerably between green and roasted coffee, indeed the roasting process of the beans leads to the degradation of approximately 70–75% of the polyphenols contained in green coffee [
14,
15,
16].
Bioactive compounds in coffee beverages have been studied using different brewing preparation techniques (espresso machines, capsule machines, pod machines, and Moka) with different infusion conditions (i.e., time, temperature, pressure, etc.). Some studies have considered the possibility of evaluating multiple bioactive compounds in coffee powder and respective brewed coffees obtained by different techniques [
13]. Therefore, this study aimed to evaluate the effect of four different coffee extraction methods (professional coffee machine, Moka machine, pod machine, and capsule machine), on the quality and safety of the final product, as shown in
Figure 1. Therefore, the effect of these four coffee preparation methods was evaluated for the content of eight biogenic amines (serotonin, histamine, spermidine, putrescine, tyramine, cadaverine, and β-phenylethylamine), the total polyphenol (TPC) and flavonoid (TFC) content, and the anti-radical capacity (ABTS and DPPH assay). For both coffee powders and the infusions obtained from them by the different extraction techniques, the quantitative determination of BA was carried out by HPLC-FD, while for TPC, TFC, and the DPPH and ABTS assays were performed by means of UV-Vis spectrophotometric analysis. Indeed, univariate, and multivariate statistical analysis was performed on the spectrophotometric and chromatographic results of coffee powder and coffee beverages. Furthermore, concerning the influence that different brewing techniques have on the final coffee beverage and packaging, an analysis of the environmental impacts could be of relevance for an all-encompassing quality and sustainability assessment. Over the latest ten years, several studies have been carried out to assess the environmental performances of the coffee production process and packing stages. Brommer et al. (2011) estimated GHGs emissions associated with the preparation of 2000 cups of coffee based on a cradle-to-gate approach, thus highlighting coffee cultivation as the most impactful phase responsible for 55.4% of total GHGs emissions, followed by post-consumer phases (36%), and coffee packaging, and distribution (6.6%) [
17]. Concerning the packaging of different brewing methods, Dubois et al. (2011) observed the environmental burdens associated with 40-mL Nespresso capsules based on the different types of packaging materials (i.e., polypropylene or PP, polyethylene or PE, polyethylene terephthalate or PET, Aluminium or Al, and PE-Al-PET multi-layer bags). They highlighted that the most impactful materials derived from the waste disposal of PE capsules in landfill are due to direct CH
4 emissions associated with the degradation of starch [
18].
The results of the above-mentioned studies were only slightly comparable since they differ in several factors (such as coffee varieties, coffee beverage volume from 40 to 237 mL, etc). Besides, with coffee brewing methods, the method-energy efficiency significantly affects the overall environmental impacts associated with a single-use phase.
In this regard, the environmental sustainability of different coffee brewing methods analyzed in the study was evaluated through the application of Life Cycle Assessment methodology (ISO 14000:2006) using the software SimaPro v. 9.2.2. The LCA analyses focused on a gate-to-gate approach, thus allowing the comparison of coffee brewing methods based in detail on the preparation technique, its energy-demand, and packaging materials.
2. Materials and Methods
2.1. Chemicals
2-phenylethylamine (B-Pea), Putrescine (Put), Cadaverine (Cad), Histamine (His), Tyramine (Tyr), Spermine (Spm), Spermidine (Spd), and Serotonin (Ser) were purchased from Supelco (Bellefonte, PA, USA), as well as the derivatizing agent (Dansyl-Chloride, DSN-CL), sodium bicarbonate (NaHCO3), ammonium hydroxide (NH4OH) and sodium hydroxide (NaOH). Folin-Ciocalteu reagent, sodium carbonate (Na2CO3), 2,2-Diphenyl-1-picrylhydrazyl (DPPH), 2,2’-azino-bis (ABTS), sodium nitrite (NaNO2) and aluminum chloride (AlCl3). In addition, the following solvents were purchased from Sigma-Aldrich (St. Louis, MO, USA): acetone (C3H6O), perchloric acid (HClO4), acetonitrile; ACN (CH3CN), methanol (CH₃OH) and double-distilled water (d-H2O).
2.2. Instruments
The following instruments were used for the analysis: Bandelin Sonorex RK100H water and ultrasonic thermostatic bath, IKA T18 digital Ultra–Turrax (IKA-group, Saufen, Germany), and Whatman 0.45 µm 100 (PTFE) syringe filters (Sigma Aldrich, Milan, Italy), UV-Vis spectrophotometer (Jenway, Stone, UK), NEYA 10R refrigerate centrifuge (Exacta Optech, Modena, Italy). The chromatographic analysis of biogenic amines was performed using an ATVP LC-10 HPV binary pump with an RF-10° XL fluorimetric (FD) detector (Shimadzu, Kyoto, Japan) operating to λ emission = 320 nm, and λ excitation = 523 nm. A Supelcosil LC-18 column (250 mm × 4.6 mm, 5 µm) with a Supelguard LC-18 (Supelco, Bellefonte, PA, USA) pre-column was used for the determination of BAs.
2.3. Sampling
Eight coffee powders and brewed beverages from two different brands belonging to the 100% Arabica variety (country of origin Brazil) were analysed. For each brand,
n = 2 coffee powders for domestic use (Moka),
n = 2 coffee powders for professional use (Bar),
n = 2 coffee powders for the capsule brewing method, and
n = 2 coffee powders for the pod brewing method were considered, as shown in
Figure 1. All types of coffee powder packaged for the above-mentioned coffee brewing methods refer to the same brand. The samples were purchased from local retailers in the city of Rome, Italy. The coffee packages were opened just before analysis to avoid and limit oxidative damage. Extracts (coffee beverages) were obtained in triplicate for each type of coffee powder and stored at T = +4 °C until the day of analysis. Different extraction methods were used for the analyses: Moka coffee machine (model Bialetti, Omegna, Italy), capsule machine (model Krups Nespresso INISSIA XN100, Naples, Italy), pod machine (model De’Longhi Dedica EC685.W, Treviso, Italy), and professional espresso machine (model Faema Hot Steam, Milan, Italy). For each type of extraction, the amount of coffee required for the specific machine was used with a known amount of demineralized water. The extraction conditions are shown in
Table 1.
For espresso coffee preparation by the traditional method, the professional coffee machine was used. After weighing 7 g of coffee powder for catering use, i.e., the quantity required for the filter holder of the machine, the coffee was pressed into the filter. While, the single-serving Moka was prepared by weighing 5 g of coffee powder for domestic use, without pressing it into the filter, and 25 mL of water, relative to the volume of the machine’s boiler. The capsule coffee was extracted by placing the capsule, containing weighted amounts of coffee powders, and sealed in a protective atmosphere (5 ± 0.5 g), into the machine with a compatible capsule system. Each capsule was used only once and then disposed of. For coffee pods, another machine specifically for this product was used, the pods consisted of pre-packaged coffee (7 ± 0.5 g) and hermetically sealed between two sheets of filter paper. In both methods, the volume of water used was approximately 20 mL. The samples obtained by the different extraction methods were stored at refrigerated temperatures (T = 4 ± 2 °C) until analysis.
2.4. Determination of Biogenic Amines
Biogenic amine extraction in coffee powder samples was performed according to the method previously described by Vinci et al. (2021) [
19] with some modifications. 1 g of coffee powder was weighed and placed in a centrifuge tube, then 10 mL of 0.6 M HClO
4 was added and homogenized in an ultrasonic bath for 10 min at 400 Hz at room temperature. Then, after centrifugation (3000 rpm for 10 min), the supernatant was stored in an amber vial. For the coffee beverage samples, the extraction was performed according to the method of Vinci et al., 2021 [
19], with some modifications. Briefly, 1 mL of sample was placed in a 10 mL amber flask then acidified by adding 0.6 mL of 10.3 M HClO
4 to obtain a final concentration of 0.6 M and made up to volume with distilled H
2O. The extracts thus obtained for coffee powders and coffee infusions were stored at a temperature of 4 ± 2 °C.
Following BA extraction in coffee powders and coffee beverages, the samples were then derivatized by adding 200 µL NaOH 2 N and 300 µL saturated NaHCO
3 solution to 1 mL of acid extract. Subsequently, 2 mL of DNS-Cl at a concentration of 2 mg/mL in acetone is added. The sample was placed in the dark for one hour at 45 °C in the ultrasonic bath (Bandelin Sonorex RK100H). Subsequently, the solutions were made up to a volume of 5 mL with acetonitrile (ACN) and filtered through 0.45 µm FPTE syringe filters. Biogenic amines were detected by HPLC-FD following the standardized method defined by ISO 19343:2017, with some modifications [
20]. Analytes were eluted using Supelcosil LC-10 column (250
× 4.6 mm; 5 µm) in reverse phase with Supelguard LC-18 pre-column (Supelco), coupled with fluorimetric detector (λ excitation = 320 nm; λ emission = 523 nm). The flow rate was set at 1.2 mL/min, while the column temperature was set at 30 °C. The elution program starts with 3 min of isocratic elution (50% ACN; 50% water) reaching 100% of ACN after 18 min to finish after 3 min of isocratic elution. After that, the start isocratic condition (50% ACN; 50% water) was restored. The results were obtained through a calibration curve ranging from 0.1 to 25 mg/L for each BA. Based on BA results, the Biogenic Amines Quality Index (BAQI) was calculated to assess the coffee samples’ quality. For BAQI values < 10, the product can be considered safe [
21]. It was calculated as follows and expressed in µg/g of coffee powder:
2.5. Polyphenol, Flavonoid, and Antioxidant Activity Determination
A hydroalcoholic extraction was performed on the coffee powder samples and their infusions. The hydroalcoholic extraction procedure in the coffee powder samples was as follows: 0.1 g of coffee powder was weighed, to which 5 mL of MeOH:H
2O (60:40,
v/
v) was added [
22]. The solutions were centrifuged at 3000 rpm for 10 min at room temperature and the supernatant was collected in a 10 mL volumetric flask. A second extraction was performed on the supernatant as described above. For the coffee infusions, the extraction was performed by placing 1 mL of sample in a 50 mL volumetric flask and making up to volume with MeOH:H
2O (60:40,
v/
v). Extractions were performed on the day the infusions were prepared and all extracts were stored at 4 ± 2 °C.
2.5.1. Total Polyphenols Content
The total polyphenols content (TPC) was assessed for both hydroalcoholic extracts of coffee powder and coffee infusions according to the method described by Vinci et al. (2022) [
22] with some modifications. 0.5 mL of the hydroalcoholic extract was mixed with 0.25 mL of Folin Ciocâlteu reagent in a 10 mL amber volumetric flask. After 3 min, 0.5 mL of aqueous sodium carbonate solution (7.5%
w/
v) was added and the flask was kept in the dark for 30 min. It was then made up to volume with distilled water. The absorbance of the samples was read at 750 nm. The results were expressed as milligrams of gallic acid equivalents per gram of coffee powder (mg GAE/g coffee powder). The results were obtained through a calibration curve ranging from 10 to 100 mg/L (R
2 = 0.9998) and the blank was the solvent used for sample extraction.
2.5.2. Determination of Total Flavonoid Content
The total flavonoid content (TFC) was evaluated in all powdered and infused coffee extracts. The TFC was determined according to the method described by Abdel-Naeem et al. (2021), with some modifications [
23]. To 0.5 mL of extract, 2 mL of distilled water and 150 µL of NaNO
2 (5%
w/
v) were added to a 5 mL volumetric flask. The solution was stirred and incubated in the dark for 5 min, then 150 µL of AlCl
3 (10%
w/
v) was added and the solution was put back in the dark for 5 min. Next, 2 mL of NaOH (1 M) was added to the solution and left in the dark for a further 15 min. Subsequently, 5 mL was made up to a volume of 5 mL. The absorbance of the extracts was read at 510 nm. TFC results were expressed as milligrams of rutin equivalents (Rut) per gram of coffee powder (mg Rut/g coffee powder). As the TPC assay, the TFC blank corresponds to the solvent used for the extraction of polyphenols from coffee samples.
2.5.3. Determination of Antioxidant Activity
The antioxidant activity of coffee powders and infusion extracts was evaluated by using two different reagents: ABTS and DPPH [
24,
25]. The scavenging activity of the ABTS radical in the samples was evaluated by measuring the decrease in absorbance at 734 nm. A 7 mM solution of ABTS was prepared by dissolving 0.19 g of ABTS powder in 50 mL of distilled water, while the PBS solution was prepared by dissolving 0.38 g of PBS powder in 10 mL of d-H
2O. 25 mL of 7 mM ABTS and 0.4 mL of PBS (1.9 mg/mL) were placed in an amber flask. The solution was kept in the dark for 16 h at room temperature to activate the reagent. 3.6 mL of the reagent was added to 0.4 mL of hydroalcoholic extract, and the sample with the reagent was placed in the dark for 15 min and then read on the UV-Vis spectrophotometer. The scavenging activity of coffee samples was also assessed for both types of extracts by DPPH assay. A 2.5 ng/mL DPPH solution was prepared by dissolving 125 mg of standard powder in 50 mL of methanol. To 1 mL of hydroalcoholic extract, 1.5 mL of DPPH solution (2.5 ng/mL) was added and kept in the dark for 30 min at room temperature. The absorbance (λ = 517 nm) was then measured against methanol using a UV-Vis spectrophotometer. The results were calculated using the inhibition rate (I%) of the radical cation for both assays, according to the following equation:
where A
0 is the absorbance of the control (blank) and A
1 is the absorbance of the DPPH or ABTS radical in the extract.
2.6. Life Cycle Assessment (LCA)
Following standards ISO 14040:2006 and ISO 14044:2006, Life Cycle Assessment (LCA) is considered a standardized and valuable tool for environmental impact assessment, and it should involve four phases [
26,
27]: (1) Goal and scope definition, describing the objective of the study, the functional unit (FU) and the system boundary; (2) Life Cycle Inventory (LCI), collecting the input data for the environmental assessment of a product, process, or activity; (3) Life Cycle Impact Assessment (LCIA), which is aimed at evaluating sustainability in terms of impacts on the environment, human health, and resources; and (4) Interpretation of results, in which LCIA results are interpreted according to the objectives and scope definition. SimaPro 9.2.2., software was used for the evaluation of environmental impacts.
2.6.1. Goal and Scope Definition
The study was aimed at assessing the environmental performances of different brewing methods (Moka, espresso bar, espresso pods, and capsules) for coffee beverages, by taking into account operational conditions in terms of time, temperature, coffee powder, water consumption, and packaging materials. The functional unit (FU) is a 40-mL cup of espresso coffee with no additional ingredients (i.e., milk, sugar, etc.) and by the Italian Coffee Committee’s disciplinaries [
28]. The system boundaries are referred to as a gate-to-gate approach. In this regard, the life cycle included the use of the aforementioned coffee machines, considering their operational conditions (in terms of electricity usage), roasted and ground coffee, water use, and primary packaging materials used (i.e., paper filters, low-density polyethylene, polypropylene, etc.). Nevertheless, the system boundaries did note GHGs emissions arising from the capital goods production, such as coffee machines, as well as their maintenance and disposal due to: i. lack of data, ii. the exclusion of operating goods in previous LCA studies on coffee brewing methods [
17,
28,
29] and, iii. the assumption that these inputs could be considered negligible because of their minor contribution to a single cup of espresso coffee. Therefore, the coffee production chain (cultivation, transportation of coffee beans, as well as coffee roasting and grounding) was excluded from the study, since it was assumed to be the same for the coffee beverages obtained from the different brewing systems analyzed [
28,
29]. Waste disposal of both spent coffee grounds, and all packaging materials used, were excluded from the study.
2.6.2. Life Cycle Inventory (LCI)
The input data concerning the preparation of a 40-mL cup of coffee beverage (FU) are shown in
Table 2.
The primary data were provided by a coffee company, located in Rome (Lazio, RM, Italy), and referred to roasted and ground coffee, as well as primary packaging materials. The secondary data for electric coffee machines usage were extracted from the Ecoinvent v3.8 database, provided by SimaPro 9.2.2. software [
30].
2.7. Statistic Analysis
The data were obtained from the analysis of three replicates and were expressed as mean ± standard deviation. The normality of the data distribution was checked using the Shapiro–Wilk test, the homogeneity of variances using Levene’s test, and the significance of differences between the extracts was tested using one-way analysis of variance (ANOVA) with p < 0.05. After ANOVA, multiple comparison tests were performed for statistically significant variables, using Dann’s post hoc test (homogeneity of variance was assumed) at the level of p < 0.05. Following the characterization of the coffee samples with different brewing methods, a multivariate analysis was carried out to interpret the results using principal component analysis (PCA). The data were pre-treated (autoscaling) to exclude variance related to the different units of measurement of the analyses performed. Analyses were performed using CAT software.
4. Conclusions
In recent years, the market for nourishing foods and beverages has become increasingly diversified in response to structural changes in consumer demand, which calls for increased attention to the health-promoting effects, the preservation of the environment, and the socio-economic well-being of small producers. As the brewing method can be considered the main contributing factor for the coffee beverage chemical-nutritional composition, this study demonstrated that bioactive compound content (polyphenols, antioxidants, and BAs) greatly depends on the brew preparation technique adopted. Coffee powders used directly for professional espresso machines, and Moka, and coffee powders packaged for pods and capsules, and subsequently extracted by different brewing methods were considered. All four different coffee beverages obtained were then compared with the corresponding non-extracted coffee powders.
Analyses of coffee powders showed total BA concentration ranging from 67.01 µg/g to 96.83, thus highlighting a decrease of 39% in coffee beverages (16.02–53.92 µg/g). Among all BAs, Serotonin was the prevailing amine in both ground coffee samples (62.13–84.24 µg/g) and coffee beverage samples (12.75–33.46 µg/g). β-Pea, Put, His, Spd, and Spm were found in wide variations of concentration observed depending on the coffee brewing method. When considering coffee brews, phenolic compounds (polyphenols, flavonoids, antioxidants) are the class of bioactive compounds most abundant in coffee, which undergo significant variation during coffee beverage preparation. It was found that the total polyphenol content was higher in the starting ground coffee powders (22.96–29.61 mg GAE/g) and decreased significantly in coffee beverages, between 80% and 90%, depending on the different beverage preparation methods. The same trend was found for the TFC assay, thus observing in ground coffee samples a flavonoid content approximately 15 times higher than coffee beverages samples.
The overall reduction of bioactive compounds in coffee beverages could probably be due to the high brewing temperatures and pressures, which lead to the degradation of these compounds; in addition, the water/coffee contact surface and the particle size of the coffee powder may affect the extractant capacity of biogenic amines and phenolic compounds [
1,
5]. Furthermore, using multivariate analysis, it was possible to show that the variables considered allowed the samples to be grouped into ground coffee and coffee beverages and that they were heavily influenced based on the brewing method adopted.
The application of LCA methodology allowed the sustainability assessment of coffee brewing methods, thus highlighting lower environmental impact for the industrial coffee machine compared to the capsule brewing method, which showed the highest environmental burden in 14 out of 18 impact categories analyzed. However, the LCA study presents limitations, since the coffee cultivation and production stages were not considered for the sustainability assessment, in a cradle-to-grave approach. For this reason, future studies will have to expand the boundaries of the system, also considering the disposal and reuse of processing by-products. In addition, different coffee preparation techniques (e.g., Turkish, French, American brewing techniques, etc.) can be compared to highlight the most efficient one in terms of both the quality and sustainability of the final coffee beverage.