Sustainable Valorization of Spent Coffee Grounds: Phenolic Compound Extraction Using Hydrophobic Eutectic Solvents

Optimization of microwave-assisted extraction of phenolic compounds from tomato: Characterization by FTIR and HPLC and comparison with conventional solvent extraction

Three-zone simulated moving bed for the separation of chlorogenic acid and caffeine fractions in the liquid extract of spent coffee grounds

Extraction of antioxidant phenolic compounds from spent coffee grounds

Coffee is considered to be one of the most renowned beverages and it is the second-most consumed product worldwide. Spent coffee grounds (SCGs) are the primary solid residue, which are generated during the coffee powder brewing in hot water or steam. The formation of huge amounts of these byproducts poses a severe threat to the environment, due to their organic nature and their high phenolic compounds concentration. Nevertheless, the latter are characterized as bioactive compounds with high antioxidant activity turning SCG into an economical raw matrix for the isolation of valuable components. Phenolic compounds that can be isolated from coffee byproducts can be potentially used as natural antioxidants in food, pharmaceutical, and cosmetics industries. Thus, the research community has focused its efforts on the optimization of phenolics extraction by the development of novel environmentally friendly techniques except for conventional maceration extraction using organic solvents. The objective of this review is to present an inclusive summary of the revalorization of SCGs and the potential uses of those solid residues through the recovery of phenolic compounds or the use of untreated or treated SCGs as biosorbents of valuable compounds from other food industry byproducts.

The aim of this study was to investigate and compare the effects of different extraction techniques (high hydrostatic pressure-assisted extraction (HHPE), ultrasound-assisted extraction (UAE), and classical solvent extraction (CSE)) on phenolic compounds from spent coffee grounds (SCG). Different HHPE parameters (300, 400 and 500 MPa at 25 °C for 5, 10 and 15 min) and UAE parameters (40%, 50%, and 60% amplitude at 25 °C for 5, 10 and 15 min) were used. These techniques were compared with CSE (at 50 °C for 30 min) according to total phenolic content (TPC), antioxidant activity (AA), high-performance liquid chromatography (HPLC), scanning electron microscopy (SEM), and infrared (IR) spectroscopy. The results showed that eco-friendly techniques increased the TPC and AA compared to CSE and morphological changes were verified by SEM results. Furthermore, chlorogenic and caffeic acid were also quantified by using HPLC. Chlorogenic acid was found as the main phenolic compound in spent coffee grounds (SCG). The highest chlorogenic acid was detected as 85.0 ± 0.6 mg/kg FW with UAE at 60% amplitude for 15 min. In brief, for the extraction of phenolic compounds from waste SCG eco-friendly techniques such as HHPE and/or UAE were more convenient than CSE.

Spent coffee grounds (SCGs) pose a significant environmental burden for coffee-producing industries due to the large quantities generated during coffee brewing. However, SCGs also represent an underexplored and sustainable source of bioactive compounds, particularly chlorogenic acid (CGA), known for its antioxidant, anti-inflammatory, and antimicrobial properties. This systematic review evaluates and compares various conventional and non-conventional extraction methods for CGA from SCGs, assessing their efficacy in terms of extraction yield, environmental impact, cost-efficiency, and processing time, factors often overlooked in earlier studies. Ultrasound-assisted extraction (UAE) emerged as the most effective technique, yielding the highest quantity of CGA (587.7 ± 46.6 mg/g), using ethanol as a solvent with a solid-to-liquid ratio of 1:30. UAE was also identified as the most environmentally friendly technique. In contrast, conventional solvent extraction (CSE) provided a moderate CGA yield (39.5 ± 2.1 mg/g) using water as a solvent and was the most cost-efficient technique. Microwave-assisted extraction (MAE) offered the fastest extraction time with a CGA yield of 84 ± 2.8 mg/g. By integrating technical performance with sustainability considerations, this study offers new insights into the optimization of SCG valorization. Furthermore, it supports the advancement of circular bioeconomy strategies through the efficient recovery of high-value bioactive compounds.

BACKGROUNDSpent coffee grounds, a valuable source of phenolic compounds, are considered beneficial for human health because of their antioxidative properties. The liquid extract containing phenolic compounds (such as chlorogenic and gallic acids) can be obtained via extraction using environmentally friendly organic solvent. The separation of chlorogenic and gallic acids from the liquid extract was carried out using isocratic chromatography technique in a three‐zone simulated moving bed (SMB). However, due to the low selectivity of separation, the productivity of three‐zone SMB was sacrificed to meet the purity criteria. Hence this work aimed to enhance the productivity of three‐zone SMB for the separation of chlorogenic and gallic acids via model simulation using partial feed operation and to improve the concentration of extract and raffinate products using partial collection strategy.RESULTSThe full feed scenario was designed based on the triangle theory, and the partial feed patterns (initial feed, middle feed and late feed) were implemented for each operating point in the triangle diagram to investigate the possibility of increasing the feed flow rate. The maximum productivity was evaluated based on the purity criteria (≥98%) for both extract and raffinate products. Under optimal conditions, productivity was doubled to 0.24 mg min−1 L−1 for both middle feed and late feed patterns compared to that of the full feed scenario. The partial collection strategy applied to the optimal point for each operational mode significantly increased the raffinate concentration to approximately 0.02 g L−1 at the optimal time fraction for discarding the solvent.CONCLUSIONThis work could be a foundation for the valorization of spent coffee ground. © 2021 Society of Chemical Industry (SCI).

Spent coffee grounds (SCGs) is the solid residue generated during coffee brewing. The amount of SCGs tends to increase annually due to the growth of the coffee industry. The valorization of SCGs can reduce this huge waste by using SCGs as the feedstock for biodiesel production. This study used green technology for biodiesel production. To evaluate the potential of SCGs, the characterization of SCGs and the optimization of biodiesel production from SCGs using supercritical fluid technology were investigated. Moreover, to understand the possibility of biodiesel production from the SCGs process on an industrial scale, techno-economic analysis (TEA) was applied to estimate the economic feasibility of the biodiesel production plant, which had been designed by Aspen plus computer simulations. The results demonstrated that SCGs had the potential to be used as feedstock for biodiesel production due to the amount of extracted oil being high and the composition in SCGs oil was suitable for converting to biodiesel. Green solvents, which are ethanol and ethyl acetate, can be applied as the alternative extracting solvent and reactant in the biodiesel production process since they gave a higher extracted SCGs oil yield when compared to standard extracting solvent and gave the FAEE content in SCGs biodiesel product higher than 80 wt% in batch and continuous reactor at supercritical state. However, TEA showed that the supercritical fluid biodiesel production from SCGs plant is still not profitable within the project life plan due to the cost of production in both plants being high from the solvent cost and waste treatment cost. This research suggested that it was necessary to investigate further the waste management of the defatted SCGs generated during the biodiesel production from the SCGs process to make the process more economically viable.

Spent coffee grounds (SCG) are a widely available agro-industrial residue rich in carbon and phenolic compounds, presenting significant potential for biotechnological valorization. This study evaluated the use of SCG as a suitable substrate for fungal laccase production and the application of the resulting fermented biomass (RFB), a mixture of fermented SCG and fungal biomass as a biosorbent for textile dye removal. Two fungal strains, namely Lentinus crinitus UCP 1206 and Trametes sp. UCP 1244, were evaluated in both submerged (SmF) and solid-state fermentation (SSF) using SCG. L. crinitus showed superior performance in SSF, reaching 14.62 U/g of laccase activity. Factorial design revealed that a lower SCG amount (5 g) and higher moisture (80%) and temperature (30 °C ± 0.2) favored enzyme production. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) analyses confirmed significant structural degradation of SCG after fermentation, especially in SSF. Furthermore, SCG and RFB were chemically activated and evaluated as biosorbents. The activated carbon from SCG (ACSCG) and RFB (ACRFB) exhibited high removal efficiencies for Remazol dyes, comparable to commercial activated carbon. These findings highlight the potential of SCG as a low-cost, sustainable resource for enzyme production and wastewater treatment, contributing to circular bioeconomy strategies.

Spent coffee grounds (SCG) are the agricultural waste generally eliminated by discarding or burning. It contains phenolic compounds with antioxidant properties (such as chlorogenic acid and gallic acid, etc.), which are beneficial in foods, cosmetics and pharmaceuticals. Apart from extraction, the purification of targeted antioxidative substances from the liquid extract is essential. This research presents the separation of chlorogenic and gallic acids using the three-zone simulated moving bed, which is based on the principle of liquid chromatography. Preliminary, SCG were extracted to assess the content of chlorogenic acid and gallic acid. After that, the adsorption behavior of both substances (chlorogenic acid and gallic acid) in a single chromatographic C18 column was studied. The suitable mobile phase was a mixture of acetonitrile, water, and acetic acid (80:20:1). The model simulation was carried out in the mono-component system to determine the adsorption parameters. Breakthrough curve experiments for a binary mixture were performed to validate the predetermined parameters. Then, a three-zone SMB was designed and the model simulation was used to optimize the operating conditions via response surface methodology based on purity and productivity. At the optimal conditions, the purity of chlorogenic acid and gallic acid were 99.27% and 98.43%, respectively.

Hot brewed coffee is the most popular hot beverage in the world, and its health properties have been published in the literature(1). Conversely, over the past decade, cold-brewed coffee has gained popularity, but its eventual nutritional properties are unclear. Both hot and cold brewed coffee produces over 6 million tons of spent coffee grounds (SCG) yearly disposed in landfills(1). Interestingly, studies have shown that SCG can improve several metabolic parameters via changes in the gut microbiome in obese and diabetic rats(2), and reduce energy consumption in overweight humans(3). However, studies investigating the nutritional properties of SCG are lacking in the literature. Hence, in this study, we aimed to identify, quantify and compare two main bioactive compounds in hot- and cold-brewed coffee as a beverage, as well as in the SCG. Samples from hot and cold coffee beverages and SCG were obtained from a local coffee shop (n = 3 per group). The coffee beans were composed of Coffea arabica from Papa New Guinea, Brazil, Ethiopia, and Colombia (in order from highest to lowest proportion). All samples were analysed by high-performance liquid chromatography and mass spectrometry (HPLC-MS). The analyses focused on two main bioactive compounds; trigonelline and chlorogenic acid (CGA). Statistical analyses were performed using an unpaired t-test with Welch’s correction and two-way ANOVA with Tukey’s post-hoc test (p<0.05). When compared to hot-brewed coffee beverages, cold-brewed coffee beverages have shown lower (p<0.05) levels of trigonelline (17.26 mg/g + 1.305 vs. 8.46 mg/g + 0.74, respectively) and CGA (9.82 mg/g + 0.93 vs. 5.31 mg/g + 0.48, respectively). In SCG obtained from hot-brewed coffee, a higher concentration of CGA was found (0.12 mg/g + 0.006), when compared to SCG obtained from cold-brewed coffee (0.10 mg/g + 0.03). However, trigonelline in cold-brewed SCG was found in higher (p<0.05) concentration, when compared to hot-brewed SCG (0.11 mg/g + 0.03 vs. 0.09 mg/g + 0.017, respectively). Moreover, hot-brewed coffee beverages showed higher (p<0.05) concentrations of trigonelline and CGA, when compared to hot-brewed SCG. Similarly, cold-brewed coffee beverages showed higher (p<0.05) concentrations of both bioactive compounds, when compared to cold-brewed SCG. Our results indicated that hot brewed coffee beverage contains high concentrations of bioactive compounds (CGA and trigonelline), which possibly explain its health properties. Although SCG obtained from hot and cold-brewed coffee showed lower concentrations of both bioactive compounds than coffee beverages, our results shed light on the possible health benefits of SCG consumption. In a world seeking more sustainable solutions, further studies investigating the potential use of SCG as a functional food are required.

Spent Coffee Ground (SCG) is the main coffee industry by-product, rich in dietary fibers and polyphenols. The extractable material of SCG was fractionated, and the phenolic compounds were identified and quantified. Chlorogenic and neochlorogenic acids were identified as the main phenolic components, and the Total Phenolic Content (TPC) of SCG was determined to be 2.16% (dry SCG basis). Furthermore, SCG was characterized in terms of Total Dietary Fiber content, which amounted to 66%. The SCG was valorized for the development of a bakery product (cookie) enhanced with fiber and bioactive polyphenols. Cookies were produced with the addition of 4% and 7% dry and defatted SCG (baked cookie basis). The produced cookie prototypes presented TPC and dietary fiber dependent on the addition level of SCG. TPC values were determined at 588 and 1017 ppm, while dietary fiber values were at 2.7 and 4.6%, respectively. The shelf life of the cookies was monitored over 143 days at three different temperatures (25 °C, 35 °C, and 45 °C) in terms of texture (hardness), color, Peroxide Value (PV), and TPC. It was observed that the PV value significantly increased in samples with incorporated SCG, stored at 45 °C, while in those stored at 25 °C and 35 °C, PV remained at low levels. The TPC of the SCG-enriched samples remained practically constant during the shelf life analysis, while color and hardness increased (mathematically modeled). SCG-added cookies were characterized by increased darkness, increased hardness, and a mild (desirable) coffee flavor. The overall sensory impression scores for 0%, 4%, and 7% SCG-added cookies were 7.5, 8.0, and 8.2, respectively. Based on sensory evaluation test results, the shelf lives of 0%, 4%, and 7% SCG at 25 °C were 359, 435, and 471 days, respectively. Overall, SCG is a potentially valuable ingredient that can be used to develop innovative food (baked) products with enhanced nutritional value and increased shelf life.

Enhancing aqueous systems fermentability using hydrophobic eutectic solvents as extractans of inhibitory compounds

Valorization of spent coffee ground through the development of alginate-based composite antioxidant films: Physicochemical properties and release kinetics

Spent coffee grounds are a promising bioresource that naturally contain around 50 wt% moisture which requires, for a valorization, a drying step of high energy and economic costs. However, the natural water in spent coffee grounds could bring new benefits as a co-solvent during the supercritical CO2 extraction (SC-CO2). This work reports the influence and optimization of pressure (115.9-284.1 bars), temperature (33.2-66.8 °C), and moisture content (6.4-73.6 wt%) on simultaneous extraction of lipids and polar molecules contained in spent coffee grounds by supercritical CO2 (SC-CO2) using Central Composite Rotatable Design and Response Surface Methodology. The results show that for lipids extraction, pressure is the most influent parameter, although the influence of moisture content is statistically negligible. This suggests that water does not act as barrier to CO2 diffusion in the studied area. However, moisture content is the most influent parameter for polar molecules extraction, composed of 99 wt% of caffeine. Mechanism investigations highlight that H2O mainly act by (i) breaking caffeine interactions with chlorogenic acids present in spent coffee grounds matrix and (ii) transferring selectively caffeine without chlorogenic acid by liquid/liquid extraction with SC-CO2. Thus, the experiment for the optimization of lipids and polar molecules extraction is performed at a pressure of 265 bars, a temperature of 55 °C, and a moisture content of 55 wt%.