BIOTEST-BASED TOXICITY EVALUATION OF BIODEGRADABLE FOOD WASTE: CONCLUSIONS BASED ON AN ANALYSIS OF SPENT COFFEE GROUNDS (SCG)

Washed hydrochar from spent coffee grounds: A second generation of coffee residues. Evaluation as organic amendment

An innovative formulation to improve spent coffee characteristics as soil fertilizer: Nutrient, chemical characterization and effects on plant germination

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.

This study explores the production of bio-nutrients from bioactive compound-rich spent coffee grounds (SCG) and biochar (BC) through composting after inoculation with a biological agent and its impact on the growth performance of garden cress and spinach. The SCG was composted with six doses of BC (0, 5, 10, 15, 20, and 25%). The compost with 10% BC exhibited the best maturity, humification, and phytotoxicity index values of dissolved organic carbon (DOC), humification index (E4/E6), and germination index (GI). A metagenome analysis showed that compost starter enhanced the bacterial community’s relative abundance, richness, and diversity in SCG and BC treatments. This improvement included increased Patescibacteria, which can break down noxious phenolic compounds found in SCG and BC. The BC enriched the compost with phosphorus and potassium while preserving the nitrogen. In plant growth experiments, the total chlorophyll content in compost-treated garden cress and spinach was 2.47 and 4.88 mg g−1, respectively, which was significantly greater (p ≤ 0.05) than in unfertilized plants and similar to the plants treated with traditional fertilizer. Overall, the results show that the compost of SCG + BC was well-suited for promoting the growth of garden cress and spinach, providing adequate nutrients as a fertilizer for these leafy vegetables.

Oil extracted from spent coffee ground (SCG) has been well known as a potential feedstock for high quality biodiesel production. This work was to investigate extraction, physical and chemical characterizations of Robusta coffee oil (CO) and its application for biodiesel production. Analysis of seven coffee ground (CG) samples showed that oil content in CGs depended on technique of the manufacturer. Morphological changes of CGs surface were recorded by FESEM technique which showed the particle size significantly increased with the oil loss. Infrared spectroscopies revealed absence of SCG oil in the de-oiled SCG, confirmed that soxhlet method in hexane was used efficiently for the oil extraction. Thermal properties of SCG oil, fresh coffee ground (FCG), SCG and de-oiled SCG samples were investigated by simultaneous TG–DTA measurement. The obtained data showed the oil content relating to thermal changes of SCG samples. Comparison between chemical components of Robusta coffee bean (RCB) and SCG reflected a fact that most of oil content in the SCG could be originated in manufacturing process of FCG. Quality biodiesel product has prepared from SCG oils via a two-step process. After pre-treatment process, transesterification of SCG oils was carried out with methanol (v/v, 30%) and NaOH (w/v, 1%) in yield 89.2%.

The study presents the results of research on the acute toxicity of a fertilizer formulas made of spent coffee ground (SCG) with addition of ash from low-temperature combustion of biomass or ash with an admixture of magnesium sulphate and blood meal. The experimental fertilizer formulas included also rape oil used as a plasticizer for controlling the nutrients release from the fertiliser. Mustard (Sinapis alba L.), oats (Avena sativa sp. L.), cucumber (Cucumis sativus L.) and cress (Lepidium sativum L.) were used as test plants species in the experiment. The toxicity tests were performed using a standard procedure of 72 h with the use of Phytotoxkit microbiotest and fertilizer application of 2.5; 5 and 10% (v/v). The obtained results indicated an increase of acute toxicity for all tested plant species, proportionally to the applied doses of the fertilizer. During the 72 h period, the strongest inhibition of seedling growth was recorded in samples consisting of 10% of the tested fertilizers, particularly when they showed considerable level of salinity or low pH values. From the tested plant species, cress (Lepidium sativum L.) turned out to be the most sensitive to the applied fertilizers, the least was cucumber (Cucumis sativus L.) for which only a small inhibition of root system growth was observed. The inhibited growth of roots could be attributed to a reduced oxygen access and excessive salinity of the substratum caused by the applied additives.

This study explored the physicochemical properties of low-moisture meat analogs supplemented with spent coffee grounds (SCGs). A base mixture comprising 50% soy protein isolate, 40% wheat gluten, and 10% corn starch was prepared, with SCGs added at levels of 0, 5, and 10% relative to the weight of the prepared base mixture. The extrusion process parameters were set at a feed rate of 100 g/min, moisture content of 35%, and screw speed of 200 rpm. As the SCGs content increased, the porous structure of the meat analogs decreased, resulting in reduced water-holding capacity. Higher levels of SCGs resulted in increased browning and enhanced antioxidant activities, as measured by DPPH and ABTS assays, which were positively correlated with SCGs content. Texture analysis revealed that SCGs supplementation enhanced chewiness and cutting strength, as well as increased the texturization degree, while no significant differences were observed in the integrity index between samples. Nitrogen solubility index (NSI) decreased with increasing SCGs content. Sensory evaluation indicated that the addition of SCGs did not diminish the flavor or appearance scores compared to conventional meat products. These findings suggest that SCGs can be utilized as a functional ingredient in meat analogs, adding value to an otherwise discarded byproduct while contributing to environmental sustainability by reducing SCGs.

Spent coffee grounds (SCGs), a globally abundant by-product of the coffee industry, represent a significant source of lignocellulosic biomass with considerable valorization potential. Rich in organic compounds, lipids, and antioxidants, SCGs are increasingly recognized as a sustainable feedstock for energy, materials, and environmental applications within a circular bioeconomy framework. This review critically examines recent advances in SCG valorization via thermochemical, biochemical, and material-based pathways. The review focuses on the conversion of SCGs into biofuels (biodiesel, bioethanol, biogas, and bio-oil), activated carbon for water and air purification, biodegradable polymers, and soil-enhancing amendments. Comparative analyses of process conditions, product yields, and techno-economic feasibility are provided through summarized tables. Although laboratory-scale studies demonstrate promising outcomes, challenges persist in terms of process scalability, environmental impacts, feedstock variability, and lack of regulatory standardization. Furthermore, comprehensive life cycle assessments and policy integration remain underdeveloped. By merging all findings, this review identifies key knowledge gaps and outlines strategic directions for future research, including the development of integrated valorization platforms, hybrid conversion systems, and industrial-scale implementation. The findings support the role of SCG valorization in advancing sustainable resource management and contribute directly to the achievement of multiple Sustainable Development Goals.

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 as a source of smart biochelates to increase Fe and Zn levels in lettuces

The agroindustry generates substantial quantities of byproducts, particularly in coffee production, which yields significant waste, most notably spent coffee grounds (SCGs). This study explores the potential of SCGs as a versatile resource for applications in both food and nonfood sectors. A comprehensive chemical analysis revealed that SCGs consist of 30.2 wt.% cellulose, 25 wt.% hemicellulose, and 12 wt.% lignin. Morphological characterization was performed using field emission scanning electron microscopy (FESEM). Additional analyses included attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR) and thermogravimetric analysis (TGA). ATR-FTIR identified key polysaccharides and oils, whereas TGA offered insights into the thermal degradation behavior of SCGs, confirming the presence of typical plant cell wall components. X-ray diffraction (XRD) patterns revealed low crystallinity, consistent with SCGs' amorphous structure. Mineral content was assessed using inductively coupled plasma atomic emission spectrometry (ICP-AES) and atomic absorption spectrophotometry (AAS). The results showed that mineral concentrations in SCGs (per 0.01 kg) were within recommended daily intake limits, confirming their safety for potential human consumption. These findings establish SCGs as a valuable lignocellulosic biomass with applications in composite materials. Additionally, it can serve as an organic soil amendment after fermentation to prevent stress on plants. This approach supports effective waste management and advances resource sustainability practices in the agro-industrial sector.

Coffee ranks as the second most consumed beverage globally, and its popularity is associated with the growing accumulation of spent coffee grounds (SCG), a by-product that, if not managed properly, constitutes a serious ecological problem. Analyses of SCG have repeatedly shown that they are a source of substances with antioxidant and antimicrobial properties. In this study, we assessed SCG as a substrate for the production of edible/biodegradable films. The κ-carrageenan was utilized as a base polymer and the emulsified SCG oil as a filler. The oil pressed from a blend of Robusta and Arabica coffee had the best quality and the highest antioxidant properties; therefore, it was used for film production. The film-forming solution was prepared by dissolving κ-carrageenan in distilled water at 50 °C, adding the emulsified SCG oil, and homogenizing. This solution was cast onto Petri dishes and dried at room temperature. Chemical characterization showed that SCG increased the level of polyphenols in the films and the antioxidant properties, according to the CUPRAC assay (CC1 23.90 ± 1.23 µmol/g). SCG performed as a good plasticizer for κ-carrageenan and enhanced the elongation at the break of the films, compared with the control samples. The solubility of all SCG films reached 100%, indicating their biodegradability and edibility. Our results support the application of SCG as an active and easily accessible compound for the food packaging industry.

Co-pyrolysis of paper mill sludge and spend coffee ground using CO2 as reaction medium

Coffee is one of the most widely consumed beverages worldwide, and spent coffee grounds (SCG) are the most abundant byproduct of the global coffee industry. Valorizing SCG contributes to ecological sustainability while at the same time providing economic advantages to the foodservice sector. Cocoa, although a preferred flavoring ingredient among consumers, presents drawbacks such as unreliable supply, high cost, and the presence of potentially toxic compounds. This study explores the potential of SCG as a sustainable alternative to cocoa in muffin formulations by analyzing its physicochemical properties and conducting a consumer sensory evaluation with 135 panelists. The most relevant improving advantages of SCG compared to cocoa powder are more fiber, a higher antioxidant capacity, and a lower cadmium content. Instrumental analysis of color, texture, and roughness indicated significant differences between SCG and cocoa muffins, influenced by their different chemical compositions. However, replacing SCG in cocoa muffins is feasible as results from the sensory analysis revealed no statistically significant differences between muffins made with SCG and those made with cocoa on preference and across key attributes, including appearance, flavor, texture, graininess, and bitterness. As expected, muffins with SCG showed a significantly higher score for coffee flavor but a comparable perception of cocoa flavor, despite lacking cocoa in the muffin formulation. These findings underscore the potential of SCG as a viable and sustainable cocoa-replacing flavoring ingredient in baked goods, supporting improved nutritional value, reduced unhealthy cadmium consumption, waste reduction, and product innovation in the food industry.

Eisenia andrei is considered in OECD and ISO guidelines to be a suitable replacement for Eisenia fetida in ecotoxicological assays. This suggests that other alternative materials and methods could also be used in standard procedures for toxicity testing. The guidelines also favor using less time-consuming procedures and reducing costs and other limitations to ecotoxicological assessments. In recent years, spent coffee grounds (SCG) have been used to produce vermicompost and biochar and as an additive to organic fertilizers. In addition, the physicochemical characteristics of SCG indicate that the material is a suitable substrate for earthworms, with the organisms performing as well as in natural soil. In the present study, a battery of ecotoxicological tests was established with unwashed and washed SCG and a natural reference soil (LUFA 2.2). The test substrates were spiked with different concentrations of silver nitrate. Survival and reproduction of the earthworm E. andrei were assessed under different conditions, along with substrate basal respiration (SBR) as a proxy for microbial activity. Seedling emergence and the germination index of Lepidium sativum were also determined, following standard guidelines. Exposure to silver nitrate had similar effects on earthworm survival and reproduction, as the estimated effective concentrations (EC10 and EC50) in unwashed SCG and LUFA 2.2 overlapped. A hormetic effect was observed for SBR in LUFA 2.2 spiked with 12.8 mg/kg but not in unwashed SCG. Both SBR and root development were inhibited by similar concentrations of silver nitrate in washed SCG. The findings indicate that unwashed SCG could potentially be used as a substrate in E. andrei toxicity tests and support the eventual inclusion of this material in the standard guidelines.Supplementary InformationThe online version contains supplementary material available at 10.1007/s11356-024-32297-y.