Production of antioxidants and other value-added compounds from coffee silverskin via pyrolysis under a biorefinery approach

Coffee Silverskin as a Potential Ingredient for Functional Foods: Recent Advances and a Case Study with Chocolate Cake

Coffee silverskin (CS) is a by-product of the coffee roasting process that is known for its potential as a fiber source with antioxidant properties. Therefore, this study aimed to provide an overview of the latest research on CS as a potential ingredient for functional foods and to evaluate the effect of adding different amounts of CS on the functional and sensory attributes of chocolate cakes. The addition of CS increased the total dietary fiber content, antioxidant capacity and the contents of extractable and non-extractable phenolics in the cakes. The evaluated sensory attributes were color, smell, taste, texture and overall impression, and they were evaluated according to a 9-point hedonic scale. Internal preference maps were obtained based on the results from acceptance and "intention to buy" tests. In general, the cakes with lower coffee silverskin content (2.6% and 3.6%) had a similar level of acceptance and the cake with 4.6% coffee silverskin content was the least accepted. The most important attributes were taste and overall impression, corresponding to "like slightly" and "like moderately" for the cakes that had better acceptance. Nonetheless, even with the lowest amount of added CS (2.6%), the produced cakes could be regarded as antioxidant fiber sources (with fiber content above 3 g/100 g), thus confirming the potential of CS as a functional food additive.

A Green Treatment Mitigates the Limitations of Coffee Silver Skin as a Filler for PLA/PBSA Compatibilized Biocomposites

The development of fully renewable and biodegradable composites for short-term applications was pursued by combining a compatibilized poly(lactic acid) (PLA)/poly(butylene succinate-co-adipate) (PBSA) (60:40 wt:wt) blend with coffee silver skin (CSS), an industrial byproduct from coffee processing. An epoxy-based reactive agent (Joncryl ADR-4468) was added as a compatibilizer. CSS was incorporated at 5, 10, and 20 wt% in the blend both in the as-received state and after a simple thermal treatment in boiling water, which was performed to mitigate the negative impact of this filler on the rheological and mechanical properties of the blend. The CSS treatment effectively increased the filler degradation temperature of 30-40 °C, enabling stable melt processing of the composites. It also improved filler-matrix adhesion, resulting in enhanced impact properties (up to +172% increase in impact energy compared to the untreated filler). Therefore, treated CSS demonstrated potential as an effective green reinforcement for PLA/PBSA blends for rigid packaging applications. Future works will focus on studying suitable surface modification of CSS to further increase the interfacial interaction and the tensile quasi-static properties, to fully exploit the capabilities of this renewable material toward the development of eco-friendly composites.

Dialysis and column chromatography for biomass pyrolysis liquids separation

In the current study, a novel approach for separating value-added chemicals from pine wood residues' pyrolysis liquids (bio-oil) was effectively carried out. It combined two separation techniques used for the first time in this field: dialysis with water, methanol and acetone, and column chromatography with Amberlite™ XAD7 resin. This strategy made it possible to separate bio-oil into four fractions: (1) pyrolytic lignin, which can be utilized in the synthesis of resins, foams, electrodes, asphalt, etc. (2) acid-rich fraction, with particular relevance to the chemical industry, (3) antioxidant fraction, containing phenolic compounds, with a lot of interest for pharmaceutical and nutraceutical industry, and (4) a final fraction containing the most non-polar chemicals from bio-oil. Thus, it was possible to develop a process that allows the obtention of bioproducts from woody biomass, a residue obtained in significant quantities in the management of non-profitable forests, making a step forward within the context of circular economy and bioeconomy.

Optimization of Major Extraction Variables to Improve Recovery of Anthocyanins from Elderberry by Response Surface Methodology

Elderberry, which is well known for its richness in anthocyanin, is attracting attention in the bioindustry as a functional material with high antioxidant capacity. The aim of this study is to optimize extraction conditions to more effectively recover anthocyanins from elderberry. In a fundamental experiment to determine the suitable solvent, various GRAS reagents, such as acetone, ethanol, ethyl acetate, hexane, and isopropyl alcohol, were used, and total phenol and anthocyanin contents were detected as 9.0 mg/g-biomass and 5.1 mg/g-biomass, respectively, only in the extraction using ethanol. Therefore, ethanol was selected as the extraction solvent, and an experimental design was performed to derive a response surface model with temperature, time, and EtOH concentration as the main variables. The optimal conditions for maximal anthocyanin recovery were determined to be 20.0 °C, 15.0 min, and 40.9% ethanol, and the total anthocyanin content was 21.0 mg/g-biomass. In addition, the total phenol and flavonoid contents were detected as 67.4 mg/g-biomass and 43.8 mg/g-biomass, respectively. The very simple and economical extraction conditions suggested in this study contributed to improving the utilization potential of anthocyanin, a useful antioxidant derived from elderberry.

Advances in Production of Hydroxycinnamoyl-Quinic Acids: From Natural Sources to Biotechnology

Hydroxycinnamoyl-quinic acids (HCQAs) are polyphenol esters formed of hydroxycinnamic acids and (-)-quinic acid. They are naturally synthesized by plants and some micro-organisms. The ester of caffeic acid and quinic acid, the chlorogenic acid, is an intermediate of lignin biosynthesis. HCQAs are biologically active dietary compounds exhibiting several important therapeutic properties, including antioxidant, antimicrobial, anti-inflammatory, neuroprotective, and other activities. They can also be used in the synthesis of nanoparticles or drugs. However, extraction of these compounds from biomass is a complex process and their synthesis requires costly precursors, limiting the industrial production and availability of a wider variety of HCQAs. The recently emerged production through the bioconversion is still in an early stage of development. In this paper, we discuss existing and potential future strategies for production of HCQAs.

Combined Pulsed Electric Field and Microwave-Assisted Extraction as a Green Method for the Recovery of Antioxidant Compounds with Electroactive Potential from Coffee Agro-Waste

Coffee agro-waste is a potential source of polyphenols with antioxidant activity and application in the food and cosmetic trades. The usage of these byproducts persists as a challenge in the industrial landscape due to their high content of purported toxic substances hindering management. This study presents a green extractive process using pulsed electric field (PEF) and microwave assisted extraction (MAE) to recover polyphenols from coffee parchment and two varieties of pulp, posing quick processing times and the use of water as the only solvent. The performance of this process with regard to the bioactivity was assessed through the Folin-Ciocalteu assay, total flavonoid content, DPPH, ABTS and FRAP antioxidant tests. The phenolic composition of the extracts was also determined through HPLC-MS and quantified through HPLC-DAD. When compared to treatment controls, PEF + MAE treated samples presented enhanced yields of total phenolic content and radical scavenging activity in all analyzed residues (Tukey test significance: 95%). The chromatographic studies reveal the presence of caffeic acid on the three analyzed by-products. The HPLC-DAD caffeic acid quantification validated that a combination of MAE + PEF treatment in yellow coffee pulp had the highest caffeic acid concentration of all studied extraction methods.

Nanoporous Carbon Electrodes Derived from Coffee Side Streams for Supercapacitors in Aqueous Electrolytes

Coffee, as one of the most traded resources, generates a vast amount of biogenic by-products. Coffee silver skins (CSS), a side stream from the roasting process, account for about 4 wt.%. Despite the abundancy of CSS, possible routes to generate added value for broad applications are limited. Herein, we present an approach to use CSS as a precursor material for supercapacitor electrodes. KOH activated carbon (AC) was produced from CSS. The resulting AC—CSS was characterized by X-ray diffraction, gas sorption analysis, scanning electron microscopy, and Raman spectroscopy. The highly porous AC—CSS exposes a specific surface area of more than 2500 m² g⁻¹. Electrodes formed with AC—CSS were electrochemically characterized by performing cyclic voltammetry and galvanostatic cycling. The electrodes were further assembled into a supercapacitor device and operated using 1 M sulfuric acid as electrolyte. In addition, various quinones were added to the electrolyte and their impact on the capacitance of AC—CSS electrodes was analyzed. In this work, we were able to show that CSS are a valuable source for supercapacitor applications and that coffee-waste-derived quinones can act as capacitance enhancers. Thus, the findings of this research show a valuable path towards sustainable and green energy storage solutions.

The effect of reactor scale on biochars and pyrolysis liquids from slow pyrolysis of coffee silverskin, grape pomace and olive mill waste, in auger reactors

Several studies have addressed the potential biorefinery, through small-scale pyrolysis, of coffee silverskin (CSS), grape pomace (GP) and olive mill waste (OMW), which are respectively the main solid residues from coffee roasting, wine making and olive oil production processes. However, increasing the scale of reactor to bring these studies to an industrial level may affect the properties, and hence applications, of the resulting products. The aim of this study is therefore to perform pilot scale experiments to compare and verify the results of analytical study (TGA) and bench scale reactor runs, in order to understand the fundamental differences and create correlations between pyrolysis runs at different scales. To this end, pyrolysis liquids and biochars from the slow pyrolysis of CSS, GP and OMW, performed using different scale auger reactors (15 kg/h and 0.3 kg/h), have been analysed (TGA, pH, density, proximate and ultimate analyses, HHV, FTIR, GCMS) and compared. The results showed no major differences in biochars when the temperature and the solid residence time were fixed. However, regarding pyrolysis liquids, compounds from the lab reactor were more degraded than pilot plant ones, due to, in this case, the vapour residence time was longer. Regarding the properties of the pyrolysis products, GP 400 °C biochars showed the best properties for combustion; CSS biochars were especially rich in nitrogen, and 400 °C GP and OMW pyrolysis liquids showed the highest number of phenolics. Hence, this study is considered a first step towards industrial scale CSS, GP and OMW pyrolysis-based biorefinery.

Coffee silverskin: Characterization of B-vitamins, macronutrients, minerals and phytosterols

The present study assessed the nutritional composition of coffee silverskin (CSS) obtained from arabica roasted coffee. Following validated analytical methods, CSS resulted to be a high source of proteins (14.2 g/100 g) and dietary fibers (51.5 g/100 g). Moreover, the mineral analysis revealed high contents of calcium (1.1 g/100 g) and potassium (1.0 g/100 g). To date, this study provided the widest mineral profile of CSS with 30 minerals targeted including 23 microminerals with high levels of iron (238.0 mg/kg), manganese (46.7 mg/kg), copper (37.9 mg/kg), and zinc (31.9 mg/kg). Moreover, vitamins B2 (0.18-0.2 mg/kg) and B3 (2.5-3.1 mg/kg) were studied and reported for the first time in CSS. β-sitosterol (77.1 mg/kg), campesterol, stigmasterol, and Δ5-avenasterol, were also observed from the phytosterol analysis of CSS with a total level of 98.4 mg/kg. This rich nutritional profile highlights the potential values of CSS for innovative reuses in bioactive ingredients development.