Review on utilization and composition of coffee silverskin

Sustainable Valorization of Coffee Silverskin: Extraction of Phenolic Compounds and Proteins for Enzymatic Production of Bioactive Peptides

Coffee silverskin (CS), a by-product of the coffee roasting process, has high protein content (16.2-19.0%, w/w), making it a potential source for plant protein and bioactive peptide production. This study aims to develop innovative extraction methods for phenolic compounds and proteins from CS. The conditions for hydrothermal (HT) extraction of phenolic compounds from CS were optimized by varying CS loading (2.5-10%, w/v), temperature (110-130 °C), and time (5-30 min) using a one-factor-at-a-time (OFAT) approach. The highest TPC of 55.59 ± 0.12 µmole GAE/g CS was achieved at 5.0% (w/v) CS loading and autoclaving at 125 °C for 25 min. Following hydrothermal extraction, CS protein was extracted from HT-extracted solid fraction by microwave-assisted alkaline extraction (MAE) using 0.2 M NaOH at 90 W for 2 min, resulting in a protein recovery of 12.19 ± 0.39 mg/g CS. The CS protein was then subjected to enzymatic hydrolysis using protease from Bacillus halodurans SE5 (protease_SE5). Protease_SE5-derived CS protein hydrolysate had a peptide concentration of 0.73 ± 0.09 mg/mL, with ABTS, DPPH, and FRAP values of 15.71 ± 0.10, 16.63 ± 0.061, and 6.48 ± 0.01 µmole TE/mL, respectively. Peptide identification by LC-MS/MS revealed several promising biological activities without toxicity or allergenicity concerns. This study's integrated approach offers a sustainable and efficient method for extracting valuable compounds from CS, with potential applications in the food and pharmaceutical industries.

Evaluation of Growth Performance and Environmental Impact of Hermetia illucens Larvae Reared on Coffee Silverskins Enriched with Schizochytrium limacinum or Isochrysis galbana Microalgae

Hermetia illucens is a promising insect due to its ability to convert low-value substrates as food chain by-products into highly nutritious feed. Its feeding and nutrition are important issues. The aim of this work was to investigate the effect of different substrates consisting of coffee silverskin, a by-product of the roasting process, enriched with different inclusions of microalgae (5%, 10%, 20%, and 25%), Schizochytrium limacinum, and Isochrysis galbana, combined with the assessment of environmental sustainability by LCA. In general, the addition of microalgae led to an increase in larval growth performance due to the higher content of protein and lipids, although S. limacinum showed the best results with respect to larvae fed with coffee silverskin enriched with I. galbana. A higher prepupal weight was observed in larvae fed with 10%, 20%, and 25% S. limacinum; shorter development times in larvae fed with 25% of both S. limacinum and I. galbana; and a higher growth rate in larvae fed with 25% S. limacinum. The 10% S. limacinum inclusion was only slightly different from the higher inclusions. Furthermore, 10% of S. limacinum achieved the best waste reduction index. The greater the inclusion of microalgae, the greater the environmental impact of larval production. Therefore, the addition of 10% S. limacinum appears to be the best compromise for larval rearing, especially considering that a higher inclusion of microalgae did not yield additional benefits in terms of the nutritional value of H. illucens prepupae.

Biocomposites of Cellulose Isolated from Coffee Processing By-Products and Incorporation in Poly(Butylene Adipate-Co-Terephthalate) (PBAT) Matrix: An Overview

With its extensive production and consumption, the coffee industry generates significant amounts of lignocellulosic waste. This waste, primarily comprising coffee biomasses, is a potential source of cellulose. This cellulose can be extracted and utilized as a reinforcing agent in various biocomposites with polymer matrices, thereby creating high-value products. One such biodegradable polymer, Poly(butylene adipate-co-terephthalate) (PBAT), is notable for its properties that are comparable with low-density polyethylene, making it an excellent candidate for packaging applications. However, the wider adoption of PBAT is hindered by its relatively high cost and lower thermomechanical properties compared with conventional, non-biodegradable polymers. By reinforcing PBAT-based biocomposites with cellulose, it is possible to enhance their thermomechanical strength, as well as improve their water vapor and oxygen barrier capabilities, surpassing those of pure PBAT. Consequently, this study aims to provide a comprehensive review of the latest processing techniques for deriving cellulose from the coffee industry's lignocellulosic by-products and other coffee-related agro-industrial wastes. It also focuses on the preparation and characterization of cellulose-reinforced PBAT biocomposites.

Influence of maturation and roasting on the quality and chemical composition of new conilon coffee cultivar by chemometrics

Coffee is one of the most consumed beverages worldwide. Espírito Santo is the largest Brazilian producer of conilon coffee, and invested in the creation of new cultivars, such as "Conquista ES8152", launched in 2019. Therefore, the present study aimed to evaluate the effects of maturation and roasting on the chemical and sensorial composition of the new conilon coffee cultivar "Conquista ES8152". The coffee was harvested containing 3 different percentages of ripe fruits: 60%, 80%, and 100%, and roasted at 3 different degrees of roasting: light, medium, and dark, to evaluate the moisture and ash content, yield of soluble extract, volatile compound profile, chlorogenic acid and caffeine content, and sensory profile. "Conquista ES8152" coffee has a moisture content between 1.38 and 2.62%; ash between 4.34 and 4.72%; and yield between 30.7 and 35.8%. Sensory scores ranged between 75 and 80 and the majority of volatile compounds belong to the pyrazine, phenol, furan, and pyrrole groups. The content of total chlorogenic acids was drastically reduced by roasting, with values between 2.40 and 9.33%, with 3-caffeoylquinic acid being the majority. Caffeine was not influenced by either maturation or roasting, with values between 2.16 and 2.41%. The volatile compounds furfural, 5-methylfurfural, and 2-ethyl-5-methylpyrazine were positively correlated with the evaluated sensory attributes and 5-methylfurfural was the only one significantly correlated with all attributes. Ethylpyrazine, furfuryl acetate, 1-furfurylpyrrole, 4-ethyl-2-methoxyphenol, and difurfuryl ether were negatively correlated. The stripping did not affect the quality and composition of this new cultivar, however, the roasting caused changes in both the chemical and sensorial profiles, appropriately indicated by the principal component analysis.

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.

Production of Cellulosic Microfibers from Coffee Pulp via Alkaline Treatment, Bleaching and Acid Hydrolysis

The present work deals with the production of cellulosic microfibers (CMFs) from coffee pulp. The experimental development corresponds to an experimental design of three variables (concentration, temperature and time) of alkaline treatment for delignification, finding that concentration, temperature and time were the most representative variables. Higher delignification was achieved by bleaching cellulosic fibers, followed by acid hydrolysis, thus producing cellulosic fibers with an average diameter of 5.2 µm, which was confirmed using scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS). An X-ray diffraction (XRD) analysis revealed, via the crystallinity index, the presence of Type I cellulose and removal of lignocellulosic compounds through chemical treatments. The proximate chemical analysis (PChA) of coffee pulp helped to identify 17% of the crude fiber corresponding to the plant cell wall consisting of lignocellulosic compounds. The initial cellulose content of 26.06% increased gradually to 48.74% with the alkaline treatment, to 57.5% with bleaching, and to 64.7% with acid hydrolysis. These results attested to the rich cellulosic content in the coffee pulp.

Coffee Silverskin Phytocompounds as a Novel Anti-Aging Functional Food: A Pharmacoinformatic Approach Combined with In Vitro Study

Coffee became a beverage that was in demand in the world and consequently produced millions of tons of coffee byproducts namely coffee silverskin (CS). Unutilized CS will be waste and cause environmental pollution such as greenhouse gas emissions, landfill waste, and groundwater contamination. This is a research concern at this time, although many studies have been conducted to find newer applications of CS, exploration of its benefits in the health sector is still limited. Therefore, exploring the benefits of CS to prevent or delay aging will be very interesting to develop in functional food industry technology. Therefore, this study aims to report profiling metabolites or phytochemicals, biological activities in terms of antioxidant activity, and potential anti-aging of CS via molecular docking simulation and in vitro modulation of the mTOR/AMPK/SIRT1 pathway. Something new has been obtained from this work, the profile of phytocompounds, and biological activities both in molecular docking simulation and in vitro studies. Some of the compounds observed in Robusta CS extract (rCSE) such as Epicatechin, Kaempferol, and Quercitrin, and Arabica CS extract (aCSE) such as (+)-Catechin dan Naringin have promising potential as inhibitors of iNOS, mTOR, and HIF-1α via molecular docking simulation. Interestingly, the in vitro biological activity assay of antioxidant and anti-aging activity, rCSE showed the same promising potential as the results of a molecular docking simulation. More interestingly, AMPK/SIRT1/mTOR expressions are well modulated by rCSE compared to aCSE significantly (p < 0.05). This makes the rCSE have promising biological activity as a candidate for functional food development and/or treatment agent in combating free radicals that cause the aging process. In vivo studies and human trials are certainly needed to see the further efficacy of the rCSE in the future.

Optimization and kinetics modeling of phenolics extraction from coffee silverskin in deep eutectic solvent using ultrasound-assisted extraction

This research investigates the effect of extraction parameters on total phenolic content (TPC) and the antioxidant capacity of coffee silverskin (CS) extract using ultrasound-assisted extraction (UAE) in deep eutectic solvent (DES). The optimization was carried out in two stages: (i) the optimization of the UAE condition with the highest TPC; and (ii) a four-factor Box-Behnken design (BBD) to optimize the UAE condition with the optimal TPC; 2,2 diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity; and ferric reducing antioxidant power (FRAP). The results showed that the optimal UAE condition with the highest TPC was 150-250 μm CS particle size; 1,6-hexanediol as hydrogen bond donor (HBD); 1:7 HBA:HBD molar ratio; and 30% (w/w) water content, given choline chloride (ChCl) as hydrogen bond acceptor (HBA), 30 min extraction time and 30 ° C extraction temperature. The BBD-based optimal UAE condition was 30% w/w water content, 45 mL/g liquid/solid ratio, 90 min extraction time and 85 ° C extraction temperature, given the CS particle size of 150-250 μm and the HBA:HBD molar ratio of 1 (ChCl): 7 (1,6 hexanediol), achieving 19.19 ± 0.20 mg GAE/g CS for TPC, 24.06 ± 1.77 mg TE/g CS for DPPH radical scavenging capacity, and 59.13 ± 4.55 mg Fe (II)/g CS for FRAP. The experimental results were in good agreement with the BBD-based predicted results (22.40 mg GAE/g CS for TPC, 24.09 mg TE/g CS for DPPH, and 59.43 mg Fe(II)/g CS for FRAP). The two-site kinetics model best fitted the experimental data, with R² of 0.991-0.999.

Coffee Silver Skin-Health Safety, Nutritional Value, and Microwave Extraction of Proteins

The aim of this research was to evaluate the health safety (concentrations of pesticide residues and heavy metals) and nutritional parameters (macro- and microminerals and crude fibre) of coffee silver skin (CS), as well to isolate proteins from this by-product using an optimised microwave extraction method. The CS by-product samples showed the highest amount of potassium, followed by calcium, magnesium, and sodium. Iron was found in the highest quantity among the microminerals, followed by copper, manganese, zinc, and chromium. The CS sample showed a large amount of fibre and a moderate quantity of proteins obtained by the optimised microwave extraction method. Four heavy metals (nickel, lead, arsenic, and cadmium) were detected, and all were under the permitted levels. Among the 265 analysed pesticides, only three showed small quantity. The results for the proteins extracted by microwave showed that the total protein concentration values ranged from 0.52 ± 0.01 mg/L to 0.77 ± 0.07 mg/L. The highest value of the concentration of total proteins (0.77 ± 0.07 mg/L) was found in the sample treated for 9 min, using a power of 200 W. Based on these results, it can be concluded that CS is a healthy and nutritionally rich nutraceutical that could be used in the production of new products in the food industry and other industries.

Effects of Species, Post-Harvest Treatment, and Roasting on Fibre, Volatile Compounds, and Polyphenol Contents in Coffee Silverskin

Although coffee silverskin (CS) has recently been used as a food ingredient, no knowledge has been reported on the effects of species or different post-harvest treatments on its chemical composition. Therefore, the fibre, volatile compounds, phenolic acid content, and antioxidant capacity of CS samples obtained at three roasting intensities (light, medium, and dark) from the Coffea arabica and C. canephora species, each subjected to a washing or a sun-drying (“natural”) post-harvest treatment, were studied. Obtained results showed that the chemical composition of CS is due to species, roasting, post-harvest treatment, and interaction. In particular, natural Arabica CS showed the highest content of volatile compounds of Maillard and varietal origin, whereas washed Arabica CS showed the highest content of soluble dietary fibre and chlorogenic derivatives. Pyrroles, sulphur compounds, and pyridines contents were higher in Canephora CS than in Arabica CS. The dark-roasted washed Arabica CS showed the highest content of 5-O- and 3-O-caffeoylquinic acids, while the natural Arabica CS highlighted the highest antioxidant capacity. The effect of post-harvest treatments seemed to be emphasised in Arabica CS, independent of roasting, which did not significantly affect the antioxidant capacity of CS from either species.

Coffee Silverskin: Chemical and Biological Risk Assessment and Health Profile for Its Potential Use in Functional Foods

The coffee supply chain is characterized by a complex network with many critical and unsustainable points producing a huge amount of waste products. Among these, coffee silverskin (CS), the only by-product of the coffee roasting phase, has an interesting chemical profile that suggests potential use as a food ingredient. However, few data on its safety are available. For this reason, the purpose of the study was to assess the occurrence of chemical and biological contaminants in CS, and the resulting risk due to its potential consumption. Essential, toxic, and rare earth elements, polycyclic aromatic hydrocarbons (PAHs), process contaminants, ochratoxin A (OTA), and pesticides residues were analyzed in three classes of samples (Coffea arabica CS, Coffea robusta CS, and their blend). Furthermore, total mesophilic bacteria count (TMBC) at 30 °C, Enterobacteriaceae, yeasts, and molds was evaluated. The risk assessment was based upon the hazard index (HI) and lifetime cancer risk (LTCR). In all varieties and blends, rare earth elements, pesticides, process contaminants, OTA, and PAHs were not detected except for chrysene, phenanthrene, and fluoranthene, which were reported at low concentrations only in the arabica CS sample. Among essential and toxic elements, As was usually the most representative in all samples. Microorganisms reported a low load, although arabica and robusta CS showed lower contamination than mixed CS. Instead, the risk assessment based on the potential consumption of CS as a food ingredient did not show either non-carcinogenic or carcinogenic risk. Overall, this study provides adequate evidence to support the safety of this by-product for its potential use in functional foods.

Valorization of Coffee Silverskin through Subcritical Water Extraction: An Optimization Based on T-CQA Using Response Surface Methodology

Coffee silverskin (CS) is the only byproduct of the roasting process for coffee beans and is rich in phenolic compounds with various bioactivities. This study proposes a valorization option for bioactive compounds (T-CQA) based on a subcritical water extraction (SWE) technique, which is known for its high efficiency and feasibility for use on an industrial scale. The use of water as a sole solvent requires a minimum number of cleaning steps and renders the extract safe for further applications, such as in either the cosmetic or food industry. Response surface methodology with a Box–Behnken design is effectively used to optimize and explain the individual and interactive process variables (i.e., extraction temperature, extraction time, and solid–liquid ratio) on the T-CQA content obtained from coffee silverskin by the SWE technique. The final model exhibits a precise prediction of the experimental data obtained for the maximum T-CQA content. Under the optimum conditions, the CS extract is found to contain a higher content of T-CQA and TPC than that reported previously. For antioxidant activity, up to 26.12 ± 3.27 mg Trolox equivalent/g CS is obtained.

The wastes of coffee bean processing for utilization in food: a review

A few million cubic tons of waste are generated annually as a result of coffee processing. As a beverage, coffee in itself is a rich source of melanoidins, phenolic compounds, and other phytonutrients which confer a wide range of health benefits. These wastes generated every year are usually discarded as landfill mass, mixed with animal fodder, or incinerated. Coffee wastes, due to their high content of tannins and caffeine, can degrade the soil quality and induce carcinogenicity when mixed with animal fodder. This review aims to identify the potential of coffee silver skin and spent coffee grounds, both generated as a result of the roasting process and instantization processes. Coffee husk and coffee flour are also well-known for their excellent bioactive roles. The proximate composition of coffee silverskin indicates a rich dietary fibre source and finds wide applications in bakery and other allied food products. This process could generate a value-added product and alleviate the disposing quality of remnant spent coffee grounds. Companies are exploring novel ideas of producing coffee flour obtained from drying and milling of coffee cherries for applications in day-to-day food products. Coffee and coffee waste combined with its high concentration of fibre, colorant pigments, and antioxidant compounds, has immense potential as a functional ingredient in food systems and needs to be explored further for its better utilization.

Scientometric Overview of Coffee By-Products and Their Applications

As coffee consumption is on the rise, and the global coffee production creates an excess of 23 million tons of waste per year, a revolutionary transition towards a circular economy via the transformation and valorization of the main by-products from its cultivation and preparation (Coffee Husk (CH), Coffee Pulp (CP), Coffee Silverskin (CS), and Spent Coffee Grounds (SCG)) is inspiring researchers around the world. The recent growth of scholarly publications in the field and the emerging applications of coffee by-products published in these scientific papers encourages a systematic review to identify the knowledge structure, research hotspots, and to discuss the challenges and future directions. This paper displays a comprehensive scientometric analysis based on 108 articles with a high level of influence in the field of coffee by-products and their applications. According to our analysis, the research in this field shows an explosive growth since 2017, clustered in five core applications: bioactive compounds, microbial transformation, environmental applications, biofuels from thermochemical processes, and construction materials.

An Overview of Natural Polymers as Reinforcing Agents for 3D Printing

Three-dimensional (3D) printing, or additive manufacturing, is a group of innovative technologies that are increasingly employed for the production of 3D objects in different fields, including pharmaceutics, engineering, agri-food and medicines. The most processed materials by 3D printing techniques (e.g., fused deposition modelling, FDM; selective laser sintering, SLS; stereolithography, SLA) are polymeric materials since they offer chemical resistance, are low cost and have easy processability. However, one main drawback of using these materials alone (e.g., polylactic acid, PLA) in the manufacturing process is related to the poor mechanical and tensile properties of the final product. To overcome these limitations, fillers can be added to the polymeric matrix during the manufacturing to act as reinforcing agents. These include inorganic or organic materials such as glass, carbon fibers, silicon, ceramic or metals. One emerging approach is the employment of natural polymers (polysaccharides and proteins) as reinforcing agents, which are extracted from plants or obtained from biomasses or agricultural/industrial wastes. The advantages of using these natural materials as fillers for 3D printing are related to their availability together with the possibility of producing printed specimens with a smaller environmental impact and higher biodegradability. Therefore, they represent a “green option” for 3D printing processing, and many studies have been published in the last year to evaluate their ability to improve the mechanical properties of 3D printed objects. The present review provides an overview of the recent literature regarding natural polymers as reinforcing agents for 3D printing.

Extraction and Chemical Characterization of Functional Phenols and Proteins from Coffee (Coffea arabica) By-Products

Not all the coffee produced goes to the roasting stage, because non-compliant green coffee beans are usually discarded by roasters and the silverskin of the coffee is usually removed and discarded. In the present work, non-compliant green coffee beans and coffee silverskins were fully characterized from a chemical point of view. In addition, enzyme-assisted extraction was applied to recover a fraction rich in proteins and polyphenols, tested for antimicrobial, antityrosinase, and antioxidant activities. Non-compliant green coffee beans showed higher amounts of polyphenols, flavanols, flavonoids, and caffeine than coffee silverskins (which were richer in tannins). The enzymatic extraction of non-compliant coffee green beans produced extracts with a good protein content and with a consistent quantity of polyphenols. The extract showed antioxidant, antityrosinase, and antimicrobial activity, thus representing a promising strategy to recover defective green coffee beans. The antioxidant and antimicrobial activity of coffee silver skins is lower than that of non-compliant coffee green beans extracts, while the antityrosinase activity is comparable.

The Role of Coffee Silver Skin against Oxidative Phenomena in Newly Formulated Chicken Meat Burgers after Cooking

Coffee Silver Skin (CSS) is the unique by-product discarded after the roasting of coffee beans. This research aimed to evaluate the effect of two levels of CSS (1.5% and 3%) added as a natural ingredient in new formulations of chicken meat burgers. This is one of the first studies proposing a "formulation approach" to control the emergence of off flavours after meat cooking. Physical, chemical, and sensory analyses were carried out, within the CSS content and the evolution of volatile organic compounds in different samples. Newly formulated chicken burgers could limit food waste, while also becoming a source of fibres, minerals, and bioactive molecules. CSS limited weight losses (after cooking process) to 10.50% (1.5% addition) and 11.05% (3% addition), significantly lower (p < 0.01) than the control (23.85%). In cooked burgers, the occurrence of hexanal was reduced from 55.1% (CTRL T₀) to 11.7% (CSS T₀ 1.5%) to 0 (CSS T₀ 3%). As for the limitation of off-flavours, CSS also showed good activity, contrasting with the emergence of octanal, alcohols and other markers of lipid oxidation. From the sensory test carried out, the volatile profile of CSS does not seem to impair the flavour of burgers, though at higher percentages hydrocarbons and pyrazines are traceable. The thiobarbituric acid reactive substances (TBARS assay confirmed the protective effect of CSS against oxidation.

Coffee Silver Skin: Chemical Characterization with Special Consideration of Dietary Fiber and Heat-Induced Contaminants

Coffee silver skin is produced in large amounts as a by-product during the coffee roasting process. In this study, coffee silver skin of the species Coffea arabica L. and Coffea canephora Pierre ex A. Froehner as well as silver skin pellets produced in the coffee industry were characterized with respect to both nutritional value and potential heat-induced contaminants. Enzymatic-gravimetric/chromatographic determination of the dietary fiber content showed values ranging from 59 to 67 g/100 g with a comparably high portion of soluble fiber, whereas low molecular weight soluble fiber was not detected. Compositional and methylation analysis indicated the presence of cellulose and xylans in the insoluble dietary fiber fraction, whereas pectic polysaccharides dominate the soluble dietary fiber fraction. The protein content as determined by the Kjeldahl method was in the range of 18 to 22 g/100 g, and all essential amino acids were present in coffee silver skin; whereas fat contents were low, high ash contents were determined. Elemental analysis by inductively coupled plasma mass spectrometry (ICP-MS) showed the presence of macroelements in large amounts, whereas toxic mineral elements were only detected in trace amounts or being absent. Acrylamide was quantified with levels of 24–161 µg/kg. Although 5-hydroxymethylfurfural was detected, its concentration was below the limit of determination. Furfuryl alcohol was not detected.

Characterization of Coffee Silver Skin as Potential Food-Safe Ingredient

By-products from the coffee industry are produced in large amounts each year. Among other wastes, coffee silver skin (CSS) is highly available and more stable due to its lower content of water. This research aimed to characterize coffee silver skin composition and evidence its potentiality for use as a food-safe ingredient in new formulations. Results showed an average total dietary fiber content of 50% but with a higher ratio for insoluble than soluble fiber. A high content of total phenolic compounds, chlorogenic acid, caffeine, and caffeic acid was found and correlated with the high measured antioxidant capacity. Moreover, minerals (e.g., calcium, magnesium, phosphorous, potassium, copper, iron, manganese) important for human wellbeing were found at a high level in CSS, while toxic minerals (e.g., nickel) were found at low levels. In conclusion, coffee silver skin could have an advantageous role for the recovery of valuable compounds and as a potential food-safe ingredient.

Potential applications of by-products from the coffee industry in polymer technology - Current state and perspectives

Coffee is one of the most popular beverages in the world, and its popularity is continuously growing, which can be expressed by almost doubling production over the last three decades. Cultivation, processing, roasting, and brewing coffee are known for many years. These processes generate significant amounts of by-products since coffee bean stands for around 50% of the coffee cherry. Therefore, considering the current pro-ecological trends, it is essential to develop the utilization methods for the other 50% of the coffee cherry. Among the possibilities, much attention is drawn to polymer chemistry and technology. This industry branch may efficiently consume different types of lignocellulosic materials to use them as fillers for polymer composites or as intermediate sources of particular chemical compounds. Moreover, due to their chemical composition, coffee industry by-products may be used as additives modifying the oxidation resistance, antimicrobial, or antifungal properties of polymeric materials. These issues should be considered especially important in the case of biodegradable polymers, whose popularity is growing over the last years. This paper summarizes the literature reports related to the generation and composition of the coffee industry by-products, as well as the attempts of their incorporation into polymer technology. Moreover, potential directions of research based on the possibilities offered by the coffee industry by-products are presented.

Coffee Silverskin as a Multifunctional Waste Filler for High-Density Polyethylene Green Composites

This work aims to describe the coffee silverskin effect as a lignocellulosic waste filler for high-density polyethylene (HDPE) composites development. The main task was to determine various modification effects resulting from the complex chemical composition of coffee silverskin containing compounds with potential antioxidative properties, including caffeine, polyphenols, tannins, or melanoidins. The processing, thermal, physicochemical, and thermomechanical properties of the HDPE-based composites with different filler content (1–20 wt%) were evaluated. Comprehensively realized thermomechanical analysis revealed the filler’s reinforcing effects on the HDPE matrix while defining problems with obtaining adequate adhesion in the interfacial area. At the same time, studies have shown a very beneficial effect of the silverskin addition on the thermal properties of composites, that even the smallest addition allows for a significant increase in the thermooxidative resistance of HDPE composites assessed using the oxidation induction time from 20 min for HDPE up to 140 min for the composites with 20 wt% of the filler. The obtained research results allow classifying the coffee silverskin waste filler, not only as a filler intended for the production of composites with a high degree of filling but also as an additive that significantly changes the properties of polyethylene in the case of using low concentrations. This can have a very beneficial impact on the development of novel wood polymer (WPC) and natural fiber composites (NFC).

Torrefaction of Coffee Husk Flour for the Development of Injection-Molded Green Composite Pieces of Polylactide with High Sustainability

Coffee husk, a major lignocellulosic waste derived from the coffee industry, was first ground into flour of fine particles of approximately 90 µm and then torrefied at 250 °C to make it more thermally stable and compatible with biopolymers. The resultant torrefied coffee husk flour (TCHF) was thereafter melt-compounded with polylactide (PLA) in contents from 20 to 50 wt% and the extruded green composite pellets were shaped by injection molding into pieces and characterized. Although the incorporation of TCHF reduced the ductility and toughness of PLA, filler contents of 20 wt% successfully yielded pieces with balanced mechanical properties in both tensile and flexural conditions and improved hardness. Contents of up to 30 wt% of TCHF also induced a nucleating effect that favored the formation of crystals of PLA, whereas the thermal degradation of the biopolyester was delayed by more than 7 °C. Furthermore, the PLA/TCHF pieces showed higher thermomechanical resistance and their softening point increased up to nearly 60 °C. Therefore, highly sustainable pieces were developed through the valorization of large amounts of coffee waste subjected to torrefaction. In the Circular Bioeconomy framework, these novel green composites can be used in the design of compostable rigid packaging and food contact disposables.

Characterization of Odor-Active Compounds, Polyphenols, and Fatty Acids in Coffee Silverskin

For the first time the volatile fraction of coffee silverskin has been studied focusing on odor-active compounds detected by gas chromatography-olfactometry/flame ionization detector (GC-O/FID) system. Two approaches, namely headspace (HS) analysis by solid-phase microextraction-gas chromatography-mass spectrometry (SPME-GC-MS) and odor-active compounds analysis by gas chromatography-olfactometry/flame ionization detector (GC-O/FID), have been employed to fully characterize the aroma profile of this by-product. This work also provided an entire characterization of the bioactive compounds present in coffee silverskin, including alkaloids, chlorogenic acids, phenolic acids, flavonoids, and secoiridoids, by using different extraction procedures and high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) system. Coffee silverskin was shown to be a good source of caffeine and chlorogenic acids but also of phenolic acids and flavonoids. In addition, the fatty acid composition of the coffee silverskin was established by GC-FID system. The results from this research could contribute to the development of innovative applications and reuses of coffee silverskin, an interesting resource with a high potential to be tapped by the food and nutraceutical sector, and possibly also in the cosmetics and perfumery.

A Review of Coffee By-Products Including Leaf, Flower, Cherry, Husk, Silver Skin, and Spent Grounds as Novel Foods within the European Union

The coffee plant Coffea spp. offers much more than the well-known drink made from the roasted coffee bean. During its cultivation and production, a wide variety of by-products are accrued, most of which are currently unused, thermally recycled, or used as animal feed. The aim of this review is to provide an overview of novel coffee products in the food sector and their current legal classification in the European Union (EU). For this purpose, we have reviewed the literature on the composition and safety of coffee flowers, leaves, pulp, husk, parchment, green coffee, silver skin, and spent coffee grounds. Some of these products have a history of consumption in Europe (green coffee), while others have already been used as traditional food in non-EU-member countries (coffee leaves, notification currently pending), or an application for authorization as novel food has already been submitted (husks, flour from spent coffee grounds). For the other products, toxicity and/or safety data appear to be lacking, necessitating further studies to fulfill the requirements of novel food applications.

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

The coffee roasting industry produces about 0.4 Mt of coffee silverskin (CSS) per year, the only residue generated from the roasting process that is mostly disposed as industrial waste. The aim of this study is to convert CSS into value-added products by intermediate pyrolysis, transforming the waste into a resource within an integrated biorefinery perspective. To this end, bio-oils and biochars from the intermediate pyrolysis of CSS at 280 °C, 400 °C and 500 °C have been studied. GC-MS analysis showed that bio-oils were composed of value-added products such as caffeine, acetic acid, pyridine and phenolics, the latter being the most interesting due to their antioxidant properties. Total phenolic content and antioxidant capacity of the samples were determined through Folin-Ciocalteu (FC) and DPPH methods, revealing an increase in phenolics in bio-oils compared to CSS extract directly from the feedstock. The bio-oil with the highest phenolic content and antioxidant properties was produced at 280 °C and contained 6.09 and 3.02 mg of gallic acid equivalents /g of bio-oil determined by FC and DPPH methods, respectively. This represents a global potential of up to 487 and 242 tones of gallic acid equivalents per year, considering the FC results and DPPH respectively. The resulting 280 °C biochar presented significant calorific values (22 MJ/kg), indicating its potential use as an energy source. Hence, CSS pyrolysis converts a waste into a by-product and a resource, increasing the environmental benefits and contributing to the circular economy and bioeconomy.

Valorization of agro-industry residues in the building and environmental sector: A review

Environmental pollution has become a relevant issue as the population rises and resources decrease. Reuse and recycling still have the greatest potential as they turn the waste into a new resource, representing the 'closed-loop' step of a circular economy (CE). Looking for new applications for agro-industry waste represents both an environmental issue, as its incorrect disposal is a cause of pollution, and a chance to exploit zero-cost natural wastes. The present review, with around 200 articles examined, focuses on possible reuses of these residues in (a) building construction, as additives to produce thermal and acoustic insulation panels, and (b) in water treatments, exploited for removal of pollutants. The selected materials (coconut, coffee, corn, cotton and rice) have industry production wastes with suitable applications in both sectors and huge worldwide availability; their reuse may thus represent a new resource, with an impact based on the production rate and the possible replacement of current inorganic materials. Along with possible implementation of the selected materials in the building industry and environmental engineering, a brief description of the production and supply chain are provided.

Chemical composition and health properties of coffee and coffee by-products

Coffee can be an ally in the fight against diseases such as type 2 diabetes, cancer, hepatic injury, cirrhosis, depression, suicidal behavior, and neurological and cardiovascular disorders. The properties of coffee also favor gastrointestinal tract and gut microbiota establishment. Coffee bioactive components include phenolic compounds (chlorogenic acids, cafestol and kahweol), alkaloids (caffeine and trigonelin), diterpenes (cafestol and kahweol) and other secondary metabolites. The image of coffee as a super functional food has helped to increase coffee consumption across the globe. This chapter addresses the main health promotion mechanisms associated with coffee consumption. Related topics on coffee production chain, world consumption and reuse of coffee by-products in the production of high-value-adding molecules with potential applications in the food industry are addressed and discussed.

Coffee silverskin as nutraceutical ingredient in yogurt: its effect on functional properties and its bioaccessibility

BACKGROUND

Silverskin is a by-product obtained from coffee roasting. It is characterized by a high content of dietary fibre, phenolic compounds and caffeine. The aim of this study was to assess the silverskin obtained from two species of Coffea (Arabica and Robusta) at three percentages (2%, 4%, or 6%) into cow whole-milk yogurt to raise the nutraceutical value of the products and to verify the bioaccessibility of bioactive compounds during the shelf-life of 3 weeks.

RESULTS

The amount and origin of silverskin significantly influenced all the physicochemical parameters. Concerning the bioactive compounds, the highest levels were observed in yogurt supplemented with 6% of silverskin. Between the coffee species, Arabica yielded the highest 5-caffeoylquinic acid content and the strongest antioxidant activity, whereas Robusta gave the highest caffeine content. The digestion increased antioxidant activity in the yogurt, possibly because of greater accessibility of compounds.

CONCLUSION

The results obtained highlighted that silverskin can be used in yogurt production to increase the nutraceutical value of the products and that the bioactive compounds are bioaccessible during the digestion process. The characteristics and bioaccessibility of the resulting yogurt were strongly correlated with the coffee species and with the percentage added. © 2019 Society of Chemical Industry.

Coffee parchment as a new dietary fiber ingredient: Functional and physiological characterization

Coffee parchment was evaluated as a potential dietary fiber ingredient. For this purpose, dietary fiber was extracted by enzymatic and non-enzymatic methods and its physicochemical and in vitro hypoglycemic and hypolipidemic properties were investigated. Results revealed that coffee parchment (flakes and flour) was a good source of insoluble dietary fiber (IDF), mainly composed by xylans (35%), lignin (32%), and cellulose (12%). From results, the IDF extraction seemed not to be required the use of enzymes. Coffee parchment did not stand out by its content of phenolic compounds and antioxidant capacity, but milling process improved them. Due to its physical structure, coffee parchment flakes exhibited high oil holding capacity (3.8 mg L^-1), gelation capacity (8%) besides hydration properties, including water holding (3.4 mg L^-1), absorption (3.0 mg L^-1) and swelling (14 mg L^-1) capacities. Its flour and water-insoluble residue showed lower capacities. Nevertheless, these coffee parchment samples presented effective in vitro hypoglycemic properties, showing high glucose adsorption capacity (50-200 mmol L^-1), and capacity to decrease its diffusion (13%), and to inhibit α-amylase (52%) that led to lower starch digestibility (until 46%); and also, outstanding in vitro hypolipidemic properties, as inhibition of pancreatic lipase (43%) and binding of cholesterol and sodium cholate (16.6 and 35.3 mg g^-1, respectively). These results provide valuable information for the potential use of coffee parchment as new food DF ingredient.

Coffea canephora silverskin from different geographical origins: A comparative study

Coffee silverskin is the major by-product of coffee roasting. Among all the coffee by-products, it is a relatively stable product due to its low moisture content. Currently, silverskin is used as direct fuel (e.g. firelighters), for composting and soil fertilization. As it is a natural source of several bioactive compounds that can be extracted and further used for food or dermocosmetic purposes, the valorization of this by-product is of utmost importance, having in view the sustainability and circular economy principles. The aim of this work was to evaluate, for the first time, the influence of different geographical origins (Brazil, Uganda, Vietnam, Cameroon, Indonesia, and India) on the chemical composition of silverskin obtained from Coffea canephora beans. Different parameters were analysed, including ashes, protein, soluble and insoluble fiber, and total lipid amounts; vitamin E, fatty acid and phenolics profiles (by HPLC-DAD-FLD, GC-FID, and HPLC-DAD, respectively); caffeine, 5‑caffeoylquinic acid and hydroxymethyfurfural contents (by HPLC-DAD); and antioxidant profile (total phenolics and flavonoids contents, DPPH inhibition, and Ferric Reducing Antioxidant Power). Significant differences (p < 0.05) were found between the samples, especially regarding the fatty acid profile and the antioxidant composition. For instance, the Brazilian silverskin was the richest in total lipids and vitamin E, while the Indian silverskin was the poorest in phenolics and antioxidant activity, and presented a higher relative percentage of saturated fatty acids. A Principal Component Analysis allowed to group the studied samples according to their geographical proximity.

Environmental Impact Associated with the Supply Chain and Production of Grounding and Roasting Coffee through Life Cycle Analysis

Coffee is the beverage resulting from the infusion of roasted and ground seeds of the coffee fruit. It is one of the most commercialized products in the world and represents a high interest agro-industrial product in Mexico. The demand for this product has grown in great measure in the last decade, thus it is becoming more important to make environmental and energetic evaluations of its manufacturing process. In this sense, life cycle assessment (LCA) is a useful tool for the purposes of this study, as it quantifies the wake of environmental impacts associated to the production and supply chain from its inputs and outputs of the product system. Therefore, the impact categories studied were carbon, energetic, and water footprints. The cultivation phase led to global contributions between 61% and 67% in magnitude for energy and carbon footprints, respectively; meanwhile, the coffee benefit process was the phase with the most contributions to the water footprint (54%). The residual biomass from the product system used as the energy supply within the coffee drying sub-phase represented energy savings of around 41% in comparison to the use of conventional fossil fuels, thus reducing the global impact associated to the system’s product.

Biobutanol production from coffee silverskin

BACKGROUND

Coffee silverskin, a by-product from coffee roasting industries, was evaluated as a feedstock for biobutanol production by acetone-butanol-ethanol fermentation. This lignocellulosic biomass contained approximately 30% total carbohydrates and 30% lignin. Coffee silverskin was subjected to autohydrolysis at 170 °C during 20 min, with a biomass-to-solvent ratio of 20%, and a subsequent enzymatic hydrolysis with commercial enzymes in order to release simple sugars. The fermentability of the hydrolysate was assessed with four solventogenic strains from the genus Clostridium. In addition, fermentation conditions were optimised via response surface methodology to improve butanol concentration in the final broth.

RESULTS

The coffee silverskin hydrolysate contained 34.39 ± 2.61 g/L total sugars, which represents a sugar recovery of 34 ± 3%. It was verified that this hydrolysate was fermentable without the need of any detoxification method and that C. beijerinckii CECT 508 was the most efficient strain for butanol production, attaining final values of 4.14 ± 0.21 g/L acetone, 7.02 ± 0.27 g/L butanol and 0.25 ± 0.01 g/L ethanol, consuming 76.5 ± 0.8% sugars and reaching a butanol yield of 0.269 ± 0.008 gB/gS under optimal conditions.

CONCLUSIONS

Coffee silverskin could be an adequate feedstock for butanol production in biorefineries. When working with complex matrices like lignocellulosic biomass, it is essential to select an adequate bacterial strain and to optimize its fermentation conditions (such as pH, temperature or CaCO3 concentration).

The Castanea sativa bur as a new potential ingredient for nutraceutical and cosmetic outcomes: preliminary studies

Chestnuts are a common food product in Mediterranean countries, being recognized also for their beneficial effects on human health. Nevertheless, during processing, these fruits generate a large amount of food by-products, such as shells and burs. In the present work, the macronutrient composition, vitamin E profile and amino acid content of the burs were determined in samples from three different Portuguese regions (Minho, Trás-os-Montes and Beira-Alta). The nutritional composition was similar for all samples, being characterised by a high moisture content and low fat amounts. All essential amino acids were present in considerable amounts. Concerning vitamin E, the predominant vitamer was α-tocopherol for the Minho and Beira-Alta samples. The total phenolic compounds were quantified, and the antioxidant activity evaluated in different extracts using two biochemical assays (DPPH˙ and FRAP). All bur extracts showed a high total phenolic content, the highest obtained being that for the Beira-Alta samples. The chestnut bur from Minho showed the highest antioxidant activity in both assays. This study aims to demonstrate the potential of the Castanea sativa bur as a cosmetic and nutraceutical ingredient.

Coffee Silverskin: A Review on Potential Cosmetic Applications

Coffee silverskin, the major coffee-roasting by-product, is currently used as fuel and for soil fertilization. However, there are several studies reporting silverskin as a good source of bioactive compounds that can be extracted and further used by cosmetic industry. Its high antioxidant potential may be due to the synergistic interaction of chlorogenic acids (1–6%), caffeine (0.8–1.25%), and melanoidins (17–23%), among other antioxidant compounds. The bioactive compounds of silverskin can answer to the new fields of cosmetic industry on natural active ingredient resources that improve health skin appearance, counteract skin aging and related diseases, in an environmentally friendly approach. Skin aging is a complex process associated with oxidative metabolism and reactive oxygen species (ROS) generation. ROS production increase matrix metalloproteinases (MMPs), as well as pro-inflammatory mediators, resulting in consequent skin damage and aging. To counteract this process, cosmetic industry is looking for compounds able to increase MMP inhibitory activities, hyaluronidase inhibitory activity, expression of collagen and elastase inhibitory activity, as potential bioactive ingredients with anti-aging purposes. This review focuses on skin aging factors and the potential anti-aging, anti-inflammatory, antimicrobial, anti-cellulite and anti-hair loss activity, as well as protection against UV damage, of coffee silverskin and their bioactive compounds.

Deep Eutectic Solvents pretreatment of agro-industrial food waste

BACKGROUND

Waste biomass from agro-food industries are a reliable and readily exploitable resource. From the circular economy point of view, direct residues from these industries exploited for production of fuel/chemicals is a winning issue, because it reduces the environmental/cost impact and improves the eco-sustainability of productions.

RESULTS

The present paper reports recent results of deep eutectic solvent (DES) pretreatment on a selected group of the agro-industrial food wastes (AFWs) produced in Europe. In particular, apple residues, potato peels, coffee silverskin, and brewer's spent grains were pretreated with two DESs, (choline chloride-glycerol and choline chloride-ethylene glycol) for fermentable sugar production. Pretreated biomass was enzymatic digested by commercial enzymes to produce fermentable sugars. Operating conditions of the DES pretreatment were changed in wide intervals. The solid to solvent ratio ranged between 1:8 and 1:32, and the temperature between 60 and 150 °C. The DES reaction time was set at 3 h. Optimal operating conditions were: 3 h pretreatment with choline chloride-glycerol at 1:16 biomass to solvent ratio and 115 °C. Moreover, to assess the expected European amount of fermentable sugars from the investigated AFWs, a market analysis was carried out. The overall sugar production was about 217 kt yr^-1, whose main fraction was from the hydrolysis of BSGs pretreated with choline chloride-glycerol DES at the optimal conditions.

CONCLUSIONS

The reported results boost deep investigation on lignocellulosic biomass using DES. This investigated new class of solvents is easy to prepare, biodegradable and cheaper than ionic liquid. Moreover, they reported good results in terms of sugars' release at mild operating conditions (time, temperature and pressure).

Manufacturing of novel low-cost adsorbent: Co-granulation of limestone and coffee waste

Limestone and coffee waste were used during the wet co-granulation process for the production of efficient adsorbents to be used in the removal of anionic and cationic dyes. The adsorbents were characterized using different analytical techniques such as XRD, SEM, FTIR, organic elemental analysis, the nitrogen adsorption method, with wettability, strength and adsorption tests. The adsorption capacity of granules was determined by removal of methylene blue (MB) and orange II (OR) from single and mixed solutions. In the mixed solution, co-granules removed 100% of MB and 85% of OR. The equilibria were established after 6 and 480 h for MB and OR, respectively.