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

Quality Attributes and Sensory Acceptance of Different Botanical Coffee Co-Products

Coffee processing is a major contributor to the creation of food and product waste. Using coffee co-products can play an essential role in addressing environmental problems and issues with nutritionally unbalanced foods, population growth, and food-related diseases. This research aimed to determine the quality and sensory parameters (aw, pH, dry matter, TAC, TPC, fat, fatty acids profile, fiber, caffeine, chlorogenic acids, color, and sensory analysis) of different botanical origins of cascara (coffee husks) and silverskin (thin layer). The results of this study show that silverskin and cascara are a good source of TAC (1S 58.17 ± 1.28%, 2S 46.65 ± 1.20%, 1C 36.54 ± 1.84%, 2C 41.12 ± 2.11%). Cascara showed the presence of polyphenols (2C 49.135 g GAE·kg^-1). Coffee co-products are good sources of fiber. Silverskin had higher values of caffeine than cascara. Palmitic, stearic, oleic, linoleic, and arachidic acids were the most represented acids in the samples. Given the obtained results, cascara can be considered "low-fat" (1C 4.240 g·kg^-1 and 2C 5.4 g·kg^-1). Based on the sensory evaluation, no sample reached the acceptable index value of 70%. Understanding the link between the character, identification properties, and composition of coffee co-products of different botanical origins can enable their application in the food industry.

Specialty and high-quality coffee: discrimination through elemental characterization via ICP-OES, ICP-MS, and ICP-MS/MS of origin, species, and variety

BACKGROUND

This study aimed to establish the elemental profiling and origin combined with the genetic asset of coffee samples collected from major coffee-producing countries. A total of 76 samples were analysed for 41 elements using inductively coupled plasma-optical emission spectroscopy (ICP-OES), inductively coupled plasma-mass spectrometry (ICP-MS), and inductively coupled plasma-triple quadrupole mass spectrometry (ICP-MS/MS). The mineral composition of the silver skin detachment during the roasting process was also evaluated to verify the loss of minerals during roasting, differences in composition with beans, and between species.

RESULTS

Application of linear discriminant analysis provided models with an accuracy of 93.3% for continents, 97.8% for countries of cultivation, and 100% for species. Discrimination between Arabica, Canephora coffee, and Eugenoides, and different varieties of Arabica species were identified in both models with calcium (Ca), barium (Ba), cadmium (Cd), rubidium (Rb), and strontium (Sr) as significant discriminant elements. Rb, Sr, sulphur (S), and thulium (Tm) were significant discriminant elements in both models for geographical distinction at different scales. Most of the elements had significantly higher values in silver skin than those in roasted coffee at different magnitudes, with exceptions of P and Rb.

CONCLUSION

In summary, determination of mineral elements, processed by multivariate statistical analysis, was demonstrated to be discriminant for different coffee species. Linear discriminant analysis of the elemental analysis of samples from the seven major producing countries provided a reliable prediction model. Elemental analysis of major and minor elements is relatively easy and can be used together with other traceability systems and sensory evaluations to authenticate the origin of roasted coffee, different species, and varieties. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Valorization of coffee wastes as plant growth promoter in mulching film production: A contribution to a circular economy

Food waste valorization, considered as energy and/or chemicals source, via biorefinery or biotechnology, gained great attention in recent years, because of the fast depletion of primary resources, increased waste generation and landfilling worldwide. Coffee by-products for example (i.e. coffee pulp, coffee husks, silver skin, spent coffee, etc.) have been investigated in different forms either as a source of antioxidant and valuable chemicals and as a filler in composites. A new valorization route for coffee silver skin (CSS), up to now just sent to damping, is here investigated: particulate bio-composites based on poly(butylene succinate-co-adipate) (PBSA), an aliphatic biodegradable polyester commercially available, have been formulated with up to a 30 wt% of CSS, in order to prepare mulching films for agriculture. The bacterial analysis of the filler indeed, has underlined the presence of potential Plant Growth-Promoting Bacteria species, mainly ascribed to the Bacillus genus, which can survive both the roasting and the compounding processes. The obtained composites have been characterized mechanically and thermally and their hydrophilic nature has been investigated by measuring their contact angle. Eventually, the bacteria release from the composite films has been examined by means of in-vitro tests. The plant growth promoting capability of the films was preliminarily evaluated in pot experiments using lettuce as a model crop. The composite films were able to release the endogenous bacteria in the soil and to stimulate plant and root growth of the assayed crop. The possibility to produce functionalized biodegradable mulching films by recycling agricultural wastes can thus be forecast, highlighting potential multiple advantages in terms of soil preservation/fertilization, decrease of polymeric materials in mulching products, exploitation of a waste.

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.

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.

Comparative Analysis of Selected Chemical Parameters of Coffea arabica, from Cascara to Silverskin

Nowadays, there is an increased interest in coffee derivatives (green beans, roasted beans, and coffee by-products (Cascara and Silverskin)) due to their particular chemical composition. This study aimed to compare the content of dry matter, total fat, fatty acids, and fiber (ADF, NDF) of coffee by-products (Cascara and Silverskin) and coffee beans (green and roasted under different conditions). Coffee beans and their by-products were obtained from 100% C. arabica coffee cherries from Panama by dry process. The lowest concentrations of fat corresponded to Cascara 4.24 g·kg⁻¹ and Silverskin 23.70 g·kg⁻¹, respectively. The major fatty acids detected in all samples were palmitic, stearic, oleic, and linoleic acids, the latter two being essential fatty acids. LDA showed that 89.01% of the variability between beans and by-products was explained by lignoceric, myristic, behenic, tricosanoic, arachidic, and heneicosanoic acids. Silverskin appeared to be a good source of lignoceric, myristic, and behenic acids and had a higher concentration of dietary fiber (314.95 g·kg⁻¹) than Cascara (160.03 g·kg⁻¹). Coffee by-products (Silverskin and Cascara) are low-fat products enriched in dietary fiber. Their incorporation, after adjustment, into the global diet may contribute to nutrition security, the sustainability of the coffee sector, and human health.

Coffee Silverskin as a Functional Ingredient in Vegan Biscuits: Physicochemical and Sensory Properties and In Vitro Bioaccessibility of Bioactive Compounds

Coffee silverskin (CS), a by-product obtained by the coffee industry after the roasting process, is scientifically known to be a source of fiber and polyphenols, which could contribute to human health. In this work, the production of CS-enriched biscuits is proposed, where the CS from Arabica and Robusta type and a decaffeinated blend of the two were used at three different levels as a replacement for wheat flour. The biscuits were analyzed for their physicochemical properties, consumer acceptability, and the bioaccessibility of polyphenols after in vitro digestion was estimated in order to identify the formulation most appreciated by consumers and most promising in terms of nutritional and biofunctional potential. From the results, CS-based biscuits represent an interesting possibility to create a more sustainable coffee chain, thanks to the valorization of the silverskin, especially if a decaffeinated CS is considered. In fact, a 4% replacement of the wheat flour with decaffeinated CS is able to give a final product with a high content of accessible polyphenols and a biscuit appreciated by the consumer.

Coffee By-Products as Sustainable Novel Foods: Report of the 2nd International Electronic Conference on Foods-"Future Foods and Food Technologies for a Sustainable World"

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 fertilizer or animal feed. Modern, ecologically oriented society attaches great importance to sustainability and waste reduction, so it makes sense to not dispose of the by-products of coffee production but to bring them into the value chain, most prominently as foods for human nutrition. There is certainly huge potential for all of these products, especially on markets not currently accessible due to restrictions, such as the novel food regulation in the European Union. The by-products could help mitigate the socioeconomic burden of coffee farmers caused by globally low coffee prices and increasing challenges due to climate change. The purpose of the conference session summarized in this article was to bring together international experts on coffee by-products and share the current scientific knowledge on all plant parts, including leaf, cherry, parchment and silverskin, covering aspects from food chemistry and technology, nutrition, but also food safety and toxicology. The topic raised a huge interest from the audience and this article also contains a Q&A section with more than 20 answered questions.

Interest of Coffee Melanoidins as Sustainable Healthier Food Ingredients

Coffee melanoidins are generated by the Maillard reaction during the thermal processes occurring in the journey of coffee from the plant to the cup (during drying and roasting). Melanoidins, the brown pigments formed as the end products of this reaction, have been reported in cascara, silverskin, spent coffee grounds, and coffee brew. The latter is one of the main natural sources of melanoidins of the daily diet worldwide. However, their presence in coffee by-products has been recently described. These complex macromolecules possess multiple health-promoting properties, such as antioxidant, anti-inflammatory, dietary fiber effect, and prebiotic capacity, which make them very interesting from a nutritional point of view. In addition, they have a great impact on the sensory profile of foods and their acceptance by the consumers. The present study is a descriptive, narrative, mini-review about the nature, structure, digestibility, properties (sensory, nutritional, and health-promoting), safety and regulatory status of melanoidins from the coffee brew and its by-products with a special emphasis on the latter.