Coffee is one of the most consumed beverages in the world, the second most popular after water. It constitutes one of the most important food products on the international market, crucial for the economy and politics of many developed countries as its cultivation, processing and treatments, transport, and trade provide employment for millions of workers.
Due to the growing interest from public opinion and the scientific community regarding issues related to food waste, its environmental impact, and the development of a sustainable economy, the recovery and valorization of the enormous quantities of by-products generated by coffee processing industries constitute an interesting opportunity for various application purposes:
- reduction of waste toxicity levels;
- reduction of the environmental impact linked to their disposal;
- production of sustainable energy;
- recovery of high added-value compounds intended for the functionalization of food, pharmaceutical, and cosmetic products.
Industrial Coffee Processing
The coating membranes of coffee beans (known as “Coffee Silverskins”) and spent coffee grounds (“Spent Coffee Grounds”) constitute the main waste products from industrial coffee processing, deriving, respectively, from the bean roasting process and from hot water or steam extraction aimed at preparing instant coffee. These are highly polluting products, as they are rich in organic substances, polyphenols, tannins, and caffeine, which give these wastes a highly toxic nature and considerable problems related to their disposal [1].
Given the enormous quantities generated not only by industries but also in domestic contexts and commercial activities, the development of appropriate and efficient extraction technologies, innovative and with low environmental impact, is fundamental for the recovery of its lipid fraction, characterized by a fatty acid profile very similar to oil derived from roasted coffee and by high concentrations of palmitic, linoleic, oleic, and stearic acids [2].
This oil is also rich in polyphenols, flavonoids, and antioxidant compounds [3], which suggests its use in food formulations and cosmetic products.
Following a transesterification process, it is possible to promote its application as biodiesel [4], also allowing the obtainment of bioethanol through subsequent hydrolysis and fermentation processes [5].
The spent solid can also be used as a raw material in various processes:
- for the production of combustible pellets [6];
- as a potential source of sugars [7], particularly mannose, galactose, and arabinose from hemicellulose, and glucose from cellulose, through acid hydrolysis;
- as an absorbent material for the removal of metal ions [8].
The presence of a residual caffeine content of 1.8 mg/g in coffee grounds also favors other types of uses such as:
- catalytic role, exercised for the oxidation of hydrogen sulfide during the activated carbon preparation process [9];
- the action of lowering the equilibrium interfacial tension in oils, which gives good emollient characteristics to pharmaceutical and/or cosmetic products containing them [10].
Bibliographical Notes
[1] Mussatto, S.I., Machado, E.M.S., Martins, S., Teixeira, J.A. (2011). Production, Composition and Application of Coffee and its Industrial Residues. Food Bioprocess Technology, 4, 661-672. Doi: 10.1007/s11947-011-0565-z
[2] Colucci Cante, R., Garella, I., Gallo, M., Nigro, R. (2021). Effect of moisture content on the extraction rate of coffee oil from spent coffee grounds using Norflurane as solvent. Chemical Engineering Research and Design, 165, 172-179. Doi: 10.1016/j.cherd.2020.11.002.
[3] Mussatto, S.I., Ballesteros, L.F., Martins, S., Teixeira, J.A. (2011). Extraction of antioxidant phenolic compounds from spent coffee grounds. Separation and Purification Technology, 83, 173-179. Doi: 10.1016/j.seppur.2011.09.036
[4] Sendzikiene, E., Makareviciene, V., Janulis, P., Kitrys, S. (2004). Kinetics of free fatty acids esterification with methanol in the production of biodiesel fuel. European Journal of Lipid Science and Technology, 106, 12, 831-836. Doi: 10.1002/ejlt.200401011
[5] Kwon, E.E., Yi H., Jeon, Y.J. (2013). Sequential co-production of biodiesel and bioethanol with spent coffee grounds. Bioresour Technol. 136, 475-480. Doi: 10.1016/j.biortech.2013.03.052.
[6] Kondamudi, N., Mohapatra, S.K., Misra, M. (2008). Spent Coffee Grounds as a Versatile Source of Green Energy. J. Agric. Food Chem., 56, 24, 11757-11760. Doi: 10.1021/jf802487s
[7] Mussatto, S.I., Carneiro, L.M., Silva, J.P.A., Roberto, I.C., Teixeira, J.A. (2011). A study on chemical constituents and sugars extraction from spent coffee grounds. Carbohydrate Polymers. 83, 2, 368-374. Doi: 10.1016/j.carbpol.2010.07.063
[8] Fiol, N., Escudero, C., Villaescusa, I. (2008). Re‐use of Exhausted Ground Coffee Waste for Cr (VI) Sorption. Journal Separation Science and Technology. 43, 3, 582-596. Doi: 10.1080/01496390701812418
[9] Kante, K., Nieto-Delgado, C., Rangel-Mendez, J., Bandosz, T. (2011). Spent coffee-based activated carbon: Specific surface features and their importance for H2S separation process. Journal of hazardous materials. 201-202. 141-147. Doi: 10.1016/j.jhazmat.2011.11.053.
[10] Ferrari, M., Ravera, F., De Angelis, E., Suggi Liverani, F., Navarini, L. (2010). Interfacial properties of coffee oils. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 365 (1–3), 79-82. Doi: 10.1016/j.colsurfa.2010.02.002.
