Extraction of Polyphenols and Synthesis of New Activated Carbon from Spent Coffee Grounds

Abstract

A valorization process of spent coffee grounds (SCG) was studied. Thus, a two-stage process, a stage of extraction of the polyphenols and a stage of obtaining activated carbon (AC) by a carbonization process, was performed. The extraction was carried out with a hydro-alcoholic solution in a pressure reactor, modifying time and temperature. To optimize the extraction of polyphenols, a two-level factorial design with three replications at the central values was used. The best results were obtained by performing the extraction at 80 °C during 30 min, using a mixture of EtOH:H2O 1:1 (v/v) as extraction solution. Caffeine and chlorogenic acid were the most abundant compounds in the analyzed extracts, ranging from 0.09 to 4.8 mg∙g-1 and 0.06 to 9.7 mg∙g-1, respectively. The precursor obtained in the extraction stage were transformed into AC. An experimental design was realized in order to analyze the influence of different variables in the AC obtained process (reaction time and amount of potassium hydroxide used). Actived carbons with BET specific surface (SBET) comprised between 1600 m2∙g-1 and 2330 m2∙g-1 had a microporous surface. Under the optimum conditions, the obtained AC presented a maximum adsorption capacity of methylene blue (qm) between 411 mg∙g-1 and 813 mg∙g-1.

Effect of Drying Methods on Bioactive Compounds and Antioxidant Capacity in Grape Skin Residues from the New Hybrid Variety “BRS Magna”

“…However, TPC and TFC had a reduction in comparison with the residues of fresh peel (control) of 69.3% and 69.7% and 31.2% and 51.2% ( p < 0.05), but an increase in TAC of 20.7% and 108.3% ( p < 0.05) in conventional drying and lyophilization, respectively. The variation in the levels of polyphenols and antioxidant activity according to the drying conditions applied has been observed in previous studies [ 5 , 15 , 18 , 32 ]. The conditions of thermal processing apparently have a significant effect on these parameters.…”

“…In addition, the results observed in the present study are in agreement with other studies reporting that the phenolic content and antioxidant activity were affected by cooking processes, such as steam, boiling, and drying. Variations in total phenolic content and antioxidant activity according to drying conditions have been reported previously [ 17 , 18 , 32 ].…”

“…Recently, Ramón-Gonçalves et al [ 32 ] observed that the temperature influenced the conditions of experimental extraction to obtain the maximum response of polyphenols from used coffee beans. The extraction was carried out with different hydroalcoholic solutions (EtOH:H 2 O, 50:50, 40:60, and 30:70, v/v ), modification times (15, 23, or 30 min) and temperatures (80, 100, and 120 °C).…”

RETRACTED: Activated Carbons From Winemaking Biowastes for Electrochemical Double-Layer Capacitors

“…Practically any raw materials with high carbon content, including several wastes, may yield interesting and useful materials (Deiana et al, 2009 ). Various waste sources have been proposed for the preparation of activated carbon, from biodiesel (Gonçalves et al, 2019 ) to food processing waste (Ramón-Gonçalves et al, 2019 ; Senophiyah-Mary et al, 2019 ; Yaglikci et al, 2020 ) or agriculture industry residues (Ukanwa et al, 2019 ), all of them with great attractiveness owing to their large-scale production and low price. Winemaking-derived waste is a major issue in the wine industry, being Spain, the origin of the precursor wine used in this work, the third world producer of wine (Maicas and Mateo, 2020 ).…”

Study of Influential Parameters of the Caffeine Extraction from Spent Coffee Grounds: From Brewing Coffee Method to the Waste Treatment Conditions

“…No experiment has been carried out with pH < 0.7 and pH ≥ 14 to confirm that caffeine cation or anion has more affinity for water. Polyphenols like chlorogenic acids are the main impurities in aqueous extract, thus, potentially transferred in ethyl acetate [55,56]. Gazzani et al have reported that chlorogenic acids from green coffee beans were more efficiently extracted in ethyl acetate at acidic pH [57].…”