# Optimized Isolation Procedure for the Extraction of Bioactive Compounds from Spent Coffee Grounds
## 4 Conclusions  
Coffee will continue to be one of the favorite beverages in the world. Therefore, more and more waste is going to be produced, and the need for its valorization will continue to grow. Based on our study, SCGs are a good source of many bioactive components, which are usually disposed of, along with the SCGs. By performing an extraction procedure using the SCGs, the valorization and reintegration of the SCGs in the industry through a circular economy concept by providing new valuable bioactive compounds are plausible. By optimizing simple experimental conditions (i.e., composition and amount of the solvent as well as time and temperature of the extraction), the extraction yield of the compounds can be altered. Under optimum conditions, the concentration of caffeine and polyphenols can be maximized, yielding extracts that can be further used in the food industry either to enhance the properties of existing products or to develop new beverages with enhanced content in antioxidant compounds. The findings of the current study suggest that a low extraction temperature (20 \({}^{\circ}\)C) may be suitable for the extraction of bioactive compounds from SCGs, which could have implications for reducing the environmental impact and cost of the extraction process. Using food-compatible solvents and benign extraction conditions, extracts from SCGs can be easily prepared, in an environmentally friendly manner. This way, new products may be obtained with additive value, while at the same time, the circular economy is enhanced, benefiting both the food sector and the ecosystems. The limitations of this study include its focus on the extraction of caffeine and the three main polyphenols, while other, potentially valuable, compounds could also be extracted. Further research could explore the extraction of a broader range of bioactive compounds from spent coffee grounds, including those that may have applications in fields beyond the food industry (such as pharmaceuticals). Moreover, alternative extraction methods (e.g., ultrasound extraction and pulsed electric field) could be compared to the method used in this study to determine the most efficient and sustainable approach. \begin{table}
\begin{tabular}{c c c c c} \hline  & **Caffeine** & **TPC** & **FRAP** & **DPPH** \\  & **(mg/g)** & **(mg GAE/g)** & **(umoL AAE/g)** & **(umoL DPPH/g)** \\ \hline Spent coffee grounds & 6.6 \(\pm\) 0.3 & 19 \(\pm\) 1 & 140 \(\pm\) 7 & 206 \(\pm\) 10 \\ Coffee grounds & 20 \(\pm\) 1 & 54 \(\pm\) 3 & 495 \(\pm\) 25 & 572 \(\pm\) 29 \\ Espresso coffee & 12.7 \(\pm\) 0.6 & 36 \(\pm\) 2 & 312 \(\pm\) 16 & 274 \(\pm\) 14 \\ \hline \end{tabular}
\end{table} 
Table 5: Content of extracts from SCGs, coffee grounds, and espresso coffee in caffeine and TPC and FRAP and DPPH values. **Supplementary Materials:** The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app13052819/s1](https://www.mdpi.com/article/10.3390/app13052819/s1)]([https://www.mdpi.com/article/10.3390/app13052819/s1](https://www.mdpi.com/article/10.3390/app13052819/s1)), Figure S1: Plot of actual vs. predicted response (caffeine, mg/g) (plot A) and desirability function (plot B) for the optimization of the extraction of spent coffee grounds performed with hydroethanolic solutions. The inset tables provide statistics related to the evaluation of the resulting model. Values with color and asterisk are statistically significant. ; Figure S2: Plot of actual vs. predicted response (polyphenols, mg GAE/g) (plot A) and desirability function (plot B) for the optimization of the extraction of spent coffee grounds performed with hydroethanolic solutions. The inset tables provide statistics related to the evaluation of the resulting model. Values with color and asterisk are statistically significant; Figure S3: Plot of actual vs. predicted response (FRAP, \(\mu\)mol AAE/g) (plot A) and desirability function (plot B) for the optimization of the extraction of spent coffee grounds performed with hydroethanolic solutions.