This study investigates the extraction of phenolic compounds and antioxidant activity from spent coffee grounds (SCG) and coffee cherry pulp (CCP) using subcritical water extraction combined with high-pressure carbon dioxide (CO₂). The objective was to optimize extraction conditions to maximize total phenolic content (TPC) and DPPH radical scavenging activity.
Researchers from Doi Chaang Original Coffee Company based in Chiang Rai, Thailand, conducted this significant work to address the increasing waste generated from coffee production. By enhancing the extraction of valuable bioactive compounds from this waste, they aim to contribute to sustainability and resourcefulness within the industry.
Using Design Expert V.13 and Central Composite Design (CCD), the scientists systematically analyzed key parameters including extraction time, temperature, and solid-to-water ratio. Their efforts led to determining the optimal conditions for SCG at 198 °C, with a solid-to-water ratio of 0.027 g/mL and extraction time of 60 minutes, which resulted in TPC of 217.26 mg GAE/g DW and DPPH value of 23.28 μMol TE/g DW.
Meanwhile, for CCP, optimal extraction conditions were set at 189 °C, 0.024 g/mL solid-to-water ratio, and 54 minutes, yielding TPC of 230.13 mg GAE/g DW and significantly improved DPPH value of 32.63 μMol TE/g DW. These findings indicate the greater potential of coffee cherry pulp as compared to spent coffee grounds when it came to phenolic content and antioxidant activity.
The extraction process utilized subcritical water at high temperatures, enhanced by CO₂, which demonstrated effectiveness due to the environmentally friendly nature of the method. By forming carbonic acid, CO₂ lowers the extraction pH which helps with solubility and cell wall disruption, increasing the yield of bioactive compounds.
Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) and Thin-Layer Chromatography (TLC) analyses confirmed the presence of several key bioactive compounds including quinic acid and caffeine. This highlights the capabilities of both SCG and CCP to not only serve as waste materials but also as rich sources of antioxidants beneficial for health.
One of the important observations from the research is the variance between extraction yields among different variables. For example, the highest yield for coffee grounds and pulp occurred at various parameters, demonstrating the relevance of careful optimization during the extraction phase.
The authors explain, “We found the optimal conditions for extracting phenolic compounds from SCG and CCP to maximize both yield and antioxidant activity.” This encapsulates the targeted approach of their research, reinforcing the concept of utilizing waste more efficiently.
These findings challenge the norm of perceiving coffee production waste as mere byproducts, instead shedding light on their potential applications in functional foods and nutraceutical products. Coffee bye-products like SCG and CCP can now be positioned as key contributors to both sustainability within the coffee industry and enhancement of nutraceutical quality.
Looking forward, the study proposes scaling up the extraction techniques under the parameters laid out to evaluate industrial applicability and energy use efficiency. Future explorations can help elucidate how additional agricultural byproducts might benefit from similar extraction methods, exploring diverse compositions and health benefits.
While subcritical water extraction and CO₂ do have significant advantages, focusing on broadening the capacity of this technology will encourage more environmentally sustainable practices within the food processing industry. The work overall provides not just insights but actionable direction moving forward.