Ultrasound‐assisted extraction (UAE) of bioactive compounds from coffee silverskin: Impact on phenolic content, antioxidant activity, and morphological characteristics

Abstract

Coffee silverskin (CSS) has various nutritional and functional properties, enabling it for valuable applications. Ultrasound‐assisted extraction (UAE) is an efficient and economic extraction technique. In this research, UAE was employed in the extraction of bioactive compounds from CSS with water and methanol–water mixture as solvent. Extraction efficacy between the UAE‐treated extracts and the UAE‐untreated (control) was assessed in terms of the total phenolic content (TPC), caffeine content, chlorogenic acids (CGAs), and antioxidant capacities. The yields of TPC were in the range from 5.80 ± 0.06 to 8.94 ± 0.01 mg GAE/g sample. Phenolic content and antioxidant activity were highly enhanced by applying UAE compared to the controls. Noticeable caffeine content in the range from 3.27 ± 0.10 to 4.29 ± 0.01 g/100 g sample was found in the CSS samples. CGAs (3‐CGA, 4‐CGA, and 5‐CGA) were all quantified. Methanol–water extracts showed significantly (p < .05) higher TPC, caffeine content, and antioxidant capacity than water extracts. The micro‐structure investigation of CSS indicated UAE can cause cell disruption and micro cracks so that it can be an effective extraction technique. Peleg's model showed a good fitting (R2 > 0.94) to the experimental results on the kinetics of UAE of phenolics compounds. Practical applications Coffee is a most consumed beverage internationally. Due to its great production, large quantities of residues including coffee pulp and husk, coffee silver skin, and spent coffee grounds are generated in the coffee industry. Among them, coffee silverskin (CSS) is a by‐product during the coffee roasting process, which contains nutritional and functional properties. As an efficient and economic novel extraction technique, ultrasound‐assisted extraction (UAE) was employed in the current study to extract bioactive compounds from coffee silverskin with water and methanol–water mixture as solvent in order to overcome various disadvantages encountered by the conventional extraction methods. Results indicated that application of UAE pretreatment showed significantly higher recovery of phenolic compounds compared to the controls and high ultrasound intensity (38 W/cm2) was more effective in recovering polyphenols compared to 5 W/cm2 ultrasonic treatments. Therefore, results from the current study provide useful and practical information for the coffee industry.

Improving the Recovery of Phenolic Compounds from Spent Coffee Grounds (SCG) by Environmentally Friendly Extraction Techniques

“…For UAE, cell damage was observed compared to CSE and HHPE ( Figure 6 C). This result has also been shown in the literature [ 26 , 41 , 42 ]. At UAE treatment, acoustic cavitation occurs and this leads to micro fissures and microchannels on the matrix surface so UAE increases the transfer of phenolic compounds into the solvent [ 43 , 44 ].…”

Environmentally Friendly Techniques for the Recovery of Polyphenols from Food By-Products and Their Impact on Polyphenol Oxidase: A Critical Review

“…This can result in an improved extraction yield [63]. As reported by Wen et al (2019), the solvent has a substantial influence on the recovery yield of polyphenols. When the combination of organic solvents and water is employed as a medium in this process, the yield rises [52].…”

“…The intensity of ultra indicates the amount of power added per unit area [47]. This factor is calculated relation between the acoustic power and the surface area of the probe (Equation (1 The higher the ultrasound intensity is applied to the solvent mixture, the more vio the cavitation bubbles implode [52]. Ultrasonic power can be determined calorimet using Equation (2).…”

Recovery of antifungal compounds from wood and coffee industry side-streams and residues for wood preservative formulations

“…Organic acids are common constituents in spent coffee and silverskin extracts. Chlorogenic acid and its derivatives are present in both extracts (Torres-Valenzuela et al 2019, Wen et al 2019. Chlorogenic acid was identified as an inhibitor of different phytopathogenic and fruit rotting fungi (Martínez et al 2017, Roy et al 2018, whereas the effects on bacterial growth were variable (Torres-Valenzuela et al 2019).…”