Effect of microwave and enzymatic pretreatment and type of solvent on kinetics of ultrasound assisted extraction of bioactive compounds from ripe papaya peel

The study was aimed to investigate the effect of pretreatment by microwave and enzyme and type of solvent on kinetics of ultrasound-assisted extraction (UAE) of bioactive compounds and antioxidant activity from papaya peels. The enzyme used was viscozyme and the solvents used were water, ethanol, and their combination (1:1). The effect of combination of pretreatments was also studied. The data from the experiments were fitted to second order kinetic model and Langmuir model. The second order rate constant (k) varied from 0.0005 to 0.0134 for total phenolic content (TPC), 0.0016-0.0080 for total flavonoid content, and 0.0004-0.0228 for antioxidant activity (2,2-diphenyl-1-picrylhydrazyl-radical scavenging activity). The comparative kinetic assessment illustrated that the progression of the extraction for TPC was higher in enzyme-water (E-W) treatment (98.91 mg Gallic acid equivalent (GAE)/100 g), followed by microwave-enzyme water (ME-W) treatment (93.98 mg GAE/100 g) while microwave-water:ethanol (M-WEt) treatment gave the lowest yield (42.56 mg GAE/100 g), respectively. The present study also investigated influences of ultrasonication on extraction kinetics and their yield. Ultrasound was clearly influencing the yield (over 72.95% increase in yield of polyphenols). Antioxidant activity of the extracts confirmed that the UAE extraction is suitable for preparing antioxidant-rich plant extracts. Ultrasound and pretreatment before extraction could provide many advantages like increased yield and quality, energy efficiency, faster extraction, and low solvent consumption. Practical Applications Papaya peels are waste products generated during processing of papaya and are valuable sources of polyphenols and natural antioxidants such as caffeic acid, rutin, ferulic acid, p-coumaric acid, and many more bioactive compounds that have significant biological activity. These bioactive compounds of papaya peel can be extracted and utilized in food and pharmaceutical industry for development of functional food or nutraceuticals. Ultrasound extraction is regarded as a green technology as it is environment friendly and energy-efficient process. When ultrasound technology is combined with microwave or enzymatic treatment, the efficiency of such process may be further improved. The present study is therefore useful as it can provide a solution for utilization of papaya peel for extraction of valuable compounds using green technology.