Abstract
The nutritional quality of kiwifruit has been highlighted by several studies, while its peel is typically discarded as a by-product with no commercial value. This study was carried out to optimize the ultrasound-assisted extraction (UAE) of phenolic compounds from kiwi peel. Three independent variables (time (t), ultrasonic power (P) and ethanol concentration (EtOH)) were combined in a five-level central composite rotatable design coupled with the response surface methodology (RSM). The extraction yield determined gravimetrically and the content of phenolic compounds identified by HPLC-DAD-ESI/MSn (namely two quercetin glycosides, one catechin isomer and one B-type (epi)catechin dimer) were the experimental responses used in the optimization. The polynomial models were successfully fitted to the experimental data and used to determine the optimal UAE conditions. The sonication of the sample at 94.4 W for 14.8 min, using 68.4% ethanol, resulted in a maximum of 1.51 ± 0.04 mg of flavonoids per g of extract, a result that allowed the experimental validation of the predictive model. The kiwi peel extract obtained under optimized conditions showed somehow promising bioactive properties, including antioxidant and antimicrobial effects, and no toxicity to Vero cells. Overall, this study contributes to the valorization of kiwi peel as a low-cost raw material for the development of natural ingredients (such as food preservatives) and also to the resource-use efficiency and circular bioeconomy.
Highlights
IntroductionApproximately 30% of the food produced each year is discarded worldwide
The extraction of polyphenols from plant materials is affected by different factors related to the compositional and structural nature of the plant material and to the factors applied during the extraction process, such as solvent type, temperature, ultrasonic power, solid/liquid ratio, and processing time
In order to valorize this by-product as a source of bioactive compounds, a five-level central composite rotatable design (CCRD) design coupled to response surface methodology (RSM) was successfully implemented
Summary
Approximately 30% of the food produced each year is discarded worldwide This represents 1300 million tons of food, one billion dollars in economic costs, 700 billion dollars in environmental costs and approximately 900 billion dollars in social costs [1]. The peels, leaves, roots, tubers and seeds of fruits and vegetables that are discarded annually generate around 25% to 30% of the food industry waste [2]. These biowaste and by-products can cause environmental problems, such as aquatic life toxicity, surface and ground water contamination, changes in soil quality, greenhouse gases emissions, in addition to attracting disease vectors such as insects and rodents, among others [3].
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