Conventional Ultrasound And Microwave-Assisted Extraction Of Phenolic Compounds From Mavrud Grape, Pomace And Seeds
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2020-01-01
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This research is dedicated to the valorization of wine industry residual products as a source of valuable compounds of interest to the food, pharmaceutical and cosmetic industries. Whole grape seeds and grape pomace of organic Mavrud of Bulgarian origin, harvested in 2016 were used. The aqueous ethanolic extracts were prepared by three different techniques: conventional extraction via magnetic stirring, ultrasound-assisted extraction (US) and microwave-assisted extraction (MW). Microwaves seemed to be more efficient in extracting the desired substances through the hard shell of the seeds. The polyphenolic content of the seed extracts, expressed as GAE (gallic acid equivalent) was remarkably higher: 58.57 mg GAE g-1 dw (first stage of MW-assisted extraction) compared to the conventional extraction with a magnetic stirrer – 7.03 mg GAE g-1 dw. The results obtained for the US extraction were similar - 49.73 mg GAE g-1 dw, but the processing time in the microwave field was considerably shorter. The US-assisted extraction was not so convenient for the grape pomace extracts - 20.47 mg GAE g-1 dw were obtained for 240 min, compared to 75.02 mg GAE g-1 dw for 20 min in the microwave field. Three analyzes were performed to determine the total polyphenolic content, antioxidant activity and anthocyanin content. The MW-assisted extraction was the most suitable for leaching of polyphenolic compounds and the extracts exhibited a higher antioxidant activity. Contrarily it has been observed that the anthocyanin content of the extracts produced via MW-assisted extraction was lower compared to the conventional and US-assisted techniques. Both techniques revealed time and energy-saving and are considered as eco-procedures.