Abstract
A fully-detailed LC-MS qualitative profiling of red grape skin, extracted with a mixture of ethanol and water (70:30 v:v) has permitted the identification of 65 compounds which can be classified into the following chemical classes: organic and phenolic acids (14 compounds), stilbenoids (1 compound), flavanols (21 compounds), flavonols (15 compounds) and anthocyanins (14 compounds). The extraction yield obtained with water at different temperatures (100 °C, 70 °C, room temperature) was then evaluated and the overall polyphenol content indicates that EtOH:H2O solvent is the most efficient and selective for polyphenol extraction. However, by analyzing the recovery yield of each single polyphenol, we found that water extraction under heating conditions is effective (extraction yield similar or even better in respect to the binary solvent) for some polyphenolic classes, such as hydrophilic procyanidins, phenolic acids, flavonol glucosides and stilbenoids. However, according to their lipophilic character, a poor yield was found for the most lipophilic components, such as flavonol aglycones, and in general for anthocyanins. The radical scavenging activity was in accordance with the polyphenol content, and hence, much higher for the extract obtained with the binary solvent in respect to water extraction. All the tested extracts were found to have an anti-inflammatory activity in the R3/1 cell line with NF-kb reporter challenged with 0.01 µg/mL of IL-1α, in a 1 to 250 µg/mL concentration range. An intriguing result was that the EtOH:H2O extract was found to be superimposable with that obtained using water at 100 °C despite the lower polyphenol content. Taken together, the results show the bioactive potentialities of grape skin extracts and the possibility to exploit this rich industrial waste. Water extraction carried out by heating is an easy, low-cost and environmentally friendly extraction method for some polyphenol classes and may have great potential for extracts with anti-inflammatory activities.
Highlights
IntroductionGrapes are amongst the most cultivated fruits in the world
A fully detailed qualitative profiling of red grape skin extracted with ethanol and water mixture has permitted the identification of 65 compounds which can be classified into the following chemical classes: organic and phenolic acids (14 compounds), stilbenoids (1 compound), flavanols (21 compounds), flavonols (15 compounds) and anthocyanins (14 compounds)
(100 ◦ C, 70 ◦ C, room temperature) was evaluated and the results indicate that extraction using water under heating conditions is effective in extracting some polyphenolic classes with a good recovery in respect to EtOH based binary extraction
Summary
Grapes are amongst the most cultivated fruits in the world. 3.5 million hectares are dedicated to grape cultivation with a production of almost 27 million tons of fruit [1]. The main component of this waste is the grape pomace, mainly composed (50–65%) of grape skin [3] Even though it is mostly used as compost or animal fertilizer, the phenolic-rich composition of the skin is what supports its use a source of bioactive phytochemicals. It contains anthocyanins alongside various members of the flavonoid family (flavan-3-ols, flavonols and flavanones), which have shown healthy activity as antioxidant and anti-inflammatory agents [4,5,6]
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