Identification of polyphenol composition in grape (Vitis vinifera cv. Bidaneh Sefid) stem using green extraction methods and LC-MS/MS analysis

The utilization of grape stems, a by-product of the grape processing industry, as a source of valuable bioactive compounds, particularly polyphenols, has gained attention in recent years. This study aimed to investigate different eco-friendly extraction methods for obtaining polyphenols from grape (Vitis vinifera cv. Bidaneh Sefid) stems, focusing on green solvents and innovative techniques. Four extraction methods were tested, involving the use of water and polyethylene glycol (PEG) as green solvents, along with maceration, microwave, ultrasound, and reduced-pressure techniques. High-performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry (HPLC-ESI-MS/MS) was used to characterize and quantify the bioactive compounds in the extracts. A total of 29 polyphenols, including phenolic acids, flavonoids, proanthocyanidins, and stilbenes, were detected. Among the four extraction methods tested, methods 1 (water + microwave + ultrasound + atmospheric pressure) and 2 (water + microwave + ultrasound + reduced pressure) were found to be the most effective. Our study demonstrated that using water and PEG as green solvents, combined with techniques like microwave, ultrasound, and reduced pressure, effectively extracted both hydrophobic and hydrophilic compounds from the grape stems. These findings suggest that further exploration of these methods could lead to the development of value-added products from grape stems, emphasizing the significance of green extraction techniques for the recovery of polyphenols from winemaking by-products.