Extraction of phenolic compounds from Siah‐Sardasht grape skin using subcritical water and ultrasound pretreatment

Abstract

The awareness of hygienic problems in solvent extraction has led to an increase in the use of green technologies. In this study, a combination of ultrasound with the power of 400 W and the frequency of 21 kHz and the subcritical water at 100–150°C and 20–40 bar was used to extract the phenolic compounds from Siah-Sardasht grape skin within an extraction time of 15–30 min. Results showed that temperature, pressure, time, and the use of ultrasound had a significant (p < 0.05) effect on the total extracted phenolic content. The maximum extraction of total flavonoid, total phenolics, antioxidants, chroma, and extraction yield were achieved at the highest temperature, pressure, and extraction time along with an ultrasound pretreatment. Scanning electron microscopy results also demonstrated the cavities opened by the ultrasound pretreatment. It can be concluded that the subcritical water extraction is a practical and efficient method for the extraction of the phenolic compounds. Practical applications Extraction of food components is an old process. Increasing the awareness on the hygienic problems in solvent extraction of food components has led to an increase in the use of green technologies. In the present study, an extractor with a volume of 1L was made in a pilot scale and experiments were done with a combination of ultrasound. Based on the results; (a) subcritical water extraction is a safe, practical, and efficient method for extracting phenolic compounds, (b) this process may scale-up to an industrial pilot plant. We believe that the result of this study will be useful in identifying the future research directions needed for food components extraction and also to facilitate the development of an analytical framework for the design of novel extraction equipment.