Insight into High-Hydrostatic Pressure Extraction of Polyphenols from Tomato Peel Waste

In this paper, high-hydrostatic pressure extraction (HHPE) as an emerging food processing and preservation technique constitutes an alternative to conventional thermal treatment that has been used for extraction of polyphenols from tomato peel waste generated by the canning industry. The impact of time (5 and 10 min), temperature (25, 35, 45 and 55 °C) and solvents (water, 1% HCl, 50 and 70% methanol with and without addition of HCl, and 50 and 70% ethanol), at a constant pressure of 600 MPa, has been evaluated in this paper with respect to polyphenols’ yields. The results showed a significant (p < 0.05) variation in the contents of a great number of phenolic compounds in respect of the applied temperatures and solvents. On the other hand, the time invested in HHPE had no effect on polyphenols’ yields. Among phenolic compounds, the p-coumaric acid (p-CA) and chlorogenic acid derivative (ChA der) are predominant, i.e., 0.57 to 67.41 mg/kg and 1.29 to 58.57 mg/kg, respectively, depending on the solvents and temperatures used. In particular, methanol (50 and 70%) at temperatures of 45 and 55 °C enhanced the recovery of polyphenols in comparison to other utilised solvents. In conclusion, this paper puts forth the theory that by applying HHPE with minimal expenditure of time, it is possible to achieve efficient production of polyphenols from low-cost tomato peel waste, generating income both for producers and agri-food industries.