Recovery of phenolic compounds from citrus by-products using pressurized liquids — An application to orange peel

Abstract

Citrus industry residues are sources of phenolic compounds, which may be extracted by pressurized liquid extraction (PLE) and volatile compounds, extractable by supercritical fluid extraction (SFE). PLE and SFE are fast and allow using non-toxic solvents and moderate temperatures. Therefore, the objective of this work was to extract volatile and phenolic compounds from orange peel by SFE and PLE. The raw material was orange peel without (Lot 1) and with (Lot 2) previous supercritical CO2 extraction performed at 40°C and 35MPa. The volatile profile was evaluated in the SFE extract by HS-SPME-CG-MS. PLE solvents were absolute ethanol and mixtures of ethanol and water (75% and 50% ethanol, v/v) at the temperatures 45, 55, and 65°C and pressure of 10MPa. Global yield, total phenolic content (TPC), antioxidant capacity by DPPH and FRAP methods, total reducing sugars and the concentration of the major phenolic compounds by HPLC were evaluated in the extracts. Temperature and ethanol concentration had significant effects on all responses. The main volatile compound found in the SFE extract was α-Terpineol, followed by d-Limonene. The major phenolic compound was hesperidin, which highest recovery (19.3±0.9mg/g dry peel) was achieved with 75% ethanol at 65°C from Lot 1. At the same condition, high TPC and antioxidant capacity were also achieved. The three-line spline and two-site kinetic models provided good adjustments to the PLE curves, being able to describe their behavior. PLE using water and ethanol can be applied to recover phenolics from a large variety of fruit by-products.