Extraction of Phenolic Compounds and Tannins from Pistachio By-products

Abstract

Aims: This study was conducted to evaluate the effects of solvent, particle size, extraction time and ultrasound on extraction and quantification of phenolic compounds and tannins in pistachio by-products (PB). Study Design: Factorial experiment based on completely randomized design. Methodology: Four solvents (70% aqueous acetone, 50% aqueous methanol, 50% aqueous ethanol and water), 2 particle size (fine vs coarse) and 2 extraction time (12 vs 24h) were used to extract total phenolics (TP) and total tannins (TT) of sun-dried PB (93.5% DM). Folin-Ciocalteu reagent was used for phenolics and tannins quantification. In another experiment, ultrasound-assisted extraction (UAE) was used for extracting phenolic compounds. Results: Using 70% aqueous acetone resulted in more TP (13.86% of DM as tannic acid equivalent) compared to other solvents and the lowest TP content was measured in water (9.87%). Particle size and time of extraction had no effect on TP content. Tannin concentration were not affected by particle size but decreased by increasing time from 12 to 24h (7.34 vs 6.81%). Higher tannin was extracted by 50% aqueous ethanol compared to aqueous methanol and/or water (7.82%). However, no differences were observed between 70% aqueous acetone and 50% aqueous ethanol and/or methanol. The interactions between main effects were not statistically significant. In another experiment, TP and TT were extracted by ultrasound-assisted extraction (UAE) and results were compared to 12h extraction (without ultrasonic). No difference was observed between two methods in terms of TP and TT. Conclusion: It can be concluded that using 70% aqueous acetone and 50% aqueous ethanol are more convenient solvent for extraction of phenolics and tannins in PB, respectively.