Optimization of the enzyme-assisted aqueous extraction of phenolic compounds from pistachio green hull

Phenolic compounds form an essential part of the human diet because of their functional properties. In this study, the extraction conditions of phenolic compounds from pistachio green hull were optimized by enzymatic method (using pectinase, cellulase, and tannase enzymes). For this purpose, the effective factors including the solid to solvent ratio, enzyme concentration, particles size, and extraction time were optimized. Also, the effect of enzymatic extraction on the antioxidant activity of the extracts were investigated using three different methods (DPPH˙, ABTS˙⁺, and FRAP). The profile of phenolic compounds was determined using HPLC/DAD. The results showed that all the studied enzymes were significantly effective in increasing the extraction efficiency. The combination of cellulase, pectinase, and tannase enzymes under their optimal conditions increased the extraction yield up to 112% in comparison with the solvent extraction method. The results of three antioxidant tests showed that the antioxidant properties of the enzymatic extracted compounds increased significantly compared to the control sample (compounds extracted by the solvent method). The DPPH˙ test results indicated that the antioxidant property of the enzymatic extracted compounds was 71% more than the control extract. The different enzymes changed the phenolic compounds' profile so that the pectinase and cellulase enzymes increased the amount of phloroglucinol (more than three times) and decreased the amount of gallic acid (more than 4.5 times) in comparison. In addition, tannase and its combination with other enzymes increased the gallic acid content by 2.6-fold and 4.6-fold compared to the control sample, respectively.