Department of Chemical Engineering,Amirkabir University of Technology
The aim of the present work was to examine the changeable relationship between antioxidant activity and the phenolic content of dried pistachio hulls during Solid-State Fermentation (SSF) by Phanerochaete chrysosporium. Recently, in the literature, mobilization of phenolic antioxidants from soybean powders by Lentinus edodes has been reported . P. chrysosporium, a well-studied white-rot fungus, was capable of producing lignin peroxidase (LiP) and manganese peroxidase (MnP) during the fermentation of pistachio hulls. Phenolic content, in the aqueous extract of the SSF of pistachio hulls, increased during the first 4 days of fermentation by 11% and decreased during the next 2 days. An increasing trend was again seen, which became evident during days 8 to 16 and which reached the highest level of 63 mg caffeic acid equivalent (CAE)/g of dried pistachio hulls. The lowest amount of phenolics was 49.28 mg of CAE/g dried pistachio hulls. The antioxidant activity of the water extract tested in terms of 2,2 diphenyl-1-picrylhydrazl (DPPH) assay. Antioxidant activity fluctuated similar to the phenolics content during the SSF period. The lowest antioxidant activity, in terms of the scavenging of DPPH, was 77%, while the highest level measured was 88%. The culture did not show any LiP and MnP activity during the first 2 days of the SSF. However, activity increased during the next 2 days and, for MnP, activity reached its highest level by day 14 (56.9 U/l), while LiP activity, which was 4.4 U/l on day 6 of fermentation, reached its highest (60.72 U/l). This work includes important points regarding the potential use of pistachio hulls as agricultural waste and as an inexpensive source of production of fungal peroxidases, while the existence of the changeable relationship between phenolics and antioxidant activity may favor the use of fermented pistachio hulls as possible functional food.