Improved production of antioxidant-phenolic compounds and certain fungal phenolic-associated enzymes under solid-state fermentation of chia seeds with Trichoderma reesei: response surface methodology-based optimization

Abstract

Chia seeds (CS) are becoming increasingly consumed due to their great nutritional and therapeutic properties. In this study, solid-state fermentation (SSF) of CS by Trichoderma reesei was employed to maximize the production of the antioxidant-phenolic compounds and some fungal phenolic-associated enzymes (α-amylase, xylanase, β-glucosidase, polygalacturonase, and phenylalanine ammonia-lyase). The SSF-conditions were statistically optimized using response surface methodology (RSM). In the statistical model, four variables were analyzed at two levels. According to RSM, the adjusted R2 (< 0.9) is reasonably consistent with the predicted R2 (< 0.9), indicating that the statistical model is valid. The optimal conditions for maximum production of both phenolic compounds and fungal phenolic-associated enzymes were found to be 28 °C, pH 7.0, 20% moisture, and 7-day fermentation. The total phenolic content of fermented CS (FCS) increased 23 folds and total antioxidant activity was enhanced by 113- and 150-fold using DPPH and ABTS methods, respectively. Three new phenolics (kaempferol, apigenin, and p-coumaric) were recognized in FCS using HPLC analysis. The activities of all the extracted phenolic-associated enzymes showed strong correlations with the phenolic content of FCS. Against some human-pathogenic bacteria, FCS extract displayed considerably better antibacterial activity than UFCS extract. Finally, the phenolic-rich-FCS can be employed as a dietary supplement as well as an antibacterial agent. Furthermore, T. reesei has produced considerable quantities of industrially valuable enzymes.