Phenolic compounds of pomegranate juice, which are responsible for haze formation and browning during storage, could be selectively removed by combined enzyme-ultrafiltration process. The pomegranate juice was treated with Fomes fomentarius laccase at various enzyme concentrations (0.5-5 U/ mL), temperatures (20-50C) and times (30-300 min). The effect of these enzymatic treatments on total phenol content and clarity of the juice were evaluated using a central composite design. The optimum treatment conditions were: enzyme concentration 5 U/mL; time 300 min; and temperature 20C. Their application led to a 40% reduction of total phenols but induced a threefold decrease of the juice clarity. This drawback was overcome by ultrafiltration of the laccase-treated juice. The pomegranate juice obtained was clear, stable and characterized by total phenolics = 864 mg/L, clarity (A 650 nm ¥ 1,000) = 86 and color (A 420 nm ¥ 1,000) = 236 versus 1,681, 127 and 382, respectively, for untreated juice.
CorrespondingThe tendency for hazes to develop in pomegranate juices during storage is a persistent problem in the fruit juice industry. In this work, laccase treatment optimized by response surface methodology followed by ultrafiltration was used to clarify the pomegranate juice. The application of the optimum enzymatic treatment conditions (enzyme concentration 5 U/mL; time 300 min; and temperature 20C) followed by ultrafiltration (cutoff value 15 KDa) decreases the total phenolics of about 50% and the antioxidant capacity of about 20% and, increases the clarity of about 30% versus untreated juice. 1200 M. NEIFAR ET AL.
Statistical approaches were employed for the optimization of different cultural parameters for the production of laccase by the white rot fungus Fomes fomentarius MUCL 35117 in wheat bran-based solid medium. first, screening of production parameters was performed using an asymmetrical design 2533//16, and the variables with statistically significant effects on laccase production were identified. Second, inoculum size, CaCl2 concentration, CuSO4 concentration, and incubation time were selected for further optimization studies using a Hoke design. The application of the response surface methodology allows us to determine a set of optimal conditions (CaCl2, 5.5 mg/gs, CuSO4, 2.5 mg/gs, inoculum size, 3 fungal discs (6 mm Ø), and 13 days of static cultivation). Experiments carried out under these conditions led to a laccase production yield of 150 U/g dry substrate.
Aim: To produce high laccase activities from the white‐rot fungus Fomes fomentarius.
Methods and Results: Different culturing methods, viz, cell immobilization on stainless steel sponges and plastic material and solid‐state fermentation (SSF) using wheat bran as substrate were used for laccase production by the white‐rot fungus F. fomentarius. The SSF study expresses the highest laccase activities, nearly to 6400 U l−1 after 13 days of laboratory flasks cultivation. When the wheat bran medium was supplemented with 2 mmol l−1 copper sulfate, laccase activity increased by threefold in comparison to control cultures, reaching 27 864 U l−1. With the medium thus optimized, further experiments were performed in a 3 l fixed‐bed bioreactor (working volume 1·5 l) leading to a laccase activity of about 6230 U l−1 on day 13.
Conclusions: The results obtained clearly showed the superiority of wheat bran for laccase production over stainless steel sponges and plastic material. Supplementing the wheat bran solid medium with 2 mmol l−1 copper sulfate allowed obtaining high activities at flask scale. The system was scaled to fixed‐bed laboratory reactor.
Significance and Impact of the Study: The high enzyme production along with the low‐cost of the substrate, showed the suitability of the system F. fomentarius– SSF for industrial purposes.
The decolorization of direct Solophenyl red 3BL (SR), a polyazo dye extensively used in textile industry was studied. The Fomes fomentarius laccase alone did not decolorize SR. The natural redox mediator, acetosyringone (AS), was necessary for decolorization to occur. Box-Behnken design was used to evaluate the effects of three parameters, namely, enzyme concentration (0.5-2.5 U mL −1 ), redox mediator concentration (3-30 μM), and incubation time (1-24 h), on the SR decolorization yield. The fitted mathematical model allowed us to plot response surfaces as well as isoresponse curves and to determine optimal decolorization conditions. The results clearly indicated that the AS concentration was the main factor influencing the SR decolorization yield. The selected optimal conditions were enzyme concentration 0.8 U mL −1 , mediator concentration 33 μM, and time 14 h 30 min. These conditions allowed 79.66% of SR decolorization versus 80.70% for the predicted value. These results showed a promising future of applying laccase-AS system for industrial wastewater bioremediation.
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