Effective clarification of pomegranate juice using laccase treatment optimized by response surface methodology followed by ultrafiltration

Abstract

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. PRACTICAL APPLICATIONS The 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. © 2009 Wiley Periodicals, Inc.