Efficiency of Enzymatic and Other Alternative Clarification and Fining Treatments on Turbidity and Haze in Cherry Juice Anne S. Meyer,* Christian Ko ¨ser, and Jens Adler-Nissen Food Biotechnology and Engineering Group, BioCentrum-DTU, Building 221, Technical University of Denmark, 2800 Lyngby, Denmark Several alternative strategies were examined for improving conventional juice fining procedures for cherry juice clarification and fining in laboratory-scale experiments: Centrifugation of freshly pressed juice from 1000g to 35000g induced decreased turbidity according to a steep, negative power function. Individual and interactive effects on turbidity and haze formation in precentrifuged and uncentrifuged cherry juice of treatments with pectinase, acid protease, bromelain, gallic acid, and gelatin-silica sol were investigated in a factorial experimental design with 32 different parameter combinations. Gelatin-silica sol consistently had the best effect on juice clarity. Centrifugation of cherry juice (10000g for 15 min) prior to clarification treatment significantly improved juice clarity and diminished the rate of haze formation during cold storage of juice. Both treatment of precentrifuged cherry juice with Novozym 89L protease and co-addition of pectinase and gallic acid improved cherry juice clarity and diminished haze levels. None of the alternative treatments produced the unwieldy colloids notorious to gelatin-silica sol treatment. The data suggest that several alternative clarification strategies deserve further consideration in large-scale cherry juice processing. Precentrifugation of juice before clarification and fining is immediately recommended. Keywords: Clarification; fining; turbidity; haze; cherry juice; protease; pectinase; gelatin; silica sol INTRODUCTION Industrial production of cherry juice includes a num- ber of steps intended to clarify the pressed juice. Clarification treatment of cherry juice typically involves addition of pectinases and fining agents such as ben- tonite or gelatin-silica sol to remove cloud, sediments, and haze-active components (1). Usually, such juice clarification also includes a slow settling of the colloid flocs resulting from the action of added pectinase and fining agents and subsequent separation and recovery of juice from the flocculated material. In Europe, industrial production of cherry juice and cherry juice concentrates is largely based on local varieties of sour (or tart) cherries (Prunus cerasus L.) (2). The main purpose of the clarification treatment employed in industrial cherry and other fruit juice processing is to take away constituents responsible for the immediate turbidity and cloudiness in freshly produced juice. The other important purpose is to remove substances that may cause haze and sediment formation during storage, at reconstitution of the con- centrate, or after bottling of the juice. Only very little is known about the identity of the substances responsible for cloud, turbidity, and haze development in cherry juice. However, in accordance with the knowledge on cloudiness and turbidity in apple juice (3, 4), the current practical experiences from use of pectinases and fining agents in the clarification of cherry juice (5) indicate that the primary cloud in freshly pressed cherry juice is mainly due to the presence of suspended proteinaceous pectin particles. Fractions of other fruit cell wall material may also be responsible for some coarse turbidity as is the case in other types of fruit juices (6, 7). The sediments and postclarification haze may result mainly from proteins, polyphenols, oxidized phenolics, insoluble tannins, and their interactions as demonstrated in apple juice, grape juice, wine, and haze model solutions (4, 8-10). There exists no specific terminology to discriminate turbidity, cloud, sediments, and postclarification haze formation in fruit juices according to their chemical origins or times of emergence in the juice process. In this paper, haze will be used to describe the turbidity that eventu- ally forms after clarification during cold storage of cherry juice. Enzymatic depectinization in fruit juice clarification is assumed to work by pectinase-catalyzed electrostatic destabilization of suspended, cloud-causing pectin par- ticles (3, 11). Clarification of fruit juices by fining treatment with bentonite or gelatin and silica sol rests on unspecific binding of haze-active polyphenols and proteins and capture of sediments and cloud substances during subsequent sedimentation of the resulting col- loidal structure (6, 12). The fining treatment may be performed after, or concurrent with, pectinase clarifica- tion treatment. The generally used criterion for cherry juice clarity is that the turbidity of the final, freshly produced juice is <5 FNU (formazan nephelometric units at 3.0 °Brix) as evaluated by nephelometry (13). In large-scale fruit juice processing, the gelatin-silica sol clarification step is slow, as it may last for a minimum of 6-18 h to accomplish the necessary sedi- mentation of the colloidal particles. Incomplete sedi- mentation of the colloidal material results in prolonged processing times and significant juice losses. The clari- * Corresponding author [fax (+45) 45 49 88 22; e-mail anne.meyer@biocentrum.dtu.dk]. 3644 J. Agric. Food Chem. 2001, 49, 3644-3650 10.1021/jf001297n CCC: $20.00 © 2001 American Chemical Society Published on Web 06/30/2001