Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 14, 1997
Publication Date: N/A
Interpretive Summary: Valencia orange fruit peel tissue extracts were prepared and the dialysis supernatant portion was used for chromatographic separation of multiple forms of the enzyme pectinmethylesterase (PME). This enzyme initiates a sequence of events that results in destabilization of the juice cloud and flocculation in beverages and drinks that contain citrus juice. Four different forms of PME were obtained and each form was tested for its affect on juice cloud stability at 30 degree C and 4 degree C. A measured amount of enzyme activity from each of the four forms was added to pasteurized, reconstituted frozen concentrated orange juice and the samples were incubated at 30 degree C and 4 degree C. At periodic time intervals the juice was assessed for juice cloud destabilization. Results indicate: (1) each form affected juice cloud stability differently, (2) one form was thermally labile, (3) one labile form had no effect at either 30 or 4 degree C, (4) at 4 degree C only the thermally tolerant form and one labil form rapidly destabilized juice cloud, and (5) the thermally tolerant PME is a glycoprotein.
Technical Abstract: Salt extractable proteins were isolated from Valencia fruit peel tissue. After dialysis the supernatant was applied to a Heparin CL-6B column and four discrete peaks of pectinmethylesterase (PME) activity were obtained (PME 1-4). The thermally tolerant PME (PME 3) was applied to a Concanavalin A column. Binding of PME 3 to Concanavalin A indicates it is a glycoprotein. Samples of pasteurized, reconstituted FCOJ containing 5 U/mL of either PME 1, 2, 3 or 4 were incubated at 30 and 4 degree C and periodically sampled to determine their effect on cloud stability. Differences in the rate of juice cloud destabilization were observed among the four forms of PME. At 30 degree C PME 1 destabilized juice cloud most rapidly followed closely by PME 3 (thermally tolerant) and PME 2. At 4 degree C PME 3 destabilized the cloud most rapidly followed closely by PME 1. PME 2 was much less active at 4 degree C than PME 3, PME 1 or PME 2 at 30 degree C. PME 4 did not destabilize the cloud at either temperature.