44C-3 |
Clarification of citrus juice is influenced by specific activity of pectinmethylesterase (PME) and inactive PME-protein complexes |
J. L. ACKERLEY1, M. Corredig, and L. Wicker. (1) Food Science and Technology, University of Georgia, Athens, GA 30602-7610 Juices and juice added beverages undergo sporadic cloud destabilization that is typically attributed to residual thermostable PME activity. Cloud loss has never been directly correlated with PME activity and this may be due to insensitive methods to detect potential PME activity. The objective of this study was to evaluate conditions, including specific enzymatic activity and cation concentration that may influence the clarification of citrus juices. Enzyme from Valencia orange pulp was extracted and partially purified by ion exchange chromatography (SP, Pharmacia) using FPLC. PME at different units/mg of protein were added at equal units/ml of juice for one study. In a second study, one PME preparation was added at the same units/ml of juice with and without cations (calcium, strontium and spermidine). All juices were stored at 4°C. The juice that contained PME that never bound to the SP column began to clarify at day one and then clarified at a faster rate after day four. PMEs of lower specific activity clarified juices at a faster rate than PMEs of higher specific activity. All other juices with added PME and without cations did not clarify in 10 days. Similarly, juices with cations and without PME also did not clarify. However, all juices treated with PME and cations, started clarifying at day one. Juices with enzyme clarified the fastest with strontium, followed by calcium and spermidine. Cations enhance clarification of citrus juices possibly by releasing PME from an inactive PME-pectin complex. The PME with the highest specific activity did not clarify the juice at the fastest rate, suggesting that a non-PME factor is involved in clarification. This is further supported by the fact that the PME that did not bind to the SP column was the only enzyme fraction to rapidly clarify juice without addition of cations.
Session 44C, Fruit & Vegetable Products: Chemistry
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