The importance of many factors for the cloud stability of orange juice was investigated. By the determination of methanol, cloud loss of orange juice could be ascribed directly to the action of pectin esterase. However, clarification only occurs if calcium ions are available to precipitate the low methoxy pectin formed by pectin esterase. This mechanism was confirmed when the addition of pectic acid clarified the orange juice artificially.<p/>Clarification did not occur if the formation of high polymer calcium pectate was prevented either by degrading the juice pectin by a purified pectin lyase before substantial action of pectin esterase, or by enzymic hydrolysis by a yeast polygalacturonase of the low methoxy pectin formed. Methanol determinations showed that cloud stabilization had been achieved in spite of normal action of pectin esterase.<p/>Methods to determine cloud stability have been discussed. Literature on the research of cloud stability of fruit juices, on pectic substances and pectic enzymes, and on methods to determine pectin esterase have been reviewed.
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