Cloud, citrus juice stability

Similarly, there are present in citrus juices active enzyme systems that destroy the important pectic constituents. These enzymes have to be rapidly inactivated to protect the desirable cloud (turbidity) which is apparently stabilized by pectic substances. ... 

If steps are not taken to stabilize cloud, most citrus juices will clarify when allowed to stand. Clarification occurs when native PE lowers the ester content of juice soluble pectin until it becomes susceptible to precipitation as insoluble pectates (23). If pectin levels are high enough, as in concentrates, these pectates may form a gel. 

Cloud stability in citrus juices Pectin manufacture from citrus pomace Distillates from fermented fruit pulps Enzymatic maceration of fruits and vegetables Self-clarification of lemon/lime and apple juices Pressing characteristics of citrus pomace Ca2 -firming of fruits and vegetables... 

Figure 7. a, Cloud loss in enzyme-inactivated orange juice by addition of citrus PE. Stabilization of cloud by adding PG together with PE. b, The activity of PE in both cases is shown by methanol release. (Reproduced with permission from ref. 52. Copyright 1974 Forster.)... 

Versteeg et al. (50) have isolated various multiple forms of pectin esterases in oranges and shown that they differ in affinity to pectins and pectates and in heat stability and therefore may play different roles in cloud loss phenomena. One form (about 5% of the total PE activity) was found to be much more heat stable than the other forms it was also active at low pH (2.5) and at low temperatures. Another form did not cause self-clarification for this enzyme a similar mode of attack was proposed as for fungal pectin esterases which produce low-ester pectins less sensitive to calcium. Multiple forms of pectin esterases are present in the fruits of all of the orange varieties and citrus species tested. The two isoenzymes known to be responsible for cloud loss and gelation in citrus products were found to occur in all of the component parts of the orange fruit (51). In the French cider industry the endogenous PE of apple is used for the self-clarification of apple juice (52). 

Collet et al. (2005) stated that the study of pectinesterase inactivation behavior is important because pectinesterase is responsible for juice cloud stability loss, is composed of several isoenzymes, and occurs naturally in orange. Freshly squeezed juice of Pera orange (Citrus sinensis) was pasteurized at temperatures of 82.5, 85.0, and 87.5°C. At least five runs with different holding times were performed for each temperature. As the isothermal curves obtained showed deviations from the expected first-order kinetics, the data was statistically treated by applying a nonlinear regression, and the estimated best fit was a three-parameter-multicomponent-flrst-order model. At 82.5°C, the isothermal curves showed a nonzero asymptote of inactivation, indicating that at this temperature the most heat-resistant... 

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