UV DISINFECTION OF SOME OF THE FRUIT JUICES

acetic acid bacteria contribute to the spoilage of fruit juices which have pH values about
4 (Lott and Carr 1964).
2.3.1. Important Enzymes in Fruit Juice Products
Deterioration of fruit and vegetable products is highly correlated with the
enzyme activity. The most important enzymes in respect of the quality of fruits and
vegetables are peroxidase, catalase, lipoxygenase, catechol oxidase (referred to as
polyphenol oxidase) and pectinesterase (referred to as pectinmethylesterase). It was
reported that pectinesterase involves in the development or loss of textural
characteristics (Vora, et al. 1999). Pectinmethylesterase (PME) is a deesterification
enzyme and it is the most important one for the citrus products (Ludikhuyze, et al. 2003,
Ingallinera, et al. 2005). It hydrolyzes the methyl ester units giving pectic acid and
methanol (Beltran, et al. 2005). After the hydrolysis, low methoxy pectin is occurred
and it links up with polyvalent cations like Ca 2+ . This cross-linking forms insoluble
pectate precipitates and causes the cloud loss in turbid juices (Guiavarc’h, et al. 2005).
Ingallinera, et al. (2005) found that inactivation of PME is related to the pasteurization
temperatures. However, all PME activity can not be inactivated by pasteurization due to
the existence of thermostable fraction of the enzyme (Kim and Tadini 1999). Vora, et al.
(1999) investigated the conditions in order to completely inactivate the enzyme in
Australian carrots. They found that at 70°C PME enzyme was totally deactivated in 10
minutes. The inactivation of PME enzyme and its izoenzymes found in orange juice was
reported to be provided by processing the juice at 90°C for 1 minute (Nienaber and
Shellhammer 2001).
2.3.2. Microorganisms Effective on Fruit Juice Quality
Many organisms, especially acid-tolerant bacteria and fungi (yeasts and molds)
can cause spoilage in the fruit juice using fruit as a substrate. Discoloration, off-flavors,
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