Ultraviolet treatment of orange juice.

摘要

UV transmittance in orange juices is low on account of their content of high suspended solids, which cause opacity. This means that UV treatments of the type used to decontaminate water are not compatible with juices. To facilitate UV treatment of orange juices, a thin film reactor was developed. The reactor was made from glass and juice could flow along the inner surface of a vertical tube to produce a thin film, suitable for UV treatment. Decimal reduction doses of 87.7 +- 7 mJ/cm2 for aerobes and 119.0 +- 17 mJ/cm2 for yeasts and other fungi were determined for reconstituted orange juices of 10.5degBrix. Treatment at a dose of just 73.8 mJ/cm2 was able to extend the shelf life of fresh juices from 2 days to >5 days, and results suggested that further shelf life extension would be possible with increased doses of UV. No significant alterations in juice pH or colour were observed. Comparison of the UV treatment (100 mJ/cm2) with thermal sterilization on the basis of ascorbic acid degradation revealed similar effects (17% degradation). UV processing, however, did not inactivate pectin methylesterase, the enzyme responsible for juice cloud loss. Further comparison with thermal treatment, revealed markedly lower energy use when UV was employed (2.0 vs. 82 kW h/m3).