Behavior of Lactobacillus plantarum and Saccharomyces cerevisiae in fresh and thermally processed orange juice

Lactobacillus plantarum and Saccharomyces cerevisiae are acid-tolerant microorganisms that are able to spoil citrus juices before and after pasteurization. The growth of these microorganisms in orange juice with and without pasteurization was investigated. Two samples of orange juice were inoculated with ca. 10(5) CFU/ml of each microorganism. Others were inoculated with ca. 10(7) CFU/ml of each microorganism and then thermally treated. L. plantarum populations were reduced by 2.5 and <1 log(10) CFU/ml at 60degreesC for 40 s and at 55degreesC for 40 s, respectively. For the same treatments, S. cerevisiae populations were reduced by >6 and 2 log(10) CFU/ml, respectively. Samples of heated and northeated juice were incubated at 15degreesC for 20 days. Injured populations of L. plantarum decreased by ca. 2 log(10) CFU/ml during the first 70 h of storage, but those of S. cerevisiae did not decrease. The length of the lag phase after pasteurization increased 6.2-fold for L. plantarum and 1.9-fold for S. cerevisiae, and generation times increased by 41 and 86%, respectively. The results of this study demonstrate the differences in the capabilities of intact and injured cells of spoilage microorganisms to spoil citrus juice and the different thermal resistance levels of cells. While L. plantarum was more resistant to heat treatment than S. cerevisiae was, growth recovery after pasteurization was faster for the latter microorganism.