A strain of Lactobacillus plantarum and 4 strains of bifidobacteria were inoculated in apple juice and in a commercial beverage labeled as “red-fruit juice,” containing citrus extracts as natural preservatives; the suitability of the probiotics was evaluated in relation to their resistance to 2 kinds of citrus extracts (biocitro and lemon extract), survival in juices at 4 and 37 °C, and inhibition of Zygosaccharomyces bailii. Cell count of L. plantarum and bifidobacteria over time was fitted through the Weibull equation, for the evaluation of the first reduction time (δ), death time, and microbiological shelf life (the break-point was set to 7 log cfu/mL). Bifidobacterium animalis subsp. lactis experienced the highest δ-value (23.21 d) and death time (96.59 d) in the red-fruit juice at 4 °C, whereas L. plantarum was the most promising strain in apple juice at 37 °C. Biocitro and lemon extract did not exert a biocidal effect toward probiotics; moreover, the probiotics controlled the growth of Z. bailii and the combination of L. plantarum with 40 ppm of biocitro reduced the level of the yeast after 18 d by 2 log cfu/mL.
Probiotics are often added to different products to provide physiological benefits, thus producing “functional food.” B. animalis subsp. lactis and L. plantarum survived in apple juice and in a commercial drink (red-fruit juice), containing a citrus extract as natural preservative, and were able to control the growth of Z. bailii, a spoiling yeast of juices.