Effect of pH upon viability of probiotic strains when in contact with fruit pulps

In recent years many probiotic-containing products have been developed, being dairy and dried products the main vehicles for probiotic intake. Fruit juices have also been studied, with less good results, probably due to their low pH values, as well as to the presence of other components, adverse to the survival of the probiotic strains. In order to pinpoint possible reasons therefore, in this study we tried to evaluate the effect of the fruit pulp pH upon the survival of Lactobacillus acidophilus LA-5 and Bifidobacterium animalis BB-12. Two fruit pulps, with different pH values, were used, namely lemon (pH=2.5) and avocado (pH=6.5), and their pH was adjusted (to 2.5, 4.5 and 6.5), in order to access the effect upon probiotic survival over one week storage. Viability was evaluated at 0, 3 and 7 days. Results showed that, although the pH value is indeed important, it is not the only reason for low viability of probiotics when incorporated in fruit pulps. Viability was, as expected, the highest when the pulps had a pH value of 6.5. At 4.5, avocado still had considerable viable cell numbers after one week contact with the pulp, while for lemon, at the same pH, no probiotics were detected after 3 days. At 2.5, for both pulps, no viable cells were detected after only 3 days. These results indicate that, although pH is important, other constituents of the fruits are also responsible for the degree of survival of probiotics in fruit matrices.