Survival of Lactobacillus rhamnosus probiotic strains in peach jam during storage at different temperatures

Survival of six probiotic wild strains of Lactobacillus rhamnosus, in comparison with a type strain, into peach synthetic medium (PSM) and commercial peach jam (PJ), was followed during 78 days of storage at 25 and 5°C. Changes in viable cell counts, pH values, sugar contents and colour parameters during storage were monitored. All strains exhibited better performances in PJ than in PSM, showing count values higher than 7 Log cfu g-1 up to 78 days of storage at 5°C. Almost all wild strains remained above the critical value of 6 Log cfu g-1 in samples stored at 25°C up to 45 days, while the Lb. rhamnosus GG type strain, used as control, was not able to survive later than 15 days. In the synthetic medium used the strains showed better survival in samples incubated at 25°C, remaining viable above the critical level up to 45 days of storage, except for the strain H12. The probiotic cultures added to jam did not significantly modify the colour parameters of the produce, however the metabolism of lactobacilli did determine changes in the pH and in the sugars composition.