Survival of freeze dried Lactobacillus plantarum in instant fruit powders and reconstituted fruit juices

Abstract

The aim of this study was to investigate the survival of freeze dried Lactobacillus plantarum cells mixed with several freeze dried instant fruit powders (strawberry, pomegranate, blackcurrant and cranberry) during storage for 12months as well as after reconstitution with water each month. Inulin and gum arabic were also added to the instant fruit powders at two levels (10% and 20% w/w of dry weight) to improve the cell survival and functional properties of the product. The best cell survival over the 12months of storage was observed for the blackcurrant powder (almost no decrease) followed by strawberry (~0.3 log decrease), pomegranate (~0.9 log decrease), whereas the worst survival was obtained in cranberry powder (~4.5 logs). To explain these results multiple regression analysis was conducted with the log decrease [log10N0month−log10N12months] as the dependent variable and water activity, pH, citric acid, dietary fibre and total phenol as the independent variables. The results indicated that among all the examined factors, the [log10N0month−log10N12months] depended only on the water activity (P<0.05). Inulin and gum arabic demonstrated a substantial protective effect on cell survival (1–1.5 log) in the case of cranberry, which was likely due to a physical interaction between the cells and the carbohydrates. After reconstituting the dried fruit powders at room temperature and measuring cell viability for up to 4h, it was shown that in the case of strawberry juice there was no decrease, and very little in the case of pomegranate and blackcurrant juices (<0.5 log). On the other hand, a significant decrease was observed for cranberry juice (P<0.05), which increased as the storage time of the dried cranberry powder increased, indicating that the cells became more susceptible with prolonged storage. Multiple regression analysis indicated that the main factors influencing cell survival were water activity and pH, while citric acid, dietary fibre and total phenol did not have an effect. Furthermore, inulin and gum arabic addition did not have a significant (P>0.05) effect upon reconstitution of the dried fruit powder. This study showed that instant juice powders are very good carriers of probiotic cells and constitute good alternatives to highly acidic fruit juices.