Osmotic dehydration assisted impregnation of Lactobacillus rhamnosus in banana and effect of water activity on the storage stability of probiotic in the freeze-dried product

In this study the impregnation of Lactobacillus rhamnosus in banana slices and the storage stability of the dehydrated product were analyzed. Banana slices were enriched with L. rhamnosus at levels of 109 CFU/g d.b. using a hypertonic solution of 50% (w/w) sucrose. The high level of probiotic impregnation occurred at high rates of mass transfer during the first 200 min of osmotic process. Since dehydration is widely used for the preservation of fruits this work analyzed the stability of probiotics impregnated in the freeze-dried banana and its relation with the thermodynamic properties of the adsorbed water. The survival kinetics showed that the viability of probiotics decrease more rapidly over water activity of 0.327, which was considered as critical for maintaining these alive. This water activity could be obtained using the minimum integral entropy of the adsorbed water at the freeze-dried banana surface. These results have shown that is possible to obtain dried fruits enriched with probiotics with good storage stability and that the thermodynamic approach is a useful tool to establish the optimal conditions of water activity to preserve the dehydrated product.