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Nutritional enhancement of probiotics and prebiotics: technology aspects on microbial viability, stability, functionality and on prebiotic function

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Enhancing bacterial stress resistance in food preparations

Focusing on improving the performance of functional foods, the PROTECH project studied extensively the stress response of bifidobacteria, a health-improving bacterial species used as a food additive.


Bifidobacteria, commonly detected in the human gastrointestinal tract, constitutea critical factor of gut homeostasis and normal development. Due to their health benefits and since this bacterial strain does not occur in natural food, it is normally added in food preparations as live bacteria. Infant formulas, cheese, dietary supplements and fermented dairy products are some examples of food products with bacteria additions. Nevertheless, bifidobacteria survival in food products is highly uncertain due to a number of factors on which the PROTECH project focused to study in detail. One of these involved the stress resistance of B. longum NCC2705 to three different types of stresses, oxidative stress, starvation and heat shock. Researchers exploited DNA-based arrays, containing a set of B. longum genes that were used for global expression profiling in response to various environmental changes. The profiles compilation offered valuable feedback on genes encoding proteins offering non-specific cell protection under adverse conditions or genes induced from a specific type of stress. Under identical conditions, cells were grown and subjected to either a heat shock, exposure to H2O2 or transition into stationary phase. These observed gene expression profiles were compared against those obtained from exponentially growing cells. The results showed that twenty-one genes including dnaK, grpE, dnaJ, hspR, groEL, groES, clpB and hrcA were induced. Moreover, several upregulated genes encoding proteins without any predicted function were identified and considered responsible for B. longum cells protection against unfavourable conditions. Most interestingly, a rapidly and highly induced gene was identified that could be developed as a stress marker. This marker could prove beneficial in the monitoring the physiological status of the cells or the identification of experimental parameters responsible for inducing a general stress response.

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