The application of sub-lethal stresses is known to be an efficient strategy to enhance survival of probiotic bacteria during drying processes. In this context, we previously showed that the application of heat stress upon the entry into stationary phase increased significantly the viability of Bifidobacterium bifidum. However, this heat shock has been considered only in small-scale bioreactor and no information is available for a possible scaling-up strategy. Five different operating scales (0.2, 2, 20, 200 and 2000 L) have thus been tested and the results showed that the viability of B. bifidum increases from 3.15 to 6.57 folds, depending on the scale considered. Our observations pointed out the fact that the heat stress procedure is scalable according to the main outcome, i.e., increases in cell viability, but other factors have to be taken into account. Among these factors, dissolved carbon dioxide seems to play a significant role, since it explains the differences observed between the test performed at laboratory scale and in industrial conditions.

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The formation of odorous compounds in piggery wastes was investigated. Phenol and para-cresol are generally encountered in these typically anaerobic environments. They are produced from L-tyrosine by microbial metabolism. Phenol is further converted to benzoate via para-carboxylation. The biochemical pathways were studied by feeding manure with miscellaneous metabolites at concentration between 5 and 20 mM. Metabolites were analyzed by gas chromatography (GC) and high-performance liquid chromatography (HPLC). Experiments were carried out at room temperature. The degradation of L-tyrosine to phenol, benzoate, and para-cresol was confirmed. 4HPPyrA and 4HPAA are not intermediate compounds in phenol production. It was shown that phenol was converted to benzoate without any production of 4HBA. Other experiments showed that 4HBA was decarboxylated to phenol, but not dehydroxylated to benzoate.When phenol was added in presence of benzoate (5 mM each) or alone at higher concentrations (10 or 20 mM), transient small amounts of 4HBA were observed (about 0.02 mM). Our experiments show that 4HBA is not an intermediate metabolite in the conversion of phenol to benzoate. The decarboxylation of 4HBA to phenol is probably the last step of another degradation pathway. This reaction is proposed to have a weakly reversible property, explaining 4HBA production.

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