A sol–gel matrix to preserve the viability of encapsulated bacteria

E. coli bacteria were encapsulated within silica gels and aged at room temperature in the absence of nutrients. Their viability was studied as a function of time using different viability tests. The plate count technique gives the number of culturable bacteria that remain able to form colonies in the presence of a culture medium. Their metabolic activity toward glycolysis was followed by 14C titration and 13C NMR spectroscopy. Several sol–gel matrices were tested in order to improve the viability of the trapped bacteria. The best results were obtained when encapsulation is performed in the presence of glycerol showing that almost 50% of the bacteria were still able to form metabolites after one month of ageing. Moreover, this study demonstrates that a wide range of viability tests can be adapted for use with cells encapsulated in mineral matrices.