Survival of Microorganisms in Galactooligosaccharide Stored at Various Temperatures

Food-grade galactooligosaccharide (GOS) has a low water activity (a_w). We investigated the survival of Escherichia coli, Salmonella spp., Pseudomonas aeruginosa, Listeria monocytogenes, Staphylococcus aureus, Aspergillus flavus and Saccharomyces cerevisiae in GOS as affected by inoculum levels and storage temperatures. The five bacteria (inoculated at 3 or 6logcfu/g), and the fungus A.flavus (3logcfu/g) and S.cerevisiae (3logcfu/g), were inoculated into GOS and the material stored at 4, 22 or 50C for 28 days. When ca. 6logcfu/g of microorganisms were inoculated into GOS, the final numbers of L.monocytogenes and S.aureus (thus after 28 days of storage) were higher than those of E.coli, Salmonella spp. and P.aeruginosa, at all storage temperatures tested. In GOS inoculated with ca. 3logcfu/g of microorganisms, A.flavus numbers were the highest after 28 days. S.cerevisiae levels were lower than those of gram-positive but higher than those of gram-negative bacteria. The overall level of survival by temperature was 4C>22C>50C, regardless of inoculum level. Thus, microbial survival in low-a_w GOS was affected by temperature and inoculum level but the microorganisms did not grow during the storage.