Comparative study of culture media used for sourdough lactobacilli

Abstract

Eleven culture media were analysed to compare their exhaustiveness for the quantification of lactobacilli type I sourdoughs. The media tested were MRS, maltose modified MRS, MRS5, SDB, SFM, MRS "Vogel", Rogosa as elective media, and FH, OH, LAMVAB, KCA as selective media. Six broth media were also tested for colony subculture. Quantitatively, maltose MRS and MRS media showed the highest counts - respectively 9.47 and 9.43 mean log(cfu)/g. SFM and Rogosa media presented slighlty lower levels - 9.1 and 9.24 log(cfu)/g respectively. Levels on the remaining media were significantly lower - lesser than 0.5 log(cfu)/g compared to maltose MRS and MRS media. From a qualitative standpoint, the bacterial diversity, based on the comparison of the whole-cell protein patterns of isolates, was the largest on maltose MRS medium. However, MRS5 medium allowed the isolation of a specific population only found on this medium. For colony subculture, maltose MRS and MRS5 appeared the most appropriate broth media. These results underline that there is no really efficient medium for the systemic study of sourdoughs. Therefore, the first step before working on these ecosystems implies a deliberate choice of the most appropriate media combination.