engleski

Description of the Microflora of Sourdoughs by Culture-Dependent and Culture-Independent Methods

The natural microflora of sourdoughs consists of two main microbial groups: yeasts and lactic acid bacteria. In this work the natural microflora of four sourdoughs from artisanal North Italy bakeries was studied using culture dependent and culture independent methods. In all samples the yeasts numbers ranged from 160 to 107 cfu/g, lactic acid bacteria numbers ranged from 103 to 109 cfu/g. From sequencing data of isolated LAB strains, there was a similarity between two samples, both for present strains and for the percentage of isolats. In fact, Lb. plantarum was present for 73% and 89%, instead Lb. brevis for 27% and 11%. Opposed to that, in the third sample, the dominant LAB strain was Lb. brevis (73%), Lb. plantarum was present only for 27%. The fourth sourdough was completely different from the others. In this sample, the most isolated species were W. cibaria (56%), followed by Lb. plantarum (36%) and P. pentosaceus (8%). The identification of yeasts showed that the species isolated from three out of four samples was S. cerevisiae, instead C. humilis (90%) and C. milleri (10%) in the fourth sample. Microbial ecology of sourdoughs was also examined with direct method of DNA and RNA extraction from sourdough. The DNA and RNA profiles were the same in all three samples, but in the fourth, DNA profile presented a band, which was not there in RNA profile. Comparing the results obtained from strain isolation and sourdough DNA and RNA extraction, it is evident that some microorganisms, although present in sourdoughs analysed, were not active, probably because they were present in low concentration in the samples. After considering all the results, it is evident that the combination of culture dependent and culture independent methods is important in obtaining the real picture in the study of sourdough microbial ecology.

sourdough; ecology; culture dependent methods; culture independent methods

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