Diversity and Stability of Lactic Acid Bacteria in Rye Sourdoughs of Four Bakeries with Different Propagation Parameters

Abstract

We identified the lactic acid bacteria within rye sourdoughs and starters from four bakeries with different propagation parameters and tracked their dynamics for between 5-28 months after renewal. Evaluation of bacterial communities was performed using plating, denaturing gradient gel electrophoresis, and pyrosequencing of 16S rRNA gene amplicons. Lactobacillus amylovorus and Lactobacillus frumenti or Lactobacillus helveticus, Lactobacillus pontis and Lactobacillus panis prevailed in sourdoughs propagated at higher temperature, while ambient temperature combined with a short fermentation cycle selected for Lactobacillus sanfranciscensis, Lactobacillus pontis, and Lactobacillus zymae or Lactobacillus helveticus, Lactobacillus pontis and Lactobacillus zymae. The ratio of species in bakeries employing room-temperature propagation displayed a seasonal dependence. Introduction of different and controlled propagation parameters at one bakery (higher fermentation temperature, reduced inoculum size, and extended fermentation time) resulted in stabilization of the microbial community with an increased proportion of L. helveticus and L. pontis. Despite these new propagation parameters no new species were detected.

Fig 1. Composition of lactic acid bacterium species, expressed in percentage of the total number of isolates, in rye sourdoughs from four Estonian bakeries (A_bakery, B_bakery, C_bakery and D_bakery).

Samples are coded according to the description reported in Table 1.

Fig 2. Relative abundance of bacterial species/genera detected in rye sourdoughs from four Estonian bakeries (A_bakery, B_bakery, C_bakery and D_bakery) using pyrosequencing of 16S rRNA gene amplicons.

Samples are coded according to the description reported in Table 1.

Fig 3. pH (red plot) and lactic acid bacterium species detected by DGGE analysis of the 16S rRNA gene amplicons in rye sourdoughs collected at the D_bakery before (D4) and after applying the new propagation protocol.

Time after transfer is indicated below the gel (d–day; m–month). Bands: 1, 7 –Lactobacillus helveticus; 2, 8 –Cereal chloroplast DNA; 3, 4, 5, 10 –Lactobacillus pontis; 6 –Lactobacillus sp.; 9 –Lactobacillus zymae; *—sample collected from sourdough after 36 h storage at 5°C.

Fig 4. Two dimensional non-metric multidimensional scaling (NMDS) of sourdough samples from four Estonian bakeries (A_bakery, B_bakery, C_bakery and D_bakery).