Rapid detection of Fructilactobacillus sanfranciscensis in sourdough by lateral flow immunochromatographic assay

When maintaining sourdough by backslopping, there is a risk that the desired lactic acid bacteria (LAB) strain may be replaced by another. To rapidly monitor the proliferative status of the desired LAB, we developed a lateral flow immunochromatographic assay (LFIA) targeting Fructilactobacillus sanfranciscensis. We investigated the detection sensitivity of LFIA for 13 strains of F. sanfranciscensis. The limit of detection was 5-6 Log (cells/test). No positive result was obtained when the newly developed LFIA was applied against 51 strains other than F. sanfranciscensis, suggesting that it can specifically detect F. sanfranciscensis. To verify the practicality of LFIA, sourdough supplemented with F. sanfranciscensis and Saccharomyces cerevisiae as starters was passaged for 10 days at three different temperatures (23 °C, 30 °C, and 37 °C) with daily backslopping. The condition of these sourdoughs was monitored by pH measurements, yeast and LAB count surveys, amplicon analysis, and LFIA, and the methods were compared for their effectiveness as a management tool. Compared to the 23 °C-incubated samples, fewer F. sanfranciscensis cells were seen in the 30 °C-incubated samples, and the major LAB was replaced by putative Pediococcus acidilactici in the 37 °C-incubated samples. LFIA was successful in detecting both of these sourdough abnormalities. Lateral flow immunochromatographic assay could detect F. sanfranciscensis within 30 min, including the pretreatment step. The newly developed LFIA is expected to be a useful tool for artisan bakeries that want to provide customers with consistent quality sourdough bread every day.