Monitoring probiotic lactic acid bacteria strains during sauerkraut production by pulsed-field gel electrophoresis.

The intrinsic health-promoting properties of sauerkraut can be successfully improved by developing effective combinations with probiotics in order to obtain innovative functional products. This study aimed to evaluate the viability and persistence of the commercial probiotic strains Lactiplantibacillus plantarum 01 (LP01) and Lacticaseibacillus rhamnosus (LR04) when used as adjunct starter cultures during the production of traditional probiotic sauerkraut.

Each strain was made resistant to rifampicin (100 µg/mL) in order to track down the inoculum during the in vivo study. Shredded cabbage was mixed with 2.0% (w/v) sea salt to create the brine. This mixture was transferred into sterilised glass jars. Control samples underwent spontaneous fermentation, while experimental samples were inoculated with spray-dried powder of either the resistant LP01 or LR04 strain, targeting a concentration of about 1 × 10⁶ cfu/g of sauerkraut. All the samples were incubated at 20°C for 28 days. The number of lactic acid bacteria (LAB) in the cabbage extracts was counted on MRS agar and on MRS agar plus rifampicin at days 0, 21, and 28. The administered strains were monitored by pulsed-field gel electrophoresis (PFGE) to confirm the persistence and genotypic identity of the isolates.

Both probiotic strains maintained high viability and predominance during the fermentation process, with only a slight but significant decline by day 28. After 21 days of fermentation, LP01 and LR04 showed viable counts of 7.43 and 7.94 log₁₀ cfu/g, respectively. At day 28, the counts decreased to 7.09 and 7.24 log₁₀ cfu/g (p < 0.001). The rifampicin-resistant colonies accounted for 87% to 99% of the total LAB population in the inoculated samples. The strains analysed had identical PFGE pulsetypes, confirming the presence of LP01 or LR04 throughout the whole study. In conclusion, sauerkraut fermented with the LP01 or LR04 strain can be considered a probiotic food, containing approximately 10⁷ cfu/g of the product.