Modified MRS Medium Using Sweet Potatoes as Main Components for Lactobacillus Cultivation

This research aimed to formulate a cheaper culture medium to replace for MRS for lactic-acid-bacteria  (LAB) cultivation. MRS was modified by using sweetpotatoes as the main component. Sweetpotato media (SPM) were formed with extract from baked orange-fleshed sweetpotatoes with elimination of magnesium sulfate and replacement of all nitrogen sources with only yeast extract. Five different SPM were formed. MRS broth was used as a control medium. Two lactobacilli, Lactobacillus brevis and Lactobacillus plantarum containing an average of 5.55 ± 0.09 log CFU/mL were inoculated individually into batches of MRS and five different SPM. They were cultivated at 180 rpm, 37°C for 24 hours. The growth patterns for both Lactobacillus strains growing in SPM4 was found to be comparable to that in MRS. The average final population at 24 h of incubation in MRS, SPM1, SPM2, SPM3, SPM4 and SPM5 reached 8.77±0.08, 8.37±0.10, 7.95±0.16, 7.94±0.14, 8.51±0.10, 7.86±0.18 log CFU/mL, respectively for L. brevis and 8.27±0.08, 8.35±0.04, 8.59±0.04, 8.31±0.07, 8.70±0.04, 8.43±0.10 log CFU/mL, respectively for L. plantarum. SPM2, SPM4 and SPM5 had 0.12- 0.27 higher % titrable acidity (TA) than MRS when they were cultivated with L. plantarum, but all of SPM had 0.3–1.2 lower %TA values than MRS when they were cultivated with L. brevis. Based on the prices of these two media, SPM seem to be less than a half compared to the cost of MRS. SPM could be further developed as an alternative culture medium for LAB cultivation.

Keywords: Lactobacillus brevis, Lactobacillus plantarum, MRS medium, Orange-fleshed sweet potatoes