Using Sweet Potatoes to Develop a Medium for Cultivation of Lactobacilli

Saeed A. Hayek and Salam A. Ibrahim

Abstract:

This study investigated the use of sweet potatoes (Ipomoea batatas) as a basic component

to develop a medium for cultivation of lactobacilli. Extract from baked sweet potatoes was used

to form a sweet potato medium (SPM). Sweet potato medium was supplemented with 0, 4, or 8

g/L of each nitrogen source (beef extract, yeast extract, and proteose peptone #3) to develop

SPM1, SPM2, and SPM3, respectively. Lactobacilli MRS was used as a control medium. Ten

Lactobacillus strains containing an average of 2.34±0.29 log CFU/mL were individually

inoculated into batches of MRS, SPM1, SPM2, and SPM3. Inoculated media were incubated at

37ºC for 48h and the growth of Lactobacillus strains was monitored using turbidity (OD at 610

nm), maximum specific growth rates (µmax), bacterial population (log CFU/mL), pH values, and

titratable acidity. Our results for OD and µmax showed similar growth patterns for all tested

Lactobacillus strains growing in MRS, SPM2 or SPM3. The population of Lactobacillus strains

reached averages of 10.59±0.27 and 10.72± 0.19 log CFU/mL in SPM2 and SPM3, respectively,

whereas the average population in MRS was 10.41±0.35 log CFU/mL. SPM1 showed slower

growth rates with 1-2 log CFU/mL less of bacterial populations compared to that in MRS. SPM2

and SPM3 maintained higher pH values throughout the incubation period compared to that of

MRS. These findings indicated that SPM2 is suitable for the growth of Lactobacillus strains and

could be used as an alternative medium.

Key words: lactobacilli, sweet potato medium (SPM), MRS, growth rate, and bacterial

population.