TY - JOUR AU - Adibi, Mina AU - Naghavi, Nafiseh Sadat AU - Zohrabi, Dina Sadat PY - 2022/06/03 Y2 - 2024/03/28 TI - Response surface methodology designation for optimization of lactic acid production by Streptococcus thermophilus isolated from industrial yogurt JF - Nova Biotechnologica et Chimica JA - Nova Biotechnol. Chim. VL - 21 IS - 1 SE - Research Articles DO - 10.36547/nbc.995 UR - https://journals.scicell.org/index.php/NBC/article/view/995 SP - e995 AB - <p>Using inexpensive sources is a crucial point in the production of valuable compounds such as lactic acid. In the present study, the production of lactic acid by an efficient isolate of <em>S. thermophilus</em> was optimized using whey as a carbon source and yeast extract as a nitrogen source. MRS culture medium with 6.5 % NaCl was used for the isolation of streptococci from industrial yogurt samples and the selected isolate was identified using the 16S rRNA gene sequencing. Evaluation of lactic acid production was done by the Randox method. Lactic acid production by the selected isolate was optimized by response surface methodology (RSM) in MRS broth regarding to different concentrations of whey and yeast extract. The isolate that produced the highest amount (8.9 g.L<sup>-1</sup>) of lactic acid within 52 h growth in MRS broth was identified as a strain of <em>S. thermophilus </em>by molecular identification. Optimization of concentrations of carbon and nitrogen sources resulted in the induction of lactic acid production by <em>Streptococcus thermophilus</em> up to 24.18 g.L<sup>-1 </sup>in the presence of 3.5 % of whey and 5 % of yeast extract as external carbon and nitrogen sources in the MRS medium, which was similar to the value predicted by RSM. Yeast extract was found to be more effective on lactic acid production than whey. Optimization of lactic acid production by low-cost substrates whey and yeast extract resulted in high induction of lactic acid production by <em>S.</em> <em>thermophilus</em> compared to some other studies that used other cost-effective substrates and/or bacteria isolated from traditional dairy products.</p> ER -