Effect of N2 laser fluence on lactic acid production by Streptococcus thermophilus

Abstract EN

The aim of this work was to improve the lactic acid production by subjecting lactic acid isolates to N2 laser radiation.

Fifteen samples of fermented dairy products were collected from local markets.

Two others were brought from the dairy product manufacture of Abu Ghraib and other dairy product factories in Baghdad. Eleven isolates were identified as Cocci lactic acid bacteria.

All isolates had been subjected to the biochemical tests (catalase production, gelatin liquefaction, growth in litmus milk, NH3 from arginine, CO2 production, growth at 10 and 45 oC, growth at 4 % NaCl, growth at 0.1 % of methylen blue and fermentation of nine carbon compounds.

For selecting efficient isolates in production of lactic acid, all isolates were propagated in whey medium.

After propagation one isolate S9 of Streptococcus thermophilus produced highst total titrable acid (TA %) when it reached 1.28 % therefore this isolate was selected for subjection to N2 laser with wavelength of 337.1 nm, with different fluences.

After treatment with N2 laser at fluence of 18.95 J/cm2, production of lactic acid by this isolate reached 17 mg / ml.