Resistance of immobilized lactic acid bacteria to the inhibitory effect ofquaternary ammonium sanitizers

The inhibitory effect of quaternary ammonium sanitizers (QAS) on the fermen tation activity of lactic acid bacteria was investigated. Benzalkonium chlo ride and didecyl dimethyl ammonium chloride show the same inhibitory effect . In MRS agar medium and MRS liquid medium their minimum inhibitory concent ration was below 2 mug/mL. Interfering molecules in milk increased this con centration of inhibitory QAS above 8 mug/mL. Both growth and acidification were decreased but by immobilizing cells in calcium alginate gel beads this inhibitory effect could be reduced. The longer the beads were used for suc cessive acidification and were colonized by lactic acid bacteria, the bette r was the acidification rate and the better they resisted to QAS inhibition . Beads used in 10 batch successive acidifications were resistant to up to 100 mug/mL of QAS and could perform a complete milk acidification. This off ers a significant advantage for the use of the immobilized cell technology over the free cell process. (C) 2001 Academic Press.