Resistance of Immobilized Lactic Acid Bacteria to the Inhibitory Effect of Quaternary Ammonium Sanitizers

The inhibitory effect of quaternary ammonium sanitizers (QAS) on the fermentation activity of lactic acid bacteria was investigated. Benzalkonium chloride and didecyl dimethyl ammonium chloride show the same inhibitory effect. In MRS agar medium and MRS liquid medium their minimum inhibitory concentration was below 2 µg/mL. Interfering molecules in milk increased this concentration of inhibitory QAS above 8 µg/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 successive acidification and were colonized by lactic acid bacteria, the better 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 µg/mL of QAS and could perform a complete milk acidification. This offers a significant advantage for the use of the immobilized cell technology over the free cell process.