1. EFFECTS OF AND RESISTANCE TO WEAK ACIDS IN SPOILAGE YEASTS

2. Some weak acids: E 200 sorbic acid 200 - 2000 mg Kg -1 E 210benzoic acid150 - 500 mg Kg -1 E 220SO 2 15 - 2000 mg Kg -1 E 260acetic acid“quantum satis” E 280 propionic acid1000 - 3000 mg Kg -1

3. AH A - + H + AH A - + H + neutral cytoplasm acidic environment

4. EFFECTS OF WEAK ACIDS - Intracellular acidification - Inhibition of glycolytic enzymes - Decrease of fermentation activity - ATP depletion - Growth inhibition - Enhancement of thermal death

5. - Intracellular acidification, but...

6. Intracellular acidification S. cerevisiae adaptation energy no adaptation energy no adaptation no energy

7. - Inhibition of glycolytic enzymes - Decrease of fermentation activity... but...

8. Specific glucose consumption rate S. cerevisiae

9. Inhibition of growth ATP is diverted for maintenance purposes...but how much ATP?

10. S. cerevisiae acetic acid

11. AH A - + H + AH A - + H + ATP H+H+ A-A- neutral cytoplasm acidic environment ?

12. glucose Extrusion of benzoic acid S. cerevisiae Adapted cells Non adapted

13. - Saccharomyces cerevisiae - Zygosaccharomyces bailii - Pichia sp.

14. Diffusion of benzoic acid Pichia sp. S. cerevisiae Z. bailii non adapted adapted

15. AH A - + H + AH A - + H + ATP H+H+ A-A- neutral cytoplasm acidic environment conversion 1 2 3 4 Mechanisms of yeast tolerance to preservatives: 1) Reduced permeability; 2) Proton extrusion; 3) Preservative conversion; 4) Preservative extrusion