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EFFECTS OF AND RESISTANCE TO WEAK ACIDS IN SPOILAGE YEASTS

EFFECTS OF AND RESISTANCE TO WEAK ACIDS IN SPOILAGE YEASTS. Some weak acids: E 200 sorbic acid 200 - 2000 mg Kg -1 E 210 benzoic acid 150 - 500 mg Kg -1 E 220 SO 2 15 - 2000 mg Kg -1 E 260 acetic acid “quantum satis” E 280 propionic acid 1000 - 3000 mg Kg - 1.

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EFFECTS OF AND RESISTANCE TO WEAK ACIDS IN SPOILAGE YEASTS

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  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 210 benzoic acid 150 - 500 mg Kg-1 E 220 SO2 15 - 2000 mg Kg-1 E 260 acetic acid “quantum satis” E 280 propionic acid 1000 - 3000 mg Kg-1

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

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

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

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

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

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

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