9/18/2016 Maintaining pH Proton Pump Acid Tolerance Response Amino acid-dependent decarboxylase/antiporter systems Consumption of protons during decarboxylation Decarboxylase catalyzes the decarboxylation of an organic molecule Deiminase and deaminase systems a .c00 H system produce ammonia which combines with NH intracellular protons to yield the ammonium b ion(NH4)thereby raising pH 0 Product NH. Deiminase and deaminase systems Maintaining pH Synthesis of Acid Shock Proteins Water Activity Regulatory genes induced by pH Major factor in controlling microbial growth and chemical reactions in food Inhibition is due to availability of free water NOT the amount of water Free water supports the growth of microbes 14 9/18/2016 14 Maintaining pH Acid Tolerance Response Amino acid-dependent decarboxylase/antiporter systems • Consumption of protons during decarboxylation • Decarboxylase catalyzes the decarboxylation of an organic molecule Deiminase and deaminase systems • produce ammonia which combines with intracellular protons to yield the ammonium ion (NH4+) thereby raising pH 53 Proton Pump decarboxylase/antiporter systems Deiminase and deaminase systems 54 Maintaining pH Synthesis of Acid Shock Proteins • Regulatory genes induced by pH Sensor Sensor Protein chaperones 55 Water Activity • Major factor in controlling microbial growth d h i l ti i f d th and chemical reactions in food • Inhibition is due to availability of free water NOT the amount of water • Free water supports the growth of microbes 56