CIostridium botulinurn Spore Gerrnination, Outgrowth, and Toxin Production Below pH 4.6; Interactions Between pH, Total Acidity, and Buffering Capacity

The effect of soy protein concentration on Clostridium botulinurn spore germination, outgrowth, and toxin production in the presence of varying levels of inorganic (HCI) and organic (citric) acids was investigated. Media were blended using deoxygenated soy concentrate (1–7% protein), acidified with deaerated acids to effect post-autoclaving pH values of 4.1, 4.3 and 4.5, and inoculated with C. botulinum Type A spores. All manipulations were conducted under conditions of strict anaerobiosis (0–2 ppm atmospheric oxygen, media E_h7 values of < — 345 mV). Germination, proliferation, active motility, and elaboration of neurotoxin occurred as low as pH 4.07. Titratable acidity, which accounted for the soy protein buffering capacity, appeared to define toxicity endpoints as pH alone could not.