The Effect of Sugars and Polyols On the Heat Resistance of Strains of Salmonella and Osmophilic Yeasts.

The heat resistance at 65° of three strains of salmonella in solutions of sugars and polyols was enhanced as the concentration of the solutes was increased. A linear relationship between heat resistance and water activity (aw ) did not exist, but for all solutes except glycerol there was a linear relationship between log D65 and per cent (w/w) solute. Comparison at one a value or per cent (w/w) solute concen- tration showed D65 value in sucrose > glucose >sorbitol >fructose > glycerol. In glycerol D65 values were always very much lower than with any other solute. In sucrose/glycerol or sucrose/glucose mixtures, salmonella heat resistance depended both on the total per cent (w/w) solutes present, and on the aw of the solution. Propylene glycol or potassium sorbate added to 48 per cent (w/w) sucrose solution decreased heat resistance. Two strains of osmophilic yeast also showed enhanced heat resistance when heated at D65 in solutions of sugars and polyols at aw 0. 95. values were less than those obtained for salmonellae at the same aw in all solutes except glycerol. Comparison of D65 values showed sucrose > sorbitol > glucose/fructose > glycerol. Study of cytoplasmic membrane permeability by both microscopic and turbidimetric methods showed that heat resistance was greatest when solutes were least able to permeate the membrane, indicating that heat resistance was associated more with dehydration of the cell than with replacement of the cell water by solutes