Heat Sterilised Reducing Sugars and Their Effects on the Thermal Resistance of Bacteria

Abstract

That the thermal resistance of at least some types of microorganisms is increased when heated in hypertonic solutions of various carbohydrates is now well established. A review of the literature concerning this subject has been presented by Fay (1934). This author found that sucrose and glucose in concentrations above 0.75 M were protective for Escherichia coli. No protection was obtained with saturated lactose solution and 50 per cent maltose solution gave only slight protection. In these experiments the bacteria were heated in nutrient broth solutions of the sugars. It was not stated by what means the solutions were sterilized. In a later paper Baumgartner and Wallace (1934) published results which were not in agreement with Fay's findings in respect to lactose. They found that lactose in 17 per cent solution and sucrose, glucose and invert sugar in 20 per cent solutions were each protective for Escherichia coli. In this investigation the sugars were sterilized by autoclaving in a dry state and then dissolved in sterile buffer solution. The effects of heat sterilization on media containing sugars have been investigated by several workers. Mudge (1917) reported that hydrolysis of lactose and maltose was greater when sterilized in streaming steam for three successive days than when once autoclaved at 15 pounds pressure for 15 minutes. Fulmer, Williams and Werkman (1931) noted growth stimulation of yeast and certain bacterial species including Escherichia coli in a medium (containing 0.6 gram NH4Cl, 0.2 gram K2HPO4 and 5.0 grams 369