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Journal Articles

Effect of water activity on the mechanical glass transition and dynamical transition of bacteria-solute systems

Kawai, Kiyoshi*; Sogabe, Tomochika*; Nakagawa, Hiroshi; Yamada, Takeshi*; Koseki, Shigenobu*

Journal of Food Engineering, 375, p.112066_1 - 112066_9, 2024/08

https://doi.org/10.1016/j.jfoodeng.2024.112066
 Times Cited Count：0 Percentile：0.00(Engineering, Chemical)

The purpose of this study was to clarify effect of glycerol and glucose on the mechanical glass transition and dynamical transition of freeze-dried bacteria at various water activity (aw)-conditions. From the water sorption isotherm, it was noted that the water content at each aw and monolayer water content were higher in the order of glycerol, glucose, non-added samples. Effect of temperature on the mean square displacement (MSD) of atoms in the samples was investigated by incoherent elastic neutron scattering. The MSD increased gradually with an increase in temperature depending on the aw and added solute. From the linear fitting, three dynamical transition temperatures (low-, middle- and high-Tds) were determined. The Couchman-Karasz model suggested that the added solute and bacteria were not completely miscible.

Journal Articles

Effect of water activity on the mechanical glass transition and dynamical transition of bacteria

Sogabe, Tomochika*; Nakagawa, Hiroshi; Yamada, Takeshi*; Koseki, Shigenobu*; Kawai, Kiyoshi*

Biophysical Journal, 121(20), p.3874 - 3882, 2022/10

https://doi.org/10.1016/j.bpj.2022.09.001
 Times Cited Count：3 Percentile：35.51(Biophysics)

The purpose of this study was to clarify the glass transition behavior of bacteria ($$Cronobacter sakazakii$$) as a function of water activity ($$a_{rm w}$$). Mechanical relaxation was investigated at 298 K, and the mechanical $$a_{rm wc}$$ ($$a_{rm w}$$ at which mechanical glass transition occurs at 298 K) was determined to be 0.667. Temperature-dependency of mean square displacement was investigated by inelastic neutron scattering. From the linear fitting, two dynamical transition temperatures (low and high-$$T_{rm ds}$$) were determined. There was a minor effect of $$a_{rm w}$$ on the low-$$T_{rm ds}$$ except for the anhydrous sample. The high-$$T_{rm ds}$$ largely increased with the decrease in $$a_{rm w}$$. The dynamical $$a_{rm wc}$$determined by high-$$T_{rm ds}$$ (0.688) was slightly higher than the mechanical $$a_{rm wc}$$ because of the difference in the measurement time-scale. The high-$$T_{rm ds}$$ was converted to the glass transition temperature ($$T_{rm g}$$), and anhydrous $$T_{rm g}$$ was estimated to be 411 K. Bacterial inactive-active transition was discussed according to the glass transition behavior.

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