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The aim of this study was to determine whether the combined effect of water activity and temperature on inactivation rates of freeze-dried microorganisms in a lactose matrix could be explained in terms of the glass transition theory. The stabilized glass transition temperature, Tg, of the freeze-dried products was determined by differential scanning calorimetry at two different temperatures, T (20 and 37 degrees C), and different water activities (0.07-0.48). This information served as a basis for defining conditions of T and water activity, which led to storage of the bacteria in the glassy (T < Tg) and nonglassy (T > Tg) states. The rates of inactivation of the dry microorganisms subjected to different storage conditions were determined by plate counts and could be described by first-order kinetics. Rates were analyzed as a function of water activity, storage temperature, and the difference between Tg and T. Inactivation below Tg was low; however, Tg could not be regarded as an absolute threshold of bacteria stability during storage. When the cells were stored in the nonglassy state (T > Tg), inactivation proceeded faster, however, not as rapid as suggested by the temperature dependence of the viscosity above the glass transition temperature. Furthermore, the first-order rate constant, k, was dependent on the storage temperature per se rather than on the temperature difference between the glass transition temperature and the storage temperature (T - Tg).

Kinetics of reduction of iron(IV) in ferrylmyoglobin by chlorogenate in neutral or moderately acidic aqueous solutions (0.16 M NaCl) to yield metmyoglobin was studied using stopped flow absorption spectroscopy. The reaction occurs by direct bimolecular electron transfer with (2.7 +/- 0.3) x 10(3) M(-)(1).s(-)(1) at 25.0 degrees C (DeltaH( )(#) = 59 +/- 6 kJ.mol(-)(1), DeltaS(#) = 15 +/- 22 J. mol(-)(1).K(-)(1)) for protonated ferrylmyoglobin (pK(a) = 4.95) and with 216 +/- 50 M(-)(1).s(-)(1) (DeltaH( )(#) = 73 +/- 8 kJ. mol(-)(1), DeltaS( )(#) = 41 +/- 30 J.mol(-)(1).K(-)(1)) for nonprotonated ferrylmyoglobin in parallel with reduction of a chlorogenate/ferrylmyoglobin complex by a second chlorogenate molecule with (8.6 +/- 1.1) x 10(2) M(-)(1).s(-)(1) (DeltaH( )(#) = 74 +/- 8 kJ.mol(-)(1), DeltaS( )(#) = 59 +/- 28 J.mol(-)(1).K(-)(1)) for protonated ferrylmyoglobin and with 61 +/- 9 M(-)(1).s(-)(1) (DeltaH( )(#) = 82 +/- 12 kJ.mol(-)(1), DeltaS( )(#) = 63 +/- 41 J. mol(-)(1).K(-)(1)) for nonprotonated ferrylmyoglobin. Previously published data on ascorbate reduction of ferrylmyoglobin are reevaluated according to a similar mechanism. For both protonated and nonprotonated ferrylmyoglobin the binding constant of chlorogenate is approximately 300 M(-)(1), and the modulation of ferrylmyoglobin as an oxidant by chlorogenate (or ascorbate) leads to a novel antioxidant interaction for reduction of ferrylmyoglobin by ascorbate in mixtures with chlorogenate.

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in Wiley InterScience (www.interscience.wiley.com).Water activity-temperature state diagrams for Lactobacillus acidophilus freeze-dried in a sucrose or a lactose matrix were established based on determination of stabilized glass transition temperatures by differential scanning calorimetry during equilibration with respect to water activity at fixed temperatures. The bacteria in the lactose matrix had higher stabilized glass transition temperatures for all a w investigated. The survival of Lactobacillus acidophilus determined as colony forming units for up to 10 weeks of storage at 20 C for (i) a w ¼ 0.11 with both freeze-dried matrices in the glassy state, (ii) a w ¼ 0.23 with the bacteria in the lactose matrix in a glassy state but with the bacteria in sucrose matrix in the nonglassy state, and (iii) a w ¼ 0.43 with both freeze-dried matrices in a nonglassy state showed that the nature of the sugar was more important for storage stability than the physical state of the matrix with the nonreducing sucrose providing better stability than the reducing lactose.