Glass Transition and Reaction Rates:  Nonenzymatic Browning in Glassy and Liquid Systems

Abstract

Effects of physical state and glass transition on nonenzymatic browning rate in water, glycerol, poly(vinylpyrrolidone) (PVP), and maltodextrin (MD) systems were studied. All systems had the same concentration of reactants, glucose and lysine, in the water phase. The systems, except water, had also comparable water activities (0.33). Sorption isotherms and glass transition temperatures (T g) at various water contents for the freeze-dried PVP and MD systems were determined. Nonenzymatic browning rate was determined at several temperatures from optical density at 280 and 420 nm. The PVP and MD systems contained 12.9 and 8.2 g of H2O/100 g dry matter and had T g values of 67 and 62 °C at 33% relative humidity and 24 °C, respectively. The liquids exhibited significantly higher browning rates than the concentrated systems, especially below the T g values. The browning rate was higher in the PVP than in the MD system, suggesting that a possible phase separation may affect nonenzymatic browning in foods. Keywords: Glass transition; nonenzymatic browning; physical state; reaction rate

Maillard Reaction Rate in Various Glassy Matrices

“…Thus, the activation energy (ÁE) for MR in each glassy matrix system was almost independent of the kind of matrix, and the values were in the range of 130 to 156 kJ/mol. Since these values were in agreement with literature values reported for other MR systems, 17) it is thought that the ÁEs obtained in this work were in the reasonable range. In contrast, the pre-exponential parameters (A) were different depending on the material.…”

“…21) Thus, in this study, k 280 obtained by the pseudo zero order reaction formula of ÁOD 280 was treated experimentally as a MR rate in accordance with the previous studies. [16][17][18]21) Moreover, the temperature dependence of k 280 was described well by the Arrhenius formula in the temper- The T g of sample was investigated by DSC, and the heating curve of every sample is shown. The arrows show the T g .…”

“…The freeze-dried sample was stored at 10 C intervals at temperatures between 40 C and 70 C. After storage, the sample was rehydrated to 0.04 sample-g/ml with distillated water, and the extent of MR was estimated spectrophotometrically (Shimadzu UV-160) by optical density at 280 nm (OD 280 ). OD 280 , which is considered to be due to the formulation of furfural compounds, is often used to detect the early stage of MR. [16][17][18]21,22) Similarly, optical density at 420 nm, which quantifies the yellow and browning pigments formed at the final stage of MR, is also used, but only OD 280 , which can detect even slight progress in MR, was used in this study. For the average of the three measurements, the difference in OD 280 before and after storage (ÁOD 280 ) was estimated as the extent of MR during storage.…”

“…Since molecular mobility usually affects the rate of physical change or chemical reaction, it is believed that the T g value of glassy food is a critical factor for the consideration of storage stability. Actually, it has been reported that the rate of some undesirable physical changes (e.g., crystallization, 10,11) and structural collapse 12) ) or chemical reactions (e.g., degradation, 13) oxidation, 14) and MR [15][16][17][18][19][20] ) have a close relation with T g . That is, the rates below T g are much slower than that above T g .…”

Effect of disaccharides on survival during storage of freeze dried probiotics

“…Differential scanning calorimetry (DSC, Mettler Toledo 821e, Schwerzenbach, Switzerland) was used to measure T g for dehydrated and rehumidified samples as described by Lievonen et al [30]. Freeze-dried samples (9 to 15 mg) were prepared in pre-weighed DSC aluminum pans (40 μL; Mettler Toledo-27331, Schwerzenbach, Switzerland) and stored in open pans for 144 h at [22][23][24][25] • C in evacuated desiccators over P 2 O 5 and different saturated salt solutions, as described previously, giving a water activity, a w , of 0.01 × RVP at equilibrium [27].…”