Freezing rate effects

Anon, M.C. and Calvelo, A. 1980. Freezing rate effects on the drip losses of frozen beef. Meat Science 4 1-14. 

There have been many modifications of this idealized model to account for variables such as the freezing rate and the degree of mix-ingin the liquid phase. For example, Burton et al. [J. Chem. Phy.s., 21, 1987 (1953)] reasoned that the solid rejects solute faster than it can diffuse into the bulk liquid. They proposed that the effect of the freezing rate and stirring could be explained hy the diffusion of solute through a stagnant film next to the solid interface. Their theoiy resulted in an expression for an effective distribution coefficient k f which could be used in Eq. (22-2) instead of k. 

Reid et al. [ 1.12] described the effect of 1 % addition certain polymers on the heterogeneous nucleation rate at-18 °C the rate was 30 times greater than in distilled, microfiltered water and at -15 °C, the factor was still 10 fold hogher. All added polymers (1 %) influenced the nucleation rate in a more or less temperature-dependent manner. However, the authors could not identify a connection between the polymer structure and nucleation rate. None the less it became clear that the growth of dendritic ice crystals depended on to factors (i) the concentration of the solution (5 % to 30 % sucrose) and (ii) the rate at which the phase boundary water - ice crystals moved. However, the growth was found to be independent of the freezing rate. (Note of the author the freezing rate influences the boundary rate). 

Thijssen, H. A. C., Rulkens, W. H. Effect of freezing rate on rate of sublimation and flavour retention in freeze-drying, p. 99-114. International Institute of Refrigeration (Comm. X, Lausanne, 1969)... 

Vemuri et al.17 looked at the effects of various cryoprotectants, freezing rates, and buffer systems on the shelf-life of lyophilized recombinant alphar antitrypsin (rAAT). Alpharantitrypsin (AAT) is labile in solution therefore, a more stable presentation was required. A competitive ELISA was used to measure total AAT in a sample. The AAT in the sample competed with HRP-labeled AAT for binding to the specific antibody. A stable formulation containing lactose as a cryoprotectant was found that maintained the protein s specific activity. 

A Lundqvist, G Ocklind, L Haneskog, P Lundahl. Freeze-thaw immobilization of liposomes in chromatographic gel beads evaluation by confocal microscopy and effects of freezing rate. J Mol Recogn 11 52-57, 1998. 

Canet, 1995). It was found that, after two or three cycles, softness ceased to be much affected by subsequent cycles (Figure 7.6). The authors concluded the following (1) that pre-cooling and a high freezing rate during the phase of maximum ice crystal formation has a positive effect on potato texture and tissue structure, (2) that slow thawing has a positive effect and (3) that it is essential not to subject potatoes to more than one freeze/thaw cycle. 

Alvarez, M. D., Canet, W. (1997). Effect of pre-cooling and freezing rate on mechanical strength of potato tissues (cv Monalisa) at freezing temperatures. Z. Lebensm. Unters. Forsch. A., 205,282-289. 

Canet, W., Espinosa, J. (1984). The effect of blanching and freezing rate on the texture of potatoes, carrots and peas, measured by mechanical tests. In P. Zeuthen, J. C. Cheftel, C. Eriksson, M. Jul, H. Leniger, P. Linko, G. Varela (Eds.), Thermal Processing and Quality of Foods (pp. 678-683). Elsevier Applied Science, London. 

To examine the effect of the freezing rate on the internal structure and the mechanical properties of hydrogels we made three types of gel film A, B and C by changing the freezing rate from 3.78, 0.0766 to 0.0329 Ks1, respectively, at the freezing point. 

Cryoinjury to the specimen is caused directly by extra- or intracellular ice crystal formation as well as by ice-induced solution effects during cryopreservation. Ice crystals seriously deform cell components. Another disadvantage of the formation of ice crystals near the specimen surface is slowing the cooling rate in areas below the surface because their thermal conductivity is about half that of solid water in a noncrystalline state. Furthermore, ice crystal formation is accompanied by the generation of latent heat, which also slows down the freezing rate. 

The best explanation of the good results for peptide syntheses in ice-water mixtures are based on the freeze-concentration-model, which just provides for a volume-reducing function for the ice while the liquid aqueous part is still the only relevant phase for the reaction. All observed enhancements of reaction rate would then have to be attributed to an increase in effective concentration. H-NMR relaxation time measurements have been used to determine the amount of unfrozen water in partially frozen systems, thus quantifying the extent of the freeze-concentration effect (Ullmann, 1997). Comparative studies in ice and at room temperature verify the importance of freeze-concentration which, however, is not sufficient for a complete understanding of the observed effects. 

As ice crystals grow in the freezing system, the solutes are concentrated. In addition to increased ionic strength effects, the rates of some chemical reactions—particularly second order reactions—may be accelerated by freezing through this freeze-concentration effect. Examples include reduction of potassium ferricyanide by potassium cyanide (2), oxidation of ascorbic acid (3), and polypeptide synthesis (4). Kinetics of reactions in frozen systems has been reviewed by Pincock and Kiovsky (5). 

Kim AI, Knopp S, Akers MJ, Nail SL. The physical state of mannitol after freeze-drying effects of mannitol concentration, freezing rate, and a noncrystallizing cosolute. J Pharm Sci 1998 87 931-935. 

Freezing processes can be divided into two categories one type is so slow, so that they run under almost equilibrium conditions others are too fast to approach the equilibrium situation. Figures 1.14.1-1.14.3 show the effect of the freezing rate on the structure of the dried product. In Figure 1.14.1, milk has been frozen slowly (0.2-0.4 °C/min) in trays. In Figure 1.14.2, mannitol solution has been frozen in vials at a rate of-1 °C/min the arch at the bottom represents the vial bottom. In Figure... 

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