Freezing, sucrose solution

The constant kf is called the freezing-point constant of the solvent it is different for each solvent and must be determined experimentally (Table 8.8). The effect is quite small for instance, for a 0.1 m C12H220n(aq) (sucrose) solution,... 

The glass transition of solutes that remain amorphous during and after the freezing process can often be seen in the DSC thermogram as a shift in the baseline toward higher heat capacity. This is illustrated in the DSC thermogram of sucrose solution in Fig. 6, in which the glass transition is observed at — 34°C. 

Fig. 1.55.3. Dimension change as a function of temperature for a 30 % sucrose solution during warming at 2 °C/min after slow freezing to -80 °C and annealing up to -35 °C.

Oesterle, J., Franks, F., Auffret, T. The influence of tertiary butyl alcohol and volatile salts on the sublimation of ice from frozen sucrose solution Implications for freeze drying. Pharmaceutical Developments and Technology, 3 (2), p. 175-183, 1998. Copyright 1998 by Marcel Dekker, Inc., New York, N. Y., USA... 

FIG. 15 Texture modification (percentage of raw fruit texture) and protopectin content (mg/100 g wet weight) before (BF) and after (AF) freezing of strawberry slices not pretreated (NT) or air dried at 80 °C up to 60% weight reduction without (AD) or following 60-min osmotic dehydration (OAD) in 60% (w/w) sucrose solution at 25 °C at atmospheric pressure (Brimar, 2002). 

The development of the freeze concentration process for fruit juices has been hampered by the fact that solute concentrate is entrained by the ice crystals. This incomplete separation of the entrained concentrate from the ice results in a considerable increase of the cost of the process. In this investigation sucrose solutions were concentrated by the formation of an ice layer on the externally cooled walls of the crystallizer. The formation of the layer was initiated by secondary nuclei induced by rotating ice seeds, at subcoolings smaller than the critical subcooling needed for spontaneous nucleation. A minimum in the amount of sucrose entrapped in the ice layer was observed at a subcooling smaller than the critical subcooling for spontaneous nucleation. The effect of soluble pectins on the minimum was also studied. 

Because the freezing point of pure water is 0° C, the sucrose solution freezes at -0.68° C. 

Fig. 7. 55.2. Dimension change as a function of temperature for 30% sucrose solution during freezing at 5 °C/min down to -80 °C. 1, Fructose alone 2, fructose plus 0.25% sodium carboxymethylcellulose (CMC) (from [1.124])...

Labrude and Rasolomana [1.80] reported an atomizer-spray-drying system for oxyhemoglobin in a 0.25 M sucrose solution at temperatures between +80 and +100 °C, which resulted in an unchanged dry product if the relative humidity was kept below 3%. When this dry product was compared with a freeze-dried product, in both cases a met-oxyhemoglobin (met-HBO) content of-3% was found. By ERP and spectro-... 

S.L. The relationship between the TMDSC curve of frozen sucrose solutions and collapse during freeze-drying. 

Table 1-7 Volume Change of Water and Sucrose Solutions on Freezing...

Figure 7.3 is another example of a typical state diagram, developed for maltose. Maltose solutions are in glassy state below Tg curve. T g (onset of glass transition) and (onset of ice melting) show constant values for the maximally freeze concentrated solutions, where maximum ice formation occurs between T and Tg, and T is at the end point region of Tg (Figure 7.3) (Roos and Karel 1991b). State diagram for sucrose (Figure 7.4) also shows similar characteristics (Roos and Karel 1991a).

An instrument performing measurements of D2 (viz. the ratio of the resistivity of ice to that of a product at a given temperature) and implementing DTA (differential thermal analysis) was developed to control freeze-drying processes the principal components are a test chamber, a cooling and heating unit, a digital computer system and a printer. It was used to evaluate the thermal features of a 20% sucrose solution [12]. 

Other applications of lactose include use in lyophilized products, where lactose is added to freeze-dried solutions to increase plug size and aid cohesion. Lactose is also used in combination with sucrose (approximately 1 3) to prepare sugar-coating solutions. 

Raffinose is a trisaccharide carbohydrate that is used as a bulking agent, stabilizer, and water scavenger in freeze-drying. It is also used as a crystallization inhibitor in sucrose solutions. 

Calculate the freezing point of the 1.25 m sucrose solution in Example 14-2. 

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