Comparisons with Freeze-Drying

Labrude, P., Rasolomana, M. Atomization of oxyhemoglobin in the presence of sucrose. Study by circular dichroism and electronic paramagnetic resonance, comparison with freeze-drying. S.T.P. Pharma 4 (6), 472-180,1988... 

Fink. J M A Simplified Cost Comparison of Freeze-Dried Food with Its Canned and Frozen Counterparts," pood Technology. 31, 4, 50-56 (1977). 

Figure 4 Comparison of freeze/thaw stability with freeze/dry stability phosphofructo-kinase with additives at 0.5 M. Hatched bar, freeze/thaw solid bar, freeze/dry. (Data from [24].)...

Figure 2 Comparison of freeze-drying with evaporation of a dilute solution (A) that is formulated to yield an amorphous solid (B). The density of stippling is an indication of the probability of reversion to the equilibrium state (e.g. by crystallisation). For details, see text. Reproduced with permission from...

In paired comparison tests two different samples are presented and one asks which of the two samples has most of the sensory property of interest, e.g. which of two products has the sweetest taste (Fig. 38.3). The pairs are presented in random order to each assessor and preferably tested twice, reversing the presentation order on the second tasting session. Fairly large numbers (>30) of test subjects are required. If there are more than two samples to be tested, one may compare all possible pairs ( round robin ). Since the number of possible pairs grows rapidly with the number of different products this is only practical for sets of three to six products. By combining the information of all paired comparisons for all panellists one may determine a rank order of the products and determine significant differences. For example, in a paired comparison one compares three food products (A) the usual freeze-dried form, (B) a new freeze-dried product, (C) the new product, not freeze-dried. Each of the three pairs are tested twice by 13 panellists in two different presentation orders, A-B, B-A, A-C, C-A, B-C, C-B. The results are given in Table 38.3. 

A number of poorly resolved proton ENDOR peaks have been observed between 10-20 MHz269-271. Only small changes of the overall shape of the ENDOR spectrum were detected when the sample was freeze-dried and redissolved in D20, i.e. no strongly coupled exchangeable protons were present. From comparison with the proton ENDOR spectrum in an anhydrous powder, it was assumed that the signals arose from the methylene protons of the cysteine ligands and that the iron-sulfur chromophore was not exposed to solvent water270/. 

Negative atmospheric pressure chemical ionization (APC) low-energy collision activation mss spectrometry has also been employed for the characterization of flavonoids in extracts of fresh herbs. Besides the separation, quantitative determination and identification of flavonoids, the objective of the study was the comparison of the efficacy of the various detection systems in the analysis of flavonoids in herb extracts. Freeze-dried herbs (0.5g of chives, cress, dill, lovage, mint, oregano, parsley, rosemary, tarragon and thyme) were ground and extracted with 20 ml of 62.5 per cent aqueous methanol. After sedimentation the suspension was filtered and used for HPLC analyses. Separations were carried out in an... 

Figure 2. Comparison of mutagenic activity in lyophilized and XAD-concentrated drinking water. The sampling 7000-fold concentration with either XAD-4/8 (XAD) or freeze-drying (FD) XAD-4/8 elution with acetone (neutral fraction) freeze-drying elution successively with acetone, ether, and DM SO and subsequent mutagenicity testing with strains TA98 and TA100 were as described in Materials and Methods. Each point represents the average of three plates, and 0.2 mL of concentrate corresponds to 1.4 L of water per plate.

There are several genetic skin diseases with known defects in the lipid metabolism. Atopic dermatitis, lamellar ichthyosis, and psoriasis have been the most widely studied with respect to epidermal barrier function and alterations in the lipid profile. Deviations in the lipid profile have been linked with an impaired stratum corneum barrier function. Atopic dermatitis is characterized by inflammatory, dry and easily irritable skin, and overall reduced ceramide levels in the stratum corneum [58-60]. In particular a significant decrease in the ceramide 1 level is observed, whereas the levels of oleate that is esterified to ceramide 1 are elevated [59]. Both aberrations may be responsible for the reduced order of the lamellar phases as observed with freeze fracture electron microscopy [61]. It has further been established that, in comparison to healthy stratum corneum, the fraction of lipids forming a hexagonal packing is increased [61]. A recent study reveals that the level of free fatty acids... 

It is generally stated that biocatalysis in organic solvents refers to those systems in which the enzymes are suspended (or, sometimes, dissolved) in neat organic solvents in the presence of enough aqueous buffer (less than 5%) to ensure enzymatic activity. However, in the case of hydrolases water is also a substrate and it might be critical to find the water activity (a ) value to which the synthetic reaction (e.g. ester formation) can be optimized. Vahvety et al. [5] found that, in some cases, the activity of Candida rugosa lipase immobihzed on different supports showed the same activity profile versus o but a different absolute rate. With hpase from Burkholderia cepacia (lipase BC), previously known as lipase from Pseudomonas cepacia, and Candida antarctica lipase B (CALB) it was found that the enzyme activity profile versus o and even more the specific activity were dependent on the way the enzyme was freeze dried or immobihzed [6, 7]. A comparison of the transesterification activity of different forms of hpase BC or CALB can be observed in Tables 5.1 and 5.2, respectively. 

Figure 22, for instance, shows the behavior of a freeze-dried plug of mannitol (residual moisture 1.5%). We can see that, in comparison with the initial solution (at 10% mannitol), the thermoluminescence of the dry material is some 20 times stronger and does not follow the same pattern. The lower peak (at -152°C) is very narrow whereas the higher one (near -118°C) is substantially depressed. This is not surprising if we assume, as we have already done, that the first peak is directly connected to the water molecule itself while the second one seems to be geared to the tridimensional network of the water molecules within the crystalline lattice. 

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