Studies freeze-dried systems

Since methloninase has potential applications in both aerobic and anaerobic food systems, a number of experiments were conducted to characterize and evaluate the performance of methloninase under a variety of these conditions. In these studies freeze-dried methloninase preparations (either 0.779 units/mg protein or 2.45 units/mg protein) were employed for generation of methanethiol, and selective flame photometric detection gas chromatography was use for quantifying methanethiol. The column was a 3 m x 4 mm id glass column packed with Carbopak BHT-100, and It was operated at 60°C isothermally for methanethiol analysis. When higher molecular weight sulfur compounds were measured also (e.g.,... 

Figure 41.1 shows the gel-to-liquid crystalline phase transition temperatures (Tm) of DPPC-cholesterol mixtures as a function of the cholesterol-lipid molar ratio. The Tm of fully hydrated DPPC is 42°C (Crowe and Crowe, 1988 Vist and Davis, 1990 McMullen et al., 1993 Ohtake et al., 2004). Upon the addition of cholesterol, the transition enthalpy decreases continuously imtil it is no longer observable at 50 mol% cholesterol. The disappearance of the melting transition has been attributed to strong interactions between cholesterol and DPPC (McCoimell, 2003). Upon dehydration, the Tm for DPPC increases from 42 to 105°C (Crowe and Crowe, 1988 Ohtake et al., 2004). This Tm increase is caused by the reduction in the spacing between the phospholipids, which allows for increased van der Waals interactions between the lipid hydrocarbon chains (Koster et al., 1994). Between 10 and 70 mol% cholesterol, two endothermic transitions are observed, both lower than the Tm of the pure phospholipid (Figure 41.1). High-sensitivity DSC studies on fully hydrated DPPC-cholesterol systems reported endotherms consisting of two components, suggesting the existence of domains enriched/depleted in cholesterol (Vist and Davis, 1990 McMullen et al., 1993). The two peaks present in our freeze-dried systems also suggest the...

As discussed in Chapter 1, this section will place emphasis specifically on DSC studies of amorphous drugs and spray- and freeze-dried systems rather than the theoretical aspects of glass formation and behavior. There will, however, inevitably be a degree of overlap with other chapters owing to the wide range of thermal techniques that are used to characterize such materials. 

Elink, J., Karel, L., 1969. Studies on mechanisms of retention of organic volatiles in freeze-dried systems. 29" Annual Meeting of the Institute of Food Technologists, May 11-15, Chicago, USA. 

The water substitute concept states that the stabilizer replaces the water and forms hydrogen bonds with the protein, like water also does. These bonds maintain the native protein conformation and, in this way, stabilize the protein. The water substitution hypothesis has been confirmed either by spectroscopy studies (FTIR), or by experimental observations that have shown that the most efficient stabilizers are sugars which form strong hydrogen bonds with the protein. Indeed, freeze-dried systems with loss of activity present notably altered IR spectra. 

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... 

Pralhad, T. and Rajendrakumar, K., Study of freeze-dried quercetin-cyclodextrin binary systems by DSC, FT-IR, x-ray diffraction and SEM analysis, J. Pharm. Biomed. Appl, 34, 333, 2004. 

In a more recent study, Webster et al. (2006) report the expression and characterization of lettuce-derived measles vaccine. The MV-H protein expressed in lettuce was demonstrated to be immunogenic in mice following intraperitoneal injection in the absence of adjuvant in addition to intranasal inoculation in the presence of a mucosal adjuvant. The highest response was observed in mice primed first with MV-H DNA and then boosted with an oral formulation of freeze-dried MV-H lettuce in conjunction with a mucosal adjuvant. In addition to this, the type of immune response was found to depend largely on the manner in which MV-H is presented to the immune system. Secreted and soluble forms of MV-H were demonstrated to induce a Th2 type response, while membrane-bound MV-H protein was found to be associated with a Thl response. 

Freeze-dried DOM samples collected with the siphon-elution system (Kuzyakov and Siniakina, 2001) for the first time showed diurnal dynamics in the molecular-chemical composition of maize rhizodeposits (Kuzyakov et al., 2003). In a forthcoming study with maize, Melnitchouck et al. (2005) showed that amino acids, especially aspartic acid, asparagine, glutamic acid, phenylalanine, leucine and isoleucine contributed to the more intensive rhizodeposition during daytime than during nighttime. Furthermore, the maximum of thermal volatilization of peptides at low pyrolysis temperature in Figure 14.8 indicates the rhizodeposition or microbial formation of free amino acids rather than amino acids bound in peptides or trapped in soil humic substances. 

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