Foam freeze-drying

This is a dry sponge of human fibrin prepared by elotting a foam of human fibrinogen solution with human thrombin. It is then freeze-dried, cut into shapes and sterilized by dry heat at 130°C for 3 hours. Before use, it is saturated with thrombin solution. Blood coagulation occurs in contact with the thrombin in the interstices of the foam. 

This quick evaporation will produce foam or bubbles in the product. This is unacceptable in most cases, since the original structure is changed and that part of the product which is vacuum dried will have different qualities than the freeze-dried part. Often the product frozen in this way can not be freeze-dried at all. 

Foam Volume. The determination of foamability was carried out using the procedure of Hermansson et al. (9.) with modifications. A 1 g sample of the freeze-dried protein fraction was homogenized with 90 ml of citrate-phosphate buffer in a Sorvall Omnimixer at 3000 rpm. The resultant foam and liquid were transferred to a 250 ml graduated cylinder and the mixer cup washed with 10 ml of buffer. The cup was drained for 2 min and the cylinder allowed to stand for 30 min at which time the foam volume was measured. The influence of pH and ionic strength on foam volume was established using the buffer systems previously described. 

A change in composition or a commercial food product s formulation is most likely to affect its cellular stmcture, especially if formed by extrusion or puffing. Thus, studying the effect of stmcture or composition in isolation may not be an easy task. However, there are ways to investigate their effects. For example, freezing at different rates usually produces ice crystals of different sizes, which upon dehydration can produce foams with almost identical composition but different cellular stmcture. Freeze-dried model foams, based on food gums with and without additives can be used to study the effect of the cell wall material in foams that have a similar stmcture (see, e.g., Nussinovitch et al. 2000, 2001). Whether this kind of study will generate wide interest, however, is uncertain. 

The conducting properties of a liquid in a porous medium can provide information on the pore geometry and the pore surface area [17]. Indeed, both the motion of free carriers and the polarization of the pore interfaces contribute to the total conductivity. Polymer foams are three-dimensional solids with an ultramacropore network, through which ionic species can migrate depending on the network structure. Based on previous works on water-saturated rocks and glasses, we have extracted information about the three-dimensional structure of the freeze-dried foams from the dielectric response. Let be d and the dielectric constant and the conductivity, respectively. Dielectric properties are usually expressed by the frequency-dependent real and imaginary components of the complex dielectric permittivity ... 

Sample Preparation of Foam and Water Samples and Humic Substances Isolation. All foam and water samples were filtered through 0.45- Lim silver filter using stainless-steel filtration units. Silver filtration of Como Creek and Suwannee River foam samples resulted in build up of a brown extract on the filter paper, which was readily solubilized in 0.1 N sodium hydroxide. This extract was refiltered through silver filters as a sodium hydroxide solution. This fraction was believed to be colloidal in nature and was treated as a separate humic fraction, called the "foam-extract" fraction. A part of the filtered foam was freeze dried directly and considered "raw" foam. Fulvic and humic acids were isolated from foam and stream-water samples via the XAD-8 adsorption technique developed by Thurman and Malcolm (77), freeze dried, and weighed. To obtain a sufficient mass of humic substances, each entire sample was used for one extraction. As multiple samples were not extracted, calculation of the error associated with humic substances isolation cannot be made, and the contributions of humic substances to the DOC content must be regarded as estimates. 

Foaming Ability and Foam Stability. Foaming ability and foam stability were determined in triplicate on 100-mg/mL solutions of freeze-dried raw foam and humic substances from stream, foam, and foam-extract samples. Measurements were made at 25 at pH 3.0, 7.0, and 10.0, with sample pH adjusted using O.IN sodium hydroxide using the Ross Miles method (D1173-53 ASTM standards, 1991). Briefly, a 200-mL... 

NMR. Quantitative liquid-state carbon-13 nuclear magnetic resonance ( 3c NMR) spectra were recorded for humic and fulvic acid from Como Creek foam and for stream and foam fulvic- and humic- acid samples from the Suwannee River at the U.S. Geological Survey, laboratory in Arvada, CO. C NMR could not be performed on other humic substances due to insufficient sample or instrument availability. The acquisition parameters used were as follows C NMR spectra were recorded on a Varian XL-300 NMR spectrometer at 75 MHz. Each sample (200 mg of freeze-dried material) was dissolved in deuterated water and deuterated sodium hydroxide was added to ensure solution a total solution volume of approximately 6 to 7 mL. Spectra were recorded using a 30,000 Hz spectral window, a 45 pulse width, a 0.199 second acquisition time, and a pulse delay of 10 seconds for quantitative spectra. The number of transients was 10,000, and line broadening was 50 Hz. 

Elemental Analysis. Carbon, hydrogen, nitrogen, oxygen, sulfur, phosphorous, and ash determinations were made on freeze-dried samples of raw foam, and humic and fulvic acids isolated from Como Creek and Suwannee River foam and water samples by Huffman Laboratories (Golden, CO). Trace-metal analysis was performed on freeze-dried Como Creek foam by Huffman Laboratories (Golden, CO). 

Titration Measurements. The carboxyl and phenolic hydroxyl content of humic and fulvic acids from stream, foam, and foam-extract samples was determined by titration using carefully calibrated O.IN sodium hydroxide. Briefly, 20 mg of freeze-dried sample were dissolved in 10 mL of distilled water, then titrated to pH 8.0 and pH... 

Phospholipid Fatty Acid Analysis. Phospholipid fatty acid analysis was carried out on selected humic and fulvic freeze-dried samples of stream, foam, and foam extract from the Suwannee River by Microbial Insights, Inc., (Knoxville, TN). Briefly,... 

Foaming, used to influence the structure and mainly to control the density of the freeze dried product... 

The physicochemical state of fat in milk powder particles, which markedly influences the wettability and dispersibility of the powder on reconstitution, depends on the manufacturing process. The fat occurs either in a finely emulsified or in a partly coalesced, de-emulsified state. In the latter case, the membrane has been ruptured or completely removed, causing the globules to run together to form pools of free fat. The amount of de-emulsified free fat depends on the manufacturing method and storage conditions. Typical values for free fat (as a percentage of total fat) in milk powders are spray-dried powders, 3.3-20% roller-dried powders, 91.6-95.8% freeze-dried powders, 43-75% foam-dried powders, less than 10%. 

PPY-PVA and PPY-PEG composites were fabricated by vapor polymerization of pyrrole onto EeCls-loaded hydrogel matrices [87]. FeCl3-loaded PVA and PEG matrices were freeze-dried to form microstructures. The resulting composites have fine foam-like lattice structure with low weight density. The tensile strength and conductivity of 20 wt% PPy-PVA were 2.0 0.2 MPa and 0.1 S cm , respectively. 

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