Drying techniques thermal extraction

Steam-solvent distillation using diethyl ether has been used to remove and analyse for odour and taint from additives in food packaging films. Another technique that has been used is vacuum/thermal extraction. This procedure has been applied to polyamides and fluorocarbon polymers. The procedure is used for the direct isolation or release of volatile components from a polymeric matrix and may involve the combined use of vacuum and heat, as for example in the mass spectrometer direct insertion probe or during dry vacuum distillation. Alternatively, the volatiles may be swept from the heated sample by a flow of inert gas for concentration by freeze trapping and/or collection on to a solid adsorbent prior to thermal or solvent desorption for GC or mass spectrometric (MS) examination. 

Alginates, unique hydrocolloids extracted from selected species of brown seaweed (kelp), interact with calcium ions to produce thermally stable gels. Using this interaction, flavor oils may be encapsulated or entrapped in the algin gel matrix. Encapsulation is accomplished at ambient temperatures. Products may be used "as is" (wet) or subsequently dried. This technique offers the potential for novel flavor effects, flavor protection, and new food products. 

The thermal desorption must take place at a temperature below the decomposition point of other materials in the sample matrix. Solid materials should have a high surface area (e.g., powders, granules, flbers). Bulk materials are ground with a coolant such as solid carbon dioxide prior to weighing. This technique simplifies sample preparation and avoids the necessity of dissolving samples or solvent extraction. Thermal desorption is well suited for dry or homogeneous samples such as polymers, waxes, powders, pharmaceutical preparations, solid foods, cosmetics, ointments, and creams. There is essentially no sample preparation required. 

The technique of DTA has been used to study the thermal degradation of balsam fir wood by Arseneau (134). Using air-dried wood and also various samples of wood that had been extracted with several reagents, Arseneau attributed the various DTA curve peaks to the reactions summarized in Table 7.5. 

For trace metals the method is usually to employ wet-ashing or dry-ashing techniques. The ashed residue is solubilized by the desired solvent, followed by colorimetric, polarographic, or emission spectroscopic techniques. Atomic absorption can also be used with many polymers analyzed directly after a proper solution is prepared, without prior ashing. For polymers that are difficult to solubilize or that provide a solution too viscous to aspirate into the flame, partial degradation by hydrolysis, thermal treatment or solvent extraction may be used to effectively alleviate these difficulties. 

AIBN monomer (2 % w/w) was used as free radical thermal initiator in 15 mL of THF solutions reaction vials. Under nitrogen atmosphere the polar composition was prepared and injected into the vials, and freeze-thaw cycles were followed to eliminate any trace amount of dissolved oxygen under 60 °C for 72 h. The excess amount of methanol (100 mL) was poured into the reaction mixture, filtered and the product obtained. The product again dissolved in DMF and, methanol was used to re-precipitate the product. The unreacted monomers were removed by extraction technique. At 70 °C under vacuum condition for several days the product was dried until the constant weight achieved. The obtained dried polymers were highly soluble in polar solvents. Gravimetric method was used for the determination of conversions. 

The aroma compounds of dry cured Parma ham have been analyzed by thermal desorption GC-MS after extraction by means of the DHS technique [7], Using GC MS, 122 substances, including hydrocarbons, aldehydes, alcohols and esters, were identified in the volatile fraction. The same research group used DHS and SDE techniques to isolate aroma components from Parmesan cheese [8], By means of GC MS, more than 100 substances were characterized in the extracts. This application is discussed later in this chapter in section 3. 

Thermogravimetric and differential thermal analysis were also performed in a TA SDT 2%0 TG-DSC simultaneous instrument. Pt crucibles containing 5-7 mg of sample were heated at 2°C/min from room temperature to 1000 °C under dry oxidizing atmosphere. In order to verify the effectiveness of the separation method, several fractions during extraction process have been analyzed by above described techniques. 

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