Freezing control

Figure 2 shows inactivation of thylakoids after 3 hours of storage at — 6 or — 12°C as a function of the NaCl concentration in the suspending medium before freezing. Controls were kept for 3 hours at 0°C. 100 mM... 

Cryopreservation process may be carried out in different ways from placing the cryo-tubes in a Mr. Frosty vessel (NALGENEtm W USA), which ensure a slow temperature decrease by 1°C to the use of computerized cryobath equipment (CryolLogic) with freeze control system. 

Sparrow EM, Ramsey IW, Kemink RG (1979) Freezing controlled by natural convection. J Heat Transf 101 578-584... 

Citric acid is used in carbonated beverages to provide tartness, modify and enhance flavors, and chelate trace metals. It is often added to jams and jellies to control pH and provide tartness. It is used in cured and freeze-dried meat products to protect the amino acids (qv) and improve water retention. Bakers use it to improve the flavor of fmit fillings in baked goods. Because citric acid is a good chelator for trace metals, it is used as an antioxidant synergist in fats and oils, and as a preservative in frozen fish and shellfish (7) (see Antioxidaisits). 

In the second process, a small particle-size latex is prepared and treated so that a limited and controlled degree of particle agglomeration occurs. The agglomerated latex is then concentrated as before but, because of the particle-size distribution obtained, the soHds may be raised to ca 70 wt %. Two methods exist for agglomeration of latices, ie, chemical and freeze agglomeration (45,46). 

Purity of toluene samples as well as the number, concentration, and identity of other components can be readily determined using standard gas chromatography techniques (40—42). Toluene content of high purity samples can also be accurately measured by freezing point, as outlined in ASTM D1016. Toluene exhibits characteristic uv, it, nmr, and mass spectra, which are useful in many specific control and analytical problems (2,43—45). 

Specifications for gas turbine fuels prescribe test limits that must be met by the refiner who manufactures fuel however, it is customary for fuel users to define quality control limits for fuel at the point of delivery or of custody transfer. These limits must be met by third parties who distribute and handle fuels on or near the airport. Tests on receipt at airport depots include appearance, distfllation, flash point (or vapor pressure), density, freezing point, smoke point, corrosion, existing gum, water reaction, and water separation. Tests on delivery to the aircraft include appearance, particulates, membrane color, free water, and electrical conductivity. 

Com symp soflds are also dry products, have a smaller average size, and are comparatively sweeter (12). Both maltodextrins and com symp soflds are used to prevent caking enhance dispersibiUty and solubiUty provide body or bulk impart deskable texture bind, carry, and protect flavors control extmsion expansion provide viscosity form films and coatings provide an oxygen barrier inhibit crystallization control sweetness improve sheen improve organoleptic characteristics slow meltdown and improve freeze—thaw stabiUty. 

Sublimation of ice crystals to water vapor under a very high vacuum, about 67 Pa (0.5 mm Hg) or lower, removes the majority of the moisture from the granulated frozen extract particles. Heat input is controlled to assure a maximum product end point temperature below 49°C. Freeze drying takes significantly longer than spray drying and requires a greater capital investment. 

Figure 22-8 shows the features of a horizontal center-fed column [Brodie, Au.st. Mech. Chem. Eng. Tran.s., 37 (May 1979)] which has been commercialized for continuous purification of naphthalene and p-dichlorobenzene. Liquid feed enters the column between the hot purifying section and the cold freezing or recovery zone. Ciystals are formed internally by indirect cooling of the melt through the walls of the refining and recovery zones. Residue liquid that has been depleted or product exits from the coldest section of the column. A spiral conveyor controls the transport of solids through the unit. 

Another center-fed design that nas only been usea on a preparative scale is the vertical spiral conveyor column reported by Schildknecht [Angew. Chem., 73, 612 (1961) . In this device, aversion of which is shown on Fig. 22-9, the dispersed-ciystal phase is formed in the freezing section and conveyed downward in a controlled manner by a rotating spiral with or without a vertical oscillation. 

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