Freeze/thaw stability

If an analyte is found to be unstable in matrix at room temperature during a validation, or if it is known prior to initiating the vahdation that room temperature matrix instabihty is problematic, the analytical method may be designed to make use of a stabilization technique (e.g. all operations conducted at 4°C or addition of a chemical stabilizer). Analyte stability should then be assessed under the conditions of the assay using the stabihzation technique. 

Latices containing up to 50% water are susceptible to freezing. Upon thawing it is possible for destabilisation of the latex to occur. The normal test method is to cycle the latex between ambient and freezing. A freezer (normally at -16°C) is often used overnight to freeze the latex and it is allowed to thaw at laboratory temperature or in a 25°C oven or bath. Stability after 3-5 cycles is considered satisfactory. 

Many latices are shear sensitive, particular to pumping, which may be essential in bulk handling facilities. There arc many ways to determine this, but an easy method is to rub the latex between finger and thumb. If it is mechanically unstable it will rapidly ball up . A certain amount of experience is required for this test 

Cationic starches are widely used as wet-end additives in the pulp and paper industry to enhance starch and filler retention during papermaking. Use of cationic starches increases paper strength and decreases biological oxygen demand (BOD) of paper mill effluent. Presently only cationic corn and potato starches are used by Canadian paper mills. The degree of substitution (DS) of normal, waxy, high-amylose barley 

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Butyl latices are prepared by emulsification of butyl rubber. Butyl latex has excellent mechanical, chemical and freeze-thaw stability, and when dried it shows the typical properties of butyl rubber [7]. 

Eliasson, A. C, Kim, H. R. (1992). Changes in rheological properties of hydroxypropyl potato starch pastes during freeze-thaw treatments I. A rheological approach for evaluation of freeze-thaw stability. J. Texture Stud, 23, 279-295. 

Baker, L. A., Rayas-Duarte, P. (1998). Freeze-thaw stability of amaranth starch and the effects of salt and sugars. Cereal Chem., 75, 301-303. 

Wu, Y, Seib, P. A. (1990). Acetylated and hydroxypropylated distarch phosphates from waxy barley paste properties and freeze-thaw stability. Cereal Chem., 67, 202-208. 

Com symp solids are also dry products, have a smaller average size, and are comparatively sweeter (12). Both maltodextrins and com symp solids are used to prevent caking enhance dispersibility and solubility provide body or bulk impart desirable 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 stability. 

In general, derivatization increases solution and gel clarity, reduces the tendency to gel, improves water binding, increases freeze—thaw stability, reduces the gelatinization temperature, increases peak viscosity, and reduces the tendency to retrograde. Combinations of substitutions are used to obtain desired properties for specific applications. 

Acrylics. There are two principal classes of acrylic sealants latex acrylics and solvent-release actylics. High molecular weight latex acrylic polymers are prepared by emulsion polymerization of alkyl esters of acrylic acid, The emulsion polymers are compounded inlo sealants by adding fillers, plasticizers, freeze-thaw stabilizers, thickeners, and adhesion promoters. As is true of the silicone lalex sealants, die acrylic latex sealants are easy to apply and clean with water. 

Specifications and Standards. Borax stability is an important property in adhesives, paper, and textile applications. Ollier emulsion properties tabulated by manufacturers include tolerance to specific solvents, surface tension, minimum film-forming temperature, dilution stability, freeze-thaw stability, percent soluble polymer, and molecular weight. 

Stability studies such as stock solution, bench-top, freeze-thaw stability... 

Freeze-thaw stability due to reasonable probability this might be necessary for repeat studies bench-top stability assessment may be prudent for chemical series with known temperature instability... 

All analytical methods must be validated in accordance with international guidelines [59-61] prior to application. As discussed in the first part of this book, minimum criteria that need to be met to in order to satisfy these guidelines are selectivity, matrix effects, extraction efficiency, process efficiency, processed sample stability, linearity, accuracy, precision, and freeze-thaw stability. 

Barley starch (see Chapter 16) has a viscosity profile similar to that of potato starch and also has a similar range of applications.159 Seib and Wu160 claimed excellent freeze-thaw stability in a hydroxypropylated waxy barley starch. 

Starch is used in retorted baby foods to thicken and provide short texture. In addition to high temperature stability, fruit-based, dessert-type products require resistance to low pH and stability in the jar, including (though it is secondary) freeze-thaw stability. Accordingly, crosslinked acetylated waxy maize and tapioca starches are favored. Tapioca starch products are favored for flavor and because they are thought to be more wholesome for babies. 

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