Glassy carbohydrates

Microencapsulation using extrusion is mainly described for glassy carbohydrate matrices [14-16, 28-29]. The glassy carbohydrates, such as starch and maltodextrins, are melted at elevated temperature and low water contents and are intensively mixed with the active in the extrusion barrel. Extrusion has been used for volatile and unstable flavours. The shelf life of flavour oils could be extended from several months to 5 years, compared with 1 year for spray-dried materials. The main drawbacks of the technology are the high investments costs and the formation of rather large particles (500-1,000 pm). 

Understanding and predicting water diffusivity in supercooled and glassy carbohydrates is of great importance in the practical applications of these mixtures, in particular to the preservation of foods and pharmaceuticals. Since the discovery more than a decade ago that water retained liquid-like heat capacity in glassy starch (Noel and Ring, 1992) several studies have shown that water is mobile in glasses of carbohydrates (van den Dries et al., 1998 van den Dries et al., 2000 Tromp et al., 1997 Hills et al., 2001 Chatakanonda et al., 2003 Kou et al., 2000 Vodovotz et al., 2000 Aldous et al., 1997) and foods (Roudaut et al., 1999). 

Encapsulation of aroma compoimds in amorphous carbohydrate matrices can be carried out, for example, by freeze- or spray-drying (Levine et al., 1991 Roos, 1995). Aroma compounds often remain encapsulated in glassy carbohydrate matrices stored at temperatures below their glass transition. Release of encapsulated aroma compounds may occur when amorphous carbohydrate matrices are stored at temperatures above their glass transition, allowing sufficient molecular mobility and diffusion. 

The main supports in food products are glassy carbohydrates alone or mixed dextrose, com syrup, glycerin, maltodextrins, sucrose added with emulsifiers, monoglycerides, gum, pectin, lecithin. Cyclodextrin complexed flavors may be prepared prior to extrusion (Bhandari et al., 2001). 

At very low concentrations of water, or in foods held below the free2ing point of water, physical conditions may be such that the available water may not be free to react. Under these conditions, the water may be physically immobi1i2ed as a glassy or plastic material or it may be bound to proteins (qv) and carbohydrates (qv). The water may diffuse with difficulty and thus may inhibit the diffusion of solutes. Changes in the stmcture of carbohydrates and proteins from amorphous to crystalline forms, or the reverse, that result from water migration or diffusion, may take place only very slowly. 

Amorphous adsorbents, 1 587-589 for gas separation, 1 631 properties and applications, l 587t Amorphous aluminum hydroxide, 23 76 Amorphous carbohydrates, material science of, 11 530-536 Amorphous carbon, 4 735 Amorphous cellulose, 5 372-373 Amorphous films, in OLEDs, 22 215 Amorphous germanium (a-Ge), 22 128 Amorphous glassy polymers, localized deformation mechanisms in, 20 350-351... 

Torimura etal. [194] developed an analytical approach capable of determining subnanomolar amounts of carbohydrates based on the indirect detection of iodate, 103 , at a glassy carbon electrode. The method was applied as a postcolumn detection system for HPLC separation. 

The transition temperatures of carbohydrates and proteins are significantly affected by water. It is often reported that an increase in water content results in a substantial decrease in transition temperatures (Slade and Levine 1995). For example, the glass transition of dehydrated food solids decreases as a result of water sorption (i.e., water uptake from its surroundings) and their properties may change from those of the glassy solid to viscous liquids or syrup (e.g., sugar systems) or leathery material (e.g., protein systems) in an isothermal process. 

The most common electrode material used in LC-EC is carbon, either as solid glassy carbon disks in thin-layer cells, or as a high-surface-area porous matrix through which the mobile phase can flow. Gold electrodes are useful to support a mercury film and these are primarily used to determine thiols and disulfides, and also for carbohydrates using pulsed electrochemical detection... 

Nevertheless, the microscopic mechanism that allows water diffusion in these glasses has remained an unsolved puzzle. We present here a computer simulation study of the microscopic mechanisms of water diffusion in carbohydrate from the viscous liquid state up to the glass. To understand the nature of water diffusion in glassy food-like systems, we employed molecular d)mamics (MD) simulations techniques to study in detail the structure and d)mamics of a concentrated glucose solution, a simple binary... 

We present here coarse grain simulation results of two simple binary water-carbohydrate mixtures that shed light on the mechanism of water diffusion in the supercooled and glassy state, the coupling of water mobility in the glass to the sub-Tg dynamics of the matrix, and the effect of the internal modes of the saccharide on the decoupling of water motion from carbohydrate translation. 

Noel, T.R., Parker, R., and Ring, S.G. A comparative study of the dielectric relaxation behavior of glucose, maltose, and their mixtures with water in the liquid and glassy states, Carbohydr. Res., 282, 193, 1996. 

Roozen, M.J.G.W., Hemminga, M.A., and Walstra, P. Molecular motion in glassy water-malto-oligosaccharide (maltodextrin) mixtures as studied by conventional and saturation-transfer spin-probe ESR spectroscopy, Carbohydr. Res., 215, 229,1991. 

Kim, Y.J., Hagiwara, T., Kawai, K., Suzuki, T., and Takai, R. Kinetic process of enthalpy relaxation of glassy starch and effect of physical aging upon its water vapor permeability property, Carbohydr. Polym., 53, 289, 2003. 

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