Starch glassy state

The use of a modified starch, corn starch sodium octenyl succinate derivative, for encapsulation of sea buckthorn kernel oil (containing polyunsaturated fatty acids, tocopherols, tocotrienols, plant sterols and carotenoids) by spray-drying was found to improve oil stability. Better protection was afforded when the starch encapsulant was stored in its glassy state (Partanen et al. 2002). Methylcellulose and hydroxymethy-oellulose in combination with soy lecithin enabled the production of 40% (W/W) fish oil powders with improved stability (Kolanowski et al. 2004). 

Attenburrow, G.E. The fracture behavior of starch and gluten in the glassy state, /. Cereal Sci., 16,1,1992. 

Native starch granules are thus very stiff or rigid particles. They have crystalline regions, which will contain about half of the water present, and the remainder of the starch and water forms a glass. The glassy state is discussed in Section 16.1. 

In most dry foods, starch is the main component responsible for a glassy state. This concerns several dry cereal products, like hard biscuits and various breakfast cereals. Figure 16.5 gives Tg for wheat starch, but if low-molar-mass components, generally sugars, are also present, the curve is shifted to lower temperatures, somewhere between those for starch and those for lactose. Another example is pasta, in the dry form in which it is commonly sold, which consists for the most part of wheat starch. Pasta has an impressive shelf life in the glassy state, and it readily takes up water upon cooking, to attain a soft rubbery texture. 

Chanviier H., Colonna P, Della VaUe G., Lourdin D., Structure and mechanical behaviour of com flour and starch-zein based materials in the glassy state, Carbohydr. Polym., 59, 2005, 109-119. 

A polymer may show its backbone chain mobility increased because of plasticization, but this may not necessarily agree with the motions of water (or diluent) molecules, which become available to chemical reactions and microbial growth when these molecules are adequately mobile (Vittadini et al., 2001). It was reported that water, for example, has been found to be highly mobile even in a glassy state of waxy corn starch (9.3% moisture content). Hence, molecular mobility of water around reactive molecules involved in the degradation of AA into the films herein formulated is, as it was above pointed, a very important feature to be considered. Local water availability (that is at a molecular level) may be a key factor for AA stability in solid-like polymeric networks. 

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