Starch water sorption

The sorption of water by excipients derived from cellulose and starch has been considered by numerous workers, with at least three thermodynamic states having been identified [82]. Water may be directly and tightly bound at a 1 1 stoichiometry per anhydroglucose unit, unrestricted water having properties almost equivalent to bulk water, or water having properties intermediate between these two extremes. The water sorption characteristics of potato starch and microcrystalline cellulose have been determined, and comparison of these is found in Fig. 11. While starch freely adsorbs water at essentially all relative humidity values, microcrystalline cellulose only does so at elevated humidity values. These trends have been interpreted in terms of the degree of available cellulosic hydroxy groups on the surfaces, and as a function of the amount of amorphous material present [83]. 

Sorption and desorption of water by starch exhibits hysteresis behavior. In maize starch, the sorption branch of the hysteresis loop corresponding to moisture contents above 16% displays exponential kinetics386 ... 

Additives to starch exert varying effects on the kinetics of water sorption. For example, lipids do not significantly affect the content of adsorbed water. The mode of starch defatting can also influence moisture sorption by molecules of the defatting solvent occupying active centers of sorption.389 The addition of either sucrose or lipids to starch has the same effect on both branches of the hysteresis curve.386,398 Some additives, such as dimethyl sulfoxide or ammonium rhodanide, induce selectivity of the adsorption and solvation of starch 411 Sulfur dioxide accelerates water sorption regardless of the temperature.412 Pretreatment of starch with sulfur dioxide usually increases the water sorption.413 Studies on the sorption of components of water-alcohol mixtures are discussed in Section IV. 

It is known that the origin of starch controls the amylose-to-amylopectin ratio, the granule size, and other properties. The role of the origin of starch on water sorption-desorption (Tables XIV and XV) and related... 

Starch has been classified as a moderately hygroscopic material.f Water sorption studies have been conducted using static methods (saturated salt solutions in closed chambers) modified inverse frontal gas chromatography, and automated moisture balance systems. " The isotherms are typically type II curves exhibiting hysteresis, as shown in Fig. 5. Hysteresis in starch samples has been attributed to intra- and... 

Faroongsamg, D. Peck, G.E. The swelling and water uptake of tablets III moisture sorption behavior of tablet disintegrants. Drug Dev. Ind. Pharm. 1994,20 (5), 779-798. Sair, L. Fetzer, W.R. Water sorption by starches. Ind. Eng. Chem. 1944, 36, 205-208. 

Paik, S.W. Gilbert, S.G. Water sorption isotherms on sucrose and starch by modified inverse frontal gas chromatography. J. Chromatogr. 1986, 351, 417-423. 

Chinachoti, P. and Steinberg, M.P. Interaction of sucrose with starch during dehydration as shown by water sorption, /. Food Sci., 49,1604,1984. 

Water sorption isotherms for starch-based edible films plasticized with different contents (a) and types (b) of binary polyol mixtures at 25°C. 

For true adsorption, several equations for adsorption isotherms have been derived, based on various theories. Such equations often are applied to water sorption isotherms of foods as well. However, one cannot speak of adsorption in the case of most foods, as mentioned above, because there is no (or a very limited) phase surface onto which water can adsorb. Moreover, most foods contain numerous components even if phase surfaces were present they must be very inhomogeneous. In the author s opinion, it therefore makes little sense to use such equations. Only for relatively simple and homogeneous systems, like pure starch granules, can some theories be more or less applicable, but not for real foods. Mathematical fitting of experimental data may be useful for practical purposes, and since the equations generally have three or four adjustable parameters, a reasonable fit can often be obtained. But one cannot attribute physical significance to the parameters derived in this way, such as a monolayer water content. ... 

Surprisingly, the association between TPS and cellulose fibres (polysaccharide-based composites) has been little analysed. In the literature, cellulose fillers used in association with a plasticized starch matrix are commercial paper fibres,10 potato pulp microfibrils,11 12 tunicin whiskers and paper bleached pulp.13-14 The literature reports that these cellulose fillers improve the tensile strength. Besides, the composite water sorption seems to be decreased. This behaviour is related to the well known lower water uptake of cellulose compared to starch.10-14... 

Figure 7.5 Water sorption behavior for different starch-cellulose composite films.

Shin M, Woo K, Seib PA. Hot—water solubilities and water sorptions of resistant starches at 25°C. Cereal Chem 2003 80 564-566. 

Slavutsky and Bertuzzi (2014) recently showed ceUulose nanociystals (C-NC) obtained from sugarcane bagasse. They formulated starch/C-NC composites and their water barrier properties were studied. The measured film solubility, contact angle, and water sorption isotherm indicated that reinforced starch/C-NC films have a lower affinity to water molecules than starch films. The same effect was observed in studies by Savadekar and Mhaske (2012). They studied the effect of C-NC incorporation on TPS matrix and found that the nanofillers addition improved their barrier and mechanical properties. 

Jimenez A, Fabra MJ, Talens P, Chiralt A (2010) Effect of lipid self-association on the microstructure and physical properties of hydroxypropyl-methylcellulose edible films containing fatty acids. Carbohydr Polym 82 585-593 Jimenez A, Fabra MJ, Talens P, Chiralt A (2013) Phase transitions in starch based films containing fatty acids. Effect on water sorption and mechanical behavior. Food Hydrocolloid 30 408-418 Jin Z, Hsieh F, Huff HE (1994) Extmsion of com meal with soy fiber, salt, and sugar. Cereal Chem 7 227-234... 

Zeppa C, Gouanve Espuche E (2009) Effect of a plasticizer on the structure of biodegradable starch/clay nanocomposites thermal, water-sorption, and oxygen-barrier properties. J App Polym Sci 112 2044-2056... 

---