Starch, sorption isotherm

Fig. 11 Sorption isotherms for water onto potato starch (0) and microcrystalline cellulose ( ). (Data adapted from Ref. 83.)...

LIG. 38 Graph of a modified state diagram for instant dent starch, which includes both DSC rg midpoint data plotted as a function of moisture content (% wb) and sorption isotherm data obtained at 20 °C. DSC Tg midpoint data were fit to the Gordon-Talyor equation, and sorption isotherm data were fit to the GAB equation. The moisture content associated with the Tg at 20 °C is called the critical me and is equal to 21.8% (wb), and the corresponding critical water activity value is 0.92. 

Figure 1-12 Sorption Isotherms of Wheat Flour, Starch, and Gluten. Source From W. Bushuk and C. A. Winkler, Sorption of Water Vapor on Wheat Flour, Starch and Gluten, Cereal Chem., Vol. 34, pp. 73-86, 1957.

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. 

Figure 1 Pregelatinized starch sorption-desorption isotherm. O Sorption Desorption.

A method to circumvent this dilemma was sought by Ferng (11). An extensive and detailed study of static sorption methodology was first conducted to provide a basis of reproducible data for starches of different macromolecular structure. This was followed by studies of sorption isotherms by IGC with different GC conditions including zero loads with empty and supposedly inert support material (diatomaceous earth). The data showed that the response of the thermal conductivity detector (TCD) to controlled chromatographic conditions of temperature, flow rate, and partial water vapor... 

Figure 2. Sorption Isotherm of Com Starch Determined at 25°C by Static Method.

Since the product of flow rate, time and concentration equal the input mass, a constant input concentration permits the calculation of mass from either time or retention volume. Empty columns provide an essentially constant ratio of input mass to time at constant flow rate with the concentration of water vapor fixed by the temperature of the carrier gas saturated with water vapor (100Z RH or Aw of 1 see Figure 6). This state can be achieved with substrates that do not dissolve in water when saturated (for example, starches and many proteins), or when the relative humidity is constant but insufficient to allow uptake to produce a highly multilayered or clustered water state in the substrate equivalent to a continuous water phase or solution. This condition requires a source of humidified gas as in (7.). The sorption isotherm equation is then given by... 

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. ... 

FIGURE 8.4 Sorption isotherms—w in g per g dry starch versus water activity uw— of native potato starch, obtained when decreasing water content (desorption) and when increasing it (absorption), (a) Linear scales, (b) Part of the same data on a log/ log scale, (c) Part of the same data, also showing intermediate curves (broken). (After results by C. van den Berg, Ph.D. thesis, Wageningen University, 1981.)... 

Zhang, Y., Han, J.H. 2008. Sorption isotherm and plasticization effect of moisture and plasticizers in pea starch film. Journal of Food Science, 13(1) 313-324. 

RgurE 12.7 Sorption isotherms for selected sorbents 1—zeolite CaA 2—activated carbon 3—peat 4—sawdust 5—kaolin 6—potato starch 7—sflica gel 8— wheat bran 9—filter paper. (Adapted from Tutova, 1988.)... 

Pig. 3. Some sorption isotherms of water vapor on native potato starch as reported in the literature (100). 

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. 

Previous reports on starch-alcohol interactions assumed that only physical sorption is involved, despite observations of the irreproducibility of successive adsorption-desorption isotherms for starch-methanol and starch-ethanol systems. This irreproducibility was assumed to be the result of swelling.354... 

Lipatov798 recognized that the sorption of Methylene Blue on starch is a heterogenous neutralization reaction of neutralization in which starch acts as an acid. Adsorption isotherms of Methylene Blue on starch indicate that it is an equilibrium process and that swelling as well as other internal structural factors are responsible for the sigmoidal shape of the isotherm.799-800 It is also known that the Langmuir isotherm is affected by equilibrium between the monomer and dimer forms of Methylene Blue, both of which are capable of adsorption on starch (Table XLV).801... 

Anionic dyes readily adsorb on starch (Tables XXXIX-XLIII).802 However, there is evidence that this rule is violated in the case of potato starch.802-803 The simplest intepretation of this fact has been presented in terms of the phosphate groups present in potato starch. A relationship exists between the phosphorus content in potato starch and the sorption capacity of that starch for Methylene Blue. The sorption follows the Langmuir isotherm. Extrapolation of the result to 0% phosphate leads to the conclusion that no Methylene Blue would be adsorbed on phosphate-free starch.804 Methylene Blue is better adsorbed on potato starch, but is also... 

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... 

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