Starch native potato

Fig. 5 Net differential heat of sorption for water vapor by native potato starch at 20°C as a function of amount of water sorbed per mass of dry starch. (From Ref. 14.)...

Figure 8.4 The gelatinization of native potato starch at 30% solid content by DSC.

In this chapter, we have presented a great deal of information on important physicochemical and functional characteristics of native potato starch in comparison with some cereal starches. In addition, we have also discussed various modification techniques being used to modify potato starch, with an emphasis on the post-modification changes (particularly after derivatization)... 

Modification, which involves the alteration of the physical and chemical characteristics of the native potato starch to improve its fimctional characteristics, can be used to tailor it to specific food applications. The rate and efficacy of any starch modification process depend on the botanical origin of the starch and on the size and structure of its granules. This also includes the surface structure of the granules, which encompasses the outer and iimer surface depending on the pores and channels, which cause the development of the so-called specific surface (Juszczak, 2003). Potato starch modification can be achieved in three different ways physical, conversion, and chemical (derivatization) (Table 10.6). 

Figure 10.9 Effects of acetylation on the granule morphology of maize and potato starches, (a) Native maize starch granules, (b) Acetylated maize starch granules, (c) Native potato starch granules, (d) Acetylated potato starch granules (Singh et al., 2004a).

Figure 7.7 Clausius-Clapeyron relationship between water activity and temperature for native potato starch. Numbers on curves indicate water content, in g per g dry starch (from Fennema,...

Native potato starch, which is used in the food, paper and textile industries, is often not optimal for a particular application. Modifications are done to obtain the properties needed for specific uses.26 28 More than 500 modifications of potato starch are currently known. This chapter presents an overview of the major commercial modifications rather than a complete bibliography of all potato starch reactions. With a distinction based on the chemical character of the product, three groups can be distinguished. Some derivatives are made from starch by a combination of reactions. 

Monophosphorylation pastes made from starch monophosphates also have greater clarity, viscosity and stability than unmodified starches,64 but are sensitive to salts, especially polyvalent cations.65 Variability in residual ash can lead to variability in the viscosity of monophosphorylated starches. Monophosphate substitution also lowers the gelatinization temperature at 0.07 DS, a value much greater than is found in food starches, the gelatinization temperature is below room temperature. Native potato starch contains 0.07 to 0.09% bound phosphorus and wheat starch contains 0.055% phosphoms, primarily as phosphoglycerides in the latter case. The FDA allows up to 0.4% phosphate as phosphoms.58 Monophosphates were used commercially in the US until about 1970. 

Thiewes, H.J., and Steeneken, P.A.M. (1997). The glass transition and the sub-T endotherm of amorphous and native potato starch at low moisture content. Carb. Polym., 32, 123-130. 

It is well known that every starch processing method is facilitated by the presence of water. Water depresses the melting point of amylopectin crystallites and lowers starch melt viscosity. Native potato starch contains about 18% water when stored at ambient atmosphere (room humidity about 55%). If one does not add more than about 10% water the melt-processed starch will solidify when cooling down. If more water is added to the starch, its glass transition falls below room temperature (Zeleznak Moseney, 1987). The moulding then exhibits a rubbery state and solidifies later when the excess water evaporates. 

In the above studies compression and injection moulding were carried out with native potato starch dried at room temperature and then mixed with 7% water. After processing, the samples were subjected to ambient atmosphere and investigated after a storage time of at least 4 weeks. 

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.)... 

Waxy corn (WCN30G30W) materials are amorphous after moulding at a temperature above 120°C. Potato starch materials (PN30G30W) show B-type crystallinity. The relative crystallinity (compared to native potato starch) decreases from 68% (at 110°C) to 36% (at 140°C). Above 140°C the relative crystallinity increases to a value of 70% at 190°C. These values are in agreement with values previously reported.14 It has been shown that the total B-type crystallinity of potato starch plasticized with glycerol and water can be considered as a summation of residual amylopectin crystallinity and recrystallization of both amylose and amylopectin depending on processing conditions. 

Films obtained cifter extrusion of native potato starch and glycerol Enzymatic test Head-space test... 

As an alternative to these materials the objective in this research will be to produce starch based resilient thermoplastic foams based totally on native potato starch. This is done in two steps the production of expandable thermoplastic starch beads by extrusion and foaming of the expandable beads after conditioning in a successive foaming step. The properties of these foams will be studied as a function of processing parameters and material composition. A further objective is to determine the ultimate properties of pure starch based foams. 

To determine the degree of destructurization X-ray diffraction measurements were performed on the extruded beads. Fig 2 shows the results of these measurements. In the figine the X-ray diagram of native potato starch is added as a reference. The curves clearly show that the initial peaks that can be attributed to native starch disappear upon processing. 

Figure 2. X-ray diagrams of 1. native potato starch 2. extruded starch using screw design A and 3. extruded starch using screw design B.

The crystalline precipitate, as synthesised, shows in X-ray wide angle powder diffraction which is equivalent to the B-structure of native potato starch. Upon heating in the presence of 18% by weight of water the crystallites transform to the A-structure of native wheat starch. 

The Neoamylose forms with iodine and analogous compounds molecular complexes. X-ray diffractograms show the same intensity distribution with scattering angle as complexes of amylose from native potato starch. In these molecular complexes amylose formes V-helices. The binding ciq>acity for iodine was higher for the new polymer. 

We have introduced carbonyl and some carboxyl groups to native potato starch by treating the starch with laccase and the mediator Tempo (2,2,6,6 tetramefiiyl-1-piperidinyloxy). Native potato starch was incubated in the buffered solution with laccase and Tempo. After reaction the starch was... 

Biodegradation — Films obtained after extrusion of native potato starch and glycerol Enzymatic test Head-space test Compost test 100% weight loss after 24 h 100% CO2 evolution after 50 days 100% weight loss after 49 days (13)... 

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

RH) and 23°C, the gfycerol-plasticized sheets with a high an lose content (HAP) were stronger and stifFer than the normal thermoplastic starch with an an lose content typical for common potato starch. The tensile modulns at 53% RH was about 160 MPa for the high an lose material and about 120 MPa for the plasticized NPS (native potato starch). The strain at break was about 50% for both materials. 

The suitability of an in vitro enzymatic method for ass ing the biodegradability of starch-based materials was evaluated [50]. The materials studied included commercial starch-based materials and thermoplastic starch films prepared by extrusion from glycerol and native potato starch, native barley starch, or crosslinked anylomaize starch. 

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