Starch systems

The xanthan gum, rice starch and potato starch system is available as a mix to be made in domestic bread makers. 

Other research using NMR techniques to study mobility in starch systems includes Li et al. (1998), who investigated the mobility of unfreezable and freezable water in waxy cornstarch using H and 2H NMR Choi and Kerr... 

Figure 7.12 Sequence of CLSM images recorded during melting of a 24-hour-old fractal particle gel formed by quenching a 1 wt% gelatin + 7 wt% oxidized starch system from 40 to 24 °C (a) immediately before heating (b) network rearrangement and coarsening (c) network break-up (d) aggregate melting into polydisperse liquid droplets. Reproduced from Firoozmand el al. (2007) with permission.

Of the myriad of modified starch systems tested, ranging from simple enzymically dextrinized starches to covalently attached amino acids and peptides onto dextrinized and/or oxidized (hypochlorite or periodate) corn starch bases, two polymers were selected as holding promise. The first system was a low dextrose equivalent (DE 5.7) enzyme-modified corn starch. The second starch-based polymer developed was a periodate-oxidized, amylase-dextrinized, covalently-attached phenylalanine glycoamine. 

The following sections focus on the description of the state and phase transition behavior of starch systems, as schematically illustrated in Figure 8.5, with an emphasis on their molecular organization and their response to various environments (temperature, solvent, other co-solutes, etc.). Selected material properties are also discussed in an effort to demonstrate structure-function relationships of this biopolymer mixture in pure systems and in real food products. 

All starch systems have to be designed to prevent settling of starch granules, which have a density of about 1.5 g/cm3. Piping has to be sized to maintain a velocity of at least 45cm/s and must be equipped for self-draining, particularly in vertical sections.91 In case of a power loss exceeding 30 minutes all slurry pipes should be flushed and drained. An air lance will be required for resuspension of settled starch. 

Carr et al.119 investigated grafting via reactive extrusion of starch with cationic methacrylate, acrylamide and acrylonitrile monomers. Starch, monomer and CAN initiator were metered into a twin-screw extruder at starch contents of approximately 35% solids. The cationic methacrylate monomer showed poor reactivity during extrusion, with essentially no add-on. Acrylamide-starch systems (1 1 w/w) gave conversions of approximately 20% and add-ons of 16% to 18%. Acrylonitrile displayed the greatest reactivity during extrusion, with conversions of 74% and 63% for 1 1 and 1 2 w/w acrylonitrile/starch ratios, respectively. The corresponding add-ons were 27% and 42%. 

Lelievre, J. (1992). Thermal analysis of carbohydrates as illustrated by aqueous starch systems. In Developments in Carbohydrate Chemistry, Alexander, R. J., and Zobel, H. F. (Eds.), pp. 137-161. Amer. Assoc. Cereal Chem., St. Paul, MN. 

The rheological behavior of systems containing starch, soybean protein, soybean oil, and water (5 10 10 40) has been studied.1038 The viscosity of the system depends on the origin of the starch. For example, the viscosity of a potato-starch gel markedly decreases upon the addition of protein. In contrast, a cornstarch gel is much more stable and does not show a decrease in viscosity after the addition of protein. The incorporation of proteins into a lipid-starch system shows that proteins are distributed among both components of the system.885... 

Starch moulding has the advantage that it is inherently more flexible. If the shape or weight of the product is being changed in a starchless system this requires a new set of moulds, whereas in a starch system all that needs changing is the mould board that stamps the impressions into the starch. 

Figure 7.9. Glass transition temperature of gelatinized WMS as a fiinetion of moisture content compared to the Gordon-Taylor predictions (Reprinted from Carbohyd. Polym., 51, Zimeri and Kokini, Phase transitions of inulin-waxy maize starch systems in limited moisture environments, pp. 183-190, Copyright (2003), with permission from Elsevier.)...

As expected, the viscosity increased at higher polymer concentrations and was greatest in the bottom phase. The bottom phase viscosities of maltodextrin systems were less than half those formed with dextran, however, and they were comparable to the PEG 8000-hydroxypropyl starch systems (5). The upper phase viscosities are increased slightly from 2 to 5 cps as compared to dextran or hydroxypropyl starch systems. These viscosities are still well below those of the bottom phase and did not appear to hinder the rapid mixing or mass transfer characteristic of these types of systems. This slight increase in upper phase... 

C in all cases, the commonly used frozen storage conditions (approximately — 18°C) would be located above the Tg temperatures thus systems stored at this temperature would be at the rubbery state and would have more molecular mobility. In this situation, deteriorative phenomena depending on diffusion could occur. As amylopectin and amylose retrogradation are crystallization phenomena occurring in starch systems, they were studied in the present work as examples of deteriorative changes. As observed in Table 18.1, values foimd for the onset temperature (T p varied between... 

Recrystallization of amylopectin is a reversible process that can be analyzed by DSC below 100°C (Miles et al., 1985). Amylopectin retrogradation was measured in starch systems containing sucrose from DSC runs immediately after freezing and after 91 days of storage at —80 and — 18°C. Aliquots of gelatinized pastes were run between 20 and 120°C at a heating rate of 10°C min in order to detect the presence of the amylopectin retrogradation peak. 

In gelatinized starch systems Tg onset is located between —4.5 and — 5.5°C small quantities of hydrocolloids did not significantly shift this temperature. 

FIGURE 17.4 Fish lipid-starch interaction. Yields [%] of lipids (upper) and PUFA (bottom) from lipid-starch system, by selective extraction. (Adapted from Bienkiewicz, G. and Kofakowska, A. 2001. Fish lipids-amylopectin starch interactions, 21st Nordic Lipid Symposium Lipidforum, Bergen, June 5-8, 2001 Bienkiewicz, G. and Kotakowska, A. 2001. Fish lipids-amylose interactions, 24th World Congr International Society for Fat Research (ISF), Berlin, September 16-20, 2001, 53.)... 

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