Starch complex formation

If the chemical system has a single unstable steady state and hence shows oscillatory behavior in the absence of starch, complex formation can stabilize the homogeneous steady state and make possible the appearance of Turing structures at parameters which would yield oscillatory kinetics in the complex-free system. Observe that in the above partial differential equation system (12) the effective ratio of diffusion coefficients is (1 -f K )c, which can be much greater than unity even if c < 1. Consequently, the presence of a species that forms an appropriate complex with the activator can allow Turing structures to form for, in principle, any ratio of the activator and inhibitor diffusion coefficients. 

Extracts from 152 plant species, representing 46 different families, were screened for effects on tobacco mosaic virus (TMV) replication in cucumber cotyledons. Twenty species have shown enough activity to warrant further study. Several members of the Caprifoliaceae family increased virus replication. An extract of Lonicera involucrata enlarged the virus lesions in local lesion hosts and produced a thirty fold increase in virus titer, but had no effect on virus replication in systemic hosts. The active material appears to affect the virus defense mechanism of local lesion hosts. An extract of common geranium is an active virus inhibitor. It inactivates TMV and TMV-RNA (ribonucleic acid) in vitro by forming non-infectious complexes. In vivo, it also inhibited starch lesion formation in cucumber cotyledons incited by TMV infection. 

The most widely used complexing agents are alcohols (butanol, n-propyl alcohol and n-pentyl alcohol1). Schoch33 now recommends the use of Pen-tasol, a commercial mixture of pentyl alcohols, for the first precipitation, and 1-butanol for recrystallizations. For com (maize) starch, this avoids contamination of the amylopectin with an intermediate fraction which is sufficiently linear to be precipitated with Pentasol and yet has a degree of branching which prevents complex formation with butanol. 

Potato starch contains fewer lipids than the cereal starches. Free latty acids in rice and maize starches result in amylose-lipid complex formation, thereby contributing to their higher transition temperatures and lower retrogradation. 

The investigations carried out by Professor French and his students were based on sound experimental approaches and on intuitive theoretical considerations. The latter often resulted in new experiments for testing a hypothesis. On the basis of theoretical considerations, Professor French proposed a model for the structure of the amylopectin molecule, and the distribution of the linear chains in this molecule. This model was tested by utilizing enzymes that selectively cleave the linear chains, and the results substantiated the theoretical deductions. He proposed a theory on the nature and types of reactions occurring in the formation of the enzyme - starch complex during the hydrolysis of starch by amylases. In this theory, the idea of multiple attack per single encounter of enzyme with substrate was advanced. The theory has been supported by results from several types of experiments on the hydrolysis of starch with human salivary and porcine pancreatic amylases. The rates of formation of products, and the nature of the products of the action of amylase on starch, were determined at reaction conditions of unfavorable pH, elevated temperatures, and increased viscosity. The nature of the products was found to be dramatically affected by the conditions utilized for the enzymic hydrolysis, and could be accounted for by the theory of the multiple attack per single encounter of substrate and enzyme. 

Figure 16-6 (a) Schematic structure of the starch-iodine complex. The amylose chain forms a helix around l6 units. [Adapted from A T. Calabrese and A. Khan, "Amylose-lodine Complex Formation with Kl Evidence for Absence of Iodide Ions Within the Complex." J. Polymer Sci. 1999, A37,2711.] (fc>) View down the starch helix. Showing iodine inside the helix.8 [Figure kindly provided by R. D. Hancock, [rower Engineering, Sett Lake City.]... 

In the cyclodextrins readily obtainable from starch, the six (a-CD), seven (P-CD) and eight (y-CD) a(l- 4)-linked glucose units are "locked up" in a strait-jacket type belt due to adoption of 4Cj chair conformations of the pyranoid rings and a net of 2-OH — OH-3 hydrogen bonds (73, 74). As this structural rigidity even persists on inclusion complex formation, as exemplified by the three represenatives in Fig. 1 (75 - 78) ... 

Starch for use in papermaking has to meet specific purity requirements in residual oil, protein, bran and ash content. Industrial starches have a protein content (N X 6.25), ranging from about 0.05% for potato starch to 0.3-0.6% for com starch, depending on separation efficiency during production. Excess protein content will induce foaming in dispersions of starch and affect the quality and strength of the coated surface. Starch for use in the paper industry should not contain more than 0.4% protein. Oxidized starches tend to have the lowest protein content. Residual oil will cause retrogradation due to complex formation with amylose. 

A minimum temperature of 88°C is required for paste storage of thermally oxidized starch in order to prevent retrogradation. Various retrogradation control agents have been recommended for stabilizing. The addition of 0.5 to 1.0% calcium stearate prevents the build up of viscosity, but could actually lead to the precipitation of amylose due to gradual stearate dissolution (ionization) and complex formation with... 

Recent experiments in our laboratory have shown that a thermal gradient is not necessary for complex formation with potato starch. In the presence of suitable compounds, the gelatinized potato starch forms helices under complex formation at isothermal conditions. The reaction takes place even at low concentrations of ligand compounds under conditions occuring in any food system containing potato starch. The reaction can easily be followed by amperome-tric titration with jodine (24). The complexes formed can be analyzed by using a combination of glucose determination and G.C. analysis. 

The formation of decanal - starch - complexes with time at different temperatures is presented in Figure 1. The reaction is completed in a matter of minutes, and a stable equilibrium is obtained. Isotherms of complex formation are shown in Figure 2. The complex formation starts at very low concentrations and comprises appreciable amounts of ligand. We are actually studying these reactions in some detail and are interested in the consequences of these interactions for taste and odor perception. As reported elsewhere, the complexed ligands, if present in dry state, have a remarkably increased chemical stability (25). 

Figure 1. Formation of decanal—starch complexes with time—starch (as glucose) 0.613mM decanal 5.31 M H20 10 mL pH 7.0 temperature 20, 35, 50°C...

Both the amylose and amylopectin components of starch form complexes with iodine, but early studies showed that there is no connection between the iodine reaction and the reducibility of starch fractions.63 The complex of amylose is pure blue, whereas the complex of amylopectin is blue-violet.5864 Thus, the varying amylose-to-amylopectin ratio can be one of the factors responsible for the various shades of blue color exhibited by various varieties of starch. Amylopectin takes up less iodine than does amylose. Also the course of complex formation uptake is different, as is evident65 from Fig. 2. 

The formation of starch complexes with metal salts of metal oxides is of practical interest in, for instance, textile finishing (see discussion by Hal-... 

The formation of a barium-starch complex is well known579-581 Stern582 determined its composition as (QHioOs BaO. Complexation of starch with barium is also used to precipitate starch from its solution. 

In some instances the carrier of the guest plays the role of emulsifier. For example, alcohols and lower fatty acids or their esters are used in the formation of fat-starch complexes.676 In this case, conditions for preparation of complexes resemble conditions for extraction, and unexpected results can accompany both processes. For example, it has been shown that extraction of lipids with 1-propanol from their surface complex with oat starch produced a helical lipid-starch complex that was absent prior to extraction.677... 

The effects of sulfonic acids on starch are discussed later (p. 375). Dimethyl sulfoxide and carbon disulfide are the only other sulfur-containing compounds that have been examined with respect to their complex formation with starch. For example, a complex of potato starch with carbon disulfide was prepared via the starch-acetone complex on refluxing. It was reported that this complex contains 5.8-5.9% of CS2.682 Dimethyl sulfoxide causes expanded coiling of amylose without the formation of a helix.378 Banks and Greenwood385 reviewed the Mark-Houwink exponent for Me2SO-starch solutions. Reported variations in this exponent are believed... 

Relationships between the structure and stability of phenol-starch complexes are not clearly understood. Apart from the complexes of phenols listed in Table XXXII, complexes of chlorocresols,712 three isomeric nitro-phenols,715 resorcinol, phloroglucinol, and rutin,716 have been reported. The formation of complexes with nitrophenols has been monitored by ultraviolet... 

The preparation of starch-fatty acid complexes is based on the use of hydrophobic solvents, which in turn open the starch lattice for penetration by acids. Such solvent molecules can become guests of inclusion complexes and are subsequently displaced by fatty acids. Extrusion has been found useful for the synthesis of such complexes.748,749 Starch should be defatted prior to complexation by using methanol,739,740 Cellosolve, or 80% 1,4-dioxane.750-752 Table XXXV summarizes the results of a classical preparation.701 As shown in Fig. 47, the amount of complex formation by extrusion is not linearly proportional to the concentration of fatty acids added.749 In... 

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