Starch phosphates reactions

FIGURE 7.23 The starch phosphorylase reaction cleaves glucose residues from amy-lose, producing a-D-glucose-l-phosphate. 

A thixotropic starch was produced in reactions of POCl3-crosslinked starch with unsaturated aliphatic aldehydes.1361 Starch phosphates have been crosslinked by various aliphatic and aromatic aldehydes in the presence of urea, melamine, and similar compounds. Among several aldehydes tested[formaldehyde, propanal (propionaldehyde), glyoxal, glutaraldehyde, 2-hydroxyadipaldehyde (2-hydroxy -1,6-hexanedial), and some aromatic aldehydes], only those products that had reacted with glyoxal were insoluble in water.1322 Significant increases in viscosity occurred after starch phosphates having a low DS were treated with urea.1590... 

Starch phosphates have been oxidized to carboxylic derivatives.1622 Starches oxidized by NaOCl could be phosphorylated with POCI3,1623 causing crosslinking. The reaction of starch phosphate with glycidyltrimethylammonium chloride gave the corresponding phosphobetaine compound, starch poly[3-(lV,lV,lV-trimethylammonio)-2-hydroxypropyl phosphate].1624... 

The reaction of starch phosphate with such proteins as soybean protein and casein was used to produce protective colloids for insolubilization of pigments in coatings and paper.1684 The complexation of starch phosphate with protein insolubilizes the latter, particularly when starch phosphate is in the form of an ammonium salt.1685... 

Of the esters, starch phosphate is produced by reaction with phosphorus oxychloride, polyphosphates, or metaphosphates a cross-bonded product results. Total degree of substitution is determined by measuring the phosphorus content, and the mono- to disubstitution ratio can be calculated by potentio-metric titration. Allowance is made for the natural phosphorus content of the starch. Treatment of starch with acetic anhydride produces starch acetate, which has improved paste stability over native starch. The acetyl group is very labile, and hydrolyses readily under mild alkaline conditions. When a known amount of alkali is used, the excess can be titrated and the ester function measured. This is not specific, however, and a method based on an enzymatic measurement of the acetate has been developed in an ISO work group. The modified starch is hydrolyzed under acidic conditions, which releases acetic acid and permits filtration of the resulting solution. Acetic acid is then measured by a commercially available enzyme test kit. Both bound and free acetyl groups can be measured, and the method is applicable... 

Starch phosphates are useful in frozen foods where they impart good freeze-thaw stability and reduce retrogradation (Chapter 10.1). The stability of ice cream and other products can also be improved. Starch phosphates can be used as cheese emulsifiers [67] and phosphates incorporated into flour will improve its properties by reaction with the starch [68]. Calcium starch phosphates are claimed to be useful components of foods, animal feeds and pharmaceutical products [69]. 

Fig. 5.9. Diagram summarising the path of carbon assimilation in chloroplasts (see also eqn. 49). The assimilation can be divided into three phases. Phase I The phosphorylation of ribulose monophosphate (Ru-5-P) to ribulose diphosphate (RuDP) which then accepts a molecule of COj and is cleaved to 2 molecules of PGA (eqn. 49 (g) and (a)). Phase II PGA is reduced to triose phosphate (eqn. 49 (b)). Phase III Triose phosphate acts as the precursor of both Ru-5-P and of hexose and starch. The reactions are driven by ATP and reduced NAD. The assimilation of 1 mole of COj requires 3 moles of ATP and 2 moles of reduced NADP. (After D. I. Amon, in Biological Structure and Function, edited by T. W. Goodwin and O. Lindberg, Academic Press, New York, 1961.)...

Starch molecules have many exposed O—bonds, so this phosphorylation reaction results in multiple phosphate groups attached to each starch molecule. The remaining —OH group on each phosphate can condense with an O— H bond on another starch molecule. This cross-linking of starch chains gives the desired thick consistency of puddings and pies. 

The construction of the structural kinetic model proceeds as described in Section VIII.E. Note that in contrast to previous work [84], no simplifying assumptions were used the model is a full implementation of the model described in Refs. [113, 331]. The model consists of m = 18 metabolites and r = 20 reactions. The rank of the stoichiometric matrix is rank (N) = 16, owing to the conservation of ATP and total inorganic phosphate. The steady-state flux distribution is fully characterized by four parameters, chosen to be triosephosphate export reactions and starch synthesis. Following the models of Petterson and Ryde-Petterson [113] and Poolman et al. [124, 125, 331], 11 of the 20 reactions were modeled as rapid equilibrium reactions assuming bilinear mass-action kinetics (see Table VIII) and saturation parameters O1 1. 

This enzyme [EC 2.4.1.1], also called phosphorylase, catalyzes the reaction of [(l,4)-o -D-glucosyl] with orthophosphate to produce [(l,4)-o -D-glucosyl] -i and a-D-glucose 1-phosphate. The name to be used with this enzyme is dependent on the naturally occurring substrate for example, glycogen phosphorylase, starch phosphorylase, maltodextrin phosphorylase, etc. 

The function of the sulfate residue in these polysaccharides is unknown but the suggestion has been made that just as starch is synthesised from D-glucose 1-phosphate by the action of phosphorylase, so the seaweed polysaccharides are formed from the appropriate sugar sulfate by reaction with a sulfatase. ... 

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