Retrogradation Control

On storage, the gel may shrink due to the loss of water (syneresis). Amylose undergoes more rapid retrogradation than does amylopectin.73 

Starches with high amylose content, such as corn starch (28% amylose) retrograde more than starches with lower amylose content, such as potato starch (20% amylose). Redispersion of retrograded starch is energy-intensive due to extensive bonding. Temperatures of 115° to 120°C are required to solubilize amylose gels or crystals. Amylopectin gels can be redispersed at temperatures above 55°C. 

Multivalent ions in starch dispersions, particularly those of aluminum, calcium, sulfate and oxalate, will induce retrogradation due to complexation or competition for water of hydration. The ions can be introduced by hard process water or accumulate by leaching from paper during surface sizing or coating. The destabilizing effect of ions follows the Schulze-Hardy rule. 

Particles of papermaker s amylose (reformed amylose particles, RAPS) appear in two shapes, Types I and II. The onset of retrogradation is indicated when a clear and transparent starch dispersion becomes opaque (turbid). Type I amylose particles are small. They are shaped like small bow ties or wedges of pie. Starch solutions with Type 

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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... 

The rate of melatonin synthesis is controlled primarily by the release of noradrenaline from sympathetic fibres originating in the superior cervical ganglion. The activity of these neurons and, consequently, the synthesis and release of melatonin, follows a circadian rhythm such that sympathetic input and melatonin synthesis are both increased in the dark. This coupling with the light cycle certainly involves the SCN since destruction of this nucleus greatly reduces the fluctuations in melatonin production. Moreover, retrograde transneural tracing has shown that there is a neuronal pathway... 

Only one study to date has been conducted on the treatment of acute pancreatitis with antioxidants. Clemens et al. (1991) were unable to show any difference in the incidence or severity of post-endoscopic retrograde cholangiopancreatography (ERCP) pancreatitis in a prospective, randomized, double-blind, placebo-controlled trial of allopurinol. However, Salim (1991) performed a similar trial of the effect of allopurinol and DMSO in patients with pain from recurrent pancreatitis, and found significant benefit. On the basis that depletion of antioxidants is important in the pathogenesis of chronic pancreatitis, the administration of a cocktail of antioxidants was assessed for its effect on pain in this disease. Treatment with a combination of organic selenium, d-carotene, vitamins C and E, and methionine was of benefit in the initial pilot study, and in a placebo-controlled trial (San-dilands etal., 1990 Uden et al., 1990). 

FIGURE 6. Histogram shows the nunber of retrogradely labeled neurons in the DR and MR nuclei in PCA-treated animals and in controls... 

The nervous system has several properties in common with the endocrine system, which is the other major system for control of body function. These include high-level integration in the brain, the ability to influence processes in distant regions of the body, and extensive use of negative feedback. Both systems use chemicals for the transmission of information. In the nervous system, chemical transmission occurs between nerve cells and between nerve cells and their effector cells. Chemical transmission takes place through the release of small amounts of transmitter substances from the nerve terminals into the synaptic cleft. The transmitter crosses the cleft by diffusion and activates or inhibits the postsynaptic cell by binding to a specialized receptor molecule. In a few cases, retrograde transmission may occur from the postsynaptic cell to the presynaptic neuron terminal. 

Starch (amylose and amylopectin) hydrolysis along with ester-fication, etherification or oxidation have been previously discussed as available methods for producing starch derivatives with improved water dispersibilities and reduced retrogradation potential (, ). Since oxidative and hydrolytic reactions are simple, easily controlled chemical modifications, starch-derived polymers made by hydrolysis alone or oxidative and hydrolytic processes were developed and tested. 

In the supercritical phase, both temperature and pressure play a significant role in determining the extraction efficiency. After the short-lived retrograde solubility effect subsides at about 55-60°C, a transition of the system back to the mass transfer controlled situation will take place where increasing temperature will, once again, bring about a surge in the extraction efficiency. In fact, for the supercritical phase,... 

Seminal emission and ejaculation are under control of the sympathetic nervous system. Emission results from a-adrenergic-mediated contraction of the epididymis, vas deferens, seminal vesicles, and prostate, which causes seminal fluid to enter the prostatic urethra. Concomitant closure of the bladder neck prevents retrograde flow of semen into the bladder, and antegrade ejaculation results from contraction of the muscles of the pelvic floor including the bulbocavemosus and ischiocavernosus muscles. 

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