Publisher Summary
Starch granules range in size from sub-micron elongated granules of chloroplasts to the relatively huge oval granules of potato and canna. Semi-compound granules originate as two or more distinct granules, which then fuse together. Pseudo-compound granules, such as pea starch granules, start out as individual granules, which then develop several large cracks while remaining a single entity. These differences in size and shape make it possible to recognize most of the ordinary food and commercial starches. Starch granules contain small amounts of non-carbohydrate components—lipids, proteins, phosphate, and ash—that affect the behavior of starch in various applications. The tiny starch granules of chloroplasts are important as a temporary carbohydrate reserve and show diurnal synthesis and degradation. Native starch granules show growth rings when observed by optical microscopy, scanning electron microscopy of eroded granules, and transmission electron microscopy of thin sections, especially after chemical treatment. Starches that show prominent growth rings, such as potato starch, require high or saturating water levels for ring visibility.

Chapter vii – organization of starch granules

The effects of ultra-high pressure (UHP) on 25 starches were characterized via microscopy and DSC. Furthermore, the swelling behaviour, digestibility, paste viscosity and gel formation was determined. With few exceptions B-starches were shown to be more pressure resistant than A- and C-type starches. The pressure range in which the gelatinization occurs is typical for the corresponding starch. Only some starches (e.g. waxy corn starch) show the extensive swelling and almost complete desintegration of the granules, which usually is observed after a heat gelatinization. Typical for a UHP-gelatinization is, that most starches show very little swelling and maintain their granular character. These starches develope very little viscosity at normal paste concentrations and form pastes of smooth texture, resp. rigid gels at concentrations above 15%.

Due to the limited swelling without any resp. very little solubilization of the amylose obviously the retrogradation occurs within the granules, which probably is a further reason for the quite different paste and gel properties of UHP-gelatinized starches in comparison to heat gelatinized ones.

Effects of high pressures treatment on starches

Reasons for starch digestibility variations are reviewed by considering starch granule structure, antinutritional factors and access problems in coarse particles. Feed technology treatments that can overcome low starch digestibilities are also reviewed. Before considering these factors, the particular features of the digestive system of chickens are briefly reviewed.The digestive system of chickens for starch hydrolysis is characterised by a high enzymatic potential. However, in contrast with mammals, the potential of chickens for completing starch digestion by microbial degradation in the distal part of the digestive tract is very low.Variations in starch granule structure especially concern legume seeds compared to cereals, with greater resistance observed for the former. Plant mutants may result in variations in amylose contents of starch granules. Those with high amylose content (70%) produce low starch digestibilities. Cereals with no amylose (waxy starch) do not show strong evidence of benefit despite lower resistance of starch granules.In practical conditions, antinutritional factors such as proteinaceous α-amylase inhibitors, condensed tannins and viscous water-soluble non-starch polysaccharides generally result in low effects on starch digestibility. However, viscosity may induce a noticeable effect with high viscosity barleys. There is much less evidence that viscosity can explain the low starch digestibilities (<94%) which are observed with some wheat samples. Positive effects of enzyme additives on starch digestibility of cereals probably result from effects both on viscosity and on disruption of coarse particles.Access problems in coarse particles are responsible for low starch digestibilities observed with legume seeds. However, mechanical treatments such as fine grinding and pelleting can readily overcome this problem. Access problem in coarse particles is also probably the reason that explains low starch digestibilities in some cereal samples, as shown by negative relationships between hardness and starch digestibility of wheats. However, grinding and pelleting of cereals seem to be less efficient than with legume seeds. Interactions with feeding behaviour and genetic origin of birds have also to be considered for explaining variations in starch digestibility of cereals.

Causes for variation in digestibility of starch among feedstuffs

Publisher Summary This chapter presents the nonconventional methods for the modification of starch. Starch is the most readily available and abundant pure carbohydrate. Native starch forms a complex matrix and water plays an important role in its construction. It is widely accepted that water fills capillaries of the matrix as well as participates in the strengthening of the amylose helices in the granule. The observation indicates that water cooperates with high pressure in causing deterioration of the starch matrix. Simultaneously, the ascending portions of the compressibility curves show that the resistance of the starch matrix toward compression decreases as the volume of added water increases. It is observed that solid starch changes its electrical conductivity on compression. At constant temperature and humidity, there is a positive correlation between the tamping of starch layers in cylinders, containers, and silos and their electrical conductivity. For the irradiation of amylose, it has been shown that the solvent may stabilize the irradiated matrix. As with starch, monosaccharides and oligosaccharides exhibit peculiar behavior in their formation of free radicals on irradiation. It is suggested that the effect of irradiation on starch gels is generally monitored by the changes in viscosity, reducing power, and reaction with iodine.

R. Charbonnière Et

Papers

Influence d'un traitement par pression sur la structure granulaire de differents amidons et sur leur sensibilité aux enzymes