What are the three classification of starch?

Enzymatic conversions of starch

Piotr Tomasik, Derek Horton, in Advances in Carbohydrate Chemistry and Biochemistry, 2012

i Chemically Modified Starches

Chemically modified starches have also been subjected to enzymatic hydrolysis. Deuterated starch is hydrolyzed more readily by amylase than native starch.2025 Sweet-potato starch is sometimes bleached with hypochlorites; this bleaching involves oxidation, and the rate of hydrolysis of such oxidized starch is similar to that of intact starch.2026 A haze-free maltodextrin is obtained.2027

Etherification of corn starch with ethylene oxide in the starch:ethylene oxide ratio of 7:1, 7:2, and 7:3 increased the rate of hydrolysis with glucoamylase by the factor of 1.5, and further increase in the degree of etherification did not further influence the rate.2028

Digestion of hydroxyethylated starch resulted in a decrease in the viscosity of the digested samples, but that effect was not accompanied by the formation of reducing centers. That observation was interpreted in terms of anhydro moieties formed instead.2029 Hydroxypropyl cassava starch and a phosphate derivative were hydrolyzed by hog pancreatin to glucosemaltotetraose mixtures. The molecular weights of oligosaccharide products were lower than those of products from nonmodified starch.2030 Hydroxypropylated maize, waxy maize, and hylon maize starches were digested also by porcine pancreatin. The product profile depended on the starch and its degree of polymerization.2031

Acetylation of starch resulted in lower production of glucose and/or maltose when alpha and beta amylases were used, and this decrease is fairly proportional to degree of substitution.2032 Acetylated starch of DS 1.5 blended with native starch was hydrolyzed with takaamylase from A. oryzae, and only the nonmodified component underwent hydrolysis. The acetylated component was degraded with the acetylesterase from A. niger interacting synergistically with alpha amylase.2033,2034Bacillus liquefaciens digests acetylated starch to give glucose and maltose. The net result depends on the degree of acetylation. At high degrees of acetylation, promoters of the acetylesterase activity have to be added.2035,2036 Because of their higher hydrophobicity, starch esterified with such higher fatty acids as dodecanoic (lauric) and hexadecanoic (palmitic) was digested by alpha amylase with more difficulty than unmodified starch.2037

Epichlorohydrin-treated starch microspheres were hydrolyzed by porcine alpha amylase, and the process was surface controlled.2038 Digestion of a cationic potato-starch derivative with alpha amylase, pullulanase, and isoamylase showed more intense fragmentation as the DS of the starch derivatives increased.2039,2040 The modification of the starches to a higher DS probably degraded the substrates prior to their enzymatic treatment. Starch cross-linked by POCl3, Na3PO4, or epichlorohydrin was digested by the alpha amylase from Rhizopus after heating or treating with alkali to decrease its crystallinity.2041 Cross-linked starch microspheres prepared by emulsion polymerization were readily digested by pancreatin.2042

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GUMS | Food Uses

P.A. Williams, G.O. Phillips, in Encyclopedia of Food Sciences and Nutrition (Second Edition), 2003

Confectionery

Gelatin, modified starch, gum arabic, and pectin are the main gums used in confectionery products. Gum arabic is the major component in traditional wine gums and is present at concentrations of 50%. Production involves dissolving the gum in water, keeping the temperature as low as possible (< 60 °C) in order to avoid precipitation, and it is then added to a preboiled sugar/glucose solution (70%) followed by flavorings and colors. After standing the liquid is deposited into starch trays and placed in a stoving room for 46 days. The gums are then removed from the starch molds, brushed to remove starch, and often glazed with oil or wax. Softer gums or pastilles can be obtained by reducing the stoving time. In view of shortages in gum arabic and severe price fluctuations, considerable efforts have been made to find alternative gums. Nowadays pastilles are commonly made with gum arabic in combination with other gums, notably, starch, maltodextrin, gelatin, pectin, and agar.

Slow-setting, high-methoxyl pectin is used in the preparation of fruit-flavored acidic confectionery jellies and is usually present at concentrations of less than 2%. Some flavors, such as liquorice and vanilla, are unstable in the acid conditions necessary for the gelation of the pectin, and low-ester pectins which gel in the presence of calcium are used instead. These pectins are also used in the manufacture of Turkish delight.

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Fiber: Resistant Starch and Oligosaccharides

A. Laurentin, C.A. Edwards, in Encyclopedia of Human Nutrition (Third Edition), 2013

Other Sources of Resistant Starch

Amyloselipid complex and modified starches have also been recognized as other sources of resistant starch (Table 1). Amyloselipid complexes occur when fatty acids (1218 carbons) are held within the helical structure of amylose. They are formed naturally during starch biosynthesis but may also be produced during cooking. Lipids may interfere with amylose retrogradation impairing the production of retrograded starch during processing. However, these complexes themselves have lower digestibility than cooked starch.

In addition to naturally resistant starch complexes, there are different types of modified starches that are manufactured by the food industry for a variety of reasons. They can be defined as native starches that have been submitted to one or more physical, chemical, or enzymatic treatments promoting granular disorganization, polymer degradation, molecular rearrangements, oxidation, or chemical group addition. According to their main physicochemical characteristics, modified starches can be classified into four main categories: pregelatinized, derivatized, cross-linked, and dextrinized starches (Table 2). However, they are usually known as physically, chemically, or enzymatically modified starches because of the way they are produced (Table 3).

Table 2. Classification of modified starches

StarchModifying agentPhysicochemical characteristicUse in foodPregelatinizedExtrusionSoluble in cold waterCake and instant productsDrum dryingDerivatizedAcetylStable at freezethawing cyclesCanned and frozen foodHydroxypropylPhosphateCross-linkedEpichlorohydrinStable at higher temperatures, extreme pH, and higher shear forcesMeat sauce thickenersTrimetaphosphateInstant soupWeaning infant foodDressingsDextrinizedIrradiationSoluble in cold waterChewing gumsHeatLower or nil viscosityJellyOxidizing agentsSyrupsAcid hydrolysisAmylolytic enzymes

Table 3. Methods of modified starch production

TreatmentModificationDescriptionPhysically modifiedPregelatinizationStarch paste is precooked and dried by extrusion or drum dryingDextrinizationStarch polymers are hydrolyzed to smaller molecules by irradiation or by heat (pyrodextrinization)Chemically modifiedDerivatizationaLateral groups are added to starch lateral chainsCross-linkingaMultifunctional groups are used to link two different starch molecules togetherDextrinizationStarch polymers are hydrolyzed by oxidizing agents or by acid hydrolysisEnzymatically modifiedDextrinizationStarch polymers are hydrolyzed to smaller molecules by incubation with amylases
aDouble-derived starches are produced by combination of these two processes.

The digestibility of these modified starches is variable and depends on the type and extent of the treatment. Some authors have proposed a new category, type IV resistant starch (RS4), to include chemically modified starches. Indeed, it has been shown that cross-linked starches have 1519% decrease in in vitro digestibility compared with their native starches, and hydroxypropylated starch is only 50% digestible. However, some fractions of physically modified starches should also be considered as a category of resistant starch. Pregelatinized starches produced by drum drying and by extrusion have 36% and 511% decrease in digestibility, respectively. Part, but not all, of this reduction in digestibility is due to the formation of retrograded starch (RS3). Moreover, stronger physical modifications, especially those produced by heating starches in a low-moisture environment, affect the starch digestibility even more. In fact, pyrodextrinization decreases starch digestibility by 5565%. These resistant fractions are due to the occurrence of new nonstarch linkages, like (12) and (13) glycosidic bonds, in the pyrodextrinized starch that cannot be hydrolyzed by the enzymes in the gastrointestinal tract. Therefore, along with chemically modified starches, type IV resistant starch should also include physically modified starches. We propose the name starch with nonstarch bonds for RS4 (Table 1).

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Analysis of Glycans; Polysaccharide Functional Properties

W. Bergthaller, J. Hollmann, in Comprehensive Glycoscience, 2007

2.18.6.3.1 Native and modified starches

Both, native and modified starches are important natural hydrocolloids to be used in food and technical industry. They find application as binders/thickeners and texture forming or influencing ingredients in food and feed preparation. In technical fields of application the ability to be degraded easily in natural environments after passing their life cycle plays more and more an important role in decision-making.

To satisfy the demands of modern technology the property profiles of native starches have to be adapted frequently. Physical, chemical, and enzymatic modification or combinations of these techniques are nowadays tools one cannot renounce to achieve the properties that suit the envisaged purposes. Details about potential modification techniques and their advantages have already been presented in Section 2.18.3. Although the importance of modification developed continuously, native starch serves still more than 60% of the market. Production shares of the US and EU markets in 2000 (see Figure 14) presented for both product categories reach impressive shares even when compared with the use of starch for starch-based sweeteners, other hydrolysates, and ethanol.117

Before going into more details it is worth to look upon Figure 15 to see the percent distribution of starch utilized in main industrial sections of the EU under condition of former 15 member states.117 Surprisingly the distribution did not change significantly in between 1996 and 2002, although total production of starch grew within a period of 6 years by approximately 40%. Food dominated nonfood uses with other food and sweets as major sections. Paper/cardboard and corrugated board were overwhelming as allied sections in nonfood uses. Growing future importance can be ascribed of course the section fermentation, where glucose syrups played a role as feedstock for lactic, citric, fumaric, propionic, and gluconic acid. Glucose syrups are also raw material for l-ascorbic acid in a combined chemical/fermentative process. The brewing industry that follows British brewing rules uses adjuncts on basis of glucose syrups high in maltose.128

Figure 15. Changes in the use of starch shares (%) in relevant sections of the European Community (based on 15 member states) food and non-food production in 1996 and 2002. Adapted from Bergthaller, W. J. The status of wheat starch and gluten production and uses in Europe. In Starch. Progress in Structural Studies, Modifications and Applications; Tomasik, P., Yuryev, V. P., Bertoft, E., Eds.; Polish Society of Food Technologists', Małopolska Branch: Kraków, 2004; Chap. 31, pp 417436.

For granular native starches only few applications are known. An example can be seen in the use as molding starches in confectionery production. The suitability depends on repeated use. Furthermore, native starches are components of baking (to isolate components) and pudding powders. Concerning bakery products native wheat starch is used to produce a sandy-type crumb structure.

The most important use of native starches is given by its addition to sauces, soups, puddings, and cake fillings, where they function at most as thickener/bodying agent. As soon as clarity of pastes and gels is required, tapioca starch offers advantages. On the other hand, waxy-starch types (i.e., waxy corn starch) play a role, if high water-binding capacity, weak gel formation, and restricted retrogradation are required.

As compared to native starches, the different types of modified starches reached a much higher importance in food production, in particular, in food industry, where requirements towards specific property profiles are much more pronounced because of modern processing techniques (high-energy stirring, homogenization, pasteurization, sterilization, and freezing) and prolonged storage and handling times. Here, adapted modification can assist to produce and maintain the desired viscosity/consistency/texture of products. However, because of the even low level of chemical treatment (DS<0.5) these starches have to be regarded as additives, which underlie regulations of labeling (E-numbers). The most challenging requirements are again swelling and pasting properties, gel formation and stability, and freeze/thaw stability. For details and examples refer to Tegge,4 Bergthaller97 and Taggart.129

As mentioned previously paper industry is the most important user of starch in native or modified form. While native starches function as binders and filler, they contribute cationic starches to additional binding sites with their positive load.

Their charges are absorbed by the negatively charged cellulose fibers. They promote also retention of negatively charged fillers and pigments (calcium carbonate and china clay) in coating paper surfaces. Another important outlet for starch can be found in preparation of glues and adhesives. In production or corrugated paper and board native and gelatinized starch are main components of glues prepared with mineral additives (alum and borax).

Many alkaline chemicals or other modifiers can be used to produce suitable and efficient starch-based adhesives. Other examples are dextrins produced in a roasting process (from white dextrins to British gums) and used in remoistening adhesive formulations. Textile industry is one of the oldest section in using starch and starch products. Besides other applications, sizing of yarn is still a technique, where modified starches are used. The range of modification reaction starts with cross-linked thin-boiling starches and ends with cationic starches. The latter may be also applied in wastewater clarification as flocculation aids. As further areas of application of highly sophisticated modified starches the following may be indicated: detergent formulations, fillers in tires, flocculants in ore processing, binder in casting molds and in building materials, and stabilizer of drilling mud. Finally, one should not miss to mention uses in chemical industry, in cosmetics, and pharmacy as well as highly specified applications in medicine (e.g., hydroxethyl starches as blood plasma expanders).4

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Binders in Wet Granulation

Thomas DürigKapish Karan, in Handbook of Pharmaceutical Wet Granulation, 2019

2.8 Starch and Modified Starches

Starch is a polymeric carbohydrate consisting of glucose monomers linked by glycosidic bonds. It is a GRAS-listed material with monographs in the USP/NF, pH.Eur., and JP. Traditionally, it was one of the most widely used tablet binders, but in today's industrial practice, pregelatinized starch or other binders are used in its place.

Starch is obtained from plant sources, such as maize, potato, wheat, rice, and tapioca. Maize and potato are major sources for excipient grade starch. It is not soluble in either cold water or alcohol. Traditionally, it is used by gelatinizing in hot water to form a paste. Starch paste can be prepared by wetting starch with cold water, followed by the addition of boiling water with continuous stirring until a translucent paste is formed. This paste can be diluted further with cold water to achieve an appropriate concentration.

Binder use levels for starch are relatively higher (5%25%) as compared to synthetic binders. The high viscosity of starch paste can make efficient binder distribution and substrate wetting problematic, generating soft and friable granules. However, it produces tablets that tend to disintegrate easily.

2.8.1 Pregelatinized Starch

Pregelatinized starch (PGS) is a modified starch with multifunctional benefits. It can be used as a binder, disintegrant, and diluent in tablet formulations. PGS is manufactured by rupturing all or part of the native starch granules using chemical and mechanical processing. This process enhances cold-water solubility and improves compactibility and flowability. It is available in fully or partially pregelatinized forms (Colorcon, 1999). The degree of pregelatinization determines its solubility in cold water.

As a binder in wet granulation, PGS typically is used in solution. It also can be used dry, but this reduces its efficiency significantly. Furthermore, its use levels (15%20% w/w) are usually higher relative to synthetic binders.

It is incompatible with organic solvents and, thus, is used only in aqueous binder systems. PGS can be used as a stabilizer or moisture sequestrant because it holds water in two states bound (e.g., water of hydration) and free water, with only a portion of the sorbed water available as free water.

Partially pregelatinized starch is the most frequently used form of PGS, but fully pregelatinized starch also is available. Commercial, partially pregelatinized starch typically has around 10%20% pregelatinized or water-soluble content, which makes it useful for wet granulation. The cold water-soluble part acts as a binder, while the remainder aids tablet disintegration. PGS is found in the USP/NF, pH.Eur., and JP.

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CARBOHYDRATES | Resistant Starch and Oligosaccharides

A. Laurentin, C.A. Edwards, in Encyclopedia of Human Nutrition (Second Edition), 2005

Others sources of resistant starch

In recent years, amyloselipid complex and modified starches have also been recognized as other sources of resistant starches (Table 1). Amyloselipid complexes occur when fatty acids (1218 carbons) are held within the helical structure of amylose. They are formed naturally during starch biosynthesis, but may also be produced during cooking. Lipids may interfere with amylose retrogradation, impairing the production of retrograded starch during processing. However, these complexes themselves have lower digestibility than cooked starch.

As well as naturally resistant starch complexes, there are different types of modified starches that are manufactured by the food industry for a variety of reasons. They can be defined as native starches that have been submitted to one or more physical, chemical, or enzymatic treatments promoting granular disorganization, polymer degradation, molecular rearrangements, oxidation, or chemical group addition. Modified starches can be classified into four main categories accordingly to their main physicochemical characteristic: pregelatinized, derivatized, cross-linked, and dextrinized starches (Table 2). However, they usually are known as physically, chemically, or enzymatically modified starch because of the way they are produced (Table 3). The digestibility of these modified starches is variable and depends on the type and extent of the treatment. Some authors have proposed a new category, type IV resistant starch, to include chemically modified starches. Indeed, it has been shown that cross-linked starches have a 1519% decrease in in vitro digestibility when compared with their native starches, and hydroxypropylated starch is only 50% digestible. However, pregelatinized starches produced by drum drying and extrusion have a 36% and 511% decrease in digestibility, respectively. Part but not all of this reduction in digestibility is due to the formation of retrograded starch; therefore, physically modified starches should also be considered as a category of resistant starch.

Table 2. Classification of modified starches

StarchModifying agentPhysicochemical characteristicUse in foodPregelatinizedExtrusionSoluble in cold waterCake and instant productsDrum dryingDerivatizedAcetylStable at freeze-thawing cyclesCanned and frozen foodHydroxypropylPhosphateCross-linkedEpiclorhydrineStable at higher temperatures, extreme pH, and higher shear forcesMeat sauce thickenersTrimetaphosphateInstant soupWeaning infant foodDressingsDextrinizedAcid hydrolysisSoluble in cold waterChewing gumsOxidizing agentsLower or nil viscosityJellyIrradiationSyrupsHeat (pyrodextrins)Amylolytic enzymes

Table 3. Methods of modified starch production

TreatmentModificationDescriptionPhysically modifiedPregelatinizationStarch paste is precooked and dried by extrusion or drum dryingDextrinizationStarch polymers are hydrolyzed to smaller molecules by irradiationChemically modifiedDerivatizationaLateral groups are added to starch lateral chainsCross-linkingaMultifunctional groups are used to link two different starch molecules togetherDextrinizationStarch polymers are hydrolyzed by oxidizing agents, acid hydrolysis, pyrodextrinizationEnzymatically modifiedDextrinizationStarch polymers are hydrolyzed to smaller molecules by incubation with amylases
aDouble-derived starches are produced by combination of these two processes.

In addition to the starch properties already described, several starchy foods (for instance, cereals and legumes) have antinutritional factors, such as lectins, tannins, phytates, and enzyme inhibitors (both protease and amylase inhibitors). Amylase inhibitors present in raw pulses may reduce the activity of amylase in the human small intestine. However, most of these factors, especially enzyme inhibitors, are inactivated during food processing and cooking.

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Polymers for a Sustainable Environment and Green Energy

D. Glittenberg, in Polymer Science: A Comprehensive Reference, 2012

10.07.2 Markets

Although starch has a quite abundant presence in the kingdom of plants (it is, e.g., present even in pepper, lilies, and amaranth) there are only a few sources utilized for industrial processing. In the United States, the base is predominantly corn as corn is the most efficient starch-producing plant growing in that climate. In Europe corn is also most important but wheat is gaining share while the potato still plays a significant role due to the EU agricultural policy. In Finland, there is also a small amount of barley starch processing. Another more exotic starch source in Western Europe is peas, which are mainly grown for their protein used in fish farming. In Southeast Asia, Latin America, and Africa, there are significant amounts of tapioca starch extracted from the roots of the manioc shrub in the tropical areas and utilized in industrial applications, in addition to corn starch grown in the other areas.

The economy of the starch industry largely depends on the availability of sufficient volumes of raw materials and the value of the so-called co-products. During corn starch processing, for example, all components of the maize grain are valorized: after steeping and coarse crushing the germ is separated and yields the valuable maize germ oil while the steeping water is concentrated and sold as nutrient for fermentations. The oil press cake together with the corn gluten (protein) and the hulls (fiber), that are separated after fine grinding in additional refining steps from the pure starch granules, are utilized as components in animal feed. The starch as the main product is either dried and sold as native starch, chemically modified to make it more suitable for more demanding end uses, or hydrolyzed to yield refinery products such as hydrolyzates, glucose syrups, and high fructose syrups. In wheat starch processing, the value of the vital gluten is an essential source of income and could be regarded as the head product. In contrast to cereal and pulse starch production, the extraction of root and tuber starches does not deliver co-products of comparable value. As the processes for the extraction are different for the mentioned crops the starch industry cannot easily switch from one source to the other in order to adapt to fluctuating market conditions both on the raw material and on the end product side.

The global starch production in 2006 was 56 Mio tons (Figure 5). The biggest producer is the United States, delivering 50% of that volume. Asia Pacific with a 16% share has bypassed Europe (EU25) which is contributing 15% of the world production followed by Latin America with 6%, Japan with 5%, and Canada with 3%. The balance of 5% is shared by the rest of the starch-producing countries.

Figure 5. Global starchy products market 2006 by region.

On a global scale from these 56 Mio tons only 30% are sold as native and modified starches (14% and 16%, respectively): the lions share of 70% is hydrolyzed into refinery products (Figure 6). In Europe, the relations are different: only 56% of the starch production is hydrolyzed into refinery products and the share of native starches with 23% is bigger than that of modified starches. The share of refinery products in Europe is smaller due to the following two effects:

Figure 6. Global starchy market 2006 by product.

the much bigger amount of bio-ethanol production based on starch hydrolyzates in the United States, and

the effects of the sugar regime in Europe that impeded the use of fructose-rich syrups as an alternative sweetener for (beet) sugar.

The different shares of native and modified starches can be explained by the following two factors:

more convenient food and thus consumption of modified food starches in the United States, and

different structures and attitudes of the paper industry: bigger machines and the high amount of recycled packaging grades favor the use of in situ-converted native starches in Europe.

Nevertheless in Europe (EU27 in 2008) the food industry is the starch industrys most important customer consuming 61% of their production while all industrial applications only account for 39% (Figure 7).

Figure 7. European starchy market (EU27) 2008 by product type.

The impact of the industrial usage of starchy products is thus relatively small with respect to the total consumption of cereals even if we take into account bioenergy as emerging consumer. If we include the mentioned 61/39 split into the food and industrial cereal consumption as projected by the European Commission we see that the impact of industrial applications and bioenergy on the cereal market cannot be called decisive with 12% and 7%, respectively, projected for 2014 (Figure 8). That means the battle between food and industrial/energy applications of starchy crops that is painted on the wall by some parties has no real background. The explosion of grain prices in 2008 was rather caused by simultaneous droughts in different parts of the world and an increased demand for animal feed as people in emerging economies want to adapt a western lifestyle.

Figure 8. Total cereal market projection 2014 (EU27).

Since more economic ways of ethanol or biofuel productionsuch as ethanol and butanol from cellulose, or green crude from algae are being developed, the starch-based bio-ethanol rally can be regarded as an interim episode.37

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Gastrointestinal Tract

Wanda M. Haschek, ... Matthew A. Wallig, in Fundamentals of Toxicologic Pathology (Second Edition), 2010

Cecal Enlargement

Cecal enlargement is a response to various compounds and food additives observed in several rodent species. These materials include antibiotics, modified starches, polyols (e.g., sorbitol and mannitol), some fibers, and lactose. Many of these compounds share the feature of being poorly absorbed and osmotically active. The mechanism for the distention has not been clearly defined. Other features include mucosal hypertrophy and hyperplasia. The morphologic response is associated with functional changes leading to soft stools or diarrhea, and increased large bowel mucosal permeability. These functional alterations are likely to be mediated by the increased osmotic activity of the cecal contents. The morphologic and functional changes probably represent an adaptational process, since the changes are reversible when the diets are returned to normal.

Generalized large intestinal enlargement is a common change observed with incompletely digested and poorly-absorbed substances that are subjected to microbial metabolism in both cecum and colon. Increased microbial metabolism of the offending substances leads to the generation of osmotically active byproducts that cause soft stools and cecal distention.

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Systems Toxicologic Pathology

Timothy A. Bertram, ... Sureshkumar Muthupalani, in Haschek and Rousseaux's Handbook of Toxicologic Pathology (Third Edition), 2013

Cecal Enlargement

Cecal enlargement is a response to various compounds and food additives occurring in several rodent species. These materials include antibiotics, modified starches, polyols (sorbitol and mannitol), some fibers, and lactose. Cecal enlargement is associated with increased death losses in rats fed raw potato starch. Enlargement of rodent ceca has been interpreted as both a toxic and an adaptive phenomenon.

Compounds that are poorly absorbed and are osmotically active are frequently associated with cecal enlargement. The mechanism for the distension has been proposed to be the attraction of fluid into the lumen. However, when the lumenal contents are removed tissue weights remain elevated, so other mechanisms are also operative. Other processes involved in cecal enlargement and dilatation include mucosal hypertrophy and hyperplasia. This morphologic response is associated with functional changes that lead to soft stools, diarrhea, and increased large-bowel mucosal permeability. These functional alterations are likely to be mediated by the increased osmotic activity of the cecal contents. Morphological changes probably represent an adaptational process, since the changes are reversible when the diets are returned to normal.

Large-intestinal enlargement is a common change observed with incompletely digested and poorly absorbed substances that are subjected to microbial metabolism in the cecum and colon. The increased microbial metabolism leads to an increase in osmotically active material, and results in soft stools and cecal distension. One functional change in rats fed sugar alcohols and lactose is increased absorption of calcium. Sequelae to this process are increased calcium excretion in the urine and nephrocalcinosis.

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