Dextran: Source, Structure, and Properties

 

1772   DEXTRAN

Holland AJ, Treasure J, Coskeran P and Dallow J (1995) Characteri Chara cteristics stics of the eatin eating g diso disorder rder in Prad Prader er–Willi Syndr Syn drome ome:: imp implic licati ation onss for tre treatm atment ent..   Journ Journal al of  Intellectual Disability Research 39(5): Research  39(5): 373–381.  James TN and Brown RI (1992) (1992) Prader  Prader – Willi Willi Syndrome: Home, School and Community Community. London: Chapman and Hall.

Waters JA (1996) (1996)   Handbook for Parents and Carers of  Adult Adultss wi with th Pr Prad ader er – Willi Willi Syndrom Syndromee, re revi vise sed d ed edn. n. Derby, UK: Prader–Willi Syndrome Association. Waters J (200 (2001) 1)   Babies and Children with Prader – Willi Willi Syndrome,, re Syndrome revi vise sed d ed edn. n. De Derb rby y, UK: UK: Prad Prader er–Willi Syndrome Association.

DEXTRAN J N BeMiller, Purdue University, West Lafayette, IN, USA Copyright 2003, Elsevier Science Ltd. All Rights Reserved.

Source, Structure, and Properties 0001

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  Dextra Dextran n is a generi genericc ter term m for a family family of glucan glucanss made by polymerization of the   a-d-glucopyranosyl moiet mo iety y of su sucr cros osee in a reac reacti tion on cata cataly lyze zed d by the the enzyme dextr enzyme dextrans ansucr ucrase ase.. The common common featur featuree is a preponderance of (1 ! 6)-linked   a-d-glucopyranosyl units.   Severa Severall microo microorga rganis nisms ms produc producee dextra dextrans ns with with ranges of molecular weights and with structures varying from from slight slightly ly to highly highly branch branched. ed. Commer Commercia ciall de dext xtra ran n is bi bios osyn ynth thes esize ized d by the the no nonp npat atho hoge genic nic organism   Leuconostoc mesenteroides  organism mesenteroides   NRRL B-512. The basic reaction catalyzed by dextransucrase is   n sucrose ! (a-d-glucopyranosyl unit) þ n d-fructose. Branch Bra nches es arise arise from from positi position on O-3 of the glucos glucosyl yl units. uni ts. The degree degree of branch branching ing of commer commercia ciall dextra dextran n is about 5%. About 40% of the side chains are single a-d-glucopyranosyl units; about 45% are two units n

long, and about 15% contain more than The av aver erag age e mole mo lecu cula larr weig we ight ht of na nati tive ve 2comm counits. mmer erci cial al Leuconostoc Leucon ostoc mesenteroides mesenteroides   NRRL NRRL B-512 B-512 dextra dextran n can range from 9 million to 500 million. Dextran of lower molecular weight is produced for clinical ap appli plica cati tion ons. s. Dext Dextra ran n prod produc uces es rela relativ tivel ely y lowlowviscosity solutions, which distinguishes it from other high-molecular-weight high-molecular -weight polysaccharides. It is a neutral polymer.

Food Uses 0003

  Many uses uses of dextrans dextrans in foods have been been described described and patented, but dextrans are not permitted as foodstuff additives in the USA or Europe. (The generally recognized as safe (GRAS) status was removed by the US Food Food and Drug Adminis Administra tratio tion, n, USA, USA, in 1977 1977

because dextran was not being, and had not been, used as an ingredient.) The principal potential uses of  de dext xtra ran n in food foodss ap appe pear ar to be re rela late ted d to its its capa capaci city ty to prevent crystallization, retain moisture, and provide bo body dy,, bu butt the the fact fact that that it is no nott be bein ing g us used ed as an ad addi diti tive ve indicates that no particularly useful functionality that cannot can not be provid provided ed by anothe anotherr hydroc hydrocollo olloid( id(s) s) is known. kno wn. Small Small amo amount untss of dextra dextran, n, primar primarily ily propro  Leuconostoc   and Lactobacillus duced by species of  Leuconostoc  and  Lactobacillus,, are are likel likely y to be pr pres esen entt in ferme ferment nted ed food foodss that that or orig igininally contained sucrose. Dextra Dex tran n format formation ion is detrime detrimenta ntall to sug sugar ar (sucro (sucrose) se) production prod uction,, as dextran dextran inhibits inhibits crystalliz crystallization ation;; increases crea ses viscosity viscosity and, hence, hence, decrease decreasess filterabili filterability ty and heat transfer transfer in evaporato evaporators, rs, crystalliz crystallizers, ers, and pans; and results in poor clarification. As a result, st step epss ar aree take taken n to min minim imiz izee de dext xtra ran n form format atio ion n by con contam tamina inatin ting g bacter bacteria. ia. Dex Dextra tranas nases es may be employed to break down any dextran produced. Preventio ven tion n of cry crysta stalliz llizati ation on of sugar sugar in foods, foods, bevera beverages ges,, and confections is a potential use.

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Metabolism Dextrans are not broken down by human digestive enzymes. They are degraded by enzymes of bacteria in the large intestine and the released glucose can be absorbed as well as fermented anaerobically.

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Medical and Other Uses Dextra Dext ran n of av aver erag agee mo mole lecu cular lar weig weight ht of 70 00 000 0 is us used ed clinically as a plasma volume expander for the treatment of shock and prevention of impending shock. The antithrombic effect of a preparation of average molecular molec ular weight of 40 000 provides a prophylactic prophylactic tre treatm atment ent for venous venous thromb thrombosi osiss and pulmon pulmonary ary emboli. These and other applications reveal that dextrans tra ns of variou variouss molecul molecular ar weight weightss can be safely safely injected into the blood stream. A complex of ferric hydroxide and dextran is used in the treatment of  neonatal anemia in pigs. A principal use is in the

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DEXTRINS   1773

prep prepar arat atio ion n of gels gels in be bead ad form form for for si size ze excl exclus usio ion, n, ion ion exchange, and hydrophobic chromatography. chromatography. See also: also: Anemia

(Anaemia): Other Nutritional Causes; Chromatography: Principl Principles; es; Dental Disease: Etiology

Further Reading DeBelder DeBeld er AN (1992) (1992) Dextra Dextran. n. In: Whi Whistl stler er RL and BeMill BeMiller er  JN (eds)   Industrial Gums, Gums, pp pp. 39 399 9–425. New York: Academic Press.

of Dental Caries; Role of Diet

DEXTRINS ar aree thos thosee pr prod oduc ucts ts of st star arch ch hy hydr drol olys ysis is with with DE IN, USA va valu lues es of more more than than 20 that that ar aree av avai aila labl blee as dr dry y po powd wder ers; s; in othe otherr word words, s, they they ar aree dr drie ied d lowlow-DE DE Copyright 2003, Elsevier Science Ltd. All Rights Reserved. glucose syrups. While dextrins are little used in foods; maltodextrins and syrup solids are used extensively. Both are Background produced produ ced from starch starch by hydrolysis hydrolysis only, only, i.e., witho without ut   Dext Dextri rin n is a gene generi ricc term term ap appl plie ied d to a va vari riet ety y of  molecular rearrangement, and are of lower average products obtained by heating a starch in the presence molecular weight than either dextrins or acid-thinned (thi hinn-bo boil ilin ing) g) st star arch ches es,, th thee latt latter er be bein ing g sl slig ight htly ly of small amounts of moisture and an acid. Dextrins (t de depo poly lyme meri rize zed d st star arch ches es that that re rema main in in gr gran anul ular ar can any starch and generally classi- form. The primary primary difference difference between thin-boilin thin-boiling g fied be as made whitefrom dextrins, yellow (orare canary) dextrins, starches, ches, maltodextrins, maltodextrins, and syrups/sy syrups/syrup rup solids is and British gums. Each is more water-soluble and star produces produ ces less viscous viscous solutions solutions or dispersions dispersions than the degree of depolymerization. The primary differits parent starch. Each is produced by combinations ence between dextrins and thin-boiling starches is the of slight depolymerization (hydrolysis) and transgly- method of preparation. cosylation cosy lation (molecular (molecular rearrange rearrangement) ment).. Transglycoransglycosylation sylat ion produces produces more highly highly branched branched structur structures es Production and forms forms glycos glycosidic idic linkages linkages not found found in native native starch sta rches. es. Most Most dextri dextrins ns are used used as adhesi adhesives ves for Dextrins are prepared by heating a starch moistened with th dilut dilutee hy hydr droc ochlo hlori ricc acid acid or he heat ating ing a mois moistt paper products. Only white dextrins and only small wi amounts of them are used in prepared foods. White starch in the presence of gaseous hydrogen chloride dextrins are prepared by heating a dried, acidified until a cold-water-soluble product is formed. starch. Maltod Mal todext extrin rinss and syrup syrup sol solids ids are prepar prepared ed in   Other hydrolytic breakdown products from starch basically the same way as are starch-based glucose are characterized by their dextrose equivalency (DE), syrups, except that the process is stopped at an earlier which is the percent of reducing power compared to stage to keep the DE value low. Depolymerization of  anhydrous   d-glucose (dextrose). The DE value is in- a starch can be effected with either an acid or an versely related to molecular weight, i.e., the degree of  enzyme(s) or by combination treatments. These propolyme pol ymeriz rizati ation on (DP), (DP), and is, theref therefore ore,, an indica indicator tor of  ces cesses ses are ref refer erred red to as aci acid d conver conversion sions, s, enzyme enzyme the degree of hydrolysis. (The DE value of anhydrous conversions, and combination conversions, respectd-glucose is 100. The DE value of native starch is 0.) ively. Conversions to produce maltodextrins are usuWhen all products of starch hydrolysis were made al ally ly do done ne in a cont contin inuou uouss pr proc oces ess. s. In a typi typica call pr proc oces ess, s, by treatment of starch with acid, the properties of  a starch slurry (30–40% dry solids, 17–22 Be ´ ´ ) at pH a product were largely a function of DE. Now with 6.0–6.5 6.5 is past pasted ed,, ge gene nera rall lly y in a jet jet co cook oker er (*105  C), a variety of treatments and processes being used, two followed by an atmospheric flash. Conversion (liqueproducts with equivalent DE values (average degree faction) is accomplished with a thermostable bacterof polymerization) can have rather different proper- ial   a-amy -amyla lase se at 95–100  C. Depoly Depolymer meriza izatio tion n is ties because of different different distributions distributions of molecular molecular sto stoppe pped d after after 60–120 min by enzyme enzyme inacti inactivat vation ion,, sizes. an and d the the pH is ad adju just sted ed.. Th Thee so solu luti tion on is filt filter ered ed,,   Malt Maltode odextr xtrins ins are those those produc products ts having having DE values values treated with carbon, concentrated, and spray-dried of le less ss th than an 20 20,, gene genera rally lly DE 5–19. Syrup Syrup sol solids ids to give a maltodextri maltodextrin n or syrup solid preparation preparation.. In J N BeMiller, Purdue Universit University, y, West Lafayett Lafayette, e,

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