Sugar beets

29Sugar Beet FiberProduction, Composition, Physicochemical Properties,Physiological Effects, Safety, and Food Applications

Jean-Francois Thibault, C. M. G. C. Renard, and F. GuillonInstitut National de la Recherche Agronomique, Nantes, France

I. INTRODUCTION

Sugar beet ber is primarily derived from the sugar beet industry, where it is obtained from theco-product (sugar beet pulp) after extraction of sucrose. Sugar beet roots contain about 15%sucrose and about 5% cell wall polysaccharides on a wet weight basis. For sugar production,the roots are rst washed to eliminate sand and other inorganic materials and then are sliced.Heat treatments aiming at facilitating diffusion and increasing sugar recovery are then applied tothe slices. These treatments typically consist of heating at 85C for approximatively 15 minutesfollowed by diffusion by water, typically 2 hours at65C and pH 6.5. The resultant productsare a sucrose-containing juice (which is treated to produce crystallised sugar) and pulp. Thepulp (dry matter 8%) may be pressed (dry matter 20%) or dried (dry matter 90%). Itis a very abundant and cheap by-productproduction in France is equivalent to 1.5 milliontons (dry matter) of beet pulp per year.

The pulp is primarily used as animal feed. However, alternative uses are currently pro-posed in order to increase the value of the pulp. The extraction of polysaccharides (pectins,arabinans, cellulose) or monomeric components (arabinose, galacturonic acid, rhamnose, ferulicacid) may be one method to increase its value (Vogel, 1991; Broughton et al., 1995; Micard etal., 1996). For example, arabinan extracted from the pulp has been investigated as a fat replace-ment (Cooper et al., 1992).

Another possibility is to nd direct uses for the pulp. Because this residue consists mainlyof cell wall polysaccharides, several if not all sugar companies have studied the use of sugarbeet pulp as a high-ber food ingredient or dietary ber.

II. PRODUCTION OF THE FIBERA. Sugar Beet Pulp ProcessingBeet pulp must be processed before it can be used in food systems because it has an unpleasantavor, may be too brightly colored, and also may contain large amounts of soil or sand (Tjebbes,1988). The way of drying (Miranda Bernardo et al., 1990), the removal of most of the taste,

Copyright 2001 by Taylor & Francis

color, and odor are especially important for beet ber, as is the removal of all traces of soil.Physical treatments including cleaning, extraction, sieving, and heating have been mainly de-scribed, although some chemical treatments have been also proposed. With special processingit is possible to produce a dietary ber with an off-white color and unobstrusive avor, suitablefor human food. The ber may be milled to a given particle size from coarse to ne, dependingon the intended use, or treated with steam in a aking process.

Another method is to use not the beet pulp but the beet root as a starting material and tomimic the sugar extraction while minimizing or avoiding color/odor formation as well as thepresence of soil or sand by special washing of the roots.

Several processes have been patented and trade names have been given for such bers asDuoFiber by American Crystal Sugar Company (Lee, 1988), Fibrex by Fibrex S.A., DaniscoSugar AB (Tjebbes, 1988), and Betaber/Atlantis by British Sugar (Williams et al., 1994).Fibers have also been developed in the United States by General Foods (Beale et al., 1984) andin France by SRD (Michel et al., 1985a, 1988). Fibrex and Atlantis are the main commercialproducts today.

Steam drying for Fibrex uses superheated steam to extract moisture from the ber, pre-venting overdrying and reducing energy costs. The process optimizes temperature, pressure, andtime, as well as removing sand from the end product.

British Sugar developed Betaber in the late 1980s (Harland, 1993) and patented theprocess to obtain, directly from beet roots, palatable products with partial or complete sugarextraction (Williams et al., 1994). The products are sold by a Atlantis Food Ingredients, foundedin 1994 by British Sugar.

The commercial bers are generally claimed to consist of one third water-soluble and twothirds water-insoluble bers; however, the values may be obtained by methods that overestimatethe water-soluble dietary bers because of some extraction of pectic material (Thibault et al.,1994).

B. Modication of Beet FiberIn order to increase the ratio of soluble to insoluble dietary ber in sugar beet as well as tochange its hydration properties, some modications have been proposed. Physical treatmentssuch as extrusion cooking (Thibault et al., 1988; Ralet et al., 1991) or enzyme treatment com-bined with extrusion cooking (Jezek et al., 1996), autoclaving (Guillon et al., 1992), or chemicalmeans (Bertin et al., 1988) have been applied to the bers, mainly at a laboratory scale, in orderto modulate the nutritional effects and/or to improve their functional properties.

III. COMPOSITION AND STRUCTURE

Dietary ber in the sugar beet comes exclusively from its cell walls and is devoid of resistantstarch or other reserve polysaccharides. The structure and composition of the dietary ber fromsugar beet is different of that of ber from cereals for two reasons: (a) botanical originthecell walls of the Poaceae (formerly Gramineae) are actually an exception among land plants,and (b) tissue typethe part of beet that is used is a reserve parenchyma, with thin, nonsecondar-ized cell walls, in contrast to brans. This leads to very different physicochemical properties,with high hydration capacities and a high proportion of soluble dietary ber. As such, beet bercan be considered as an intermediate between the insoluble dietary bers from cereals and thesoluble dietary bers.


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Table 1 Dietary Fiber Composition of Sugar Beet Fiber Preparations

TDF SDF IDF ADF NDF

Sugar beet ber (1)native 871 40 154 2 717 38autoclaving 122C 784 19 259 11 525 80autoclaving 136C 786 19 297 11 489 8

Sugar beet ber (2) 723 202 521723 125 603

Sugar beet ber (3) 722 161 561Sugar beet ber (4) 740 245 495 267 556(pepsin/pancreatin) 874 205 669 304 748Sugar beet ber (5) 291 569Sugar beet ber (6) 245 560Apple AIS 859 225 634Apple ber 597 134 463

Source: (1) Guillon et al., 1992; (2) Thibault et al., 1994; (3) Dongowski et al., 1998; (5) Ozboy et al., 1998; (4)Schweizer and Wursch, 1979; (6) Michel et al., 1988; (7) Renard and Thibault, 1991.

A. CompositionSugar beet pulp has a high dietary ber content, typically 750 mg/g, and is known for itshigh soluble ber content (1020%) (Table 1). The AOAC method, because of its lengthyenzyme incubations at pH close to neutral, may overestimate the amount of ber actually solubi-lized in the upper parts of the digestive tract. Extraction of beet pulp with water at low pH onlyleads to solubilization of approximately 20 mg of polymeric material per g of beet pulp (Rom-bouts and Thibault, 1986a; Thibault et al., 1994) (Table 2). The lignin content of beet ber islow (Table 1 and 3). The remainder of the ber preparations (Table 1 and 3) consist of proteins,in amounts varying according to the mode of preparation, ash, and lipids (20 mg/g) (Harland,1993). Some sugar beet pulp fractions may be high in ash (Michel et al., 1988) arising fromcontamination by soil particles.

Global characterization of beet ber often refers to a high hemicellulose content (Table1), (Harland 1993; Clarke and Edye, 1996), but the methods used, developed for grasses orforage crops, do not adapt very well to this type of material. Whether measured by differencebetween neutral detergent soluble fraction and acid detergent soluble fraction, by differ-ence between total carbohydrates and the sum of cellulose and galacturonic acid, or as pentosans(by analogy with cereals in which pentose sugars are present as hemicellulosic heteroxylans),in beet cell walls this mainly refers to arabinose, by far the main pentose present (90%). This

Table 2 Global Composition of Beet Fibers

Cellulose Hemicellulosea Pectinb Lignin Proteins Ash

Sugar beet bre (1) 230270 260290 240290 3050Sugar beet pulp (2) 220 320 270 20 70 80Sugar beet ber (3) 272 221 19 87 32Beta bre (4) 184 294 220 95 35Source: (1) Clarke & Edye, 1994; (2) Dinand et al., 1997; (3) Ozboy et al., 1998; (4) Harland, 1993.a Pentosans or difference between cellulose and galacturonic acid; here mainly as arabinan components of beet pectin.b Galacturonic acid.


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Table 3 Composition of Sugar Beet Cell Walls and Fiber Preparations (mg/g)Phenolicacids

Rha Ara Xyl Man Gal Glc GalA MeOH AcOH (FeA) Protein Lignin AshSugar beet AIS (1) 18 189 15 11 58 263 194 25 44 15 86 41Sugar beet ber (2) 10 201 14 12 49 216 221 26 38 (8) 36 44Sugar beet ber (3) 11 173 15 15 43 217 189 23 36 13 (9) 80 18 84Sugar beet pulp (4) 24 209 17 11 51 211 211 18 39 8 113 36Sugar beet NSP (5) 12 190 14 14 40 243 153Apple AIS (6) 15 81 51 18 64 277 345 36 21 0 69 22Apple ber (6) 7 62 33 23 35 266 142 17 12 67 29AIS Ethanol insoluble solids (from fresh beets or apples); NSP nonstarchy polysaccharides.Source: (1) Renard and Thibault, 1993; (2) Guillon et al., 1992; (3) Bertin et al., 1988; (4) Micard et al., 1996; (5) Spagnuolo et al., 1997; (6) Renard and Thibault, 1991.


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arabinose forms arabinan and the arabinogalactan side chains of the sugar beet pectins and isa small part of hemicellulose.

In more detailed studies of their composition, beet cell walls, and therefore sugar beetber, are characterized by a very high pectin content (Table 3), with about 200 mg/g each ofgalacturonic acid and arabinose. This amount of pectin and more specically of arabinose isexceptionally high even in comparison to cell walls from other dicotyledons (Table 3). Sugarbeet ber also contains approximatively 200 mg/g of glucose, mainly of cellulosic origin; intotal, sugars add up to about 80% of the dry weight, with remarkably low amounts of xyloseand mannose, again also in comparison with other dicotyledons. The pectin in sugar beets ismethylated (DM 5070), although with a lower DM than apple or citrus, and is also acetylated(DAc 60 on the whole cell wall). Sugar beet cell walls also contain phenolic acids (10 mg/g), mainly ferulic acid. Although quantitatively minor, these phenolic acids are thought to beof major importance in the structure of the beet cell wall.

There are few differences in global sugar composition between cell wall material isolatedfrom raw beets and sugar beet pulp (Table 3). Le Quere et al. (1981) found 45 mg of water-soluble pectin per g of alcohol-insoluble solids (AIS) for beet slices and, surprisingly, still 33mg/g for beet pulp after diffusion. This low extraction of pectins could be due to physicallimitations to diffusion of the pectic polymers from the cell wall network or to the structure ofbeet cell walls. Little material is extracted from beet cell walls in mild, nondegradative condi-tions. Dea and Madden (1986) only extracted a total of 50 mg/g dry matter from whole beetsby successive cold and hot water treatments at pH 3.7, and Renard and Thibault (1993) onlyextracted 56 mg/g from whole beet AIS by buffer at pH 4.5 and room temperature, in contrastto 289 mg/g at pH 6.5 and 80C. This material as well as the soluble dietary ber in sugar beetare of pectic nature, rich in galacturonic acid and arabinose; soluble dietary ber of beet probablyhas a relatively low viscosity, as might be inferred from low intrinsic viscosities obtained forpectin extracts, whatever the method (Table 4).

B. StructureSugar beets are mainly composed of parenchymal tissue with thin, supple and hydrophilic cellwalls. Typical primary cell walls of dicotyledonous plants are composed of almost equal amountsof three types of polysaccharides: (a) pectin, rich in galacturonic acid and containing the mainneutral sugars galactose, arabinose, and rhamnose, (b) hemicelluloses, typically xyloglucanswith minor amounts of (gluco)mannans, and (c) cellulose. The structure of these cell walls has

Table 4 Composition (mg/g) of Beet IDF and SDF According to the AOAC Method and of Water-Insoluble and Soluble Material

Yielda Rha Ara Xyl Man Gal Glc GalA MeOH AcOH Protein Ash

AOAC method:IDF 603 16 246 16 14 61 296 196 14 35 SDF 125 9 79 tr. 42 31 6 434 44 43

Water at 2022CResidue 815 12 192 14 10 49 222 217 20 38 95 54Soluble polymers 18 12 161 tr. tr. 61 12 316

a In mg/g beet pulp.: Not determined; tr.: traces.Source: Thibault et al., 1994.


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given rise to a number of models (Carpita and Gibeaut, 1993) and can be summarized as threeinterlocking networks, namely cellulose/xyloglucans, pectin, and cell wall glycoproteins. Sugar-beet cell walls differ from this blueprint in a number of key points which will be unterlined inthe next paragraphs.

1. PectinsMost data on the structure of the constitutive polysaccharides of sugar beet cell walls and berdeal with the pectic fraction (Table 5). Sugar beet pectins have distinctive features, notably highacetic acid contents and presence of phenolic esters on their side chains. They also contain ahigh proportion of hairy regions, with very high arabinose and lesser rhamnose contents.

The pectins from sugar beet do not form gels in the usual conditions, i.e., either withcalcium or with high sugar concentrations and acidic conditions (Michel et al., 1985b; William-son et al., 1990). This inability has been ascribed variously to the presence of acetyl groups(Pippen et al., 1950), which indeed hinders binding of ions (Kohn and Malovikova, 1978), to lowmolecular weight (Roboz and Van Hook, 1946; Michel et al., 1985b), or to excessive amounts ofside chains (Keenan et al., 1985). Acetyl groups are the most likely candidates for this inhibitionof gelication. The presence of phenolic acids (mostly ferulic acid) (Rombouts and Thibault,1986a) as esters on the side chains can, however, be used for chemical crosslinking of pectins,which can lead to gel formation in vitro (Thibault and Rombouts, 1986).

a. Backbone. The backbone of pectins is composed of -(1 4)-linked d-galacturonicacid units interrupted by the insertion of -(1 2)-rhamnose. Controlled acid hydrolysis ofbeet pectins (Thibault et al., 1993) led to isolation of homogalacturonans of DP 70100, com-prising less than one rhamnose unit per polymer. The rhamnose residues are concentrated inrhamnogalacturonans, where they alternate with the galacturonic acid residues (Sakamoto andSakai, 1994; Renard et al., 1998). Beet pectins, with a rhamnose: galacturonic acid ratio of 1:10 in the cell wall, are rich in rhamnose (Table 3). In the pectins, about 40% of the rhamnoseresidues are further substituted at position 4 by neutral sugar side chains (Table 6).

Rhamnogalacturonan II, a small complex pectic polysaccharide, and its boron-crosslinkeddimer can be isolated from beet after enzymic digestion (Ishii and Matsunaga, 1996).

b. Side Chains. Other constituent sugars are attached in side chains. In beet pectins,the side chains are composed of arabinose and galactose; other sugars (xylose, glucose, mannose)are present in negligible amounts (Rombouts and Thibault, 1986a; Guillon and Thibault, 1989).The xylogalacturonan subunit of pectins is thus very low if not absent in beet pectins.

Methylation analysis (Table 6) shows presence of arabinans with a backbone of -(15)-linked arabinofuranosyl residues carrying ramications predominantly on O-3. With similaramounts of chain and ramied residues, beet arabinans are highly branched.

The galactose residues are mostly present as type I galactans, i.e., linear chains of -(14)-linked galactose residues, but the partially methylated derivatives also indicate presenceof type II galactans (Table 6) (Guillon and Thibault, 1989; Oosterveld et al., 1996).

NMR analysis of sugar beet pectin supports the evidence of methylation analysis withpresence of 15-linked -l-arabinose and 14-linked -d-galactose residues (Keenan et al.,1985).

c. Nonsugar Substituents. In sugar beet, the pectin backbone carries both methyl esters(on the carboxylic group) and acetyl esters on the secondary alcools. Sugar beet pectins are nothighly methylated, having a degree of methylation of about 5060 (Table 5). The degree ofacetylation of extracted beet pectins is generally 2030, slightly lower in acidic extraction con-ditions (Table 5). The precise location of the acetyl groups is not known, but they are presentboth on the homogalacturonans of the smooth regions and on the rhamnogalacturonans of


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Table 5 Extraction Conditions and Characteristics of Beet Pectins

MeOH AcOH []Yield GalA Rha Ara Gal (DM) (DAc) FeA (mL/g)

HCl pH 1.5, 80C, 4 h (1) 177 682 122 (75) 47 (25) 110Oxalate NH4 0.25%, pH 3.5, 75C, 1 h (1) 218 641 110 (67) 53 (29) 158EDTA 0.5% HCl 0.01 M 90C 1 h (1) 189 532 97 (59) 49 (27) 208EDTA 2% 85C 1 h (2) 136 552 19 337 73HNO3 pH 1 85C 1 h (3) 129 623 (53) (25)Cold water (pH 3.7)(4)a 23 600 57 (54) 74 (55) 200Hot water (pH 3.7, 70C)(4)a 28 520 39 (40) 90 (71) 140Water 3 30 min, 2022C (5)a 22 544 9 84 65 72 (76) 57 (31) 1.0 259Oxalate NH4 1%, 3 30 min, 2022C (5)a 5 779 9 19 24 81 (60) 40 (15) 0.4 57HCl 0.05 M, 3 30 min, 85C (5)a 199 651 23 100 59 71 (62) 75 (35) 4.8 225NaOH 0.05M, 3 30 min, 4C (5)a 111 549 32 125 81 7 (8) 7 (4) 5.7 181Buffer pH 4.5 2022C (6) 56 513 13 101 51 28 (63) 56 (32) 187CDTA pH 4.5 2022C (6) 71 484 11 82 46 46 (52) 44 (27) 257Buffer pH 6.5 80C (6) 289 456 19 164 55 43 (52) 53 (34) 70CDTA pH 6.5 80C (6) 275 484 16 143 48 48 (55) 57 (35) 100Water 2022C (7)a 64 76 3 73 40 6 (41) 11 (41) 0NaOH 0.15 M EDTA 0,05 M, 2022 (7)a 151 388 30 293 46 1.5Autoclave pH 5.2 121C (7)a 178 399 21 267 39 51 (70) 65 (48) 6.1a As part of a fractionated extraction scheme.Source: (1) Arslan, 1995; (2) Wen et al., 1988; (3) Michel et al., 1985b; (4) Dea and Madden, 1986; (5) Rombouts and Thibault, 1986; (6) Renard and Thibault (1993); (7) Oosterveldet al., 1996.


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Table 6 Glycosidic Linkage Analysis of Beet Cell Walls and Some Fractions Thereof (linkage types in mol%)Pectin

(Autoclave) 4 M NaOHTotal ber Pectin

Derivatives Linkage (1) (HCl)(2) Total (3) DEAE (4) Total (3) DEAE (4)Rhamnose 2.6 (2.1)a 9.3 (10.5) 1.3 5.7 2.6 0.4

2,3,4-Me3 Rha Rhap-(1 0.5 0.9 0.53,4-Me2 Rha 2)-Rhap-(1 5.6 0.4 2.8 1.1 0.43-Me Rha 2,4)-Rhap-(1 2.6 3.7 0.4 2.1 1.0

Arabinose 37.7 (40.6) 67.9 (67.5) 47.0 73.3 71.0 44.22,3,5-Me3 Ara Araf-(1 11.8 22.5 17.4 27.2 25.3 19.42,3,4-Me3 Ara Arap-(1 tr.3,5-Me2 Ara 2)-Araf-(1 0.72,5-Me2 Ara 3)-Araf-(1 0.6 1.5 0.5 0.7 0.82,3-Me2 Ara 5)-Araf-(1 14.0 20.6 14.2 21.4 23.1 13.32-Me Ara 3,5)-Araf-(1 11.7 18.7 11.8 17.5 16.9 10.23-Me Ara 2,5)-Araf-(1 2.3 0.9 1.2 1.5Ara 2,3,5)-Araf-(1 tr. 1.6 2.2 5.3 3.4 1.4

Galactose 7.6 (9.6) 22.8 (22.0) 3.7 13.9 7.9 4.02,3,4,6-Me4 Gal Galp-(1 0.7 5.2 1.8 4.1 2.7 2.22,4,6-Me3 Gal 3)-Galp-(1 1.2 3.82,3,6-Me3 Gal 4)-Galp-(1 4.6 8.0 0.9 2.7 2.6 1.82,3,4-Me3 Gal 6)-Galp-(1 0.9 1.1 0.4 1.8 1.5 0.12,6-Me2 Gal 3,4)-Galp-(1 0.9 1.92,4-Me2 Gal 3,6)-Galp-(1 2.8 0.3 0.32,3-Me2 Gal 4,6)-Galp-(1 0.3 5.4 0.8


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Xylose 4.1 (3.2) 1.9 5.7 6.9 12.92,3,4-Me3Xyl Xylp-(1 0.8 0.8 1.9 1.2 6.72,3-Me2Xylb 4)-Xylp-(1 3.3 0.3 2.5 5.3 6.1c3-Me Xyl 2,4)-Xylp-(1 0.4 1.7 0.22-Me Xyl 3,4)-Xylp-(1 0.4 0.6 0.2

Mannose 2.4 (2.1) 0.8 0 2.2 7.32,3,6-Me3 Man 4)-Manp-(1 2.4 0.8 0 2.2 7.3

Glucose 45.3 (42.2) 1.0 1.3 3.2 31.12,3,4,6-Me4 Glc Glcp-(1 0.32,3,6-Me3 Glc 4)-Glcp-(1 40.9 0.9 0.5 2.8 21.12,6-Me2 Glc 3,4)-Glcp-(1 0.5 0.1 0.43,6-Me2 Glc 2,4)-Glcp-(1 1.52,3-Me2 Glc 4,6)-Glcp-(1 2.1 0.8 10.1

Galacturonic acidd 44.2 6.12,3,4,6-Me4 Gal GalAp-(1 2.3 0.62,3,6-Me3 Gal 4)-GalAp-(1 39.4 4.22,6-Me3 Gal 3,4)-GalAp-(1 2.5 1.3

a Total (based on analysis of alditol acetates).b Not distinguished from 3,4 Me2 Xyl.c 3,4 Me2 Xyl exclusively.d Determined as galactose residues after carboxyl reduction.Source: (1) Thibault and Rouau, 1990; (2) Guillon and Thibault, 1989; (3) Oosterveld et al., 1996.


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the hairy regions (Rombouts and Thibault, 1986b). The rhamnogalacturonan fraction couldhave a higher degree of acetylation and lower degree of methylation than the homogalacturonans(Oosterveld et al., 1996). Location of the acetyl groups at position 2 or 3 of galacturonic acidis still uncertain; Keenan et al. (1985) by 13C-NMR and Dea and Madden (1986) by 1H-NMRidentied three signals for acetyl groups, which would imply location at one position or bothpositions at once. In other plant materials, acetylation occurs mainly at O-2 in rhamnogalacturo-nans (Ishii, 1995) and at O-3 in homogalacturonans (Ishii, 1997a).

Among the dicotyledons, Chenopodiaceae in particular contain cell wallbound phenolicacids (Table 3) (Ishii, 1997b). These include mainly ferulic acid, which represents about 0.8%of beet cell walls, and to a lesser extent p-coumaric acid (Rombouts and Thibault, 1986a). Thesephenolic acids are carried by the neutral sugar side chains of pectins (Rombouts and Thibault,1986a, b). More precisely, they are esteried about 5060% to the O-2 position of arabinosemoieties and 4050% to the O-6 position of galactose residues (Ishii, 1994; Ralet et al., 1994).Structural analysis of longer oligosaccharides (up to DP 8) showed that the feruloyl groups arelinked to arabinose residues of the core chain of arabinans and to galactose residues of the corechain of type I galactans and not to extremities of the side chains (Colquhoun et al., 1994).

Phenolic acids are bifunctional and thus a potential crosslink of the beet cell wall (Fry,1986). Indications in favor of that role are the presence of dehydrodimers of ferulic acid insugar beet pulp (Table 7) and the possibility of crosslinking extracted beet pectins in vitro byoxidation of their feruloyl groups (Thibault and Rombouts, 1986; Oosterveld, 1997).

d. Distribution of Structural Elements. After degradation of extracted pectins eitherby chemical -elimination or using enzymes, two fractions are obtained, with the neutral sugarsconcentrated in a high molecular weight fraction and the galacturonic acid in a low molecularweight population (Rombouts and Thibault, 1986b; Guillon and Thibault, 1988). These resultsare in conformity with the perception of pectins as composed of smooth, homogalacturonicregions and hairy regions where the rhamnogalacturonic backbone carries neutral sugar sidechains (Voragen et al., 1995). The highest degradation occurred with polygalacturonase or pec-tatelyase after saponication (Rombouts and Thibault, 1986b). After degradation with polygala-cturonase (Guillon and Thibault, 1988), most of the galacturonic acid is obtained as oligomer,with less than 20% of the galacturonic acid initially present being recovered in the high molecu-lar weight fraction. This fraction (hairy region) is composed mostly of neutral sugars, notablyarabinose, galactose, and rhamnose.

The distribution of arabinans and galactans in the hairy regions has been studied bydegradation with dilute acids (Guillon and Thibault, 1989) or specic enzymes (Guillon et al.,1989; Sakamoto et al., 1993; Sakamoto and Sakai, 1994). Digestion by a mixture of endo-arabinase and arabinofuranosidase can lead to complete separation of the arabinose while thegalactose is retained with the rhamnogalacturonan. These results indicate that galactan chainsare directly linked to the backbone, while arabinans might be connected through an interposed

Table 7 Contents (mg/g) of Ferulic Acid and Its Dehydrodimers in the Cell Walls of Sugar Beet andin Extracted Pectins

Repartition of the types of dimersTotal

FeA diFeA 8-8 8-5 5-5 8-O-4 4-O-5

Sugar beet pulp (1) 8 1.40 12 48 9 31 ndSugar beet pectin (2) 15 1.43 27 21 16 37 ndSugar beet cell walls (3) 4 1.30 3.5 40.3 10.6 45.6 ndnd: Not detected.Source: (1) Micard et al., 1997; (2) Oosterveld et al., 1997; (3) Waldron et al., 1997.


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galactan (Sakamoto et al., 1993; Sakamoto and Sakai, 1994). This is conrmed by the isolationof a small polymer composed exclusively of galactose, rhamnose, and galacturonic acid (molarratio 1:1:2) after autoclaving and acid hydrolysis (C.M.G.C. Renard, unpublished results).

e. Extraction and Molecular Weight. Sugar beet cell walls contain a very low amountof readily extractable pectin (by water or chelating agents at room temperature) even prior tothe diffusion step (Table 5). Although calcium is present in sugar beet in amounts sufcient toneutralize most nonmethylated uronic acid (K. Fare`s et al., unpublished results), calcium cross-links do not seem to be the main mechanism holding the pectins in the beet cell wall.

Efcient extraction can be obtained either by heating or by alkaline treatments (i.e., de-mands degradation of pectin). Autoclaving as well as heating at pH 6.5 (either with buffer,EDTA, or CDTA) leads to degradation of the pectic backbone through -elimination and there-fore to extraction. This results in the presence in the extract of two populations, namely a highmolecular weight, neutral sugarrich fraction (analogous to the hairy regions obtained afterenzymic degradation) and a lower molecular weight fraction almost exclusively composed ofgalacturonic acid (Guillon et al., 1992; Renard and Thibault, 1993, Oosterveld et al., 1996).

Hot acid treatments, comparable to those used for industrial extraction of pectins, leadto degradation rst of the arabinan side chains. Acid-extracted sugar beet pectins can thus becharacterized by a low neutral sugar content and conversely high galacturonic acid (Table 5).These acid-extracted sugar beet pectins have relatively low intrinsic viscosities and molecularweight (Rombouts and Thibault, 1986; Michel et al., 1985b; Arslan, 1995), compared in particu-lar to pectin extracted in similar conditions from citrus or apple.

Some pectins can be extracted from beet cell walls by alkali at room temperature (Ooster-veld et al., 1996) and are therefore thought to be held in the wall by ester bonds, i.e., in beetcell walls to be crosslinked by dehydrodiferulates.

2. HemicellulosesHemicelluloses can be dened as cell wall polysaccharides that have the capacity to bind stronglyto cellulose microbrils by hydrogen bonds (Roland et al., 1989). The common structural fea-tures of hemicelluloses are a main chain with a structural resemblance to cellulose and eithershort side chains that result in a pipe cleanershaped molecule or a different sugar interpolatedin the main chain, both modications preventing further aggregation (Carpita and Gibeaut,1993). In the cell walls of land plants, three classes of polymers correspond to that denition,namely xyloglucans, heteroxylans, and mannans. In the primary cell wall of dicotyledons, themain hemicellulose is usually xyloglucan, which accounts for 1520% of the dry weight of thewall.

Beet cell walls have very low concentrations of the sugars that denote hemicelluloses,i.e., xylose, mannose, noncellulosic glucose, and fucose (Table 3), and their hemicelluloses havebeen very little studied. One of the problems encountered is prevalence of arabinans in all stepsof fractionnated extraction schemes, as can be seen in Table 8. Oosterveld (1997) isolated froma 4 M NaOH beet extract a fraction enriched in hemicelluloses (Table 8), and methylationanalysis of this material indicated presence of xyloglucans and mannans (Table 5). Degradationby a puried endo-glucanase of this fraction allowed identication of xyloglucan oligomers,which conrmed the presence, though in very low amounts, of a standard fucogalactoxyloglucanin beet cell walls.

3. CelluloseCellulose is the second most abundant polymer in beet ber (200 mg/g). Cellulose is a linearchain of -(14)-linked glucopyranose. In cell walls, these chains form microbrils with a


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Table 8 Concentrated Alkali Extracts of Sugar Beet Pulp

Yield GalA Rha Fuc Ara Xyl Man Gal Glc

NaOH 4 M, 2022C (after autoclave)(1) 263 123 29 296 30 17 71 36NaOH 4 M, 2022C (after NaOH 0.15 M)(1) 208 106 47 389 43 20 91 42KOH 1 M, 2022C (after oxalate 100C)(2) 150 370 52 4 432 0 6 126 10KOH 4 M, 2022C (after oxalate 100C)(2) 95 231 46 12 379 123 4 138 66NaOH 2.5 M, 2022C (after EDTA 85C and pectinase) 168 5 108 140 232 220 130 214pH 5 precipitate (3)NaOH 2.5 M, 2022C (after EDTA 85C and pectinase) 88 41 105 217 125 144 169 260pH 5 supernatant (3)Source: (1) Osterveld et al., 1996; (2) Kobayashi et al., 1993; (3) Wen et al., 1988.


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parallel arrangement of the polymer chains. Beet cell walls contain typical primary cell wallmicrobrils, 24 nm in diamater (Dinand et al., 1996). X-ray diffraction patterns indicate pres-ence of cellulose IVI, i.e., of a type I cellulose with limited lateral order, probably due to limitedsize of the microbrils (Dinand, 1997). Solid-state NMR of beet cell walls (C. M. G. C. Renardand M. C. Jarvis, unpublished results) indicates presence of 42% of crystal-surface chains, ingood agreement with the diameter observed by microscopy (Dinand et al., 1996).

IV. PHYSICOCHEMICAL PROPERTIESA. Cation-Exchange CapacityFibers from sugar beet behave as weak monofunctional cation-exchange resins with a CEC ofabout 0.5 mEq/g (Table 9). This ion-binding capacity is due to the presence of nonmethylesteri-ed galacturonic residues, and the CEC is equal to the concentration of nonmethylated galacturo-nic acid residues calculated from independent galacturonic and methyl groups measurements(Bertin et al., 1988; Dronnet et al., 1997). Beet bers are devoid of phytic acid, the main ion-binding species in cereal bers. Beet pulp itself contains enough calcium to neutralize most ofthe free galacturonic acid (K. Fare`s et al., unpublished results). This calcium may be endogenousbut may also arise from the pressing aids used during the sugar recovery process.

In spite of the presence of acetyl groups (Dronnet et al., 1996), pectin in sugar beet pulpis able to bind divalent cations, with higher afnities than in solution (Dronnet et al., 1997) butwith the same selectivity scale: Cu Pb Zn Cd Ni Ca.

B. Hydration CapacitiesBasically, three different parameters can be measured: (a) swelling, (b) water retention capa-city (WRC), i.e., the amount of water retained by a known weight of ber measured bymethods such as centrifugation, and (c) water absorption capacity (WAC), i.e., the ability ofthe ber to absorb water measured using a Baumann apparatus or osmotic pressure/dialysistechniques.

Beet ber has generally high hydration capacities, especially compared to bers fromcereal brans. However, these hydration properties are very variable depending on the ber prepa-ration and also on the conditions of measurement (Table 9). The main intrinsic factors areparticle size and drying condition. High-temperature drying results in a decrease of hydrationcapacities (Cloutour, 1997), as does a decrease in particle size (Table 9). The effect of particlesize on swelling can be due to increased interparticular spaces rather than increased hydrationof the particles. Thermal or thermomechanical treatments increase the amount of soluble berin beet pulp and modify its hydration properties.

In addition, the measured hydration capacities are sensitive to extrinsic factors, such asionic strength of the hydrating solution (Table 9) and its ion composition. These effects aremostly visible after conversion to the H or Na form or after saponication. Beet pulp thenappears to behave as a polyelectrolyte resin. Presence of divalent cations results in a decreasein observed hydration capacities of deesteried beet pulp (Renard et al., 1994). A number ofthese effects might be masked in native beet pulp by the presence of a high calcium concentra-tion. The conditions of hydration also play a role: presence of shear forces in the form of intensestirring can lead to a destructuring of the beet ber and an increase in apparent WRC. Thissensitivity to the exact method and conditions of measurement explains the variability of theresults.


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Table 9 Physicochemical Properties of Beet Fibers

Swelling WRCSubstrat CEC (meq/g) (mL/g) WAC (centrifugation)Beet pulp (1) 0.62Beet ber (2) 0.47

Native 11.5a 26.5aNa form 32.6a 30.8a

Beet ber (3) 0.42 23.0a 34.0a (18.0a)Beet pulp (4) 0.48

Native 11.0a (10.0d) 26.6aH form 25.0a 22.5a

Beet pulp (5) 0.55H form 17.8a (13.4d) 23.9a (16.0d)Na form 32.0 (15.3a)

Beet ber (6) 0.60Beet ber (7) 0.64 16.6Beet ber (8)

540 m 21.5a (19.8d) 8.5a Baumann 24.2b 12.6c (11.8d) 385 m 21.4a (19.3d) 8.8a 22.6b 12.0c (10.9d) 205 m 15.9a (16.3d) 7.3a 19.2b 9.2c (9.6d)

Beet ber NDF fraction (9) 0.70Beet ber NDF fraction (10) 0.57Saponied beet pulp (4) 1.12

Native 25.0a (20.0b) 24.8aH form 20.0a 20.7a

Saponied beet pulp (11) 1.13H form 21.9a (12.6b) 18.3a (8.3d)Na form 32.4a (19.3b)

Extruded beet pulp (12) 0.39 14.4a 28.2aAutoclaved beet pulp (3)

at 122C 0.35 20.0a (21.3b) 35.0a (30.0d)at 136C 0.20 21.0a (26.7b) 38.4a (40.0d)

NDF: neutral detergent ber.a In water.b Long incubation, heavy stirring (in water).c Short incubation, gentle stirring (in water).d In presence of supporting salts.Source: (1) Langenhorst et al., 1961; (2) Bertin et al., 1988; (3) Guillon et al., 1992; (4) Renard et al., 1994; (5) Dronnetet al., 1997; (6) Michel et al., 1988; (7) O zboy et al., 1998; (8) Auffret et al., 1994; (9) McBurney et al., 1983; (10)Allen et al., 1985; (11) Dronnet et al., 1998; (12) Ralet et al., 1991.

V. NUTRITIONAL STUDIESA. Apparent Fermentability or Apparent DigestibilityApparent fermentability and apparent digestibility were investigated in vitro with fecal inoculate(Guillon et al., 1992, 1998; Auffret et al., 1993; Salvador et al., 1993; Fardet et al., 1997) orin vivo in rats (Nyman et al., 1981; Champ et al., 1989) or in pigs (Graham et al., 1986; Longlandet al., 1993). All indicated a high fermentability or apparent digestibility of sugar beet ber, inthe range of 7090%. Galacturonic acid and arabinose were virtually completely digested; glu-cose about 8588%; only xylose, present in small amount, was of low digestibility. It was shown


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in vitro that all sugars are not fermented at the same rate; glucose disappearance began moreslowly than that of uronic acid and arabinose (Guillon et al., 1992, 1998; Auffret et al., 1993;Salvador et al., 1993; Fardet et al., 1998). The tridimensionnal arrangement of the polymerswithin the cell wall, and thus the access of bacteria or associated enzymes to the polymers, mayaccount for this difference.

In these studies, the chemical composition of the bers were identical or very close buttheir physical form and hydration properties varied greatly (Table 10), leading to differencesin the rate of fermentation (Table 10). Processing of ber, such as autoclaving or chemicalextraction followed by drying, also inuenced its fermentability (Table 10). Porosity, whichcould be approached by measurement of the swelling and water retention capacity, is an impor-tant factor controlling the ber fermentation (Guillon et al., 1998).

The production of short chain fatty acids (SCFA) was analyzed in vitro (Rumney andHenderson 1990; Guillon et al., 1992, 1998; Auffret et al., 1993; Salvador et al., 1993; Fardetet al., 1997) and in vivo. In the latter case, the production was deduced either from measurementof SCFA in feces or cecal digesta of animals (Champ et al., 1989) or from dynamic analysisof porto arterial differences in the concentration of SCFA and of the portal blood ow rate inpigs (Michel and Rerat, 1998). The data conrmed the high fermentability of sugar beet ber,especially when compared to other insoluble bers (from cereal or legumes). Fermentation pro-les, expressed as molar percent of each of the major SCFAacetic (C2), propionic (C3), andbutyric (C4)was characterized by a high ratio of C2 (6080) followed by C3 (1123) andthen C4 (915). In vitro, no alterations in the SCFA prole were observed when modulatingthe chemical composition and physicochemical properties of sugar beet ber (Auffret et al.,1993; Guillon et al., 1998). The fact that both uronic acid and cellulose produced high amountsof acetate could be the explanation (McBurney and Thompson, 1989; Vince et al., 1990).

B. Sugar Beet Fiber, Transit Time, and Stool OutputThe effect of sugar beet ber on transit time and stool output was evaluated in healthy subjects(Cherbut et al., 1991), in patients complaining of chronic constipation (Giacosa et al., 1990),and in rats (Nyman and Asp, 1982; Johnson et al., 1990; Gallaher et al., 1992; Harland, 1993).Supplementation with sugar beet ber increased wet fecal mass and number of daily stools.More diverse were the effects on transit time and dry fecal mass.

Sugar beet ber (33 g/day) in the diet decreased transit time by 25%, as did the wheatbran supplemented diet (Cherbut et al., 1991). Both increased the number of daily stools andwet fecal mass. Weight of fecal water but not the dry fecal mass changed, while wheat branincreased both dry weight of fecal mass and fecal water. In rats the sugar beet diet increasedthe fecal output, as did the other ber diets (Nyman and Asp, 1982; Johnson et al., 1990; Gallaheret al., 1992; Harland, 1993). Nyman and Asp (1981), Johnson et al. (1990), and Harland (1993)reported both wet and dry fecal mass increase. In constipated patients, a marked decrease insevere and moderate constipation at both the 15th and 30th days of treatment with sugar beetber was found, with a signicant increase in fecal frequency normalization (Giacosa et al.,1990). Moreover, fecal consistency changed from hard and semi-hard stools to soft ones.

The mechanisms by which ber inuences transit time are still not fully understood. Dif-ferent mechanisms have been suggested, which depend on the physical properties and fer-mentability of the ber (Cherbut, 1995, 1998; Cherbut et al., 1998). The ber may act by increas-ing the lumen volume, depending on the amount of indigestible residue in the colon, the waterretention capacity of the residue, the stimulation of microbial growth, and the production ofgas. The ber can also reduce transit time through modulating colonic motility either by amechanical stimulation of mechanoreceptors by the edges of the ber particle (Tomlin and Read,


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Table 10 Apparent Total Sugar Disappearance of Sugar Beet Fiber Samples after 6, 12, and 24 Hours of Incubation with Fecal Bacteria

Apparent total sugardisappearance (%)

Particle size Water retention capacityRef. Treatment (geometric mean particle size) (g water/g pellet dry matter) 6 h 12 h 24 hGuillon et al., 1992 No 570 m 18 32 64 86Auffret et al., 1993 No 390 m 17 43 72 85Salvado et al., 1993 No 80 m 7 45 68 81Guillon et al., 1998 No 480 m 12 55 73 84Guillon et al., 1992 Autoclaving Not indicated 28 69 80 88Guillon et al., 1998 Pectin extraction followed

by soft drying 430 m 15 28 48 72Auffret et al., 1993 120 m 22 58 81 87Guillon et al., 1998 by harsh drying 120 m 6 24 33 41


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1988), or by a chemical stimulation by the products of fermentation (Cherbut, 1995), or by therelease of compounds trapped by ber, such as biliary acids or fatty acids (Cherbut, 1998). Inthe latter case, these products can stimulate not only colon motility but also secretion (Cherbutet al., 1998). Except for stimulation of mechanoreceptors, the different mechanisms mentionedabove could contribute to the effect of sugar beet ber on transit.

The increase in stool output by dietary ber intake may have several causes (Cherbut,1998); it could be related to the amount of excreted residue and its water-binding capacity. Theincrease of the bacterial mass can also contribute, since bacteria contain 80% water. Finally,the excreted water could be water not absorbed in the colon because of the short transit timeor changes in colonic motility. Again, these different mechanisms can all participate in theincrease in stool output.

C. Sugar Beet Fiber and MineralsThe effect of sugar beet ber on the absorption of zinc, iron, copper, calcium, and magnesiumwas investigated in humans (Sandstrom et al., 1987; Cossack et al., 1992; Coudray et al., 1997)or rats (Fairweather-Tait and Wright, 1990; Harland, 1993) and led to the same conclusions.Sugar beet ber has no negative effect on any of the minerals studied. These studies stressedthe fact that beet ber generally has a relatively high mineral content and can therefore contributeto mineral intake.

D. Sugar Beet Fiber and Glucose MetabolismThe effects of sugar beet ber on glucose metabolism were investigated with different objectives.The effects on fasting plasma glucose and insulin values and on glucose tolerance of sugar beetber intake over a period of several weeks (from 3 to 8) were studied in normal (Tredger etal., 1991), normal but with high fasting cholesterol value (Frape and Jones, 1995), or noninsulin-dependent diabetes mellitus (NIDDM) subjects (Hagander et al., 1988, 1989). Theseparameters were regarded together with lipid parameters in order to better understand the mecha-nisms by which daily intake of dietary ber can decrease the risks of cardiovascular disease.Experiments were also concerned with glucose tolerance (Tredger et al., 1981; Morgan et al.,1990; Lecle`re et al., 1993; Thordottir et al., 1998) in healthy volunteers or pigs and focused onacute effects of ber supplementation.

No clear effect of long-term sugar ber supplementation on fasting as well as postprandialblood glucose and insulin levels has been demonstrated (Table 11). The source, processing, andphysical form of the ber in the diet but also the nature of the meal (amount of ber, amountof lipids, sources or carbohydrates, etc.), the metabolic status of the subjects, and the durationof the experiment may explain these differences. Similarly, discrepancies in blood glucose andinsulin responses in normal subjects to a single meal with added sugar beet ber are recordedin the literature (Table 12).

No clear mechanism explains the effect of sugar beet ber on postprandial glucose level.It is well known that soluble high molecular weight ber, such as oat or guar gum, can signi-cantly decrease the postprandial circulating glucose level by slowing down the gastric emptyingand/or inuencing the diffusion and mixing of the intestinal contents. Sugar beet ber is onlypartly soluble, and it is unlikely that this soluble ber fraction can induce a sufcient increasein the viscosity of digesta to delay starch digestion or absorption, especially in the case of asolid meal. Another mechanism suggested is by changing transit time, but again, results in theliterature are discordant. Morgan et al. (1990) observed a slightly accelerated liquid gastric


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Table 11 Chronic and Postprandial Responses of Plasma Insulin and Glucose in Volunteers Given Sugar Beet Fiber Supplements

Ref. Intake (g/day/subject) Subjects Duration ResultsHagander et al., 1988 8 NIDDM 8 wks Improvement in glucose response to a standardized

breakfastHagander et al., 1989 40 NIDDM 8 wks Blood glucose and insulin fasting or postprandial levels

were not signicantly affectedIn obese NIDD patient, postprandial insulin level tended to

be lower after the beet diet periodTredger et al., 1991 20 Healthy 16 days No changes in blood fasting glucose and insulin concentra-

tionsFrape and Jones, 1995 18 Healthy middle aged with 3 wks No effect on fasting plasma glucose and insulin

mild risk ischemic heartdisease

Effect on the postprandial parameters:decrease in the area under the glucose response curves by

6.9%decrease in the area under insulin response curve by

9.6%, although not signicant


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Table 12 Postprandial Responses of Plasma Insulin and Glucose in Volunteers Given Sugar Beet Fiber Supplements

Ref. Intake (g per meal) Carbohydrate (g per meal) Subjects ResultsTredger et al., 1981 20 86 Healthy No difference in the mean blood glucose and plasma

male human insulin curves at any time between the control andvolunteers ber diets

Morgan et al., 1995 10 100 Healthy An improved glucose tolerancemale human No change in insulin levelvolunteers Failure of sugar beet ber to decrease postprandial in-

sulin secretion despite improved glucose tolerance wasascribed to increased secretion of gastric inhibitorypolypeptide

Thorsdottir et al., 1998 7 51 (liquid formula) Healthy Lower postprandial blood glucose and serum insulinmale human response compared with the formula without bervolunteers

Lecle`re et al., 1993 56 653 Pigs No effect on postprandial glycaemic and insulinemicvalues

Michel and Rerat, 1998 114 446 Pigs No difference in glucose absorption between sugar beetber and wheat bran supplemented diets


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emptying with both sugar beet ber and guar gum supplementation, which was unexpected.Hamberg et al. (1989) and Cherbut et al. (1991) found, respectively, a decreased and an increasedmouth-to-cecum transit time in subjects fed sugar beet ber.

E. Sugar Beet Fiber and Lipid MetabolismSugar beet ber, because of its signicant content of water-soluble ber, has been investigatedfor its effects on lipid metabolism. Studies were carried out in humans with either healthy(Lampe et al., 1991; Tredger et al., 1991; Frape & Jones, 1995), hypercholesterolemic (Israelson,1988,), or NIDMM subjects (Hagander et al., 1988, 1989; Travis et al., 1990) and in animals,pigs (Fremont et al., 1993), or rats (Johnson et al., 1990; Mazur et al., 1992; Nishimura et al.,1993; Overton et al,., 1994; Sonoyoma et al., 1995; Hara et al., 1998). Despite the fact that thedietary pattern (daily intake of dietary ber, high-fat, low-carbohydrate diet, and vice versa)and the duration of the experiments (from 2 to 8 weeks) differed between the studies, mostconcluded that sugar beet ber is hypocholesterolemic (Tables 13, 14). In humans, it tends toreduce serum total cholesterol and apo B levels without altering or even slightly increasing high-density lipoprotein cholesterol. Only some studies reported a decrease in serum triglycerides(Hagander et al., 1989, Travis et al., 1990, Mazur et al., 1992, Overton et al., 1994).

The mechanisms sustaining such effects are still not clear (Lairon, 1996). Dietary ber mayact as an hypocholesterolemic resin, which sequesters bile acids and cholesterol, with consequentinterruption of the enterohepatic bile acid cycle in the small intestine (intestinal reabsorptionof bile salts in humans is 9698% efcient) and loss of cholesterol from increased fecal bileacid excretion. This mechanism was clearly demonstrated for viscous ber such as guar gumand oat gum. In the case of sugar beet ber, it seems not to be valid or at least not important,as most of the studies did not nd a signicant increase in excretion (fecal: Lampe et al., 1991;Gallaher et al., 1992; Overton et al., 1994; ileal: Langkilde et al., 1993) of bile acids. Theseresults are in agreement with those from Morgan et al. (1993), who did not observe changesin concentrations of circulating postprandial bile acids in humans given an acute test meal sup-plemented with sugar beet ber (10 g Betaber per meal), contrary to guar gum or cholestyra-mine. This also t with in vitro data, which showed that the insoluble fraction of sugar beetber bound only a small quantity of glycocholate and that no bile acids were associated withthe soluble fraction (Morgan et al., 1993). In a study with ileostomists (Langkilde et al., 1993)a decrease of 26% of ileal bile acid excretion was noted while cholesterol excretion increasedby 52% with the sugar beet ber diet. The excreted amount of cholesterol corresponded to halfof the mean daily intake of cholesterol in this experiment. This pattern is different from thepattern generally reported for water-soluble ber such as oat, guar gums, or pectins. The choles-terol-lowering effect of sugar beet ber may result from its interference with lipid absorptionthrough alteration of the digestive processes. The reduced absorption of cholesterol results ina reduced supply to the liver, which as a secondary effect could decrease excretion of bile acidsas they are synthesized from cholesterol in the liver (Langkilde et al., 1993). The inuence ofsugar beet ber on lipid absorption may account at least for the acute postprandial effect ofdietary ber on lipemia, but the mechanisms involved have not been explored. Moreover, theextent to which the repetition of the single meal effect can lead to a new metabolic steady statein the long run remains be further investigated. In sugar beet berfed rats, hypocholesterolemiawas accompanied by a reduction in hepatic cholesterol and in circulating triacylglycerol andbile acids, with no increase in bile acid fecal excretion (Overton et al., 1994). The authors pointedout another possible mechanism involving disruption of the bile acid circulation, possibly viachanges in the rate of absorption patterns of triacylglycerol and its subsequent handling bycirculating lipoproteins.


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Table 13 Effect of Sugar Beet Fiber on Lipid Metabolism (Human Studies)Ref. Intake (g/day/subject) Subjects Duration ResultsIsraelsson et al., 1998 30 Hypercholesterolemic women 24 wks Signicant reduction of LDL cholesterol with no change

in HDLHagander et al., 1988 8 NIDDM 8 wks Lower fasting blood glucose

Reduction of LDL cholesterol with no change in HDLLower fasting levels of triglyceridesImprovements in glucose response to a standardized

breakfastHagander et al., 1989 40 NIDDM 8 wks Decrease of 8% in total cholesterol when compared with

the habitual diet, but no decrease compared with thelow-ber diet

Travis et al., 1990 18 NIDDM 6 wks Decrease of 6.2, 10.6, and 6.0% in, respectively, totalcholesterol, triglycerides, and Apo B levels

Lampe et al., 1991 30 Healthy volunteers 3 wks Decrease of 12 and 15% in total and LDL cholesterolSmall changes in HDLSignicant decrease in serum triglycerides

Tredger et al., 1991 20 Healthy volunteers 16 days Decrease of 4.6% in total cholesterol; decrease moremarked with subject with a high habitual fat intake

No change in HDL cholesterol and triglyceridesFrape and Jones, 1995 18 Healthy middle-aged 3 wks Decrease of 8 and 9.6% in total and LDL cholesterol in

volunteers subjects in whom fasting plasma cholesterol wasabove normal

No difference in HDL cholesterol


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Table 14 Effect of Sugar Beet Fiber on Lipid Metabolism (Animal Studies)Level of incorporation

Ref. g/kg diet Animals Duration Results

Johnson et al., 1990 100 g/kg semi- Rats 28 days Signicant reduction of serum cholesterol, but less than that of guarsynthetic diet gum

Mazur et al., 1992 300 g/kg fructose- Rats 3 wks Decrease in plasma triglyceride and cholesterol concentration in thebased diet postprandial as well as the postabsorptive period

Depress of the liver triglyceride level in concert with decreased liverlipogenesis

No change in liver cholesterol levelAnimals less fat

Overton et al., 1994 100 g/kg semi- Rats 28 days Lower circulating cholesterol, hepatic cholesterol, and circulatingsynthetic diet triacylglycerol

No change in total hepatic lipid concentrations and hepatic andadipose tissue lipogenesis

Sonoyoma et al., 1994 150 g/kg a cholesterol- Rats 14 days Lower nal total plasma cholesterol Lower HDL cholesterol andfree diet Apo A-I concentrations

No signicant changes in hepatic cholesterolThe hypocholesterolemic effect is associated with diminished ex-

pression of the hepatic apolipoprotein A-I geneNishimura et al., 1993 100 g/kg 25% casein Rats 28 days Lower plasma total cholesterol

diet Lower HDL cholesterolLower digestive tract, especially cecum, seemed to be necessary for

this effectFremont et al., 1993 120 g/kg semi- Weaning piglets 4 wks No change in serum cholesterol and HDL cholesterol concentrations

synthetic diet Lower fasting triacylglycerol due to reduction in VLDL synthesis


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Other mechanisms of action of dietary ber have been suggested. Modication in hor-monal status, especially insulin, could inuence lipoprotein lipase activity, cholesterol and bileacid synthesis, and VLDL secretion. Only a few groups (Hagander et al., 1988, 1989; Tredgeret al., 1991; Frape and Jones, 1995) have investigated the effects of sugar beet ber on gastro-intestinal hormones and cholesterol. Most of the authors reported no signicant changes in thefasting levels of insulin.

It has been suggested that the hypocholesterolemic effect of dietary ber might also bemediated through the fermentation products, which can modify the activity of regulatory en-zymes involved in hepatic cholesterol synthesis. A study in rats (Nishumura et al., 1993) hasdemonstrated that an intact cecum and colon is necessary for the ber to be effective. One ofthe SCFA, propionate, has been shown in pigs and rats to signicantly lower plasma and livercholesterol concentrations and to inhibit cholesterol synthesis in isolated rat hepatocytes. How-ever, no such effect has been reported in humans, and the role of propionate in reducing LDLcholesterol levels is controversial. Recently, Hara et al. (1998) suggested that acetate can contrib-ute to the reduction in plasma cholesterol concentration in rats. However, no mechanism wasproposed. Moreother, this conclusion was drawn from SCFA feeding. The absorption ratio ofindividual SCFA ingested orally may be different from products in the large intestine, whichmay result in a different effect on cholesterol metabolism. SCFA reaching the liver may havemodulate lipid and carbohydrate metabolism, but more comprehensive studies with human orwell-validated animal models and protocols must be carried out to elucidate the mechanismsinvolved. It seems therefore likely that the cholesterol-lowering effect of sugar beet ber is notdependent on increased fecal bile acid and is affected by a number of factors rather than a singlemechanism.

F. Further Information1. Growth Performance in AnimalsIn rats, sugar beet ber represented 100300 g/kg in the diet. Inclusion of ber in the diet hadno effect on food intake in ve of the six rat studies. Live weight gain and feed conversionwere generally similar in rats fed control or ber-supplemented diet (Johnson et al., 1990; Mazuret al., 1992; Harland, 1993; Nishimura et al., 1993; Overton et al., 1994; Sanoyama et al., 1995).However, Dongowsky et al. (1998) reported a higher consumption of food when the diet isenriched with sugar beet. They found a reduced mean food efciency and a signicant growthretardation in animals fed the highest ber diets.

In pig studies, semi-synthetic diet or growing pig feed was used as control diet. The levelsof sugar beet ber varied from 170 to 330 g/kg diet. No particular adverse effect was reported.Longland et al. (1993) found a slightly reduced digestibility and metabolization of energy whenpigs were fed a semisynthetic diet with high levels (287g/kg diet) of sugar beet pulp. Fremontet al. (1993) in weaning piglets found a 47% increase in the apparent feed-conversion efciencyafter 4 weeks of dietary treatment with sugar beet ber (120 g/kg diet). The higher feed intakecould compensate for the energy dilution by ber.

2. Tolerance to Sugar Beet FiberIn human studies, the daily intake varied greatlyfrom 7 to 40 g per subject. Generally theintake of ber was gradually increased, in particular when large doses were concerned. Theform in which ber was ingested also differed: it was included in foods (prepared dishes, bread,biscuits, chocolate bars), pressed into tablets, or mixed as a powder in water. Generally tolerancewas good. Only a few studies reported cases of discomfort, abdominal cramping, and bloating


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or trouble with atulence or borborygmi. This generally occurred with the largest doses. Onestudy (Travis et al., 1990) mentioned that subjects (ve of seven) found the sugar beet bersupplemented bread and biscuits less palatable than normal products, which led to a reductionin compliance during the last 2 of 6 weeks of sugar beet ber supplementation.

Three studies (Israelsson et al, 1988; Travis et al., 1990; Tredger et al., 1991) reportedan increase in energy and mean daily fat intakes during the period of sugar beet ber supplemen-tation. In these studies, ber was incorporated into bread, and it was suspected that the increaseresulted from an increased use of high-fat spread. However, no changes in subject body weightwere noticed.

3. Sugar Beet Fiber and Colon CancerHigh concentrations of bile acids in the colon, particularly secondary bile acids, are generallyassociated with an increased risk of colon cancer. Gallaher et al. (1992) evaluated the effect offeeding high-ber diets on bile acid excretion in rats. They showed that sugar beet ber slightlyincreased the total bile acid daily excretion, but the fecal bile acid concentration was muchlower than with the ber-free basal diet. This concentration was even lower than with oat orrye bran diets. When compared to other sources of ber, sugar beet produced the lowest concen-tration of lithocholic acid but the highest lithocholic acid:deoxycholic acid ratio. Which of theseparameters is the most signicant is still not clear. In vitro studies (Wilpart and Roberfroid,1986) suggested that lithocholic acid is a potent promoter of mutagenesis. However, Owens etal. (1984) postulated that lithocholic acid:deoxycholic acid ratio is an indicator of increasedcolorectal cancer.

Ishizuka and Kasai (1997) found that sugar beetsupplemented diet fed for 4 weeks hada suppressive effect on the formation of aberrant crypt foci induced by 1.2-dimethylhydrazinein the colon rectum of rats. They suggested that butyrate may reduce the number of initiatedcolonocytes by apoptosis, which would result in a decrease of aberrant crypt foci.

4. Toxic EffectsPotential toxic effects of sugar ber supplementation have not been extensively investigated(Gallaher et al., 1992; Dongowski et al., 1998). Dongowski et al. (1998) showed in rats thatenrichment of the diet with sugar beet ber preparation up to a level 10% for 4 weeks did notsubstantially inuence urinary, hematological, or serum parameters indicative of a toxic effect.

VI. FOOD APPLICATIONS

Sugar beet ber is claimed to offer nutritional benets to consumers as well as manufacturingand functional advantages to food processors. Moisture retention, good texture, and mouthfeelare the main technical properties of the beet bers, which are proposed with a variety of particlesizes for easy blending with other ingredients. The particle size is important for applicationsbecause the ability to bind water may be affected (Auffret et al., 1994) and because it mayinuence the texture of the product and the mouthfeel properties (Christensen, 1989). Generally,pale bers with pleasant avor are preferred, although some color may be of interest for someapplications, for example, in cooking where some Maillard (browning) reactions occur.

Beet ber also has the advantage of containing no phytic acid, a substance that may befound in cereal ber and can tighly bind minerals, and no gluten, protein from wheat to whichsome people are allergic (Tjebbes, 1988).

Potential applications include cereals, bakery products, pasta, processed meats, soups, andsnacks. Successful recipes have been proposed for pastries, cakes, biscuits, snack foods pasta


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and meat products. It can be used in breads as a natural improver and to maintain freshness.In biscuits, it increases the ber content and in meat products, it may provide chewy and juicycharacter.

A. Ready-to-Eat Breakfast CerealsThe properties of the sugar beet ber make it a good candidate for ber enrichment in high-berready-to-eat cereal applications (Christensen, 1989). It has been incorporated into extruded ready-to-eat cereals at high quantities (up to 40%) without affecting the mouthfeel, avor, or color.This property can probably be ascribed to the high water-binding properties of the beet ber.

Nonmilled version of the bers or aked versions are used in rather high amounts (up to25%) in muesli products.

B. Bakery ProductsFiber-enriched breads have had large commercial success. Beet ber can be successfully incor-porated into a large variety of products; it acts as bulking agent as well as a dietary ber source.The high water uptake of beet ber can enhance the qualities of baked products as a result ofsofter mouthfeel, less staling, and low calorie content (Christensen, 1989; Svensson, 1992). Nogritty mouthfeel is encountered with this type of ber, in contrast to cereal bers. Beet bercan also be used for the production of soft cookies or mufns for which bers with a high waterbinding capacity are required.

Cereal bran is generally used to increase the amount of dietary ber content in breads,but this addition inuences the color, the taste, as well as the texture/consistency of the product.Beet ber may be used as a bread improver and may be added directly to the dough. Thefreshness of the baked products is increased without addition of additivesthe bread is softer.Beet ber may also be used to lower the calorie content of the bread product as its content ofdietary ber and its water uptake are high.

C. Other UsesBeet ber (12%) may be incorporated into meat loaves, pates, meat products, and sausagesto give a juicy character even to frozen products and to improve consistency or texture (Chris-tensen, 1989; Svensson, 1992).

VII. CONCLUSION

Historically, beet ber has been the most extensively studied ber and almost all sugar compa-nies have invested in research and efforts to produce ber with high qualities. Beet ber hasproperties such as a signicant proportion of soluble dietary ber and a high water-bindingcapacity, which make it advantageous for many applications. Furthermore, this ber is extremelywell documented because it has been used as a standard ber in many studies, both nutritionalas well as functional.

Sugar beet ber may fulll a need and is a good complement to other dietary ber sources.It is easy to include as an ingredient in different well-accepted foods at a level ranging generallyfrom 5 to 15% (Harland, 1993). It is therefore easy to plan palatable diets that can give dietaryber intake of about 3540 g/day, which is excellent from a nutritional point of view. However,the presence of ash as well as the odor and taste of the pulp require physical treatments in orderto obtain acceptable ber. The cost of the product is therefore increased, which probably explainsthe relatively small amount of sugar beet ber produced.


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