Current Nutrition & Food Science, 2006, 2, 181-191 181
Fructooligosaccharides of Edible Alliums: Occurrence, Chemistry andHealth Benefits
Noureddine Benkeblial,2,* and Norio Shiomil
'Department of Food and Nutrition Sciences, Graduate School of Dairy Science Research, Rakuno Gakuen University,Ebetsu, Hokkaido 069-8501, Japan, 2Graduate School of Agriculture, Hokkaido University, Kita-v, Nishi-v, Kita-ku,Sapporo, Hokkaido 060-8589, Japan
Abstract: During the past decade, there has been vast expansion in the research of fructooligosaccharides (FOS),including their chemistry, biochemistry, and enzymology in living organisms, as well as nutritional and health benefits.However, in spite of these considerable advances in FOS science, many other aspects of the mechanisms of FOS behindtheir involvement in well being have not been fully understood. FOS constitute the major part of the dry matter of edibleAlliurns, and the knowledge of the mechanisms of their mode of action in human metabolism are of great interest.Important progress has been made in the chemical, nutritional and clinical research areas of A/liurns FOS, as well as onother FOS, and in addition to their role as quality attribute, FOS participate in other processes. This paper aims to reviewthe occurrence, chemistry and health benefits of Alliums' FOS including nutritional contribution ofFOS in health and wellbeing.
Alliums are supposed to be ones of the world's oldestcultivated vegetables and large was reported on them. It ispresumed that our predecessors discovered and consumedwild A/hums long before farming or writing was invented.Because All iu ms are small and leave no archaeologicevidence, the exact origin remains still mysterious. Onionand garlic could probably be the first cultivated crops due totheir growing versatility, long storage time, and portability.They could be dried and preserved for times when food wasscarce. The Chinese have cultivated Alliums in gardens for5000 years, and have been referenced in the ancient Vedicwritings of India. 'Alliums can be traced back as far as 3500B.C. in Egypt, where they served as an object of worship.The onion symbolized eternity to the Egyptians who buriedthe root vegetable alongside Pharaohs. At the present time,the Allium family has over 500 members, each differing intaste, form and col or, but close in biochemical, phyto-chemical. and neutraceutical content. Besides theirremarkable medicinal powers, Alliums are generallyconsumed for their flavors, while their nutritive values havebeen appreciated only recently [1]. Carbohydrates in Alliumsaccount for a major portion of their dry matter, contributingas much as 65 to 80% of the dry weight. The principlecomponents of the non-structural carbohydrates are glucose,fructose, sucrose and a series of fructooligosaccharides(fructosyl polymers) with degrees of polymerization (DP) upto c.a. 12 [2-5].
•Address correspondence to this author at the Department of Food andutrition Sciences, Graduate School of Dairy Science Research, Rakuno
Fructooligosaccharides (FOS), as fructan molecules, havea history of more than 150 years, and some review articleshave reported some historical aspects including little on thegeneral history on fructans research [6-8]. First and prior tothe contemporary science of fructans, ancient peoples usedfructans containing plants as food, feed or medicine. One ofthe most and old vegetable used is onion, which was widelyused by Pharaoh civilization in their rituals. However, themodern history of fructans began with their discovery byRose (1804) and known at the turn of the past centuryconsiderable development with Edelman's proposalconcerning their metabolism in higher plant. More recently,FOS research has known a considerable progress, especiallywith the molecular biology tools, thus the scope of FOSresearch has expended from basic to applied science. Atpresent time, FOS are considered food not food ingredients,and are found in more than 500 food products resulting insignificant daily consumption. Because the science ofnutrition itself has changed, FOS are now considered asfunctional foods which have been introduced as a newconcept [9,10]. In addition, they are nowadays used as feedadditive in poultry in USA and Japan. This passionatehistory of FOS concerning their safety and health benefitscontinues to arise interest of scientists who discover everyday their potentials as food and ingredient.
1.3. Edible Alliums and Diet
Interests in the potential health benefits of edible Alliums,mainly onion and garlic, have origins in antiquity, and areones of the earliest documented examples of plants used forhealth maintenance and treatments of diseases [11-14].Edible Alliums formed an important part of the daily diet ofancient Egypt, and Pharaohs fed working class involved inheavy labor, as in building pyramids [15]. The Jewish slaves
in Egypt were fed Alliurns, apparently to them strength andincrease their productivity. In ancient Greece, edible Alliurnswere associated with strength and work capacity, and garlicformed an important part of the military diet [IS]. By theRomans, Alliurns were considered as an aid to strength andendurance, and, were fed to both soldiers and sailors andwere part of a ship's manifest when it set out to sea [16]. Inancient Chinese civilization, Alliums were evidently andfrequently used in combination therapy as medicinal agent[17], and also formed a part of the daily diet particularlywhen consumed together with raw meat [12].
During the middle age, knowledge of the therapeutic useof plants was gained, and Alliurns were though to havemedicinal properties and were grown inmonasteries [12].With onset of the renaissance, increasing attention was paidin Europe and America to the medical uses of Alliums, suchas other aromatic plants. Thus, onion and garlic were one ofthe major plants and ruling class began to adopt garlic andnot to restrict its consumption to the working class.Moreover, contemporary researches are tending, from onepart to validate many of the earlier views concerning theefficacy of Alliurns, from the other part seek to elucidate themechanisms behind the actions of the major components ofonion and garlic such as FOS.
Inulin type Levan type
Benkeblia and Shiomi
2. CHEMISTRY OF ALLIUMS' FOS
2.1. Definition
The fructooligosaccharides (FOS), also known asfructans, polyfructosylsucroses of varying molecular sizebuilt on a sucrose starter unit, are IF (l-fJ-D-fructo-furano-syl), sucrose oligomers where n may vary. FOS areconsidered as carbohydrates with low degree ofpolymerization (DP) and consequently low molecular weight[18]. They consist of sucrose molecule to which othermolecules of fructose have been added (Fig. 1). The term ofFOS is somewhat ambiguous since the number of fructosemoieties added varies. However, major researchers agree thatFOS have a polymerized chain if n varying from I to c.a. 12units of fructose, while longer chains are considered as inulinpolymers. However, FOS have been variously definedincluding anything from 2 to 20 monosaccharides units.While, according to IUB-IUPAC terminology, the dividingpoint between oligo- and poly-fructooligosaccharides is 10.
2.2. Structure
Because Alliurns' FOS, as well as fructans, are not simplesince their structures are variables, the nomenclatures forFOS proposed by Lewis [19], and, Waterhouse andChatterton [20] are first used in literature. However from the
Mixed type
6-K estose (n = I)
J-Kestose (n =1)
Inulin neoseries
1f, 6G-Di-~-D-fructofuranosylsucrose (n = 1, In = I)
Bifurcose (n = 1, In = I)
Levan neoseries
l6G(6-~-D-fructofuranosylhsucrose (n = 1)
Fig. (1). Molecular structures of the different types on fructooligosaccharides found in higher plants.
Fructooligosaccharides of Edible Alliums
purely chemical point of view, some controversies wereraised in the scientific literature concerning thisnomenclature. Thus, in a recent paper, Yun [18] hassuggested that FOS are a common name for only fructoseoligomers that are mainly composed of I-kestose [GF2 = 1kestotri ose, IF-.B-D-fructofuranosy Isucrose], nystose [GF 3 =I, I kestotetraose, IF ( 1-/3-D-fructofuranosyl)] sucrose], andIF-fructofuranosyl nystose [GF4 = I,I,I-kestopentaose IF (1-/3-D-fructofuranosyl)3 sucrose] (Fig. 2).
Thus, the simple FOS are "inulin-type' which consist of/3(l-2)-linked fructose residues and found in almost allfructan-containing plant. In Liliaceae e.g. onion and garlic, adifferent type of FOS are present and named the inulin neo-series. These type of FOS have two /3(1-2)-linked fructosechains attached to the sucrose starter unit. One chain islinked to the C I of the fructose residue (as is also the case ofinulin-type), and the other to the C6 of the glucose residue(Fig. 2).
Furthermore, the analytical studies carried out on theirstructures were characterized by a relative lack of databecause chemical and/or enzymatic methods were used toassess and to deduce high polymerized FOS on one hand,and techniques used for analyses did not allow the separationor identification of higher polymerized FOS on the otherhand. Recently, new techniques for separating anddetermining the structural composition of the different FOSin onions have been developed. Shiomi [21] and Shiomi etal. [22,23] separated the FOS of onion bulbs using theHPAEC-PAD technique, while Stahl et al. [24] usedsimultaneous MALDI-MS and HPAEC methods andobtained similar results (Table 1).
3. OCCURRENCE AND DISTRIBUTION OF FOS INEDIBLE ALLIUMS
,The occurrence of FOS in some Allium species has been
known since 1894 as reported by Archbold [25], and lateralmost all the investigation carried out focused on onionbulbs, two on garlic while none on leek, shallot, chives orother edible Alli~ms (Table 2). Their content, distributionand structure were first investigated during the 1970s byBacon [26] and Darbyshire and Henry [27,28]. Later, FOScontent and distribution were subject of vast investigation[29-33]. Thus, the advanced analytical techniques led to anideal separation and identification of the different FOS foundin onion bulbs [23]. However, this composition varies,although slightly, according to the type of Allium, cultivar,dry matter content and stage of maturity [34], and also thecontent of the FOS increases from the outer (old) to the inner(young) scales [27]. It has been noted that content of low-DPFOS is correlated to that of dry matter (DM < 10%) [35],while in high dry matter onion bulbs, the maximum degreeof polymerization is between 10 and 15 [5,36].
In garlic, few studies investigated the presence of FOS.Das and Das [37] studied the structure of the fructans ingarlic bulb and suggested that FOS are linear and haveinulin-type structure. Recent results showed that fructans ofgarlic belongs to the inulin neo-series type, and laterBaumgartner et al. [38] isolated a high molecular weighfructans, and studied their structure by enzymatic, chemical
and NMR spectroscopy and confirmed the inulin neo-seriesstructure.
For leek, shallot and other edible Alliums, no data areavailable regarding the structure of their nonstructuralcarbohydrates, and the nature of the potential FOS present intheir tissues are unknown.
4. HEALTH BENEFITS OF FOS
Generally, it is recommended to eat an average of 400 gof fruits and vegetables per day, and scientific advanceslinking diet and health have fostered unprecedented attentionon the role of nutrition in health promotion and diseaseprevention. This is fortunate as considerable evidenceindicates that adequate fruits and vegetables consumptionhas a role in preventing many chronic diseases, includingheart diseases, stroke and several cancers [39-48]. Becauseof the great interest of consumers in diet food; and also FOSare not yet being marketed widely throughout the world asfood ingredients or additive, cultivated crops remain themain source of FOS such as banana, wheat, barley,asparagus and Jerusalem artichoke [49-51]. In A lliumsspecies, onion and garlic are considered as major source ofFOS since FOS constitute 25 to 35% of total non structuralcarbohydrate [35], while leek and shallot are minor source[29,52]. Thus, FOS are presently produced industrially andused as food ingredients, while in Japan they are consideredas food and are found in more than 500 food productsincluding soft drinks, cookies, cereals and candies, resultingin significant daily consumption [50,53].
Surprisingly, Alliums were consumed mainly for theirflavor and used as condiments, while the fructan-containingfoods have been consumed because availability, low cost,and personal preference rather than for any specific effect onnutrition and health. In fact, the use of FOS in the humandiet has increased since the initial commercial production ofa specific oligofructan (Neosugar'") in Japan in 1983. Thebenefits of adding FOS to the human diet has been firstreported by the NSG (Neosugar Study Group) at a series ofconferences held in Japan to highlight research withNeosugar" in 1982, 1983 and 1984. The reports given havelinked biochemical-nutritional-health changes in humanresulting from eating Neosugar", and these results wereconfirmed later by Buddington et al. [54]. Although thishistory started with Neosugar", it has become evident thatmany of the conclusions could be extended to other FOS[55].
FOS have numerous physiological actions [56] (Fig. 3),and Tomomatsu [53] enumerated health benefits attributed tooligosaccharides:
• Encourage proliferation of bifidobacteria and reducedetrimental bacteria
• Reduce toxic metabolites and detrimental enzymes
• Prevent pathogenic and autogenous diarrhea
• Prevent constipation
• Protect liver function
• Reduce serum cholesterol
• Reduce blood pressure
184 Current Nutrition & Food Science, 2006, VoL2, No. 2
l-kestose
nystose
Sa
HOH2~OJ-;:20\
\JH20H YHOH2C0 0
OH20H
neokestose
Benkeblia and Shiomi
4b4c
Sb,1. _, ., '
t1F(I-~-F-f)m sucrose
t1F(l-~-F-f)m-6G-
t6G(1-~-F-f)n sucrose
~-f-f-sucrose
Sd
t1F(l-~-F-f)m-6G( 1-
~-f-f)n sucrose
Fig. (2). Molecular structures of the different fructooligosaccharides found in onion and other edible Alliums [1,23,38].
Fructooligosaccharides of Edible Alliums
Table 1. The Structural Composition of the Different Fructooligosaccharides of Onion Bulb Separated by HP AEC
6d, I F-f}-D-fructofuranosyl- 6° (I-/3-D-fructofuranosyl)J sucrose
6d, IF (l-/3-D-fructofuranosyl),- 6° (1-/3-D-fructofuranosyl)l sucrose
7a IF (1-/3-D-fructofuranosyl),sucrose
7 1F(1-/3-D-fructofuranosyl)m- 6° (1-/3-D-fructofuranosyl)n sucrose (m + n = 5)
8 IF (1-/3-D-fructofuranosyl)m- 6° (1-/3-D-fructofuranosyl)n sucrose (m + n = 6)
9x 1F(1-/3-D-fructofuranosyl)m- 6° (1-/3-D-fructofuranosyl)n sucrose (m + n 2: 7)
Table 2. The Distribution of Fructooiigosaccharides inEdible Alliums
FOS (mg g" FW) DP' Source
Bunching onion - - -
Chinese chive <0.1 - [29]
Garlic 3.9' 3-5 [29]
Garlic, powder 1.7' 3-5 [29]
Leek 0.9' 2-4 [29]
Onion, welsh 1.1' 3-5 [29]
Onion, white 3.1' 3-5 [29]
Onion, yellow 26.3b 3 - 12 [31,32]
Onion, red 27.lb 3 - 12 [2]
Onion, powder 47.7' 3-5 [29]
Shallot 8.5' - [29]
• Degree of polymerization.• values are total of DP 3 to 5.• values are total of DP 3 to up to 12.'values are total ofDP 3 to 5 estimated on dry weight basis.
• Have an anticancer effect
• Produce nutrients
Thus, these physiological effects are the basis forassociating FOS intake with reduced diseases andprevention. However, only some predominant effects will bedeveloped in the paragraphs below.
4.1. Prebiotic Effects
The large bowel is by far the most colonized region ofthe gastrointestinal tract, with c.a. 1012 bacteria per gram ofgut content. Through the fermentation process, colonicbacteria, most of which are 'anaerobes, produce a widevariety of compounds that may affect gut as well as systemicphysiology. Thus, fermentation of carbohydrates reachingthe large bowel produces short-chain carboxylic acids mainlyacetate, propionate and butyrate and lactate which allow thehost to salvage part of the energy of nondigestibleoligosaccharides and that may play a role in regulating bothcell division and cellular metabolism. In addition to theirselective effects on bifidobacteria and lactobacilli, FOSinfluence many aspects of bowel function throughfermentation, and are mildly laxative [57]. Indeed, FOSconstitute a carbon source for microbial flora of bowel andthe ability of bifidobacteria to utilize FOS was welldemonstrated [58-63]. These works reported also that themajority of Bifidobacterium strains fermented all FOS andeven low polymerized inulin. Biedrzycka and Bielecka [62]claimed that the results of in vitro studies indicate thespecificity of Bifidobacter-ium except B. bifidum to utilizeshort-chain FOS and oligofructose, but not HP-inulin.However, according to Van Laere et al. [64], the mainfactors affecting the susceptibility of FOS to fermentationare: chemical structure, degree of polymerization, andpossible linear or branched structure, as well as solubility inwater. Generally, FOS with short chain length, unbranchednature and high solubility in water are well and preferentiallyfermented. Nevertheless, discrepancies in the capability ofdifferent Bifidobacterium species'to metabolize FOS may bedue to the differences in the expression of fructan-
Fig. (3). Potential physiological effects of FOS (left column) and possibly related health benefits (right column). (SCFA, short-chain fattyacids) [56].
hydrolyzing enzymes, since these later have not beenextensively investigated.
4.2. FOS and Mineral Absorption
Contrary to the fact that nondigestible carbohydrateshave been accused of causing an impairment in the smallintestine absorption of minerals [65], van den Heuvel et al.[66] and van den Heuvel et al. [67] demonstrated that theamount of Ca, Mg and Fe ions recovered in the ileostomateover a period of 3 days is significantly modified aftersupplementing the diet with IS g per day of these fructans.Later, a vast number of studies were carried out on theeffects of FOS and, mineral absorption and reviewedby Scholz-Ahrens et al. [68] and Scholz-Ahrens andSchrezenmeir [69], and the scientific evidence claiming thatFOS enhance mineral absorption is based on both animal[70-73] and human experiments [74-76]. Coudray et al. [72]studied the effects of different chain length and type ofbranching on intestinal absorption and balance of calciumarid magnesium in rats and their results showed that all testedfructans seem to have similar activity by increasingabsorption and/or balance of Ca and Mg. However, thecombination of oligofructose and HP-inulin showedsynergetic effects on intestinal calcium absorption andbalance. In humans, van Heuvel et al. [67] reported that 15 gof oligofructose per day stimulates fractional calciumabsorption in male adolescents. Tahiri et al. [76] noted thatshort-chain FOS may influence positively calciumabsorption in the late postmenopausal phase in women.Moreover, Griffin et al. [75] noted also that calcium
absorption is increased by combination of oligofructose +inulin in girl at or near menarche.
In fact, the hypotheses most frequently proposed toexplain the enhancing effect of FOS on mineral absorptionare the osmotic effect, acidification of the colonic contentdue to fermentation and production of short-chain carboxylicacids formation of calcium and magnesium salts of theseacids' and hypertrophy of the colon wall [74,77]. However,according to Ohta et al. [70], different mechanisms may beinvolved in the increased absorption of calcium andmagnesium, the former being absorbed mostly in the cecumand the later mostly in the colon.
4.3. FOS and Lipid Metabolism
Many attempts have been made in control oftriacylglycerol concentrations through the modification ofdietary habits [78,79]. The hypotriglyceridemic effect ofFOS, as well as other nondigestible carbohydrates, has beendescribed both in humans [80-83] and animals [84-87]. Infact almost all studies were carried out on inulin or HP-inulin, and none concerned short-chain FOS and lipidmetabolism in healthy men. On the other hand, the dailyaddition of 109 inulin to the diet significantly resulted inlower plasma triacylglycerol (TAG) levels, supporting thatfructans influence the formation and/or degradation of TAG-rich lipoprotein [83]. Letexier et al. [83] also reported thataddition of HP-inulin has a beneficial effect on plasma lipidsby decreasing hepatic lipogenesis and plasma TAGconcentrations. Indeed, this effect is likely to result from a
Fructooligosacchurides of Edible Alliums
decrease in the hepatic synthesis of TAG rather than fromhigh catabolism of TAG-rich lipoproteins.
Unfortunately, the mechanisms behind the serum-lipidlowering effects of FOS remain still unclear and have to beelucidated [88] (Fig. 4). In fact, liver plays a key role intriacylglycerol-rich lipoprotein homeostatis and becausenewly synthesized fatty acids are preferentially channeledinto VLOL, the lipogenic activity of the liver is a key factorfor the hepatic triacylglycerol- VLDL output [89]. Fatty acidsynthase (FAS), among the key enzymes that controllipogenesis, is the most sensitive to nutrients and hormones[90]. Thus, it is supposed that decreased lipogenesis in liveris a key event in the reduction of VLDL-triglyceridesecretion in fructan-fed rats, and the activities of manyenzymes e.g. acetyl CoA carbyxylase, FAS, malic enzyme,ATP citrate lyase and G-6-P I-deshydrogenase, aredecreased by 50% [78].
4.4. FOS and Short-Chain Carboxylic Acids Production
The colonic fermentation of FOS produces short-chaincarboxylic acids, lactate and gases. However, only part ofthese carbohydrates energy is salvaged, and consequently,they are classified as low energy food ingredients [91,92].Indeed, the available energy content of FOS is only 40 to50% that of digestible carbohydrates, giving them a caloricvalue of 1.5 to 2 kcal/g [91]. Castiglia-Delavaud et al. [93]studied the net energy of soluble and insoluble polysac-charides and found that sugarbeet fibers and inulin digestibleenergy values averaged 2.65 and 3.22 kcal/g respectively,while metabolizable energy values averaged 2.55 and 3.10kcal/g, respectively.
Concerning the pattern of production of short-chaincarboxylic acids, unless very sophisticated studies areperformed in humans to measure them in situ and/or in portal
Pancreas
TG
11or Fatty acid
Bile
~(m11I Glucose I
~ GLP-l
~ Acetate
NDC
c::o<3u
Glucose
Adiposetissue
c::o.~c§}~
Acetate
Propionate
Butyrate
faecesFig. (4). Putative mechanisms involved in the modulation of lipid metabolism by dietary fructooligosaccharides in rats, including effects ongastric emptying and glucose absorption, production of short-chain carboxylic acids (acetate, butyrate, propionate), secretion of incretins, andsubsequent actions on liver, adipose tissue, and pancreatic insulin output [88].
blood remains still unclear and almost unknown. Becausewhat is excreted in the feces does not represent the in situsituation since more than 90% of the acids produced in thecolon are probably absorbed in the ascending part of thecolon, and data reported in human could be not relevant [94].Thus, experiments carried out on animal showed thatsupplementing diet with FaS decreases the cecal pH,increases the size of the cecal pool of short-chain carboxylicacids, with acetate being primary acid, and butyrate andpropionate as secondary acids [95,96]. The increase in thepool of short-chain carboxylic acids could probably due tothe effects of Fas on intestinal tissue [96], on eithermicrobial [54] or intestinal [97] enzymes, or effects on. theconcentrations of metabolites [98]. Furthermore, possiblyrelated to this increase in the effect in the pool of short chaincarboxylic acids is the effect of some nondig.estibleoligosaccharides on the intestinal tissue leadmg tohyperplasia of the mucosa and increased wall thickness bothin the small intestine and the cecum [96]. Moreover, becauseof the stimulation of bacterial growth leading to an increasein bacterial biomass, oligofructose have been shown toincrease fresh fecal mass either in rats or in humans.
4.5. Effects of FOS on Glycemia and Insulinemia
The effects of FaS on glycemia and insulinemia are notyet fully understood, and the nondigestible oligosaccharidesfor which published data are available on the effect related toglucose are inulin-type fructans [99,100]. Besid.e th~tavailable data on the effects of FaS on glucose and insulinconcentrations are sometimes contradictory; these effectsalso may depend on physiological (fasting compared topostprandial or disease (diabetes) conditions [78,94,10 I].Moreover, other nondigestible carbohydrates are known tomodify the kinetics of absorption of carbohydrates, thusdecreasing the incidence of glycemia and insulinemia [102].The effects of inulin type fructans on glycemia andinsulinemia are not fully understood, and available data aresometimes contradictory, indicating that these effects maydepend on physiological or disease conditions. Luo et =[103] reported that chronic ingestion of short~chaInfructooligosaccharides (20 g per day for 4 weeks) did notmodify fasting plasma glucose and insulin in healthyhumans even if it lowers basal hepatic glucose production.However, in diabetic 'subjects taking 8 g per day of short-chain fructooligosaccharides for 14 days leads to a decreasein fasting blood glucose [99].
4.6. FOS and Nitrogen/Urea Disposal
Almost all studies carried out on the effects ofnondigestible carbohydrates were performed on animals, andresults showed that FOS decrease uremia [104], enhancefecal nitrogen excretion and reduce renal excretion ofnitrogen, and feeding rats a diet supplemented witholigofructose (10%) for a few weeks decreased uremia [104].Dietary short-chain fructooligosaccharides effectivelyenhanced fecal nitrogen excretion and reduced renalexcretion of nitrogen in rats [105]. This occurs because thesefermentable carbohydrates serve as energy source for theintestinal bacteria, which during growth, also require asource of nitrogen for their protein synthesis. In addition,their osmotic. effect in the small intestine accelerates thetransfer of urea into distal ileum and the large intestine
Benkeblia and Shiomi
where highly ureolytic microfiora may proliferate [105].Propionate, an important end product of the bacterialfermentations of inulin-type FaS, also inhibits ureagenesisin the liver in the presence of ammonia and amino acids[106].
However, in humans consumption of nondigestiblecarbohydrates also results in a higher fecal excretion ofnitrogen [107], and limits the formation of ammonia andother end products of catabolized proteins which could berisk factor of colonic carcinogenesis in the distal part of thelarge bowel [108].
4.7. FOS and Cancer
The effect of nutrition on tumor incidence and growth isa subject of priority interest [109, II 0], and amongst the ~ostfrequently investigated dietary compounds, the nondigestiblecarbohydrates play a major role in nutritional prevention[110, Ill]. FaS were used in various experimental modelsto study their cancer risk reducing capacity. Initial researchesdemonstrated that Fas have anticarcinogenic and tumorgrowth inhibitory effects [112,113]. However, the mostsurprisingly activity of FaS is the capacity to significantlyreduce the number of metastases [114]. Moreover, FOS alsohave potentiation of cancer chemotherapy and have be~nshown to potentiate the therapeutic effects of all SIX
investigated cytotoxic drugs representatives of the differentgroups of cytotoxic drugs classically used in human cancertreatment [lIS]. From the review of the availableexperimental data, it is concluded that fat ha~, m?stprobably, no modulating effect but that unbalanced diets richin lipids could act as a positive modulator of chemicallyinduced carcinogenesis by virtue of their capacity to cause abreak in metabolic and proliferative homeostatis. Thus,vegetable carbohydrates and fibers as well as restriction incaloric intake could act as negative modulators of the sameprocess because they could restore this homeostatis '. It is thussupposed that to maintain dietary balance either .byincreasing nondigestible carbohydrates and/or reducingcalorie 'intake is the most effective way to negativelymodulate chemically induced carcinogenesis in animals[110]. Beside these encouraging resul ts regardi ngfructooligosaccharides and inulin in experimental animals,however, to make the same recommendations to humanscould most probably help preventing some major cancers.
4.8. Other Insights of FOS and Health
Beside the numerous health benefits describedpreviously, other roles of Fas have been a topic of muchresearch recently and investigation reported other benefitsand interesting actions of FaS. Due to their positive actionon mineral absorption, FaS have been proposed to enhancebone health in animals. This concept is provocative andsome recent finding in animals should be extended to man[116]. Recent data also provide first evidenc~ that. FaSmodulate function of the immune system especially In thearea of the gut-associated lymphoid tissue (GALT) [117].
However, more recently some controversies werereported on FOS and their roles in intestinal disorders. It wasreported that FaS dose-dependently impairs the resistance toSalmonella in rats [118]. Later, similar results were reportedand it has been shown that FaS inhibit intestinal
Fructooligosaccharides of Edible Alliums
colonization but stimulate translocation of Salmonella [119],and increase the intestinal permeability [120,121]. However,results showed that impairment was partially prevented bycalcium phosphate [121]. Nevertheless, these investigationswere carried out on animal models and they require furtherstudies to be extrapolated to humans.
CONCLUSIONS
In conclusion, and after reviewing their occurrence,chemistry and health benefits, it is presently admitted thatAlliums' FOS, as well as other vegetables' FOS, fit wellwithin the current concept of the class of dietary material andcould be labeled as "functional foods' since their vast healthbenefits are continuously appreciated. Likely due to theirspecific properties, FOS affect several functions andcontribute to reduce the risk of many diseases. Thus, theymay contribute in a significant way to a well being by theirspecific effects on several physiological functions. However,and bearing in mind their superior functional properties, suchas the bioavailability of minerals, prebiotic effects andmodulation of colonic microflora, improvement of thegastrointestinal physiology, the metabolism of lipids, orprevention of some cancers, further basic researches on theirreal utilization in the human feeding are needed. Havingmore and more improved technical tools, such as genetic andmolecular biology, the methodology can be reversed,showing the consequences under the administration ofFOS.
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Received: May 28, 2005 Accepted: lune 23, 2005Revised: June 17, 2005
