Food Hydrocolloids

-Vof. 11 no. 4 pp. 401--408, 1997

Physicochemical characterization of mung bean starch

R.Hoover1, Y.X.Li, G.Hynes and N.Senanayake

Department of Biochemistry, Memorial University of Newfoundland, St John's, Newfoundland AlB 3X9, Canada

ITo whom correspondence should be addressed

AbstractStarch from mung bean (Vigna radiata) was isolated and some of the important characteristicsdetermined. The yield of starch was 31.1% on a whole-seed basis. The shape of the starch granule wasoval to round to bean shaped, with granules 7-26 f.!m in diameter. Scanning electron micrographsrevealed the presence of smooth surfaces. The gelatinization temperature range was58-67-82°C and theenthalpy of gelatinization was 18.5 JIg. The total amylose content was 45.3%, of which 12.1% wascomplexed by native lipids. The X-ray diffraction pattern was of the'C' type and the X-ray intensitieswere much stronger than in other legume starches. The starch exhibited a high swelling factor (43.6 at95°C) in water. The viscoamylographic examination of the starch paste (6% wlv) showed the absence ofa peak viscosity, a low 95°C viscosity [200 Brabender units (BU) J, an increase in consistency (140 BU)during the holding cycle at 95°C and a set-back of220 BU Native granules were readily hydrolyzed byporcine pancreatic a-amylase (76.4% in 72 h). Retrogradation of mung bean starch (as measured bychanges in syneresis, gel strength, enthalpy and X-ray diffraction intensities) appeared to be more severethan in other legume starches.

Introduction

Legumes are dicotyledonous seeds of plants that belong tothe family Leguminosae [16 000-19 000 species in -750genera (1)]. The grain legumes collectively (includingsoybean and groundnut) are ranked fifth in terms of annualworld grain production (171 million metric tons), afterwheat, rice, corn and barley (2). Legumes are grown inPakistan, India, Sri Lanka, Bangladesh, Mexico, Canada,South America and Africa. The production of legumes inCanada amounted to 1.3 million metric tons in 1993. Themajor legumes produced in Canada are lentils, peas andfababeans. Starch is the most abundant carbohydrate in theseed (22--45%). Legume starches have occupied an importantplace in noodle preparation in several countries, and mungbean (Vigna radiata) has been reported as being the best rawmaterial for starch noodle preparation (3,4). Zhu et al. (5)reported that noodles manufactured from mung beans arewhite and smooth, pliable, and have good cooking quality.Lii and Chang (6) described an ideal starch for noodlemanufacture as having high amylose content, restrictedswelling and a C-type Brabender viscosity curve. Mestres etal. (7) described the structure of mung bean starch noodlesas a ramified three-dimensional network held together byshort segments of strongly retrograded amylose. These

© Oxford University Press

strongly retrograded zones melt at temperatures above theboiling point of water. Xu and Seib (8) showed that incooked mung bean starch noodles, micelles of retrogradedamylose form a structural network that resists disintegrationduring cooking. The above reports suggest that the quality ofmung bean starch noodles is influenced by the extent ofretrogradation. Therefore, it is rather surprising that there isno information in the literature on the retrogradationcharacteristics of mung bean starch. Furthermore, detailedinformation on proximate composition, X-ray diffractionintensities, granular susceptibility towards acid and enzymehydrolysis and amylose leaching is also lacking. Thus, as partof our studies on improving the functionality of legumestarches, it was considered worthwhile to investigate thephysicochemical characteristics of mung bean starch.

Materials and methods

Materials

Mung beans (Vradiata) were obtained from the Departmentof Crop Science, University of Saskatchewan. Crystallineporcine pancreatic a-amylase (EC 3211) type lA was

402 R Hoover et al.

obtained from Sigma Chemical Co. (St Louis, MO). Otherchemicals and solvents were analytical grade. Solvents weredistilled from glass before use.

Starch isolation

Mung bean seeds were divided into two lots representingwhole samples. Each lot was further subdivided into twoparts and starch was extracted from them using theprocedure outlined in an earlier publication (9).

Chemical composition of starch

Quantitative estimations of moisture, ash and nitrogen wereperformed by the standard American Association of CerealChemists (AACC) procedures (10). Starch lipids weredetermined by procedures outlined in an earlier publication(11). Apparent and total amylose content were determinedby the method of Chrastil (12).

Swelling factor

The swelling factor of the starches when heated from 50 to95°C in excesswater was measured according to the methodof Tester and Morrison (13). This method measures onlyintragranular water and, hence, the true swelling factor at agiven temperature. The swelling factor is reported as a ratioof the volume of swollen starch granules to the volume of thedry starch. Results used for calculation were means of fourmeasurements.

Extent of amylose leaching

Various concentrations of the starches (15-20 mg) in waterwere heated in volume-calibrated sealed tubes (50-95°C) for30 min. The tubes were then cooled to ambient temperatureand centrifuged at 2000 g for 10 min. The supernatant liquid(1 ml) was withdrawn and its amylose content wasdetermined by the method of Chrastil (12). Results used forcalculation were means of four measurements.

X-ray diffraction

X-ray diffractograms were obtained with a Rigaku RU 200RX-ray diffractometer with a chart speed of 20 mm/min. Theoperation conditions were as described elsewhere (14).

Pasting behavior

A Brabender viscoamylograph (Model VA-V) equipped witha 700 em cartridge was used to study pasting properties at aconcentration of 6% (w/v). Four replicates were used for thisdetermination.

Differential scanning calorimetry

Gelatinization temperatures were measured and recorded ona Perkin-Elmer DSC-2 (Norwalk, CT) differential scanningcalorimeter (DSC) equipped with a thermal analysis data

station as reported previously (14). All DSC experimentswere replicated four times.

Enzymatic digestibility

Enzymatic digestibility studies on mung bean starch werecarried out using a crystalline suspension of porcinepancreatic a-amylase in 0.5 mol/dm! saturated sod iumchloride (in which the concentration of a-amylase was 23.9mglml and the sp. act. was 1240 U/mg protein). The detailsof the procedure have been outlined in an earlier publication(15). The above experiment was replicated four times.

Scanning electron microscopy

Granule morphology and the mode of action of a-amylasewere studied by scanning electron microscopy (SEM).Specimen preparation and SEM were carried out byprocedures outlined in an earlier publication (9).

Gel preparation

Gels (40% w/v) were prepared as described by Kriisi andNeukom (16). Mung bean starch (4 g dry basis) was carefullyweighed into circular aluminum molds (diameter 3.0 em,height 3.0 em) with removable tops and bases, and thenmixed with 10 ml of distilled water containing 0.02%Na2S20s as preservative. The molds were then heated in awater bath at 95°C for 30 min. The resulting gels wereallowed to cool within the molds for 30 min at 4°C prior tostorage at 25°C for periods ranging from 1 to 15 days.

Gel powder preparation

The extent of retrogradation of stored mung bean starch gels(at 25°C) was followed by X-ray diffraction and DSC. Theprocedure (with minor modifications) of Roulet et al. (17)was used to convert the stored gels to a powder prior toexamination by DSC and X-ray diffraction. The gels wererinsed with water, cut into small pieces and mixed with 100ml of acetone. After homogenization using a polytron, themixture was left to decant for 5 min. The liquid wasdiscarded and the rest was transferred to screw-cap tubes.Acetone was again added , the mix centrifuged (3000 g) andthe supernatant discarded. This procedure was repeatedthree times and the remaining mass was dried in an air ovenfor 6 h at 30°C.

Freeze-thaw stability

The gels (6% db) were subjected to cold storage at 4°C for16 h (to increase nucleation) and then frozen at - 16°C for24 h, thawed at 25°C for 6 h and then refrozen at -16°C.To measure freeze-thaw stability, the gels frozen at -16°C for24 h were thawed at 25°C for 6 h and then refrozen at -16°C.Five cycles of freeze-thaw were performed. The excludedwater was determined by centrifuging the tubes (30 mm

Physicochemical characterization ofmung bean starch 403

Figure 1 Scanning electron micrographs of native mung bean starch granules (A) and a-amylase-hydrolyzed (24 h) mung bean starchgranules (B, C and D).

diameter x 100 mm) at 1000 g for 20 min after thawing.Values are the means of four replicates.

Gel strength

The resistance to penetration of the gel during storage (1-12days) at 25°C was determined with a Model 6000 R Lloydtexture testing machine (Omnitronix Instruments Ltd,Mississauga, Ontario, Canada) equipped with a dataacquisition and processing station. The SON load cell was

used. The gels within the aluminum molds were placed on thecompression table. The cross-head of the machine, fittedwith the load cell and a cylindrical probe (5 mm diameter),was driven down so as to just touch the gel surface. Theprobe was then driven at a constant speed (0.5 mm/min)into the gel for a distance of 6 mm. The load at 1 mmcompression was termed firmness. The resultant readingswere in units of load grams. The results are the means of fourreplicates.

404 R.Hooveret al.

Results and discussion Table 1 Chemical composition (%) and some of the properties ofmung bean starch"

packed and/or are better orientated (to diffract X-rays) thanthose of other legume starches.

aAlI data reported on a dry basis and represent the mean of fourdeterminations.bLipids obtained by acid hydrolysis (24% MCL) of the native starch(total lipids).CLipids extracted by 2:1 chloroform-methanol at 25°C (mainlyunbound lipids).dLipids extracted by hot I-propanol-water (3:1 v/v) from theresidue left after chloroform-methanol extraction (mainly boundlipids).eApparent and total amylose determined by 12 binding before andafter removal of bound lipids by hot l-propanol-water extraction.f«Total amylose - apparent amylose)lTotal amylose) x 100.gWater:starch ratio, 3:I.hStandard deviation, 0.1 (n =4).

0.04 ±0.020.27 ±0.02

31.10 ±2.5010.03 ± 0.080.11 ± 0.020.05 ± 0.01

Composition (%)h

39.8 ± 0.545.3 ± 0.412.158-69-8218.5 ± 0.2

Characteristics

Yield (% initial material)MoistureAshNitrogenLipid

Acid hydrolyzed"Solvent extracted

Chloroform-methanol?l-Propanol-water'l

Amylose content" (% of total starch)ApparentTotal

Amylose complexed by native lipidfGelatinization temperature range (0C)

Enthalpy of gelatinization (JIg)

Starch granule characteristicsGranule shape oval to round to bean shapedGranular size (urn) 7.1-26.1

Swelling factor and amylose leaching

The swelling factor (SF) and amylose leaching (AML) wereinvestigated over the temperature range (60-95°C). Theresults are presented in Table 3. The SF and AML werehigher than those reported for other legume starches(15,19,20). The SF and AML increased dramatically between70 and 80°C and 60-70°C respectively (Table 3). Similarrapid increases have also been reported to occur withintemperature ranges of 60-90°C in other legume starches(15,19,20,26-29). The high SF of mung bean starch suggeststhat amylopectin chains within crystalline regions are morestrongly associated in mung bean than in other legumestarches. Oates (30) also postulated that amylopectin ofmung bean starch is tightly compacted within the granule.The differences in AML are probably due to the higheramylose content (Table 1) and/or to a weaker associationbetween amylose chains within native mung bean starchgranules.

Morphological granular characteristics of mung bean

Microscopic examination showed that most mung beanstarch granules had irregular shapes, which varied from ovalto round to bean shaped. A large variability existed in thestarch granule size (7.1-26.0 urn). The sizes of mung beanstarch granules were smaller than those reported (12--48/lm)for other legume starches (18). The surfaces appeared to besmooth and showed no evidence of fissures when viewedunder the SEM (Fig. 1).

Chemical composition of the starch

The data on composition and yield are presented in Table 1.The yield of mung bean starch was 31.1% on a total seedbasis. This was within the range reported for most legumestarches (18). The nitrogen content was 0.05%. This lowvalue indicated the absence of non-starch lipids (lipidsassociated with endosperm proteins). Therefore, total lipids(0.32%) (obtained by acid hydrolysis) mainly represent thefree and bound starch lipids. The total lipid content (Table 1)was beyond the range reported for most legume starches (18),but was within the range reported by Hoover and Manuel(19) for lentil starches (0.27-0.38%). The amounts of freelipids (obtained by extraction with chloroform-methanol)and bound lipids (obtained by extraction of chloroform­methanol residues withJ-propanol-water) in mung beanstarch were 0.04 and 0.27%, respectively (Table 1). Thebound lipid content of mung bean starch was beyond therange reported for pigeon pea (0.10%) (20), lima bean(0.22%) (21) and CC gold lentil (0.13%) (19) starches, butwas close to that reported (19) for laird lentil (0.35%). Thetotal amylose content of mung bean starch was 45.3%)(Table I). This value was much higher than that reported byBiliaderis et al. (22) (34.9%), Naivikul and D'Appolonia (23)(19.5%), Reddy et al. (24) (13.8-35.0%) and Galvez andResurreccion (25) (26-29.0%) for mung bean starch.However, it was comparable to the value reported by Singh etal. (4) (47.0%). The apparent amylose content was 39.8%(Table I). Further studies are needed to assess the variabilityin amylose content. A comparison of the apparent and totalamylose content (Table 1) showed that 12.1% of the totalamylose was complexed by native starch lipids in mung bean.This was higher than those reported for pigeon pea (20)(2.7%) and CC gold lentil (19) (5.6%) starches, but wascomparable to that reported (19) for laird lentil (12.4%).

X-ray diffraction

Mung bean starch showed the characteristic 'C' type X-raydiffraction pattern (Fig. 2) (18,19). The X-ray pattern wascharacterized by five strong intensity lines centered at 5.84,5.19,5.12,4.89 and 3.81 A (Table 2). The intensities of thesepeaks were much higher than those reported (9,19) forlegume starches. This indicated that crystallites withingranules of mung bean starch are probably more compactly

Physicochemical characterization of mung bean starch 405

Table 2 X-ray diffraction intensities of the major peaks of nativemungbean starch"

Interplanar spacings (d) in A with intensities (c.p.s.j''

5.84(852) 5.19(1348) 5.12(1498) 4.89 (134) 3.81 (1227)

aMoisture content 10.03%.bCounts per second.

Table 3 Effect of temperature on swelling factorandamyloseleaching (%) of native mung bean starch

9590807060

Parameters Temperature COC)

Swelling 3.ge ± 0.2 16.7d ± 0.5 31.9c ± 1.5 37.8b ± 1.843.6a± 0.6factorAmylose 3.6e ± 0.1 26.7d ± 0.6 32.3c ± 1.4 35.1 b ± 0.7 39.0a± 0.5leaching(%)

lDl

10 15 aJ2-Thetll

s II

The data represent the mean of four determinations ± SD. Meansin each row with different superscripts are significantly different(P < 0.01).

Figure2 X-ray diffraction pattern of nativemung bean starch.

Pasting characteristics

The pasting characteristics of mung bean starch at aconcentration of 6% (w/v) and pH 5.5 were investigated withthe Brabender viscoamylograph and the results are presentedin Table 4. At this pH and concentration, most legumestarches exhibit pasting temperatures in the region 65-87°C,95°C viscosities >80 Brabender units (BU), a gradualincrease in viscosity (40-140 BU) during the holding periodat 95°C and a set-back in the range 100-200 BU (19,21,26).The pasting curve (type C) differed from those of otherlegume starches only with respect to the low viscosityincrease (20 BU) during the holding period at 95°C.

Differential scanning calorimetry

The gelatinization transition temperatures [at a volumefraction of water (u\) = 0.85] of mung bean starch were58-67-82°C (Table 1), corresponding to the onset (To),midpoint (Tp) and end of gelatinization (Tc)' The enthalpyof gelatinization (t:.H) at u I = 0.85 was 18.5 JIg (4.4 callg).These values were within the range reported by Califano andAnon (29) . The gelatinization temperature range (T; - To)(14°C) and the t:.H (4.4 callg) were much higher than thosereported (18) for black bean (8°C , 3.2 callg), kidney bean(15°C), pinto bean (8°C, 4.0 cal/g), adzuki bean (8°C),smooth pea (15°C, 3.5 callg) and lentil (14°C, 3.2 callg)starches (no reports are available on the DSC data of otherlegume starches). Slade and Levine (31) have ascribed thegelatinization endotherm to the melting of microcrystallites

Table 4 Pasting characteristicsof native mung bean starch"

Pasting Viscosity at Viscosity Viscosity at Set-back?temperature 95°C(BU)b after30 min 50°C(BU) (BU)(0C) at 95°C(BU)

80 ± 1.0 200± 10 220± 10 360 ± IO 140

aMeans of four determinations; 6% w/v, starch concentration, pH5.5.bBrabender units.cViscosity at 50°C- viscosity (after 30 min) at 95°C.

(hydrated clusters of amylopectin branches) in the presenceof plasticizing water, in which crystallite melting is indirectlycontrolled by the kinetically constrained continuousamorphous region. The t:.H primarily represents the loss ofdouble-helical order (32). The high T; - To of mung beanstarch suggests the presence of crystallites of varyingstability within the crystalline domains of the granule. Thehigh 6.H suggests that the double helices (formed by the outerbranches of adjacent amylopectin chains) that unravel andmelt during gelatinization are strongly associated within thenative granule.

In vitro digestibility by porcine pancreatic a-amylase

The extent of hydrolysis of native mung bean starch ispresented in Table 5. From the results, it is apparent thatmung bean starch is a better substrate for a-amylase thanmost other legume starches. For instance, lima bean (21),pigeon pea (20), laird lentil (19), CC gold lentil (19), kidneybean (9), navy bean (9), northern bean (9), pinto bean (9) andblack bean (9) are hydrolyzed (in 6 h) by porcine pancreatica-amylase (at the same enzyme concentration used in this

406 RHoover et al.

Table 5 Timecourse of hydrolysis of nativemung bean starch byporcinepancreatica-amylase

Table 6 Freeze-thaw stabilityof nativemung bean starch gelsstored at -16°C

Time (h) Hydrolysis (%) Number of freeze-thaw cycles Syneresis1 (%)

The data represent the mean of four .determin.ati~ns ± SD..Meansin the column with different superscnpts are significantly different(P < 0.01).

Retrogradation of mung bean starch gels

The extent of retrogradation during gel storage wasmonitored by determining changes in freeze-thaw stability,X-ray intensities, enthalpy of melting of recrystallizedamylopectin and gel strength.

Amylolytic susceptibility of native mung bean starch granulesas viewedby scanning electron microscopy

The mode of attack by a-amylase on native granules (after24 h) was investigated using SEM. The results are presentedin Figure 1. It can be seen from Figure IB-D that a-amylaseinitially makes a depression on the peripheral region of thegranule and these penetrate deep into the granule interiorduring subsequent attack. The outer surface of the granulewas spongy (Fig. 1C,D) as a result of surface erosion over thewhole surface.

study) to the extent of 2.0, 0.5, 7.0, 13, 23, 31.4, 32, 29 and34.8%, respectively, whereas the corresponding value formung bean starch is 38.0% (Table 5).

Differences in the in vitro digestibility of native starchesamong and within species have been attributed to theinterplay of many factors such as starch source (33), granulesize (33,34), amylose/amylopectin ratio (9,35), extent ofmolecular association between starch components (9,35,36),degree of crystallinity (9,33) and amylose-lipid complexes(19,37). Furthermore, it has been reported (38,39) thathydrolysis by a-amylase predominantly occurs in theamorphous regions of the granule. The results suggest thatthe difference in digestibility between mung bean (45.3%amylose) and other legume starches (29-35.0% amylose) isprobably due to its higher amylose content, and/or to aweaker association between amylose chains within itsamorphous regions.

34.0± 2.0a

78.0± 2.0c

82.0± 1.0d

86.0± l.5e

86.0± 2.0e

12

345

Values weremeans of four determinations. Means within a columnwithout a common letter differ significantly (P ~ 0.05).ISyneresis wasdeterminedat a centrifugal force of 1000 g.

Retrogradation enthalpy (AHR)

The retrogradation endotherm of mung bean starchappeared after 1 day of storage (at 25°C). To (44°C), Tp(52°C) and T; (63°C) of the retrogradation endothermremained practically unchanged during the time course ofretrogradation. However, at the end of 20 days, AHR hadincreased by 10.5 J/g (Table 7). This increase was muchhigher than that reported by Hoover et al. (41) for lentilstarch (7.8 J/g) (same gel concentration, storage temperatureand time). Unfortunately, comparison of our data with otherlegume starches is not possible, since the DSC technique hasseldom been applied to the investigation of legume starchretrogradation. The data suggest that the formation andlateral association of double helices involving amylose chains(during storage) is much faster and much stronger in mungbean than in lentil starch [retrogradation endotherm occurs

Freeze-thaw stabilityThe freeze-thaw (FT) stability of starches is generallydetermined by estimation of the amount of water excludedfrom the starch gel system stored at low temperatures. Theamount of water excluded would be the result of increasedintermolecular and intramolecular hydrogen bonding dueto interaction between starch chains (amylose-amylose,amylose-amylopectin and amylopectin-amylopectin) duringfrozen storage. The percent syneresis in the mung bean starchgel was 86.0% after five FT cycles (Table 6). This was higherthan those values reported for the following legume starches[% syneresis determined under identical experimentalconditions (19,20)]: laird lentil (74% after two FT cycles), CCgold lentil (56% after two FT cycles) and pigeon pea (46.1%after five FT cycles). It is difficult to compare our results withliterature data on the syneresis of other legume starches dueto differences in starch concentration and centrifugal forces.The average degree of polymerization DP of amylose chainson mung bean starch [1585 (40), 1900 (23)] has been shown tobe higher than those of lentil starches [(1400 (23)], whereasmung bean and lentil starches differ only marginally inamylopectin chain length (40). Thus, syneresis in the abovestarches is probably influenced to a large extent byinteraction between amylose chains. This interaction wouldbe of a greater order of magnitude in mung bean amylosedue to its higher DP.

3.4± 0.6g

3.8± O.4f

7.0±0.4e

7.5±0.4d

18.4± 0.2c

19.9 ± 0.2b

38.3 ± 0.2a

40.3 ± o.i'52.2± O.3m

61.0± 0.2h

71.1 ± 0.976.3 ± 0.9k

76.4± 0.7k

0.51.02.03.05.06.09.0

10.014.018.024.048.072.0

Physicochemical characterization of mung bean starch 407

Table 7 Thermal characteristics of retrograded mung bean starchgels]

Table 9 X-ray diffraction spacings and intensities of the majorpeaks of stored mung bean starch gels"

Storage time (days) Enthalpy of retrogradation (ilHP)2.3 (J/g)

Table 8 Gel strength of mung bean starch as a function ofstorage (at 25°C) time

'Starch:water 40:60 (w/w dry basis).2Gels were converted to powders prior to examination by DSC~starch:water 3:1).The data represent the means of four determinations. Means in

the column with different superscripts are significantly different (P< 0.1) .

12468

1620

Time (days)

1248

12

4.23 ± 0.55.8b ± 0.57.5c ± 0.28.4d ± 0.2

11.7e ± 0.512.6f ± 0.514.7g ± 0.5

Gel strength (g)

1503 ± 1.5159d ± 1.0170b ± 3.0185c ± 1.5197f ± 2.0

Day of storage Interplanar spacings (d) in A with intensities''at 25°C (counts/s)

2 5.25 4.40 4.10 3.8(620 ± 10) (340 ± 10) (380 ± 10) (330 ± 0)

7 5.30 4.50 4.15 3.8(900 ±5) (520 ± 5) (500 ± 10) (450 ± 0)

20 5.35 4.60 4.20 3.9(1250± 10) (900 ± 5) (870 ± 5) (800 ± 10)

3The gels (40%) stored at 25°C were converted to powders prior toX-ray diffraction.bThe data represent the mean of four determinations.

higher than those observed (19) for lentil starch cultivars. Forinstance, the intensity increase (at the major d spacings)between the fourth and seventh day of storage for lentilstarch gels (40%) stored at 25°C was 232, 123,97 and 80 c.p.s.for laird lentil (19), and 112,55,56 and 80 c.p.s. for CC goldlentil starch gels (19). However, the intensity increase (at themajor d spacings) between the second and seventh day ofstorage (at 25°C) for the mung bean starch gels was 280,180, 120 and 120 cps (Table 9). The results suggest thatretrogradation due to both amylose and amylopectin ishigher in mung bean than in the lentil starches.

Means ± SD (n =4). Mean values in each column not followed bythe same superscript are significantly different (P S; 0.01) .

only after 3 days of storage at 25°C (41)]. These data alsosuggest the presence of amylose chains of a higher DP inmung bean starch.

Gel strengthThe gel strength of mung bean starch after storage (at 25°C)for periods ranging from I to 12 days is presented in Table 8.The gel strength of mung bean starch was higher than thevalues reported for laird and CC gold lentil starches (19). Forinstance, at the same gel concentration, the gel strength ofmung bean (Table 8) and laird and CC gold lentil (19)starches are 150, 136.4 and 89.8 g (19), respectively. Theresults suggest that amylose retrogradation is higher in mungbean (due to a higher degree of AML) than in the lentilstarches (19). This seems plausible, since the short-termdevelopment of the structure and crystallinity of starch gelsis dominated by irreversible (T < 100°C) gelation andcrystallization of amylose within the gel matrix.

X-ray diffractionThe X-ray diffraction spacing and intensities of the majorpeaks of mung bean starch gels stored at 25°C for 2, 7 and 20days are presented in Table 9. The 'B' X-ray pattern which istypical of retrograded starch was evident in the X-ray spectraof the gels.The 'B' pattern has been shown to result from theretrogradation of both amylose (42) and amylopectin (43).The intensity increase of the 'B' pattern on storage was

Summary and conclusionThe results showed that mung bean starch differssignificantly from other legume starches (15,19,20,26-29)with respect to the amount of amylose, the degree ofaccessibility of water and a-amylase into the amorphousregions of the granule, the extent of association of starchchains within the amorphous and crystalline regions, andX-ray diffraction intensities. These differences influence theobserved variations in swelling factor, amylose leaching,enzymedigestibility, gelatinization parameters and the extentof retrogradation.

AcknowledgementsThe authors wish to thank Dr F.WSosulski (Department ofCrop Science, University of Saskatchewan, Canada) forproviding the mung bean seeds. The senior author gratefullyacknowledges research funding from the Natural Sciencesand Engineering Research Council of Canada.

ReferencesI. Allen,o.N. and Allen,E.K. (1981) In The Leguminosae. A

Source Book of Characteristics, Uses and Modulation.Macmillan, London.

2. Deshpande,S.S. and Damodaran,S.S. (1990) InPomeranz,Y. (ed.), Advances in Cereal Science andTechnology. American Association of Cereal Chemists, StPaul, MN, Vol. 10, pp. 147-241.

408 RHoover et al.

3. Chen,C.Y (1978) MS Thesis, National TaiwanUniversity, Taipei, Taiwan, R.O.C.

4. Singh,U., Voraputhapom.W, Rao,P.Y. andJambunathan,R. (1989) J. Food Sci., 54, 1293-1297.

5. Zhu,IH., Haase,N.U. and Kempf,W (1990) Starke, 42,1-4.

6. Lii,C.Y and Chang,S.H. (1981)1 Food Sci., 46,78-81.7. Mestres,c., Colonna,P. and Buleon.A. (1988) 1 Food Sci.,

53,1809-1811.8. Xu,A. and Seib, P. (1993) Cereal Chern., 70, 463-470.9. Hoover,R. and Sosulski,EW (1985) Starke, 37, 181-191.

10. American Association of Cereal Chemists (1984)Approved Methods of the AACC, 8th edn. AACC, StPaul, MN.

11. Vasanthan,T. and Hoover,R. (1992) Food Chern., 45,337-347.

12. Chrastil,l (1987) Carbohydr. Res., 159,154-158.13. Tester,R.E and Morrison,WR. (1990) Cereal Chern., 67,

551-557.14. Hoover,R. and Vasanthan,T. (1992) Carbohydr. Polyrn.,9,

285-297.IS. Hoover,R. and Vasanthan,T. (1994) 1 Food Biochern., 17,

303-325.16. Kriisi,Y.H. and Neukom,H. (1984) Starke, 36, 40-45.17. Roulet,P.H., Maclnnes,WM., Wursch,P., Sanchez,R.M.

and Raemy,A. (1988) Food Hydroco//., 2, 381-396.18. Hoover,R. and Sosulski,EW (1991) Can. 1 Physiol.

Pharrnacol., 69, 79-92.19. Hoover,R. and Manuel.H, (1995) Food Chern., 53,

275-284.20. Hoover,R., Swamidas,G. and Vasanthan,T. (1993)

Carbohydr. Res., 246,185-203.21. Hoover,R., Rorke,S.C. and Martin,A.M. (1991) 1 Food

Biochern.,25,117-136.22. Biliaderis,C.G., Grant,D.R. and Vose,IR. (1981) Cereal

Chern., 58, 496-502.23. Naivikul.O, and D'Appolonia,B.L. (1979) Cereal Chern.,

56,24-28.24. Reddy,N.R., Pierson,M.D., Sathe,S.K. and Salunkhe,

D.K. (1984) Food Chern., 13,25-29.25. Galvez,EC.E and Resurreccion,A.Y.A. (1993) 1 Food

Biochern., 17, 93-107.26. Schoch,T.1 and Maywald,E.C. (1968) Cereal Chern., 45,

564-573.27. Tolmasquim,E., Correa,A.M.N. and Tolmasquim,S.T.

(1971) Cereal Chern., 48, 132-139.28. Wankhede,D.B. and Ramteke,R.S. (1982) Starke, 34,

189-192.29. Califano,A.N. and Anon,M.C. (1990) 1 Food Sci., 55,

771-773.30. Oates,c.G. (1991) Food Hydroco//., 4,365-377.31. Slade.L, and Levine,H. (1988) Carbohydr. Polyrn., 8,

183-208.32. Cooke,D. and Gidley,M.l (1992) Carbohydr. Res., 227,

103-112.

33. Ring,S.G., Gee,M.I, Whittam,M., Orford,P. andJohnson,I.T. (1988) Food Chern., 28, 9-19.

34. Snow,P. and O'Dea,K. (1981) Am. 1 C/in. Nutr. 34,2721-2727.

35. Dreher,M.L., Berry,IW and Dreher,C.1 (1984) Crit. Rev.Food Sci. Nutr., 20, 47-71.

36. Holm,J. and Bjorck.I, (1988) 1 Cereal Sci., 8, 261-268.37. Holm.L, Bjorck.L, Ostrowska,S., Eliasson,AC., Asp,

N.G., Larsson,K. and Lundquist,I. (1983) Starke, 35,294-297.

38. Marsden,WL. and Gray,P.P. (1986) Crit. Rev. Biotechnol.,3,235-276.

39. Franco,C.M.L., Preto,S.l doR., Ciacco,C.E and Tavares,D.Q. (1988) Starke, 40,29-32.

40. Oates,c.G. (1990) Starke, 42, 464-467.41. Hoover,R., Vasanthan,T., Senanayake,N.I and Martin,

AM. (1994) Carbohydr. Res., 261, 13-24.42. Gidley,M.1 (1989) Macromolecules, 22, 351-358.43. Zobe1,H. (1988) Starke, 40, 1-7.

Received on November 23, 1995; accepted on June 12,1996