RESEARCH

Gliadin Electrophoregrams and Measurements of Gluten Viscoelasticity in Durum Wheats 1

Rene Damidaux, Ph.D., Jean-Claude Autran , D. Engr., and Pierre Feillet, D. Engr. Production of cultivars with high pasta-making quality is a major objective of durum wheat breeders. Evaluating the ability of a cu ltivar to be processed into yellow amber pasta is no problem. Severa! la bora tories have developed technological (color index measurements) and biochemical (caroten o id content, lipoxygenase activit y, iso perox id ase composition) tests tha t meet breeders' requirements. F ast sma ll-scale methods for direct estimation of the cooking quality of durum wheats are also available. Sorne consist of processing grains into semolina and pasta disks or spaghetti , cooki ng them, and determining thei r characteristics with an aleurograph or a viscoelastograph apparatus. However, cooking quality evaluation at the breeding stage is a more critical problem. In opposition to its color and particularly to its yellow component, a varietal cha racteristic, cooking quality of durum wheat is highly influenced by growing co nditions. Ta ble I shows the cooking quality scores ( 10 =excellent, 0 = very poor) of 24 durum w heat sa mples made up ofthree cultivars grown in eight different locations. Breeders clearly cannot get entire satisfaction from these meth ods, which are hardly a ble to account for the respective influences of the genotype and the environment except by multiplying the number of field tests. Therefore, we think it

fruitful to clearly dist inguish between two types of tests: 1) breed ing tests that must account for the va rietal intrinsic quality of genotypes a nd 2) co mmercia l tests (including microcooking tests) that must assess the co mmercial quality of wheat sa mples, ie, the result of interactions between the va rietal intrinsic qualities and the growing conditions of the plant. ln this paper, we present our recent progress in developing breed ing tests that are required to have the following characteristics: 1) ind ependence of the results with rega rd to the agronomical record of the sample, 2) high correlati on with the varietal ranking tha t would have resulted from conventional experiments; and 3) potential for analyzi ng a large series or a small amount of material. In developing the breeding test for coo king qua lity of durum wheats, we have evaluated: 1) the varietal nature of the viscoelastic properties of the cooked gluten, 2) the relationship Table 1. Variabillty of Cooking Quality' of Three Durum Wheat Cultivars Grown in Eight Locations Varieties

Aga thé

Location

10 10 10 8 8 6 6 4

A B

c

1

Laboratoire de Technologie des Céréales, Institut National de la Recherche Agronomique, 9 Place Via la, 34060 Montpellier CEDEX, France.

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0146-6283/80/12075403/$02.00/0 c 1980 American Association of Cereal Chemists, 1ne.

HEAT SHAPING

D E F

Lakota

V 39

8 8 8 4 4 4 4 0

8 6 4 4 0 0 0 0

• 10 = Excellent, 0 = very poor.

COOLING

STORING

~

0

/).....

• 0

/ 0

T

90

SEC,

120

20°C SEC,

Fig. 1. Dlsk gluten shaplng by heat treatment. A = piston, C = clamp. PAGE 754/DECEMBER 1980 VOL. 25, NO. 12

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GLUTEN DISK

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•

1°

20°C

60 SEC,

500

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DISPLACEM ENT

V!SCOELASTOGRAM

GAU GE

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GLUTEN DISK

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LOAD !NG ON

DISK THICKNESS

LOADING

OFF

Fig. 2. Evaluation of gluten viscoelasticity wlth a vlscoelastograph.

LOADING ON

Table Il. lntrinsic Cooking Qua lity and Gluten Viscoelasticity' lntrinsic Cooking Quality Variety

High

Aga thé Bidi 17 Blond ur Brumaire Diabolo Ed more Mondur Montferrier Trinakria Va ldur D urtal Lakota Poinville Randur Rikita Tomclai r Valsacco Wells

1.79 170 1. 9 1 1.90 1. 77 1.7 1 1.9 1 1. 90 1.81 1.82

Low

5 LOADING

4 0.79 1.28 0.72

0.75 0.47 0.59 0.59 0.7 1

' Abs olute elastic recover y (e2-e1 in millimeters) o f thermom olded gluten (average of analyses of sam ples of d ifferent origins).

between t he viscoclast ic properties of cooked g luten a nd the cooki ng quality o f durum wheat varieties, a nd 3) the clear-cut relatio nship bctween g liadin electrophoret ic patterns and viscoelastic properties of gluten.

Genetie Dependency of Vlscoelastlc Propertles F i rst, a new me th od for th e eva l uat i o n of glut e n viscoelasti city was perfected. After ext raction throug h ma nua i dispersion, 1 g of gluten was put into a mo lding cell (Fig. 1). Pistons were placed on either side of the glute n ba ll a nd he ld by a clam ping frame. The ce ll was immersed for 90 sec in bo il ing water, then fo r 120 sec in 20° C water. The result ing gluten disk was take n out of the cell a nd put into wa ter for about 1 min. The viscoelastic properties of the gluten were then determined by a viscoela stograph (Tripe tte Rena ud-Chopin) ( 1). T his a ppa ratus ( Fig. 2) fo llows the stra in of a so lid in terms of ap plied stress and of time. The glute n disk was take n o ut of t he wa ter a nd put on a sample plate; a constant load was applied for 40 sec and then removed. The time dependence of the thick ness va ria tion of the glute n disk was sca nned before a nd after loading off (Fig. 3). The glute n abso lu te elastic recovery (e2 - e 1) was computed from the value of e 1 (thickness immedia te ly before loading off) and e ~ (final t hick ness, 20 sec afte r loading o ff). Elastic recovery was determined for a la rge number of sa mples of diffe rent varietal and agro nomical origins (2).

l

Vl Vl

UJ

z

::. 1

1 1

1

1

~ 1

40

60

TIME (S ECONDS) Fig. 3. Cooked gluten dlsk vlscoelastogram. (Absolute elastlc reéovery: ei-ei. Flrmne11: e,.)

Within ail samples, absol ute elast ic recovery values ranged from 0.3 to 2. 1 mm. ln a g ive n variety, absolute elastic recovery varies within narrow limits a ro und an average value t ha t decreases as the wheat protein con tent increases. The lower t his average va lue is, the mo re important a re the fluctuatio ns. A va rie ty can be c haract er ized by t h is ave rage val u e o f its g l uten viscoelasticity. The 1 17 sam plcs that werc analyzed segregated into two classes around the mean val ues 0.6 and 1. 8 mm (Fig. 4).

Relatlonshlp of Elastlc Recovery Value and lntrinslc Cooklng Ouallty Well-known cultivars with either high or low cooking qualities were checked for t heir gluten viscoelastic properties CEREAL FOODS WORLD/ PAGE 755

30

Vl

N "'

(Ta ble Il). Gluten in ail cultivars known for good cooking qua lity had absolute elastic recovery values above 1.6. Glutens in low or medium cooking quality cultivars had absolute elastic recovery values below 1.0 (except fo r Lakota, which can be regarded as a medium quality cultivar).

117

Agreement Between Glladln Electrophoretlc Patterns and Absolute Recovery

20

w

1-

w

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10

0

o.

0.4

0.6

0 .8 1.0

1. 2

1.4

1. 6

1.8

2.0 2.2

Fig. 4. Distribution of absolute elastic recovery of glutin in sample of durum wheat.

TYPE 42

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Conclusions

1

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Fig. 5. Electrophoregrem1 of durum wheet verletlee (polyacrylamlde gel/elumlnum lactate butter, pH 3.1 ).

30

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TYPE

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TYPE

20

45

The results raise many questions about the nature of the linkage b etween the gliad in ele ctrophoregrams and the viscoelastic properties of gluten. Is the linkage a genetic markcr? Is it a functional relationship? At present, we ca n only speculate. Our work has led us to several practical deductions, h owever. The results provide plant breeders with a new tool to screen new high cooki ng quality du rum wheat varieties. To assist in this program, we would suggest using the fo llowing breeding diagram: 1) screen at the F3 or eve n the F2 generation, on half kernels, for the p resence of the electroph oretic component 45; 2) screen the F5 generation of lines tha t consistently belong to the 45 type for high elastic recovery of gluten (about 1.5 mm); 3) confirm end-use properties a t the la ter b reedi ng stages by checking the cooking quality through microtests and pilot plant tests a nd evaluating the effects of growing conditions. Simultaneo us breeding for high protein content would be advisable.

42 Llterature Clted

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O ne hundred seventeen durum wheat varieties of different genetic origins were examined (3). After extraction by 70% ethanol, gliadins were fractionated in polyacrylamide gel by the electrophoretic technique of Bushuk a nd Zillman (4). Component mobilities were esta blished by reference to the sta ndard 5 1 band, in agreement with the common wheat gliadin nomencla ture (5). Wheats were classified into two main groups accordi ng to the gamma gliadin region (Fig. 5). One was characterized by the presence of a stro ng band 45 a nd the absence of a band in the 38-42 region, the other by the absence of a band 45 a nd the presence of a strong band 42. S ixt y-six varieties belonged to the 45 type, 47 to the 42 type, and four to neither. One of the most interesting resu lts of this study was the excellent agreement between the electrophoretic patterns of the durum varieties and their viscoelastic propert ies (Fig. 6). ln 59 of the 66 varieties (89%) of the 45 gliad in type, the elastic recovery of gluten was above 1.2 mm. ln 46 of the 47 va rieties (98%) of the 42 gliadin type, the elastic recovery was below 1. 2 mm.

1

1

10

1 1

,---· 1 1

1

•.---• 1

0 0.2

0.4 0.6

0.8

1.0

1.2 1.4

1.6

1.8 2.0

2.2

Fig. 6. Relalionship of electrophoretlc patterns and viscoelaslic properties of durum wheat samples. PAGE 756/DECEMBER 1980 VOL. 25, NO. 12

1. Feiilet, P., J. Abecassis, and R. A lary. D escription d' un nouvel appareil pou r mesu rer les propriétés viscoéiast iques des produits céréaliers. Application à l'appréciation de la qualité du gluten, des pates a limentaires et du riz. Bull. Ec. Nat. Super. Meun. Ind. Cereal. 273:97- 101, 1977. 2. Damidaux R. , a nd P. Feiilet. Relation entre les p ropriétés viscoélastiques du gluten cuit, la teneur e n protéines et la qualité culinaire des blés durs (T. durum). Ann. Technol. Agric. 28(4):799808, 1978. 3. Da midaux, R. , J. C. Autran, P. Grignac, and P. Feillct. Relat ion applicable e n sélection entre l'électrophorégramme des gliadines et les propriétés viscoélastiques d u gluten de Triticum durum Desf. C. R . Hcbd. Scanccs Acad. Sei. Ser. D 287:701 - 704, October 2, 1978. 4. Bushuk, W., and R. R. Zillman. Wheat cultivar identification by gliadin electrophoregrams. 1. Apparatus, method a nd nomenclature. Can. J. Plant Sei. 58:505-5 15, 1978. 5. Ziilman, R. R., and W. Bushuk. Wheat cultivar identification by gliadin electrophoregrams. Ill. Catalogue o f e lectrophoregram formulas ofCanadian wheat cultivars. J. Can. P lant Sei. 59:287-298, 1979. D