Appraisal of sorghum quality for making tô

Tô is a traditional

W est A frican dish prepared

from sorghum, millet o r maize

flour. A lthough im proved

sorghum varieties are

agronom ically productive,

their technological and

cooking qualities do not match

those o f local varieties.

A research study was

conducted to assess these

qualities and their determ ining

factors. It is thus now possible

to predict the technological

potential o f sorghum varieties

during the breeding process.

characteristics. Moreover, very few selected sorghum varieties proposed to farmers have been successfully cropped.

The Centre de coopération internationale en re c h e rc h e a g ro n o m iq u e p o u r le d é v e lo p ­ p e m e n t (C I R A D , France) has d e v e lo p e d a l a b o r a t o r y te st f o r tô p r e p a r a t i o n and evaluation of its quality; it should be a useful tool for breeders seeking to develop sorghum varieties w ith high technological and agrono­ mic qualities. Some technological aspects of tô p r e p a r a t i o n p r o c e d u r e a n d som e physico-chemical characteristics of the grain (varie ty-dependent) d eterm ine the ultimate consistency of the porridge.

T

ô is a v e r y t h i c k c e r e a l p o r r i d g e usually eaten at the t w o main meals, garnished w ith a sauce, vegetables and s o m e tim e s m e a t. T he l e f t o v e r tô ca n be stored o v e rn ig h t and served the next m o r­ ning, cold or warmed up, w ith m ilk or sauce. The m ain q u a lit y c r ite r ia fo r a good tô in decreasing order o f importance are its consis­ tency (i.e. texture or firmness of the porridge), o v ernigh t keeping q ua lity, c o lo u r and taste (no t c r u c i a l , sin c e it is d o m in a t e d b y th e accom pa nying sauce). For African families, tô should be firm , unsticky, lig h t co lo u re d and keep its firmness overnight w ith o u t any liquid exudation on the surface.

O n l y tô made w it h flo u r o f local sorghum varieties can meet these criteria . Im proved c u l t i v a r s are m o r e p r o d u c t i v e b u t o fte n h a v e p o o r t e c h n o l o g i c a l a n d c o o k i n g Pounding sorghum grain. Photo G. Fliedel G. FLIEDEL CIRAD-CA, BP 5 0 3 5 , 3 4 0 3 2 Montpellier Cedex 1, France.

Traditional tô

preparation

Sorghum flour

Tô is trad ition ally made from sorghum flour o b ta in e d after d e h u l l in g and g r in d in g the grain w ith a mortar and pestle (Figure 1 ). This flour is always ground just prior to preparing the tô, as old flour cannot produce good t ô 1. It is sifted to rem ove coarser p articles and th e n a sm all a m o u n t is d is p e rs e d in c o ld water (two-thirds water, one-third flour) that has been a c id ified w it h lem on or tam arind juice, or alkalized w ith potassium (wood ash e x t r a c t ) , d e p e n d i n g on t h e c u l i n a r y preferences of the consumers.

This "flo ur m ilk " is then poured into a pot of b o i l in g w ater. A th in p o rrid g e is o b ta in e d after 5-8 min cooking; about one-third is set aside in a calabash. The rest o f the flo u r is added by h a n d fu ls to the p o t o f p o rrid g e , w h ile stirring vigorously w ith a flat w oo de n s p o o n . T h e p o r r i d g e t h e n t h i c k e n s and becomes firm, smooth and unifo rm ; some of the th in p orridge th at was set aside can be a dd e d if th e m ix t u r e gets to o t h ic k . A fte r 20 min cooking, the tô is ready to be eaten.

Cold water Wood ashes Lemon juice Tamarind iui< Boiling water 8 minutes cooking 20 minutes cooking

Figure 1. Traditional tô preparation procedure.

Tô prepared traditionally in Burkina Faso, final porridge obtained. Photo P. Ollitrault

1. The fact th a t freshly ground , w ell-s ifte d flo u r has to be used c o n s id e r a b ly l im its th e m a n u fa c tu r in g p o te n tia l. T ô cooks d o no t like m ille d flours as the y are considere d t o be t o o o l d a n d o f p o o r q u a l i t y ( to o h ig h fa t /b r a n contents).

tô quality

Laboratory preparation

of to and testing

T h e m a in a d v a n t a g e o f th e l a b o r a t o r y te c h n iq u e o v e r the tr a d it io n a l m e th o d for preparing tô is that it is carried out w ith only sm all q u a n tit ie s o f g ra in , i.e. a b o u t 10 g o f grain for a tô sample (Figure 2). Several p a ra m e te rs w e r e s tu d ie d to o b t a in g o o d r e p e a t a b i l i t y a n d b e t t e r d i f f e r e n t i a t i o n between sorghum varieties.

Tô preparation

Sorghum grain is first d e h u lle d in a T A D D laboratory d e h u lle r at a constant d e h u llin g y i e l d 2 o f a b o u t 7 5 - 8 0 % , th u s a v o i d i n g a p o s s ib le d e h u l l i n g e ff e c t on th e f i n a l tô consistency.

T h e d e h u l l e d g r a in is th e n g r o u n d in a C yclotec helical g rind er e qu ipped w it h a 500 pm screen. The resulting flour is fine and h o m o g e n e o u s , w it h a m ean p a r t ic le size of 75-100 (jm.

These tw o operations are performed the day before tô preparation (24 h) since tô firmness was found to drop markedly as a function of the storage time of the flour, even under cold storage conditions (4°C).

The flo u r is slurried in 90 ml distilled water (16.6 g flour at 11.5% moisture) in a stainless steel beaker.

T he p o r r id g e is th en c o o k e d in a b o i l i n g w a t e r - b a t h f o r 2 0 m in w i t h m e c h a n ic a l stirring (helix-stirrer at 400 rpm). Under these c o n tro lle d c o n d itio n s , the m ixture remains h om ogeneous, w it h o u t lum ps, th ro u g h o u t the cooking process.

O n ce cooked, the tô is imm ediately poured into tw o stainless steel cylinders (2 cm deep, 4 cm diameter), set on a flat glass plate and heightened w ith 0.5 cm adhesive tape. The cylinders are then stored for about 20 h in an oven at 35°C and 85% relative h u m id ity to lim it surface-drying of the tô samples. After storage, the adhesive tape is removed and sur- p lu s tô is sh a v e d o f f w i t h n y lo n t h r e a d . Tô samples of constant size (3 cm diameter, 2 cm deep) are obtained with a h ollo w punch.

Cold water Sorghum flour Homogenization Mechanical stirring Flour storage Water quality Dry flour/water ratio

24 h distilled water 18.5% Cooking Stirring velocity boiling water-bath 20 minutes 400 rpm f 24 h Storage — 350 q I 85% humidity Tô sample

Figure 2. Laboratory preparation of tô.

2 . D e h u ll in g y ie ld Is g iv e n as: d e h u lle d g ra in w e ig h t / In itial w h o le grain w e ig h t (% ).

Compression test of a tô sample with an Instron machine.

tô quality

Texture assessment

T ô s a m p le t e x t u r e is m e a s u r e d w i t h an I n s t r o n u n i v e r s a l f o o d t e s t i n g m a c h in e (model 4300). The samples are compressed between a metal plate and a piston lubricated w i t h p a r a f f in o i l . C o m p r e s s iv e s tr e n g t h ( n e w t o n s [ N ]) is r e c o r d e d as t h e p is t o n co m p re s s es th e s a m p le (5 m m / m in ) . The fo rc e req uired to break d o w n a tô sample is m onitored to measure tô texture because o f better d if fe r e n t ia t io n b e tw e e n varieties (Figure 3). C o o k in g tests are p e rfo rm e d in duplicate for each sorghum variety, w ith tw o tô cylinders obtained after each cooking, so textu re results are based on q u a d r u p lic a te c o m p re s s ion m easurem ents. A c c o r d in g to this method, tô samples differing in firmness b y o n l y 1 N a re s i g n i f i c a n t l y d i f f e r e n t at P = 0.05.

This precise repeatable te chnique has been used to e v a lu a t e a g re a t m a n y c u l t i v a r s during the breeding process, along w ith local varieties. A sorghum tô quality scale was thus established (Table 1 ).

Effect of technological

characteristics

Tô consistency seems to be governed by the grain deh ullin g te chnique and flo ur particle size.

Grain dehulling

Tw o French varieties and 20 tropical varieties (local or improved) were analysed in terms o f dehullin g factors.

M a rk e d dehulling effect

The tw o French varieties, available in large q u a n t it ie s and d if f e r i n g in te rm s o f t h e ir hardness index (PSI: particle size index), were p ro g re s s iv e ly d e h u lle d fo r 19 m in ; flo u rs obtained from the dehulled grain were used to make tô.

Tô consistency was found to be substantially affected by dehullin g (Figure 4). The firmness o f the porridge increased as grain abrasion in c re a s e d , r e a c h in g a p la te a u at 1 1 m in dehullin g tim e (corresponding to a dehullin g yield of about 70%). The results were signifi­ c a n t (P < 0.05 ) at fiv e d iffe r e n t d e h u l l in g times: 0, 1, 3, 5 and 15 min.

A h ig h l y s i g n i f i c a n t c o r r e l a t i o n b e tw e e n d e h u llin g yield and tô firmness (correlation coefficient r = -0.74**) was obtained w hen all 20 v a r ie t ie s w e r e p ro c e s s e d f o r th e f iv e s i g n i f i c a n t d e h u l l i n g t i m e s ( F ig u r e 5). Nevertheless, there was marked v a ria b ility between varieties. For instance, flour ground from w h o le grain (undehulled) pro duced tô w it h a texture range o f about 5-14 N. Note that, regardless o f the variety, tô quality was never poor (breaking force higher than 12 N) at d ehulling yields of less than 75%.

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Figure 3. Graph of compression test results (Instron machine) for a tô sample compressed between a metal plate

and a piston (compression rate: 5 mm/min).

Table 1. Sorghum tô quality scale.

Breaking force Tô Tô

(newtons) texture quality

< 10 very soft very poor

10-12 soft poor

12-15 acceptable acceptable

15-18 firm good

> 18 very firm excellent

Preparation of a tô sample in the laboratory.

tô q u a lit y

H o w grain com position is m odified

D u r in g th e a b ra s io n process, th e o u te r grain layers are chafed away, thus changing the d e h u lle d g rain c o m p o s it io n . The tô firm n e s s results in d ic a te d a n e g a tiv e correlation w ith the flo u r mineral content (r = -0.80**), fat content (r = -0.64**), fibre content (r = -0.74**) and even the protein content (r = -0.60**). Conversely, there was a p o s itiv e c o rr e la tio n w ith starch c o n te n t (r = +0.74**). In our conditions, the protein content varied a ccording to the extent of grain dehulling, i.e. the longer the dehulling time - the lower the protein content, whereas the starch content increased on the basis of dry matter.

W hen d e h u llin g was sufficient, i.e. when removal of the outer layers and germ was suitable, the resulting tô was never of poor quality. Indeed, regardless of the sorghum variety, a breaking force higher than 12 N was obtained with a flour mineral content of less than 1% (Figure 6), and a fat content of less than 2% (Figure 7).

Flour particle size

Several sorghum varieties were dehulled to the same y ie ld (about 75-80% ) and then ground in nine diffe re n t types of m ills to produce flours of different particle sizes, but w ith the same b io c h e m ic a l co m p o sitio n . D e p e n d in g on the m ill used, the mean particle size ranged from less than 75 |jm ( C y c lo te c o r A lp i n e m ill) to m ore than 900 pm (KT30 mill).

Figure 4. Effect of dehulling time on tô firmness for two French sorghum varieties.

Tô preparation: adding dry flour to the thin porridge.

Photo G . Fliedel

G o o d tô with fine flours

W ith the same sorghum variety, tô quality ranged from very good to very bad depending on the flo u r particle size. Very fine flours (mean p a r t ic le size less than 150 pm) produced acceptable or good tô (breaking force above 12 N), contrary to coarse flours.

Starch effect

Starch occurs in granular form in the grain endosperm. These granules can be broken (damaged) during m illin g , especially with fine milling (e.g. tightly adjusted millstones). Damaged starch levels were evaluated in the fin e s t m i l l i n g p ro d u c ts (m ills : C y c lo te c 0.5 mm, C y c lo te c 1 mm, A lp in e , M iag, 20 -15 10 O

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Dehulling times I 0 min + 1 min A 3 min O 5 min • 15 min *

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—I— 40 60I— —r~80 100 Dehulling yield (%)

Figure 5. Relation between tô firmness and dehulling yields for 20 tropical sorghum cultivars, and five different dehulling times.

tô quality

Samap). It was significantly and negatively correlated w ith the p a rticle size o f these flo u rs (r = - 0 .6 9 * * ) : very fin e flo u rs had much higher damaged starch levels than coarse flours.

Tô q u a lity was p o sitive ly correlated w ith dam aged starch le ve ls o f th e flo u rs (r = + 0 . 4 9 * * ) . H e n c e , flo u r s w i t h high damaged starch levels generally produced f ir m e r tô th a n those c o n t a i n i n g coarse particles and with low damaged starch levels. This p h y s ic a l e ffe c t seemed to be m ore important for flours from sorghum varieties that naturally produced good tô (Figure 8). For in sta n ce , the regression c o e f f ic ie n t between tô firmness and the percentage of damaged starch was sixfold higher for variety IS 15255 (of the good quality variety group) as compared to IS 24761 (of the poor quality variety group). 20 1 5 -1 0 -/ • • • • Dehulling times I 0 min ^ 1 min A 3 min O 5 min • 15 min

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Figure 7. Relation between tô firmness and the flour fat content for 20 tropical sorghum cultivars and five different dehulling times.

Effect of physico­

chemical grain

characteristics

18 sorghum cultivars from Mali and Burkina Faso were analysed. Their tô firmness results ranged from 9.5 to 22.4 N (mean 14.2 N), w h ic h g enerally corresponded to a good quality tô. 7 2 5 -, s ! ° 20 1 5 -1 0 -- • » < • • •

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T 1,2 1,6 2 M ineral content [% d.m.)

Figure 6. Relation between tô firmness and the flour mineral content for 20 tropical sorghum cultivars and five different dehulling times.

Vitreousness, hardness and

protein content have no impact

Despite wide variability in the vitreousness and hardness (PSI) indexes, w h ic h ranged from 1.7 (vitreous grain) to 4.9 (floury grain) and 12.1 (hard grain) to 28.4 (soft grain), re s p e c tiv e ly , th e re w e re no s ig n if ic a n t co rre la tio n between these physical grain characteristics and tô texture. Moreover, vitre o u s grains w ere g e n e ra lly hard and floury grains generally soft.

Similarly, total proteins and protein fractions in the flour were not significantly correlated w ith tô consistency, again despite a w ide range of results for each of these chemical components. In this case, the grain dehulling yields were constant and thus the protein content was that of the endosperm; but these proteins did not have as important an effect on tô quality as starch.

Effects of starch

In contrast, starch characteristics were found to be highly and significantly correlated with tô texture, particularly in terms of the starch amylose content (r = + 0 .8 1 **) and starch solubility at 85°C, the temperature at which tô is cooked (r = +0.86**). Therefore, the tô becom es f ir m e r as the a m ylo se c o n te n t increases and starch m a c r o m o le c u le s solubilize better at 85°C (Table 2).

to quality

Q uality analyses of sorghum used to make tô

These la b o r a to r y a nalyses are o n ly

perform ed on w h o le grains or flours. However, some can be used to assess both products.

W hole grain analyses

Before a ll analyses, th e g ra in s are c le a n e d (to e lim in a te dust, glum es, b ro k e n kernels) and c o n d it io n e d to obtain a moisture content o f 11 -1 2%, a level at which hardness varies very little. The vitreousness index is determined by v is u a l assessment o f the p r o p o r t io n o f vitreous and flo u r y endosperm on 20 lo n g itu d in a l h a lf kernels c u t w ith a razor blade. Each grain is graded on a 1-5 scale (± 0 .2 5 p o in ts ); a score o f 1 c o r r e s p o n d s to a t o t a l l y v itre o u s endosperm , and 5 to a t o t a lly flo u r y endosperm.

The hardness index (PSI: particle size index) is determined after milling 20 g of grain in a Falling N um ber KT 30 type m ill (coarse burr, setting 4) and 1 min s iftin g o f m ille d m a te ria l th r o u g h a 250 |jm sieve (Alpine type 200 LS air jet sifter). PSI represents the percentage of m illed material passing through the sieve. The lo w e r the PSI, the h arder the grain.

The d e h u llin g yield is o b ta in e d after 5 min grain d e h u llin g in a Tangential Abrasive Dehulling Device (TADD). This laboratory dehuller is equipped w ith a c a rb o ru n d u m abrasive disk that turns h o riz o n ta lly under a steel plate w ith eight sample cups. Each cup is filled with 30 g of grain, and eight different varieties can be processed at once. The dehulling yield is the percentage dehulled grain weight/initial whole grain weight (30 g).

Flour analyses

Flours are p re p a re d by g rin d in g the dehulled grain (constant dehulling yield of 75-80%) in a Cyclotec helical mill. The mean particle size is determined by successive sievings, from a 75 pm mesh sieve to a 2 000 pm sieve, depending on the flour; there is a total of 16 sieves (75, 100, 125, 150, 180, 200, 250, 315, 400, 450, 710, 800, 900, 1000, 1400 and 2 000 pm). These siftin g tests are performed with 50 g samples of flour at constant low hum idity (about 10-11%) through an Alpine air-jet sifter for 5 min. The percentage o f flo u r that does not pass through each sieve is measured.

The mean particle size C 50 corresponds to the sieve mesh that retains 50% o f the flour.

T h e s ta rc h c o n t e n t is d e te r m in e d th ro u g h e n z y m a tic and c o lo r im e t r ic analyses. The starch is first gelatinized b e tw e e n 8 0 ° C and 9 0 ° C , and then d e x tr in iz e d w it h th e r m a m y l, a th e r m o s ta b le a m y la s e . T h ro u g h a re a c tio n w it h a m y lo -g lu c o s id a s e at 5 5 °C , th e d e x tr in s are h y d ro ly s e d into glucose, w hich is measured by spec- to p h o to m e tr y after re a c tio n w it h an enzymatic oxydo-reducer enzyme-stain (glucose-oxydase, peroxydase, ABTS) system. U s in g a sta n d a rd scale, the glucose concentration o f the sample is d e te r m in e d , a lo n g w it h its starch c o n te n t , by m u l t i p l y i n g by the conversion factor (0.9).

The am ylose co n ten t is evaluated by the ISO 6 6 4 7 standard c o lo r im e t r i c technique. The flour is first defatted with 85% methanol, remilled and solubilized in a mixture of 95% ethanol and normal soda. Am ylose staining is done in the presence o f a s o lu tio n o f m o le c u la r io d in e and io d id e ions (p o ta s s iu m io d id e ) . The o p t ic a l d e n s ity o f e ach s a m p le is m e a su re d w it h a s p e c tr o p h o to m e t e r at 6 2 0 nm and com pared to th a t of a standard scale p re p a re d fro m d if fe r e n t m ix tu re s o f control amylose and amylopectin. The starch swelling pow er and starch so lub ility are measured as fo llo w s : a flour-water mixture (1 g/25 ml) is stirred in a w ater-bath at 85°C fo r 1 h. After centrifugation, the percentage of soluble starch in the w a te r is o b ta in e d after d e s ic c a t io n o f th e s u p e rn a ta n t; the quantity of water absorbed by the flour s ta rc h ; i.e. s ta rch s w e llin g p o w e r (g water/100 g d.m.) is determined after desiccation of the pellet.

The starch gelatinization temperature is d e te r m in e d by d iffe r e n tia l sca n n in g c a lo r im e t r y a n a lysis, w h ic h is used to measure energy variations required to heat a sample at constant v e lo c ity . T he f l o u r is p la c e d in a w a t e r t ig h t capsule with a certain amount of water and the m ixture is subjected to linear heating kinetics.

E x tra c tio n and m easu re m e n t o f fo u r p ro te in f r a c tio n s w e re p e rfo rm e d sequentially with different solvents: - albumins and globulins w ith a saline solution (0.5 M NaCI);

- p r o la m in s o r k a fir in s w it h a 6 0 % ter-butanol solution;

- re d u c e d p r o la m in s (o r re d u c e d kafirins) with a 60% ter-butanol solution containing 0.1 M 2-mercaptoethanol; - g lu te i ins w it h a b o ra te b u ffe r s o lu t io n (pH 10) c o n t a i n in g 0 .6 % 2-m ercaptoethanol and 0 .5% sodium dodecylsulfate.

P ro te in s w e re m e a su re d in th e supernatants by the m ethod used for total proteins (described below).

Chemical analyses of whole grain and flour

T h e w a t e r c o n t e n t (m o is tu re ) is d e te r m in e d a c c o r d in g to th e NF V 0 3 .7 0 7 standard, from 5 g samples, by d if f e r e n t i a l w e i g h in g a fte r 2 h oven-drying at 1 30°C.

T h e m i n e r a l c o n t e n t is d e te r m in e d according to the NF V03.702 standard, fr o m 5 g sa m p le s , by d if f e r e n t i a l weighing after 3 h calcination at 900°C. For fat content, the Soxhlet extraction technique is used with a Tecator Soxtec HT distiller. Fats are extracted at 100°C by soaking and rinsing the sample in diethyl ether. Ether-soluble fat contents (or free fats) are determined by weighing the extracted fats after desiccation. Total pro tein co n ten t (% N x 6.25) is measured after the sample is mineralized w ith concentrated sulfuric acid in the presence of a catalyst (99.5% potassium sulfate + 0.5% selenium), by the Kjeldahl method with a Tecator automatic Kjeltec apparatus.

Tô preparation: washed sorghum being poured into a mortar.

tô quality

Progressive m u l t i p l e lin e a r regressions h ig h lig h te d th a t 79% o f the tô firm n e ss 2. could be positively explained by the starch ü macromolecule solubility in water at 85°C and negatively by the starch granule swelling ^ power. W hen s o lu b ility and swellingness factors were not taken into consideration, 65% of tô firmness could be explained by starch amylose content.

Tô texture, like the consistency of a mixed starch gel, depends on the viscosity of the liq u id phase — w h ic h increases w ith the q u a n tity o f s o lu b iliz e d m a cro m o le cu le s, e s p e c ia lly a m y lo s e — and also on the firm n e s s o f the s o lid phase — w h ic h increases w h e n the starch g ra n u le s are not very swelled.

Flours fro m va rie tie s w it h high am ylose content (more than 25% starch) generally produce good tô. They are often vitreous or have a vitreous tendency. Moreover, varieties containing high water soluble starch (above 18% d.m. at 85°C), also produce good tô. Starch s o l u b i l i t y in cre a se d w i t h the percentage of damaged starch, e.g. during fine milling, but this also depended on the variety. There was a p o sitive c o rre la tio n between the amylose content and the starch s o lu b ilit y at 85°C (r = + 0 .8 4 * * ) . In fact, starches from high amylose sorghum varieties are h ig h ly so lu b le d u rin g the tô c o o k in g process.

Grinding of dehulled grain is also a quality factor. Tô firmness is linked w ith the flour damaged starch content (higher in fine than in coarse flours), w h ic h promotes starch macromolecule s o lu b ility during cooking. High amylose varieties (25% higher on a star­ ch basis) with high starch solubility at 85°C, produce high quality tô. However, with the same starch solubility, tô firmness depends on the e xtent o f starch gra n u le s w e llin g power, i.e. the lower the water uptake, the firmer the tô.

Concl usion

The la b o ra to ry test described here for tô preparation and textural assessment is precise and re p e a ta b le . In a d d i t i o n , it has the advantage of only requiring small grain quan­ titie s . Breeders c o u ld use th is test to e v a lu a te the q u a lit y o f c u ltiv a r s d u rin g the breeding process. The results cle a rly demonstrate that tô quality is dependent on the technology used in its preparation and on the sorghum variety.

G ra in d e h u l l i n g is also a v e ry c r i t i c a l operation. All of the outer grain layers have to be c h a fe d o f f in o r d e r to p r o d u c e tô of suitable q u a lity . Hence, it is essential to select sorghum varieties with good dehulling properties — with grains that are not too soft, not too floury and that w ill not break during manual or mechanical dehulling.

Table 2. Relationships between the flour starch characteristics of 18 West African sorghum varieties and tô texture.

Characteristics Minim um Maximum Mean Correlation coefficient Starch (% d.m.) 68.5 79.7 76.6 0.27 Amylose (% starch) 19.6 29.3 24.7 0.81** Gélatinisation temperature (°C) 72.3 74.5 73.3 -0 .2 3 Starch solubility (% d.m.) 12.2 23.9 16.2 0.86**

Starch swelling power 8.8 11.8 9.7 0.23

(grams water % d.m.) Tô firmness (N) 9.5 22.4 *: highly significant at P = 0.10. 14.2 Variety Amylose (% d.m.) • IS 24761 ■ WS 1297 ▲ IS 24729 ♦ IS 152255 24.0 24.1 24.6 27.5 30 35

Starch damage level [%)

Figure 8. Effect of the starch damage level cultivars on tô firmness.

tô quality

Bibliography

Tô preparation: before serving, some of the porridge is poured into a small calabash.

Photo G . Fliedel

FLIEDEL G ., FLACHER K., MESTRES C., 1 9 9 1 . Physico-chemical characteristics of sorghum grains and tô q u a lit y . In te rn a tio n a l Cereal C h e m is t Congress, Prague, C z e c h o s l o v a k ia , June 1 0 - 1 3 , p o s te r. Montpellier, France, CIRAD-CA.

FLIEDEL G., GRENET C., G O NTARD N ., PONS B„ 1989. Dureté, caractéristiq ues p h ys ic o -c h im iq u es et aptitude au décorticage des grains de sorgho. In Comptes rendus du C o llo q u e in t e r n a t io n a l de t e c h n o lo g ie , c é ré a le s en ré g lo n s c h a u d e s : c o n s e r v a t io n et transformation, Centre universitaire de N 'G aoundéré, Cameroun, p. 187-201, Paris, France, AUPELF-UREF, Eds. John Libbey Eurotext.

FLIEDEL G., PEREZ E., 1989. Sorghum tô texture and its r e l a t io n s h ip s w i t h some p h y s i c o c h e m ic a l characteristics o f grain and flo ur. AACC 74th Annual Meeting, Washington DC, USA, October 29-November 2, 1989, Montpellier, France, CIRAD-CA.

FLIEDEL G., YAJID M ., 1992. Effect o f m illin g on s o rg h u m tô q u a l i t y . In p ro c e e d in g s o f th e 9 th International Cereal and Bread Congress, 5th quadrennal s y m p o s iu m on s o rg h u m and m ille t , Paris, France, June 1-5, 1992, p. 73-86. Associa tio n in te rnatio nale des sciences et technologies céréalières, Paris, France.

Abstract... Resumen... Résumé

G. F L IE D E L -Appraisal of sorghum quality

for making tô.

Tô is o troditionol porridge prepared doily in West Africo from sorghum, millet or maize flour. The porridge must be firm to be appreciated. Good quality tô depends on the technology used in flour preparation (dehulling and milling) ond the physico-chemicol charocteristics of the gra in . A la b o ra to ry m eth od fo r the p re p a ra tio n of s o rg hu m p o rrid g e and a p p ra is a l o f its firm n e s s is a v a i la b le lo r b re e d e rs f o r the p r e d ic tio n o f the technological and cooking quality of the varieties being bred. Dehulling plays an important role because much of the outer layers of the grains as possible should be removed. Likewise, the dehulled grain should be milled to fin e flo u r for m a k in g firm tô. A strong positive correlation was found between firmness ond the amylose content of flours and storch solubility ot 8 5 ° C . The amylose content varies according to the sorghum variety. It would seem opportune in varietal im provem ent of sorghum to determine dehulling suitability of the grain on the one hand and its amylose-starch content on the other to assess suitability for making firm tô. In contrast, characteristics such as grain vitreousness and hardness are not determinant.

Keywords: sorghum, flour, porridge, technology, cooking quality, variety, storch, laboratory analysis, West Africa.

G. FLIEDEL - Evaluación de la calidad del sorgo

para la fabricación del tô.

El tô es una papilla tradicional preparada a diario en Africa occidental a partir de una harina de sorgo, mijo o maiz. Para ser apreciada, esta papilla debe ser firme. La ob te n c ió n de un tô de b u e n a c a lid a d d e p e n d e de la te c n o lo g ia e m p le a d a p a ra su p re p a ra c ió n (descascarillado y m olienda de los granos) y de las características fisico químicas de los granos). Un método de labo rato rio de preparación del tô de sorgo y de evaluación de su firm eza se encuentra disponible para los seleccionadores con el fin de p re v e r la calidad tecnológica y culinaria de las variedades que se estén s e le c c io n a n d o . El d e s c a s c a rilla d o de los gra n os desempeña un papel importante y requiere eliminar al m áxim o las capos periféricas del grano. Asimismo, la molienda de los granos descascarillados debe dar harinas finas para obtener un tô de firm e z a correcta. Se ha puesto de relieve una fuerte correlación entre la firmeza del tô y el contenido de amilosa de las harinas, asi como la solubilidad del a lm id ón a 8 5 ° C . El contenido de amilosa varia en función de las variedades de sorgo. Para la m ejo ra v a rie to l del sorgo, parece indicado determinar la aptitud al descascarillado de los granos y, por otro lado, su contenido de am ilo sa-alm idó n con objeto de evaluar la capacidad de fabricación de un té de buena firm eza. En cambio, las características como lo vidriosidad y la dureza del grano no son determinantes. Palabras clave: sorgo, harina, papilla, tecnología, calidad culinaria, variedad, alm idón, análisis de laboratorio, Africa occidental.

G. FLIEDEL - Evaluation de la qualité du sorgho

pour la fabrication du tô.

Le tô est un e b o u illie t r a d i t io n n e ll e p r é p a ré e quotidiennem ent en Afrique de l'Ouest à pa rtir d'une farine de sorgho, de mil ou de maïs. Cette bouillie doit être ferm e pour être appréciée. L'obtention d'un tô de bonne qualité dépend de la technologie employée pour sa préparation (décorticage et broyage des grains) et des ca ra ctéristiq ues physico-ch im iqu es des gra ins . Une méthode de laboratoire de préparation du tô de sorgho et d 'é v a lu a t io n de sa f e r m e t é est d is p on ib le po ur les sélectionneurs afin de prédire la qualité technologique et culinaire des variétés en cours de sélection. Le décorticage des grains joue un rôle important et nécessite d'éliminer au m a x im u m les couches périphériques du grain. De même, le broyage des grains décortiqués doit donner des farines fines pour obtenir un tô de bonne fermeté. Une forte corrélation positive a été mise en évidence entre la ferm eté du tô et la teneur en amylose des farines, ainsi que la so lu bilité de l'a m id o n à 8 5 °C . La te n e u r en amylose varie en fonction des variétés de sorgho. Pour l'amélioration variétale du sorgho, il apparaît opportun de déterminer l'aptitude au décorticage des grains d'une part, puis leur teneur en amylose-amidon d'autre part, a fin d 'é v a lu e r la capacité à la fabrication d'un tô de bonne fermeté. En revanche, les caractéristiques telles que la vitrosité et la dureté du grain ne sont pas déterminantes. Mots-clés : sorgho, farine, bouillie, technologie, qualité culinaire, variété, amidon, analyse de laboratoire, Afrique de l'Ouest.