QUALITY INDEX AS A PREDICTOR FOR INDUSTRIAL QUALITY
OF WHEAT VARIETIES
 

Miranda R and Salomón, N.

rmiranda@criba.edu.ar

 

INTRODUCTION: 

  Wheat is the most important crop in Argentina. Between 4 and 5 million tons of their production are used internally for human consumption, and the rest (leaving out the seed needed for the next sowing) is exported. 

Our country is one of the five biggest exporters of wheat in the world. Its production capacity has grown, and its share in the world trade stays between 4.7 and 5.5% of the world market, except for the crop 1996/97 in which its production reached 15.5 million tons, as a consequence of a bigger sowed surface. This crop volume has been repeated, in the campaign 99/00 with 16.3 millions, about 16.5 million tn. in the campaign 2000/01, and a hope of more than 18 millions for the present harvest.  

With the base of the campaign 1999/2000, a constant increase in production, consumption and exports is foreseen until the year 2009 (1). 

Historically, Argentina has exported quality wheat grains, but of a single type and according to the climatic conditions of each crop, that is to say, without segregation. 

The law 12.253 of the year 1935 forced the diffusion of hard wheat varieties, in substitution for soft or weak varieties, that had spread for their bigger yield capacity. When being punished by the prices, the latters were quite quickly discarded by farmers.

It should be also kept in mind that during many years, the soil fecundity added high protein values to the grains, and this characterization (hard wheat with high protein) extended until the end of the ´70. The usage of wheat-soya double crop in a vast area (which removed physical-chemical properties from the soils and forced anticipatory harvests and drying of wheat grains with high humidity content), the irruption of the Mexican green-revolution germplasm with dwarf genes which brought in an important increase in yields, and the scarce use of fertilizers at that time, seemed to threaten the reputation won by the quality of the Argentinian wheat.

As in the previous stage, the answer of breeding arrived inmediately, with the search of the best quality in the varieties from the green revolution, and selecting from the numerous crosses made between traditional Argentinian varieties and "Mexican" wheat, new varieties that contributed to the maintenance of a normal or acceptable quality level for all markets. 

The beginning of the MERCOSUR placed Brazil as the main buyer of the exportable balances of Argentinean wheat, after an aborted intent of self‑sufficiency through the use of subsidies, and though initially the quality of the shippings didn't mean an important commercial obstacle, the requirements have expanded, and they are no longer bounded to the quantitative protein values, but instead other demands are added (minimum W, alveograph stability, etc.). 

   GENERALITIES 

  Our main competitors in exporting are engaged in characterizing and differentiating their products, trying to satisfy all the needs that each market consumer outlines (from the point of view of bread making quality).

The commercial standard has been the decisive official regulation of the production price. At the moment, the Resolution SAGPyA 557/79 (Norma de Calidad para la Comercialización de Trigo Pan) determines the Degrees in which production can be framed, the discounts and/or bonuses corresponding to the each degree, and the compensations or discounts by protein contain with based on 11% (13.5% humidity content), whenever the hectolitric weight reaches 76 kg/hl. 

For conventional operations among parts, the milling industry normally applies the art. 12 (Resolution JNG 26776), that states the need for gluten to tie, that is to say, that the insoluble protein fraction in water agglutinates, e.g. it maintains those characteristic properties of tenacity and elasticity unaffected. These properties allow the protein matrix to retain the gases produced in the flour fermentation. 

Except for these two items (protein and gluten), the commercial classification does not make reference to any attributes of the wheat grain for its end-use quality, but rather considers resultants of crop management,  harvest and storage and the climatic conditions of the year. 

The pressure of the Brazilian milling industry  possibly hastened the creation, in Argentina, on the part of the Secretariat of Agriculture, Livestock, Fishery and Food (SAGPyA), of the Trigo Plata standard, that fixed specifications for hectolitric weight, and protein, wet gluten and ash content, but since it does not include quality variables of those proteins, it represented a commercial failure: little or no Trigo Plata was separated, and the one that made it, predictably did not get a compensation on price since this standard did not assure a quality flour.  

  Still with these backgrounds, a change has taken place in the attitude of the different sectors involved with the productive-industrial chain; the attainment of many deals where the quality of wheat shipments receives a price superior to that of the basic rate transcend, and the farmers who get to know this, care to improve the profitability of an activity that is not brilliant.

 

NECESSITY TO REVEAL THE CAPACITY OF USE 

 For industrial quality we understand the aptitude of a wheat variety to achieve appropriately the two stages of its transformation: milling quality and bread making quality.  

The parameters of the first concept that can usually be determined in the samples of pure varieties or of blended commercial lots are: Hectolitric weight, one thousand kernel weight, grain ash content, milling yield and flour ash. The determinants that make to bread making quality are: protein content, wet gluten, dry gluten, flour protein, and reological properties of dough measured by alveograph, farinograph, mixograph and bread making trials (2). 

At the moment, all the wheat varieties approved for their diffusion are inside the hard type, although the real parameters of this type are not legally defined.  

The official policy for the release of new varieties is unrestricted, although the breeders are forced to present information of agronomical characteristics and behaviour against deseases, and bread making quality of each new variety compared with three or more commercial varieties that act as checks, during two years in three environments, or three years in the same environment. No comparative quality classification was assigned to the new registered varieties until three years ago, in spite of having a series of values of very different variables measured on the new variety and different checks, in three different environments during two years, or only one environment during three harvests. 

The Winter Cereal Committee (CCI), which is an advisory board of the National Seeds Commission (CONASE), planned to reveal the comparative bread making qualities of Argentinian wheat varieties. For this purpose, the board uses the (above mectioned) information given by the breeder, and the annual data from the Wheat trials Net (RET), valuable private information from more than 20 experimental environments of the whole country, where every commercial variety (uncompulsorily) participates. During the last years, the Argentinian Milling Industry Federation (FAIM) has run the corresponding costs of the industrial quality analyses.

The agronomic information allows the Committee to annually recommend the checks that the breeders must use in their trials, and besides, according to the results of quality analyses, to locate into quality groups the varieties participating in the trials. 

This type of recommendation unifies the criterion of all the main involved actors in the last 20 years, Government Laboratory specialists and milling industry being included.

This proposal is detailed in Table 1, and the orientative parameters used in different parts of the world serving as help to complete the classification are given in Table 2.

Normally, we have mensurations of hectolitric weight and one thousand kernel weight (on grain), of protein and ash (on grain and flour), wet gluten and dry gluten (on flour), flour yield, falling number, Chopin alveograph, Bravender Farinograph and experimental baking test. 

It is also understood that in numerous circumstances, a variety will be able to be located in a group for some variables, but not able to reach the minimum value for other variables on this group. 

The idea arises of applying an index that uses the most important variables, and that allows a quick comparison with varieties of well-known bread making quality (pattern or variety type). 

How to compare two varieties? How to establish which varieties are similar in their possibilities of offering the same final product, a flour of similar properties that adapts (without too many corrections) to a specific use? 

THE INDEX 

Let me define the concept: an index is an evidence, a sign of something. 

The use of indexes has been described for a lot of time in plant breeding. Their development has aimed at making the genetic gain for yield more efficient. According to Borojevic (3) this theory would have found wider application in animal improvement than in vegetable improvement. 

Hazel (4) stablishes that for a character to be important (and advisable that it participates in an index of animal breeding), we should know: 

a) relative economic importance of this character,  

b) genotypical and fenotypical variances of the character, and  

c) genotypical and fenotypical covariances among characters to integrate the index. 

In vegetable breeding, Smith (5) in 1936 developed an index of vegetable selection, on the base of discriminant functions of Fisher (6), and after that other authors applied different indexes, without obtaining the expected results, according to Borojevic (3). 

The improvement of the crops’ industrial quality, together with yield and resistance against deseases, is a high-priority target in some species that play a specific role in human feeding.  

In the brewery industry, the industrial quality of the malt is a consequence of several and complex determinations. The Brewer Technology I Subject, of Welhenstephan, Germany ( Savio, H., personal communication) has summarized the conformation of a malt quality index (MQI) when it compares varieties in four steps:

1. Lineal transformation of the parameters analyzed as marks of the variables: VZ at 45ºC, Friability, Extract, and limit attenuation. 

2. Sumatory of the marks weighted by their factors. 

3. Transformation of the scores into transitory classes of the MQI. 

4. Correction according to the crop year, regarding the averages of several years of standard varieties.

In wheat, if an apparatus measures a value, a certain property of the dough, how does that value compare with the ideal one? And how do we compare two different values that correspond to different genotypes grown in similar conditions? Which one is better?  

Let us see a simple example shown by Branlard and Dardevet (7) for alveogram data to explain the differences among tenacious and extensible doughs.

The values are:

 

Variety Type                Poor Quality               Good Quality

W ( Joule x 10^-4)                     230                                   285

G (ml)                                   27.1                                  19.8

P (mm H₂O)                         56.7                                102.8

L (mm)                               131.6                                  71.9

 

If we intend to compare the behavior of both samples for an industrial use where the balance P/L were essential, we can adjust the value of W to a corrected W (Wc), regarding the deviation of the balance P/L = 1, that is to say:  

 Wc = W x /[1 - abs(1-P/L)], then,  

 

Wc                                       97.29                                 162.6        

 

…values that are useful to characterize better the varieties or even to know when to correct a certain kind of flour. 

Back to the problem of the analysis of the Argentinian wheath varieties, the help that a Quality Index could mean, depends on the number of variables that integrate it, with the smallest possible collinearity, and on the fact that these variables be of economic interest for all the involved sectors: farmers, milling industry and the food elaboration  industry.

Based on these specifications, we have built an index (AQI). The variables used for this indicator, and the ranges for each variable, as well as their weights, are detailed in Table 3 and Table 4, respectively. Initially, the CCI used seven determinations. Later on, the farinographic stability was added, given the importance that our main external buyer (Brazil) assigns to this item.  

For the time being, at the beginning of each campaign the capacity of use for each commercial wheat variety becomes public, using for this purpose not only the breeder’s information, the AQI and the RET data, but also all the information of official and private labs and of the technicians with knowledge of the topic (Table 5). This classification, carried out on living organisms, is not definitive, it can be updated as long as more data are available, and an appeal can be lodged providing data that justify it.   

This information, revealing the bread making quality of the varieties, allow each participant of the system to produce, industrialize and/or export the product that suits better his/her interests or satisfies the market requirements.

  On the other hand, the AQI, that combines the milling quality appropriately with the bread making quality, is a good help to characterize, after 2-3 years of analysis (neccessary to separate the environmental-genetic interaction effect), the varieties from the point of view of adaptation and stability for quality, as can be seen in the Figures 1 and 2 on data of hard wheat trials carried out by the Argentinian Producers Association (AAPROTRIGO) and analyzed by Salomón (8).

It is also possible to use it to characterize the production of the different areas and crop years (Table 6). 

  In the case of breeding projects without so many measured variables to characterize quality, or when the objectives are less specific, indexes can be built with a smaller number of variables, adjusting the weights, and with full knowledge of the indispensable minimum values for a genotype to be considered good for the final use to which it is intended.  

As long as variables like high molecular glutenin weight, low molecular glutenin weight, gliadins, or QTL factors are measured regularly over the advanced lines of the breeding programs, it will also be possible to integrate them into the index, and contribute to a more integral knowledge of the industrial quality of the wheat genotypes.

BIBLIOGRAPHY:

 

(1) Koo, W.W. and Taylor, R.D. 2000.Outlook of the U.S. and wheat industries, 1999-2009, NDSU, Agr. Economics Report Nº 438.

(2) Wrigley, C.W. and Bietz, J.A.l, 1988. Wheat: Chemistry and Technology.Vol.I, Chap.11, Rheology and chemistry of dough. Edited by Y.Pomeranz. Thrid Edition.

(3) Borojevic, S.: Principles and Methods of Plant Breeding, Fac. of Agriculture, University of Novi Sad, 1981,Yugoslavia,

(4) Hazel, N.L.:”The genetic basis for constructing selection Indexes”, Genetics,28, 476-490, 1943.

(5) Smith, H.F.: A discriminant function for plant selection, Ann. Eugenics, 7, 240-250, 1936)

(6) Fisher, R.A.: The use of multiple measurements in taxonomic problems. Ann. Eugen. (London) 7, 179-189, 1936.

(7) Branlard, G. and Dardevet, M.: Diversity of Grain Protein and Bread Wheat Quality, Journal of Cereal Science 3  (1985) 345-354.

(8) Salomón, N. 2000.Análisis estadístico de la calidad comercial e industrial de trigo pan, campañas 97/98 y 98/99. AAPROTRIGO.

Table 1: Genotypes Classification – Bread Wheat.

 

 

The analyses must be performed over comparative experimental trials samples, against checks of well-known bread making quality.

Table 2: Orientative Parameters – Bread Wheat.