Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
2005
Volume 8
Issue 1
Topic:
Agricultural Engineering
ELECTRONIC
JOURNAL OF
POLISH
AGRICULTURAL
UNIVERSITIES
Pikus S. , Jamroz J. , Olszewska E. , W這darczyk-Stasiak M. 2005. AN ATTEMPT TO USE SAXS METHOD IN EVALUATING DIFFERENT TYPES OF WHEAT FLOURS, EJPAU 8(1), #21.
Available Online: http://www.ejpau.media.pl/volume8/issue1/art-21.html

AN ATTEMPT TO USE SAXS METHOD IN EVALUATING DIFFERENT TYPES OF WHEAT FLOURS

Stanis豉w Pikus1, Jerzy Jamroz2, El瘺ieta Olszewska1, Marzena W這darczyk-Stasiak2
1 Department of Crystallography, Maria Curie-Sk這dowska University, Lublin, Poland
2 Department of Food Quality Assessment, Agriculture University in Lublin, Poland

 

ABSTRACT

Small Angle X-ray Scattering (SAXS) has been applied to the study of starch structure in wheat flour. The quality of the range changes of starch microstructure after milling was analysed and a certain relationship of SAXS scattering magnitudes with alveographic study was shown.

Key words: SAXS scattering, wheat flour, alveographic study.

INTRODUCTION

The technology of the milling process is used to modify the functional properties of cereal flours. An estimation of the milling value of wheat grain is determined among other things on the basis of the chemical composition of flours, especially the content of protein, the quantity and quality of gluten, ash, sedimentation index and the rheological properties of dough. Rheological methods are commonly used in studying the technological value of flour. In recent years alveographic evaluation has found wide application in studying the quality of wheat flour [1]. Certain alveographic parameters are closely connected with the chemical composition of flours and they are a characteristic feature of the quality of wheat from which flour was produced (Fig. 1) www.chopin-sa.com

Fig. 1. The recorded parameters are: P - tenacity (max. pressure reached blowing the dough piece to rupture),
L - extensibility (length of the curve), W - strength of the flour (area of the curve), P/L - configuration ratio of the curve,
Le - P200/P Elasticity (P200 = pressure after 200 ml blowing or 4 cm from origin of the curve)

Values of alveographic parameters point to the utility properties of flour. Parameter P gives information on flour elasticity and is related to the consistency, plasticity and water-absorptiveness of a sample. Parameter L refers to dough extensibility, depending on the elasticity of gluten and the ability of dough to hold gases. Parameter G is equal to square root from the air volume in ml necessary to fill in an air bubble. Parameter W - characterizes the strength of flour and it is directly proportional to the area of the alveograph. Parameter P/L reflects the shape of the graph and points to utility properties. Parameter Ie means the index of elasticity and it correlates with dough elasticity.

The possibilities of using alveograph in the milling industry are enormous. Alveographic indexes are used in controlling the quality of dough, both in the sphere of storage conditions and the study of flour mixtures of different extensibility (controlling the milling process) or with such additives as improvements, emulgents and gluten. A special importance is attached to the classification of a portion of wheat grain and composing their mixtures in order to obtain the flour with the desires technological parameters, useful in the production of a given assortment of baking products. The analysis of alveographic indexes in relation to the chemical composition of flours contributes to a more complete evaluation of flour. Hence, it is justifiable to seek the relation between its structure and certain quality characteristics.

There is no doubt that the properties of flour of different origin depend for instance on the structure of the grain from which that flour was produced. However, in the light of contemporary studies we do not know the relation between the grain structure on the nano-scale and the properties of flour. Therefore, it seems interesting to use the method of small angle X-ray scattering (SAXS) in the studies of flour of different extensibility. The literature data point to the changes in the structure of starch of different origin [7]. Hence, the main assumption of the thesis was to search for the structural changes in starch granules on the level of nano-scale. Changes in the structure of starch polymers could constitute the basis of studying the relation between the structure and the utility properties of a given flour.

That was the reason why the purpose of the present studies was to analyse the nanostructure of selected samples of wheat flours using the SAXS method.

BASIS OF SAXS METHOD

Small angle X-ray scattering (SAXS) appears when some inhomogeneities exist in the studied material. Their magnitude should be in the diameter range of 10Ǻ to10000Ǻ. SAXS scattering intensity depends on the difference in electronic density between the inhomogeneities and the surrounding area as well as on the shape and size of these inhomogeneities [11].

Besides, if there is spatial arrangement of the far range of the existing scattering areas, then a peak appears on the scattering curve SAXS. Therefore, SAXS method is successfully used for the study of the structure of polymer carbohydrates [4, 8]. In particular, SAXS method is fairly frequently used for the study of starch structure, both native and submitted to various physico-chemical processes [4, 5, 6, 8].

Possibilities of SAXS method in studying starch materials

Native starches are built of amorphous amylosis and semicrystalline amylopectin. The semicrystalline structure of starch contains crystalline areas where the chains of amylopectin form double helises arranged parallelly and amorphous areas containing points of amylopectin ramification. Crystalline and amorphous areas are alternate, forming a lamellar structure with the thickness of lamella ranging from 9 to 10mm. Such kind of structure is reflected in the occurrence of a peak on the SAXS curve. The location of this peak is related to the thickness of lamella, while the size is connected with the regularity of the arrangement of lamella as well as with the differences in electron density between various parts of the lamella structure [4, 5, 7].

As mentioned before, the intensity of SAXS scattering is dependent on the inhomogeneity in the distribution of electron density in a sample. The scattering curve SAXS is obtained from relatively large volume of the sample and therefore, it reflects the mean values. In the case of starch materials (e.g. cereal flours), the shape of SAXS curve is affected not only by the lamella structure of starch but also all other inhomogeneities in the distribution of electron density, e.g. the presence of amorphous rings of growth, the areas of increased content of proteins or mineral compounds, or even the structures of "blocklets". Therefore, SAXS method can also be used for the study of materials where the lamellar structure of starch has been destroyed, for instance in the process of extrusion [6, 8, 9].

Frequent SAXS scattering fulfills the involutionary law of dispersion:

where: I0, α - constants,

2q - scattering angle,
λ - X-ray wavelength.

Fulfilling the involutionary law with a wide range of value q and an analysis of the values of coefficient α make it possible to categorize the studied material, i.e. to determine the structural character; we can establish whether a given structure has the form of thin rods, thin layers or it is of fractal character, etc. [3, 9, 11].

On the other hand, lack of fulfillment of the involutionary law by SAXS curve suggests a complex and complicated structure.

Experimental materials

A number of samples of wheat flour were obtained at the Krauze Mill in Lublin. They differed with their chemical composition and utility properties. The flours were composed from various milling passages and different types of wheat.

Table 1 contains some chosen values characterizing the chemical composition of the studied samples [2].

Table 1. Characteristic parameters of studied wheat flours

Kind of flour

Protein
%

Starch
%

Falling number
s

Ash
%

Gluten (wet)
%

T-450

11.2

69.3

260

0.44

25.0

T-500

11.3

62.5

287

0.50

26.0

T-550

11.2

61.8

304

0.54

25.0

T-550hg

13.0

59.1

257

0.55

30.0

T-650lg

10.6

64.6

263

0.64

23.6

T-750

12.1

65.7

263

0.74

28.0

T-850hg

15.3

60.3

296

0.88

33.0

Methods

Alveograph analysis. The alveographic analysis was conducted on the apparatus ALVEOGRAPH "Chopin" according to standard procedures [1]. The content of protein, starch and ash was marked according to standard AOAC [2].

SAXS measurements. Measurements were performed on a slit-collimated Kratky camera using a Cu anode tube with a nickel filter as the radiation source. A proportional counter and a pulse-height analyzer were used to measure the scattered intensity.

Because a slight amount of water increases the differences in the distribution of electron density and at the same time the scattered intensity SAXS through the selective diffusion to various starch areas, the measurements were performed for the samples of flour suspensions in water [10]. The suspensions containing 45% of flour were used. The measurements were performed immediately after preparing the suspension. During the measurement the suspension was tightly locked in a special dish. Besides the measurement of the sample, the measurement of scattering of an empty dish was performed, treating the obtained curve SAXS as the background curve. The measurements were carried out in the range 2θ from 0.076 to 6.52 degrees with changing step from 0.0076 to 0.038 degrees and a counting time of 100 s.

After smoothing the scattering curve and background scattering the subtracting value of the background scattering curve from that of the sample scattering curve, the desmearing procedure was used with an aim of calculating the desmearing scattering curve. The above calculations were carried out using a modified VONK愀 programme [12].

RESULTS AND DISCUSSION

Results of alveographic studies are included in table 2. The analysis of alveographic values suggests that the analysed flours clearly differ with their utility properties. The basis of quality differences is a wide range of parameter changeability: W, L or P/L. An estimation of certain alveographic indexes corresponds to the chemical composition of flours (Tab. 1).

Table 2. The results of alveograph analysis for the studied samples

Kind of flour

W
J g-1.10-4

P
mm H2O

L
mm

P/L

G
mm0.5

Ie

T-450

197

54

129

0.42

25.3

52.2

T-500

231

76

100

0.77

22.2

51.5

T-550

232

75

102

0.74

22.4

51.6

T-550hg

245

67

123

0.54

24.7

55.0

T-650lg

138

52

98

0.53

22.1

43.9

T-750

196

67

107

0.63

23.0

47.0

T-850hg

157

69

102

0.68

22.5

35.4

The analysis of SAXS curves of selected flour samples was conducted in a few aspects. Firstly, a diagram logI(q) vs logq was prepared with an aim of analyzing the obtained values in the context of fulfillment or lack of fulfillment of the involutionary law of scattering. Figure 2 and 3 show exemplary curves of scattering for two flours: T-450 and T-850hg. It is visible that the scattering curves do not show a rectilinear course, but they are distinguished by considerable fluctuations. A similar course of the scattering curves in the relation logI(q) vs logq was obtained from the other studied samples. This testifies to the fact that the studied materials show a very complicated structure considering SAXS scattering and - at the same time - very difficult to determine in the distribution of electron density.

The obtained SAXS curves were also analysed in the aspect of the volume and location of the peak coming from the lamellar structure of amylopectin.

Fig. 2. The scattering curve SAXS for the sample T-450, in the logarithm scale (logI vs logq)

Fig. 3. The scattering curve SAXS for the sample T-850hg in the logarithm scale (logI vs logq)

Figure 4 shows exemplary curves of scattering obtained by means of the desmearing procedure for the samples T-450 and T-750. It is visible that the scattering curve for sample T-450 shows a very distinct peak at the value q = 0.063Ǻ-1, while on the curve for flour T-750 the peak at this value q is hardly visible. Table 3 lists the values characterizing the location of maximum peak and the volume of the peak. It can be seen that the location of the peak changes between values 0.058Ǻ-1 and 0.066Ǻ-1. The location of this peak is related to the thickness of the lamellar structure of amylopectin; hence, for the analysed samples it changes only a little - from 108Ǻ for flour T-650 to 96Ǻ for flour T-550. Much greater differences were observed in the volume of the peak. As was already mentioned, its size will be mainly related to the regularity in the location of lamellas, but also to the differences in electron density between various areas of lamella and their surrounding region. It cannot be excluded that the latter value can also be affected by different speed of water diffusion to amorphous areas of different studied flours.

Fig. 4. Scattering curves SAXS after desmearing procedure for 2 selected samples
(*a peak responsible for the lamellar structure of amylopectin)

The greatest value of the peak area was obtained for the samples T-450 and T-500. Those flours, characterized by little extensibility, mainly come from the central part of the caryopsis endosperm. A slightly lower value of the peak area, but much bigger than for the other flours, was observed for samples T-550hg, although that sample contained the smallest amount of starch (cf. table 1). In its alveographic analysis this flour was distinguished by high quality (W = 245, L = 123, Ie = 55). Flour sample T-550, with a lower content of gluten (by about 17%) shows the value of the peak area smaller by about 44.39% (cf. table 3). At the same time in the studies of the nano-structure, starch from this flour is distinguished by the highest value q (0.066), with the largest falling number (304) for this sample It seems that the observed properties of flour are much related to the origin (wheat cultivar) or differentiated soil-climatic conditions during the growth and development of caryopses. It is interesting to note that flour samples T-550hg and T-550 have similar contents of ash (0.55 and 0.54, respectively).

Table 3. Values obtained by SAXS method (desmearing procedure) for the studied flour samples

Kind of flour

Peak maximum (q)
Å-1

Area of peak
impulse

T-450

0.063

1.00

T-500

0.065

0.97

T-550

0.066

0.32

T-550hg

0.063

0.57

T-650

0.058

0.38

T-750

0.061

0.18

T-850hg

0.062

0.32

Samples T-650, T-750 and T-850, with a high content of ash (from 0.64% to 0.84%) have a relatively low value of the peak area, which confirms the fact that mineral elements are distributed in another part of the caryopsis structure as compared to the semicrystalline area of amylopectin. If they were distributed in this area, then differences in electron density would be greater, and hence SAXS scattering should be greater, too.

The alveographic analysis of those samples shows tendencies for the flour quality to get worse (W = 138; W = 196; W = 157), which is related to decreased extensibility of dough (Ie: 43.9; 47.0; 35.4, respectively).

The analysis of the value of the peak area (Tab. 3) leads to the conclusion that the higher the extensibility, the smaller peak area, but growth of gluten content makes the area under the peak larger.

It would be interesting to find out the relationship between the parameters obtained from the alveographic analysis and the location of the peak (q) or its size. At the present stage of studies the flour samples came from different wheat cultivars. The formation of caryopses took place in various soil-climatic conditions. Differentiation of the structure of starch is connected with its origin [7]. Results of studies presented here do not point to a simple dependence between the state of the flour structure in the nano-scale and the utility properties of flours, but certain correlations between those values do take place.

CONCLUSIONS

  1. The analysis of alveographic parameters in relation to the chemical composition and the results of SAXS method made it possible to provide a more complete characterization of the quality properties of flours.

  2. The type of flour extensibility affected the range of SAXS scattering. With higher extensibility on the SAXS curve, a smaller peak area was observed and it increased with increased gluten values.

  3. Further studies should be conducted to search for a correction between the structure in the nanoscale and the utility properties of flours.

ACKNOWLEDGEMENTS

The authors would like to thank Mr Krzysztof Gaczkowski, manager of Mill No. 1 in Lublin - Lubella Company - for his support in preparing the flour samples and in carrying out alveographic analyses.

REFERENCES

  1. The Alveograph Handbook Edited by Hamed Faridi, Vladimir F. Rasper, and B. Launay ISBN 0-913250-52-X, St. Paul, Minn., 1987.

  2. AOAC. 1984. Official Methods of Analysis. 14th ed., Association of Official Analytical Chemists, Arlington, Virginia, United States.

  3. Barrett A. H. and Peleg M., 1995. Applications of fractal analysis to food structure. Lebensm. -Wiss. u. -Technol. 28, 553-563.

  4. Cameron R. E., Donald A. M., 1992. A small-angle X-ray scattering study of the annealing and gelatinization of starch. Polymer. 33, 2628-2636.

  5. Cie郵a K., 草速owski T., Diduszko R., 1993. Physico-chemical changes occuring in gamma irradiated flours studied by small-angle X-ray scattering. Food Structure 12, 175-180.

  6. Jamroz J., Pikus S., 1997. New aspects of small angle X-ray scattering investigations on potato extrudates. Ital. J. Food Sci. 9, 205-214.

  7. Jenkins P. J., Cameron R. E., Donald A. M., 1993. A universal feature in the structure of starch granules from different botanical sources. Starch 12, 417-420.

  8. Pikus S., Jamroz J., 1997. Small-angle X-ray scattering investigations of extrudates. X-Ray Investigations of Polymer Structures, SPIE. 3095, 167-173.

  9. Pikus S., Jamroz J., Kobylas E., 2000. Fractal structure of starch extrudates -investigation by small angle X-ray scattering. International Agrophysic 14, 93-98.

  10. Pikus S., Jamroz J., Kobylas E., 2000. Small angle X-ray scattering (SAXS) investigations on potato starch in suspensions. 砰wno嗆-Nauka-Technologia-Jako嗆 (Suplement) 2(23), 160-168.

  11. Schmidt P.W., 1991. Small angle scattering of disordered, porous and fractal systems. J. Appl. Cryst. 24, 413-435.

  12. Vonk C.G., 1975. FFSAXS - computer program for SAXS data treatment. J. Appl. Cryst. 8, 340-344.


Stanis豉w Pikus
Department of Crystallography,
Maria Curie-Sk這dowska University, Lublin, Poland
sq. Marii Curie Sk這dowskiej 3, 20-031 Lublin, Poland
email: stanpik@hermes.umcs.lublin.pl

Jerzy Jamroz
Department of Food Quality Assessment,
Agriculture University in Lublin, Poland
Akademicka 13, 20-950 Lublin, Poland

El瘺ieta Olszewska
Department of Crystallography,
Maria Curie-Sk這dowska University, Lublin, Poland
sq. Marii Curie Sk這dowskiej 3, 20-031 Lublin, Poland

Marzena W這darczyk-Stasiak
Department of Food Quality Assessment,
Agriculture University in Lublin, Poland
Akademicka 13, 20-950 Lublin, Poland

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