Classification of protein content and technological properties of eighteen wheat varieties grown in Iran

Abstract

The best method for wheat planning and its food industrial usage is evaluation of its technological properties. Classification of protein content and some technological properties of eighteen important Iranian wheat cultivars were investigated. Statistical analysis revealed, highest protein content (11%), protein quality (SDS = 35.6 mL), hardness degree (63%), in Rooshan of Karaj (I), Zagroos of Ahvaz (K) and Marvdasht of Karaj (O) varieties, respectively. On the basis of the quality, the Zagross of Ahvaz (K), Zarrine of Aurumieh (L), Rooshan of Karaj (I), and Chamran of Ahvaz (D) varieties were recognized for their farinograph and extensograph characteristics (water absorption = 61–65%, dough development time = 2.3–5.3 min, dough stability to break down = 15–19.3 min, mixing tolerance index = 22.3–32.3 BU, valorimetry index = 55–64.3 Unit, maximum resistance to extension = 134–450 BU, dough energy = 11.3–100.3 cm² and extensibility = 156–179 mm). The dendrogram was classified into four groups and in general, the wheat cultivar K was the most separated from the other cultivars, followed by L and I.

Introduction

Kind of varieties and environmental conditions exert significant influence on chemical composition of wheat (Ereifej et al., 2001). Breadmaking quality of wheat flour is largely determined by its proteins. That both quantity and composition (quality) of proteins are important for bread making is evident from the observation that breadmaking performance of wheat flour is linearly related with its protein content and that different linear relationships exist for different wheat varieties (Toufeili et al., 1999; Goesaert et al., 2005).

A strong linear relationship has been reported between breadmaking performance as measured by loaf volume, and quantity of proteins with in a wheat cultivar (Toufeili et al., 1999). Protein content within the wheat varieties has been found to be the major factor influencing the quality of the end product it has a linear relationship with the loaf volume of bread (Pomeranz, 1987). Protein content has long been known to be closely related to loaf volume, a primary measure of baking quality (Preston et al., 1992). Both quantitative and qualitative properties of proteins have been shown to be associated with dough strength properties. These properties may also play an important role in determining baking quality (Preston et al., 1992).

Relationship between and among protein fractions and quality parameters may also be strongly influenced by the choice of samples. In many of studies cited above, relationships may be biased due to insufficient numbers of samples or the inclusion of soft, low-protein wheat's of poor baking quality and weak dough properties that would normally not be included in bread-wheat breeding programmes, as pointed out by Wrigley et al. (1982) and Branlard & Dardevent (1985) (Preston et al., 1992). It was found that breads of optimal quality were produced with flour from hard wheat's with protein contents of between 100 and 120 g kg⁻¹ (Quail et al., 1991; Indrani & Venkateswara Rao, 2000).

The main objective of this study was to investigate classification of protein content and some technological properties of seeds in eighteen important wheat cultivars grown under Iranian environments. This study has been was undertaken at Tarbiat Modarres University (Scientific Center of Excellent: Recycling and Losses of Strategic Agricultural Products).

Materials and methods

Wheat varieties

Eighteen Iranian aquatic wheat cultivars [Alvand of Arak (A), Khorasan (B) and Hamedan (C); Chamran of Ahvaz (D), Khorasan (E) and Shiraz (F); Rooshan of Arak (G), Isfahan (H), Karaj (I) and Yazd (J); Zagroos of Ahvaz (K); Zarrine of Aurumieh (L); Shiraz of Fars (M); Gods of Isfahan (N); Marvdasht of Karaj (O); Mahdavi of Khorasan (P) and Karaj (Q); Navid of Hamedan (R)] were chosen in the present study. The experimental material consisted of eighteen important wheat cultivars. These cultivars were selected based on their highest production in Iran. Provision Institute and Improvement of Plant and Seed of the Ministry of the Jihad-e-Agriculture located in Karaj provided of these cultivars. These wheat cultivars were grown under identical condition at this institute for two consecutive crop years 2002–2003 and 2003–2004. Tempered wheat samples of each wheat cultivar were prepared as described by Butt et al. (2001). They were transferred to the university laboratory in suitable package. Grains after harvest were conditioned to 14% moisture content and milled to flour using an experimental Brabender Quadrumat Sr Mill (Duisberg, Germany) (Zhu et al., 2001).

Wheat flour and evaluation of its properties

Samples were milled on a Buhler experimental mill in to flours of 72% extraction rate. Wheat protein was determined by an automatic Kjeldahl method (Kjeltec auto, model 1030, Tecator Co., Hoganas, Sweden). SDS sedimentation values (the quality protein test) were obtained by the British standard international (British Standard Online, 1990). Wheat hardness was assessed by the particle size index method using a NIR-Informatics 8100, Perten Co. (Hoganas, Sweden) and Cyclotec lab mill (Tecator Co.). Flour protein content was determined using NIR according to standard American Association of Cereal Chemists (1995) (AACC) method. Dough properties were measured with 10 g farinograph tests at the plant Breeding Institute, Narrabi, NSW, Australia (Zhu et al., 2001). Farinograph properties (water absorption, dough development time, dough stability to break down, mixing tolerance index and valorimeter value) and extensograph properties (maximum resistance to extension, dough energy and extensibility) were obtained using AACC method. All wheat and flour test results were calculated and reported on a 14% moisture basis and all analysis were made triplicate.

Statistical analysis

The data was statistically evaluated by cluster analysis, using the multivariate analysis of the SPSS package. Within this analysis various items are grouped or classified in a cluster by their similarities of data. Cluster analysis was displayed by Ward's method. The linkage in a dendrogram shows the order of dissimilarity designated as a distance index (Krzanowski, 1995). Statistical analysis of data for chemical and rheological characteristics was carried out using one-way analysis of variance and using Duncan's test separated means; correlation (parametric) analysis was done using SAS and MSTAT-c softwares (Hicks & Turmer, 1999).

Results and discussion

Quantity and quality of wheat protein (protein content and SDS) are two important factors influencing the quality of the final product; therefore, in this research the cluster analysis was based on mentioned two factors and overall quality parameters were obtained by pooling all other attributes. The result of the cluster analysis is shown in Fig. 1. The dendrogram was classified into four groups by arbitrarily applying a rescaled distance cluster Ward's method. The cluster classification of wheat cultivars into four groups is shown in Table 1. Chemical and rheological characteristics of wheat flours and their comparison of averages (Duncan's Multiple Range Test) are presented in Table 2. Statistical analysis of data for chemical and rheological characteristics showed significant differences at several varieties.

Chemical results showed that the protein content varied from 8% to 11%. Averages comparative of protein showed that, the variety of I, F, K and N, respectively, had highest protein content (10–11%). Data showed that the quality of protein (SDS) varied from 19 to 36 mL and hardness varied from 45% to 63% and the highest were in K and H (for SDS) and in O (for hardness) varieties, respectively. In addition, in these wheat varieties protein content was higher, the SDS-sedimentation as quality parameter of flour obtained from the investigated wheat cultivars was lower and hardness was higher than those reported previously (Faergested et al., 2000; Ereifej et al., 2001). Debbouz (1983) and Rao et al. (1993) reported that grain protein contents in wheat varied under different environmental conditions. Moreover, these studies indicate that the environmental factors might have affected the assimilate transport to the grain and influenced chemical composition of grains. The variation in SDS-sedimentation and hardness values of the several tested cultivars (specifically first and second groups) might be attributed to the comparatively good quality of their gluten (Kitterman & Barmore, 1969; Chung et al., 2003).

The farinograph characteristics as water absorption, dough development time, dough stability to break down, mixing tolerance index and valorimeter value of flours differed widely (55–65%, 1–5.33 min, 3–19.33 min, 22.3–117.3 and 30.33–64.33 BU, respectively) and it was maximum for the flours sample I (followed by L, A, B, M, N and K), K (followed by I, L and G), L (followed by J, I and K), Q (followed by P, O and E) and K (followed by L, I and J), respectively. In the several varieties, the averages comparative of farinograph values were similar and higher than those reported previously (Quail et al., 1991; Preston et al., 1992; Qarooni et al., 1993; Farvili et al., 1997; Indrani & Venkateswara Rao, 2000; Zhu et al., 2001).

The extensograph characteristics as maximum resistance to extension, dough energy and extensibility of flours differed widely (62–450 BU, 2–100 cm² and 30–179 mm, respectively) and it was maximum for the flour sample K and D (followed by J, M, L and F), K and D (followed by J, L, F and H) and I (followed by L and M), respectively. In the several tested varieties, the averages comparative extensograph values were higher than those reported previously (Quail et al., 1991; Gupta et al., 1992; Indrani & Venkateswara Rao, 2000).

Dough strength was assessed by farinograph and extensograph measurements, including dough development time, mixing tolerance index and stability. Dough strength was also determined by measurement of the optimum (Peak) mixing time of full-formula fermented dough's for the remix peak baking procedure. Flour protein content was significantly correlated to these farinograph and extensograph parameters. Both the maximum resistance to extension and extensibility increased monotonically with increases in protein content. These relations varied from cultivar to cultivar, suggesting that, mean resistance and response to total protein content were both genetically determined (Preston et al., 1992; Uthayakumaran et al., 1999).

Protein content was shown to be an important determination of various bread qualities (Preston et al., 1992; Toufeili et al., 1999). Among the chemical characteristics, quantity and quality of protein was found to be the best index in predicting the quality of optimal breads. Rheological characteristics such as farinograph water absorption; extensograph ratio figure, extensograph area and hardness were found to be highly correlated to overall quality score of optimal bread (Preston et al., 1992; Toufeili et al., 1999; Indrani & Venkateswara Rao, 2000). The varieties tested were shown to differ in their suitability for the production of bread, the third and forth groups of wheat are appearing least suited. Among the wheat's, over strength and shortness of dough's appear to be major limiting factors for production of quality optimal breads (Quail et al., 1991; Kieffer et al., 1998; Veraverbeke & Delcour, 2002). Totally, the first group of these wheat verities could be recommend for bread and fermentative products and the others for production of biscuit, cake and cookie. On the basis of the quality, the K, L varieties and I were recognized for cultivation for their farinograph and extensograph characteristics. Comparison of chemical and rheological characteristics of the best wheat varieties from Iran with wheat varieties from other countries, without any interpretation, is presented in Table 3.

Conclusions

The breadmaking performance of wheat flour is governed by the quantity and quality of its protein. Increase of protein content could significantly improve dough properties. Increases in the protein content increased mixing time, farinograph peak stability, extensibility and maximum resistance to extension. Difference in the quality observed from flour to flour is thus determined, in part, by superimposition of the effects of protein content. This effect is not sufficient to fully describe the structure–function relationships in dough, and further work is required to determine the effects of the chemical composition on functional properties.

Acknowledgement

The authors are grateful to the Provision Institute and Improvement of Plant and Seed of the Ministry of Jihad-e-Agriculture for supplying the wheat seeds.

References