Isolation and characterization of starch from synthetic hexaploid wheat samples

Wheat (Triticum aestivum L.) is one of the most widely grown and consumed cereals in the world. As one of the basic food sources, wheat is of great importance in human nutrition by providing basic calories. At the same time, wheat is used in the production of many food products, especially bread, pasta, biscuits and various bakery products. It is also evaluated in various industrial applications with its components such as starch, gluten and bran. Wheat is an annual plant species that has been improved all over the world, belonging to the genus Triticum. The genera Triticum and Aegilops are involved in the Triticeae tribe of the Poaceae family. The Triticum includes mostly the cultivated species of wheat, while the Aegilops includes wild species. There are similarities between Triticum and Aegilops in terms of morphological and adaptation characteristics. In wheat breeding, the Aegilops genome is an important gene source that helps increase the quality and resistance of wheat to biotic and abiotic stresses. Some Aegilops species have been reported to be resistant to various diseases and pests, drought and salinity. Aegilops species genes also have the potential to improve the quality of bread wheat. In the classification made according to the number of chromosomes, wheats are divided into three groups as diploid (2n=14 chromosomes; A, B or D genomes), tetraploid (2n=28 chromosomes; A and B genomes) and hexaploid (2n=42 chromosomes; A, B and D genomes). Approximately 1 million years ago, the diploid wheat species Triticum monococcum and Triticum urartu separated from each other and became two different species. Later, it was determined that the species Triticum turgidum and Triticum timopheevii with tetraploid AABB and AAGG genome structures developed. Around 500 thousand years ago, the wild diploid wheat Triticum urartu (AuAu, 2n=14) and the wild grass plant Aegilops speltoides (BB, 2n=14) naturally hybridized with each other and their chromosomes were folded to form the tetraploid wheat Triticum dicoccoides (AuAuBB, 2n=28). A cultivated wheat Triticum dicoccum (AuAuBB, 2n=28) was domesticated through natural or artificial selection from Triticum dicocoides species. Hexaploid wheat Triticum spelta (AABBDD, 2n=42) developed by the natural hybridization and the chromosome doubling of the Triticum dicoccum species with another grass plant, the diploid Aegilops tauschii (DD, 2n=14). Hexaploid bread wheat (Triticum aestivum) developed through natural hybridization and chromosome doubling between the tetraploid (AABB) cultivar T. turgidum ssp. durum (durum wheat) and the diploid (DD) wild species Aegilops tauschii. Recently, the yield of common wheat varieties has been decreasing that causes concern over the world about food safety. To improve and enrich the gene pools of cultivated wheat, primary synthetic hexaploid bread wheat (2n=42, AABBDD) is obtained by using hybridization techniques with the wild species Ae. squarrossa (2n=14, DD) and T. dicoccum (2n=28, AABB) or T. durum (2n=28, AABB) species. These primary genotypes are backcrossed with modern hexaploid wheat to obtain agronomically more suitable genotypes, and these are defined as "synthetic hexaploid wheat". Approximately 1200 synthetic hexaploid wheat lines with different characteristics have been developed by the International Maize and Wheat Improvement Center (CIMMYT) from 1980 to the present. Many valuable genetic variations in wild relatives of modern wheat have been lost during the domestication of wheat. Crossings between synthetic and modern wheat varieties are introducing new traits needed to improve both yield and stress tolerance in wheat. Synthetic wheat provides resistance to some stresses such as drought, salinity, rust diseases, leaf spot, head germination, and improves some traits such as protein content and dough extensibility. Synthetic wheat is seen as an important source of new varieties in different regions due to its superior properties in terms of resistance to various biotic and abiotic stress factors. New resistance genes have been reported for stem, spike and leaf rust diseases in synthetic wheat. Additional genetic variation for salt tolerance that is limited in other common wheat genotypes has also been reported in synthetic hexaploid wheat. High temperature and drought during the wheat growing cause serious yield reductions by reducing grain size, grain number and grain weight. It has been reported that synthetic wheat produces larger spikes and grains under these stress factors and thus has a higher yield potential. Pre-harvest sprouting is an important issue as it results in poor quality wheat flour and financial losses to farmers, especially in cases of high rainfall and humidity before and/or during the harvest season. Aegilops has an important component for pre-harvest sprouting resistance. Normal wheat cannot provide sufficient iron (Fe) and zinc (Zn) for humans. Approximately ¼ of the total population suffers from various health problems due to Fe deficiency. Some synthetic wheats have been reported to have high concentrations of micro and macronutrients. It was also showen that synthetic hexaploid wheat samples are valuable resources for breeding programs to develop new wheat varieties with higher concentrations and health beneficial phytochemical compositions. Protein and gluten content is one of the most important parameters in determining the quality of wheat. Although the amount of protein depends on genetic factors, it is known that environmental factors (rain, temperature, soil, diseases, etc.) also affect the protein ratio. It has been reported that protein, sedimentation and glutenin subunits in synthetic hexaploid wheat line are superior to modern bread wheat. Wild species used in synthetic wheat production have great potential for quality improvement. While cereal products such as bread, pasta and cookies are produced from wheat, by-products from wheat are also very important in today's world. One of the most important of these by-products is starch. Starch, which constitutes approximately 70–75% of the dry weight of wheat grain, is the most dominant carbohydrate component of wheat and has functional properties such as thickening, water retention, film forming and texture provider in the food industry. Starch is basically composed of two polysaccharides called amylose and amylopectin. The ratio, molecular structure and distribution of these two fractions affect the technological properties of starch such as swelling, solubility, gelatinization, retrogradation and viscosity. In addition, the size, shape, crystallinity structure and morphology of the starch granule are also important parameters that determine the functional properties of starch. Therefore, the characterization of starches obtained from different wheat species or newly developed genotypes is of great importance. The main purpose of this study is to determine the physicochemical and functional properties of starches obtained from different synthetic wheat lines and to compare these properties with natural wheat starch. It was aimed to reveal the potential of starches obtained from synthetic wheat genotypes in industrial food applications and to establish a scientific basis for the functional usage areas of these new resources. No study has been found in literature on the extraction of starch from synthetic wheat and its characterization. In this study, starch was isolated from 20 different synthetic wheat lines. The moisture content, amylose level, crystallinity (XRD), morphological structure (SEM), solubility, water binding capacity, swelling force and pasting properties of the obtained starch samples were examined. The results obtained were compared with the properties of natural wheat starch in the literature. According to the findings; flour yields of synthetic wheats vary between 69-78%. It was observed that starch yields obtained from synthetic wheat flours were between 16.7-32.1%. Starch yields were found to be lower than natural bread wheat starch yields (approximately 65-75%). The moisture content of synthetic wheat starches was found to be between 7.2-10.5% which is suitable for storage the samples. Amylose contents of starch samples obtained from synthetic wheat ranged between 28.7-33.4%. Amylose contents of most samples were found to be above 25-30% which is reported in the literature for wheat starch. Wild genome contribution and adaptation strategies in synthetic wheats may lead to higher amylose contents in starch. In the obtained SEM images, it was determined that synthetic wheat starch granules were mostly oval, spherical and flat in shape and granule diameters varied between approximately 5-30 μm. It is consistent with the morphological characteristics of natural wheat starch. The crystallinity ratios of synthetic wheat starches were between 63.7-70.6% and A-type XRD pattern was observed in all samples. Crystallinity ratios were found to be high when compared to the crystallinity ratios of natural wheat starch (29-42%). Solubility values of synthetic wheat starches were determined as 0.18-1.78%, water binding capacity as 102.5-125.5% and swelling force as 8.90-11.65 g/g. It was observed that it had lower solubility, water binding and swelling values compared to natural wheat starch. RVA analyses of synthetic wheat starches revealed that the samples had high viscosity values. On average, peak viscosity of 5525 cP, final viscosity of 6686 cP, breakdown of 1556 cP and setback values of 2717 cP were obtained. The samples also have an average peak time of 6,13 min and pasting temperature of 70,2C. The findings show that synthetic wheat starches have a strong potential in terms of thickening and gel formation. As a result, it has been demonstrated that synthetic wheat starches have significant potential as an alternative to natural wheat starch in industrial and food applications.