Phytochemical and Mineral Composition of Flour Blends Produced From Wheat, Sweet Potato and Soybean Flour
Objective of the Study
The objective of this project research was to determine the phytochemical and mineral composition of flour blends produced from wheat, sweet potato and soybean flour.
Wheat is counted among the ‘big three’ cereal crops, with over 600 million tonnes being harvested annually. For example, in 2007, the total world harvest was about 607 m tonnes compared with 652 m tonnes of rice and 785 m tonnes of maize (http://faostat.fao.org/). However, wheat is unrivalled in its range of cultivation, from 67 N in Scandinavia and Russia to 45 S in Argentina, including elevated regions in the tropics and sub-tropics (Feldman, 2005). It is also unrivalled in its range of diversity and the extent to which it has become embedded in the culture and even the religion of diverse societies.
Most readers will be aware of the significance of bread in the Judaeo-Christian tradition including the use of matzo (hard flat bread) at the Jewish Passover and of bread to represent the ‘host’ at the Christian Eucharist (Holy Communion). The latter may be a thin unleavened wafer, similar to the Jewish matzo, in the Roman Catholic Church and some Protestant denominations, or leavened in other Protestant denominations and the Eastern Orthodox Church. But how many readers are aware that bread is treated as sacred in everyday life in the largely Muslim communities of Central Asia, such as Uzbekistan and Kyrgyzstan? In this culture, the leavened round breads (nan) are stamped before baking and must be treated with respect, including being kept upright and never left on the ground or thrown away in public. These customs almost certainly originate from earlier indigenous religions in the Middle East in which wheat played a similar role and was sometimes equated with the sun and its god.
Although such cultural and religious traditions are fascinating and will certainly reward further study, they are essentially outside the scope of this article which will examine why wheat has developed and continues to be so successful as a crop and food source.
Origin and evolution of wheat
The first cultivation of wheat occurred about 10 000 years ago, as part of the ‘Neolithic Revolution’, which saw a transition from hunting and gathering of food to settled agriculture. These earliest cultivated forms were diploid (genome AA) (einkorn) and tetraploid (genome AABB) (emmer) wheat and their genetic relationships indicate that they originated from the south-eastern part of Turkey (Dubcovsky and Dvorak, 2007). Cultivation spread to the Near East by about 9000 years ago when hexaploid bread wheat made its first appearance (Feldman, 2001).
The earliest cultivated forms of wheat were essentially landraces selected by farmers from wild populations, presumably because of their superior yield and other characteristics, an early and clearly non-scientific form of plant breeding! However, domestication was also associated with the selection of genetic traits that separated them from their wild relatives. This domestication syndrome has been discussed in detail by others, but two traits are of sufficient importance to mention here. The first is the loss of shattering of the spike at maturity, which results in seed loss at harvesting. This is clearly an important trait for ensuring seed dispersal in natural populations and the non-shattering trait is determined by mutations at the Br (brittle rachis) locus (Nalam et al., 2006).
The second important trait is the change from hulled forms, in which the glumes adhere tightly to the grain, to free-threshing naked forms. The free forms arose by a dominant mutant at the Q locus which modified the effects of recessive mutations at the Tg (tenacious glume) locus (Jantasuriyarat et al., 2004; Simons et al., 2006; Dubkovsky and Dvorak, 2007). Cultivated forms of diploid, tetraploid, and hexaploid wheat all have a tough rachis apart from the spelt form of bread wheat. Similarly, the early domesticated forms of einkorn, emmer, and spelt are all hulled, whereas modern forms of tetraploid and hexaploid wheat are free-threshing.
Whereas einkorn and emmer clearly developed from the domestication of natural populations, bread wheat has only existed in cultivation, having arisen by hybridization of cultivated emmer with the unrelated wild grass Triticum tauschii (also called Aegilops tauschii and Ae. squarosa). This hybridization probably occurred several times independently with the novel hexaploid (genome AABBDD) being selected by farmers for its superior properties. The evolution of modern wheat is illustrated in Fig. 1 which also shows examples of spikes and grain. The genetic changes during domestication mean that modern wheat are unable to survive wild in competition with better adapted species. This was elegantly demonstrated by John Bennet Lawes in the 1880s when he decided to allow part of the famous long-term Broadbalk experiment at Rothamsted to return to its natural state (Dyke, 2003). He therefore left part of the wheat crop unharvested in 1882 and monitored the growth in successive years.
After a good crop in 1883 the weeds dominated and in 1885 the few remaining wheat plants (which were spindly with small ears) were collected and photographed. The A genomes of tetraploid and hexaploid wheat are clearly related to the A genomes of wild and cultivated einkorn, while the D genome of hexaploid wheat is clearly derived from that of T. tauschii. In fact, the formation of hexaploid wheat occurred so recently that little divergence has occurred between the D genomes present in the hexaploid and diploid species. By contrast, the B genome of tetraploid and hexaploid wheat is probably derived from the S genome present in the Sitopsis section of Aegilops, with Ae. speltoides being the closest extant species. The S genome of Ae. speltoides is also closest to the G genome of T. timopheevi, a tetraploid species with the A and G genomes (Feldman, 2001).
The spread of wheat from its site of origin across the world has been elegantly described by Feldman (2001) and is only summarized here. The main route into Europe was via Anatolia to Greece (8000 BP) and then both northwards through the Balkans to the Danube (7000 BP) and across to Italy, France and Spain (7000 BP), finally reaching the UK and Scandanavia by about 5000 BP. Similarly, wheat spread via Iran into central Asia reaching China by about 3000 BP and to Africa, initially via Egypt. It was introduced by the Spaniards to Mexico in 1529 and to Australia in 1788.
MATERIALS AND METHODS
Collection of Materials
Wheat, sweet potato and soybean were all purchased from the main market (Oja-oba) in Owo, Ondo State. The raw materials (wheat, sweet potato and soybean) were all processed into flour in the processing laboratory of Food Science and Technology, Rufus Giwa Polytechnic, Owo, Ondo State.
Preparation of sweet potato
The potato skin were peeled off from the tuber, the edible portion of the sweet potatoes were washed in clean tap water, before they were sliced into pieces and sun dried. After two weeks of sun drying, the dried potatoes chips were milled into sweet potato flour and the sweet potato flour were sieved to obtain fine flour and stored in plastic containers (fig 2).
RESULTS AND DISCUSSION
Table 2: Phytochemical composition of wheat, sweet potato and soybean flour blends
CONCLUSION AND RECOMMENDATIONS
The result revealed the potentials of flour blends from wheat, sweet potato and soybean flour. The processed 100% wheat flour appeared to have a higher phytochemical profile compared with the other products in terms of phenol, flavonoid, saponin and tannin. The phytochemical contents of the 100% wheat were significantly higher (p ≤ 0.05) than its (wheat) blends of sweet potato and soybean flour. The mineral composition of the flour blends revealed that all the samples contain some significant amount of minerals, although the highest mineral content was found in sample 100% wheat flour (control sample). In conclusion, the combination of wheat, sweetpotato and soybean flour blends in adequate proportion has better phytochemical properties and some essential mineral composition as seen in sample 90% wheat flour + 5% sweet potato flour + 5% soybean flour, 85% wheat flour + 10% sweet potato flour + 5% soybean flour and 70% wheat flour + 20% sweet potato flour + 10% soybean flour, the utilization of this flour blends can be put to good use in the food industries due to its minerals especially calcium and phosphorus content and low phytochemicals compositions.
It is recommended that the formulation of flour blends from wheat, sweet potato and soybean flour up to 70% wheat flour + 20% sweet potato flour + 10% soybean flour could be used as food-based approach to solve the problem of protein-energy malnutrition in Nigeria and other Africa countries. Further work is recommended on appropriate packaging for wheat, sweet potato and soybean flour blends.]
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