Beta-Glucan Content In Tropical Maize Genotypes: Extractability, Structural Analysis, Rheology And Function

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Beta-glucan is a complex soluble dietary fiber with (1→3),(1→4)-β-D linkages in a repeating unit of cellotriosyl, cellotetraosyl glucose chains interspersed with β-(1→3) linkages, found mainly in the cell walls of cereal endosperm and specifically in oat and barley. Beta-glucan is known to impart some health benefits to consumers including lowering of blood glucose and cholesterol level, as well as prevention of colon cancer. Beta-glucan research has concentrated on oat, barley and wheat. The absence of these cereals in tropical West Africa necessitates an exploration into the use of cereals of tropical origin such as maize to identify their potential of being good sources of β-glucan. The objectives of this study weretoscreen tropical maize genotypes for β-glucan content,and evaluate their structure and functionality in food systems. In the present study, β-glucan contents ofseventeen Ghana maize genotypesviz., ‘Mamaba’, ‘Suwan 1 QPM’, ‘Obatanpa GH’, ‘Omankwa’,‘GH9’, ‘Catete’, ‘Dodzi’, ‘Okomasa’, ‘Aburohemaa’, ‘Abontem’, ‘SotuBaka’, ‘Dorke’, ‘Akposoe’, ‘Abeleehi’, ‘Safita 2’, ‘Ohawu Local’ and ‘Golden Jubilee’ were analyzed using hot water, acid, alkaline and alcohol-enzyme based extraction procedures. Gum content varied by extraction method and genotype. Hot water and alkaline procedures produced low extractability demonstrating gum yield ranging from 0 to 2.29 % and 0 to 22.12 %, respectively. Significantly higher gum yields were produced by the acid and alcohol-based enzyme extraction procedures. The acid treatment produced a mean yield of 45.97 % which was not significantly different from 39.97 % yield obtained by the alcohol-enzyme treatment (P>0.05). With regard to genotype, hybrid maize varieties contained the highest mean gum content of 31.83 % while the landraces contained lowest value of 19.11 %. Genotypes having the highest β-glucan content were 1.4 % for ‘Obatanpa GH’, 1.68 % for ‘Abeleehi’ and 2.56 % for ‘GH 9’. Gum content of kernels had positive correlations with protein and fibre but negative correlation with nitrogen free extract. Minimal levels of impurities in the form of starch, protein and fat were present in the gum isolates. Structural analysis of maize β-glucan by 13CNuclear Magnetic Resonannce produced chemical shifts similar to that of standard oat and barley spectra and characterized by slight displacements as upfield and downfield shifts. The aniline blue fluorescence microscopy revealed that β-1→3 branching in maize β-glucan was less than that in oat and was genotype dependent. ‘Abeleehi β-glucan demonstrated higher β-1→3 branching than ‘Obatanpa GH’ β-glucan. The flow behavior of 10 % maize β-glucan dispersion was pseudoplastic and non-Newtonian just as 5 % oatβ-glucan. High water binding capacity of maize β-glucan up to 232 % makes it a suitable ingredient in food products which should resist syneresis. Maize β-glucan was found to be a good fat replacer, replacing up to 15 % of fat in pie crust without compromising sensory attributes.
A Thesis Submitted to the Department of Food Science and Technology, Kwame Nkrumah University of Science and Technology in Partial Fulfilment of the Requirement for the Award of Doctor of Philosophy.