Determination of zinc, iron, resistant starch, phytic acid and their effect on rheological and organoleptic properties for selected Kenyan wheat varieties

Abstract

Micronutrient deficiency of zinc and iron is a major problem worldwide, especially in the developing countries that heavily rely on cereal rich diets for sustenance. Wheat is a popular staple cereal crop containing substantial levels of micronutrients and could be used as a tool for alleviating their deficiencies. The study reported herein focused on determining the concentration of zinc, iron, resistant starch (RS) and phytic acid in 9 newly released wheat varieties and their effect on rheological and organoleptic properties of dough and bread, respectively. The varieties were planted in three agroecological zones namely Eldoret, Mau-Narok and Naivasha in a randomized complete block design after which whole meal flour was analysed for zinc, iron, resistant starch and phytic acid levels. Zinc and iron concentrations were determined by digesting flour samples using the khejdal method and their absorbance read at 213.86 and 248.33 nm, respectively using the Atomic Absorption Spectrophotometer (AAS). RS was determined using megazyme assay kit following manufacturers protocol, while phytic acid was determined using a modified protocol previously used on rice mutants. The proximate composition of whole meal flour was determined using the Near Infrared Spectrophotometer (NIR), while rheological properties were determined using the Farinograph and Chopin Alveograph machines using procedures adapted from method 54-21 and 54-30A, of the approved methods of the American Association of Cereal Chemists. Results obtained showed that genotype and environment greatly influenced levels of micronutrient analysed ranging between 26 to 91 ppm and 111 to 305 ppm for zinc and iron, respectively. Naivasha recorded the highest concentration for zinc while Eldoret had the highest concentrations for iron. The levels of phytic acid ranged from 2.66 to 5.05µg/g, with Naivasha recording the highest concentrations among the three sites. Resistant starch results ranged from 0.37 to 6.03g/100g with the highest levels recorded in Eldoret while the lowest were in Naivasha. Rheological properties of whole meal flour showed increased water absorption for all the varieties across the three sites which ranged from 72 to 80%, while the resistance to elasticity (P) and resistance to extensibility (L) values ranged from 21 to 79mm and 16 to 51mm, respectively. Organoleptic analysis revealed that varieties from Eldoret were much preferred for bread baking compared to the Mau-Narok and Narok, while correlation analysis revealed no major effect of micronutrients on either the rheological or organoleptic properties. The information on nutritional quality of the nine wheat varieties provides an insight on the potential use these varieties in addressing micro nutrient deficiencies.