After reduction of phytate with phytase, water slurries of two high-tannin cereal flours were incubated with polyphenol oxidase (mushroom tyrosinase), and the effects on different phenolic groups and on in vitro accessible iron were studied. Enzyme incubation was also performed after cooking, soaking, and germination of the cereals. Phytase incubation significantly decreased the phytate content, and incubation with polyphenol oxidase had a reducing effect on the total phenol content, as well as on the amount of catechol and resorcinol groups. The in vitro accessible iron increased when the cereals were incubated with phytase and polyphenol oxidase, and the highest accessibility of iron was obtained when the germinated samples were incubated. The results from this study imply that oxidation of polyphenols in high-tannin cereals, after reduction of phytate, may be used to increase the bioavailability of iron in foods prepared from these cereals.
Extractable phenolic compounds, classified as total phenolics, resorcinols, catechols and galloyls, were determined in cereals and legume food grains commonly consumed in Tanzania, using various colorimetric methods. Grain samples of red sorghum (udo), finger millet, cowpea, mung bean and brown kidney bean were further processed-soaked in water at different pHs, germinated, cooked or dehulled (legumes only)-and the effect on extractable phenolics was analysed. In untreated grains, total phenolics ranged from 0.9 to 33.7, catechols from 0.8 to 13.5 and resorcinols from 0.2 to 11 mg catechin equivalents (CE) g −1 . Galloyls (tannic acid equivalents, TAE) were found in negligible amounts in most grains, but in appreciable amounts in red sorghum (5.5 mg g −1 ). Processing of grains led to variable effects on the extractable phenolics. Soaking the grains significantly (p < 0.05) reduced the amount of total extractable phenolics in red sorghum, finger millet and cowpea, with alkali and acidic media being more effective. Water soaking had no effect on total extractable phenolics in mung bean and water, while alkali and acidic soaking had no effect on total extractable phenolics in brown kidney bean. Extractable catechols and resorcinols were affected by soaking in a similar pattern to total extractable phenolics. Germination reduced total extractable phenolics, catechols and resorcinols in all samples, except for catechols in mung bean. Cooking (boiling of grains) was more effective in reducing total extractable phenolics in cereals than germination and water soaking, while dehulling was the most effective method for reducing total extractable phenolics in legumes (p < 0.01).
Iron deficiency anaemia is highly prevalent in Tanzania-affecting predominantly children and women. Fortification of cereal flour with micro-nutrients is being carried out as a strategy for combating micro-nutrient deficiencies. Four different cereal flours were fortified with micro-nutrients and evaluated for total and bioavailable iron and zinc, iron binding polyphenolics, phytate content and ascorbic acid. The extractable total phenolics ranged from 1.3 (maize) to 19.4 (redsorghum) mg catechin equivalent (CE) g -1 . Catechols ranged from 1.1 (maize) to 11.7 (red-sorghum) mg CE g -1 . Red sorghum was the only flour that contained a high amount of galloyls (4.0 mg tannic acid equivalent (TAE) g -1 ). All samples contained high amounts of phytate (10.7 ± 1.0 µmol g -1 ). The average total iron was 42.26 ± 10.26 mg kg -1 in the unfortified and 52.67 ± 10.19 mg kg -1 in the fortified cereal flours and the average in vitro available iron was 1.03 ± 0.30 mg kg
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