Effect of Malt Pretreatment and Fermentation on Anti-Nutritional Factors and Mineral Bioavailability of Pearl Millet (Pennisetum glaucum L.)

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Abdelrahman, Samia Mohamed
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Pearl millet (Pennisetum glaucum L.) is a source of carbohydrate, protein and minerals that is comparable to other common cereal grains. However, anti-nutrient factors like phytate and polyphenols reduce nutrient bioavailability which can be improved by suitable processing methods such as germination and fermentation with and without malt pretreatment. In this study of 8 pearl millet cultivars Ashana, Dahabaya, Dembi, GB-87-35, Kordofani, Madelkawaya, population I Shambat and Ugandi were investigated. Results showed that pearl millet contained 7.7–8.9% moisture, 1.6–2.3% ash, 11.4–13.0% protein, 4.0–7.7% oil and 2.1–3.2% crude fiber. Major mineral contents were 13.0–19.4, 370.0– 547.5, 70.3–93.3, 49.1–61.9 and 551.0–1290.4mg/100g for Na, K, Mg, Ca and P respectively. Trace mineral contents were 1.3–1.8, 7.5– 11.7, 0.8–1.7, 0.5–1.5 and 0.062–0.103mg/100g for Zn, Fe, Mn, Cu and Co respectively. HC1-extractability of these minerals (an index of their bioavailability to humans) were 63.1–73.3% Na, 64.9– 73.3% K, 55.7–61.4% mg, 27.7– 88.3% Ca, 31.0–38.5% P, 41.2– 45.9% Zn, 22.5–27.7% Fe, 44.3–48.8% Mn, 21.3–28.6% Cu and 85.3–88.6% Co. Phytic acid content ranged from 422.3–1101.0 mg/100g and polyphenol ranged from 306.7 – 669.4 mg/100g. Cooking caused slight increase in mineral content and significantly (P < 0.01) improved the bioavailability of all the minerals investigated; phytic acid reduced by 6 – 10% and polyphenols by 6 – 8%. Germination for 2, 4 and 6-days showed significant (P < 0.01) differences in the concentration of minerals during the course of germination. Total content of Fe, Zn and Mn were increased significantly (P < 0.01) for all cultivars. The bioavailability of all the minerals was significantly (P < 0.01) improved throughout all the time intervals of germination. Phytic acid was reduced by 66.3 – 81.0% after 6-days of germination while polyphenol content was reduced by 34.3 – 44.0% Fermentation of cultivars: Ashana and Dembi affected the minerals content and significantly (P < 0.01) improved the HCl extractability (extractabilities were more than doubled). Phytate content was reduced by 64.4 and 66.6% for Ashana and Dembi, respectively. An increase in polyphenols content of the fermented flour was noticed for both cultivar towards the end of fermentation. Fermentation with 5% malt addition showed significant (P < 0.01) enhancement of the HCl-extractability of minerals compared to fermentation alone. Also, phytic acid was significantly reduced by 70.4% and 76.0% for Ashana and Dembi, respectively. Polyphenol showed an increase in content after 14h of fermentation. Fermentation with malt is a potential process for decreasing the anti-nutrient levels and enhancing mineral bioavailability which is attributed to phytase activity inherent in pearl millet seeds.
November - 2004
Malt , Pearl Millet (Pennisetum glaucum L.)