Losses of nutrients and anti-nutritional factors during abrasive decortication of two pearl millet cultivars (Pennisetum glaucum)

Losses of nutrients such as starch, lipids, proteins, iron and zinc as well as phytase activity and of recognised anti-nutritional compounds (some insoluble fibres, iron-binding phenolic compounds and phytates) were determined following abrasive decortication of grains from two pearl millet cultivars (Gampela and IKMP-5) with different composition cultivated in Burkina Faso. In both cultivars, abrasion of the starchy endosperm started when about 12% of the dry matter had been removed from grains but lipid and protein losses followed the loss of dry matter. Zinc loss (%) was lower than that of iron; however, both were higher than dry matter losses. By contrast, phytate loss was lower than dry matter loss. Interestingly, decortication led to significant losses in fibres and iron-binding phenolic compounds with different level depending on the cultivar. Changes in phytase activity also differed in the two cultivars (42% and 11% losses of phytase activity in grains from Gampela and IKMP-5 cultivars, respectively, at 12% of abrasion). Hence, decortication of pearl millet grains does not decrease lipid and protein contents but does considerably decrease some anti-nutritional factors (part of the fibres and iron-binding phenolic compounds). However, as mineral contents and particularly iron content decreased while phytate content remains high, decortication may be insufficient to increase Fe and Zn bioavailability.     

Influence of grain quality characteristics and basic processing technologies on the mineral and antinutrient contents of iron and zinc biofortified open-pollinated variety and hybrid-type pearl millet

The present study aimed at determining whether mineral biofortified pearl millets will continue to maintain significantly higher iron and zinc contents after processing, and the effects of decortication, steeping/fermentation and parboiling on mineral, phytate and total phenolic contents in eight varieties of pearl millets (two biofortified hybrids, Dhanashakti and ICMH 1201, five improved varieties with high iron content and one traditional variety) were also investigated. The hybrids showed higher iron and zinc contents after processing compared to the improved varieties, for example, 17–51% and 10–26% higher iron and zinc contents, respectively, after steeping/fermentation followed by decortication compared to the best varieties. Phytate:mineral ratios also indicated that iron bioavailability was higher in the hybrids after processing, several times above the critical 1:1 ratio. Across all the types, iron content after processing was positively correlated (P ≤ 0.05) with high kernel weight, large kernels, and high fat content, and zinc content was positively correlated with high fat content. These kernel characteristics should aid in the selection of high iron and zinc pearl millet types.     

Effect of food processing of pearl millet (Pennisetum glaucum) IKMP‐5 on the level of phenolics,phytate, iron and zinc

Pearl millet is consumed as a staple food in semi‐arid tropical regions. With a view to upgrading the micronutrient status of pearl millet‐based foods, the effects of single operations and of porridge preparation scenarios on levels and in vitro solubility (IVS) of iron and zinc and mineral complexing factors (phytates: inositol phosphates and phenolic compounds) were tested. Disc milling of grain may add significant iron but this is not necessarily IVS iron. Soaking of grains results in a 25% loss of iron, but also facilitates endogenous phytate degradation, particularly when combined with milling and cooking. Germination and lactic acid fermentation both result in partial phytate degradation. Cooking does not decompose phytates, but results in complex formation of phenolic compounds as measured by a significant reduction in reactive hydroxyl groups. Because of its different distribution in the grain, zinc is generally less affected than iron. Phytate reduction by endogenous phytases is inhibited at low pH as caused by fermentation. Kanwa (alkaline rock salt) could be a functional cooking ingredient as a source of minerals and to react with phenolic substances. The relative IVS of iron was doubled by germination of grain and increased 3‐fold by fermentation of wholemeal slurry. Zinc IVS tended to increase on cooking with kanwa, but decreased in cooked fermented flour. Copyright © 2006 Society of Chemical Industry     

Use of soaking to enhance the bioavailability of iron and zinc from rice‐based complementary foods used in the Philippines

Complementary foods used in the Philippines are predominantly rice‐based, although enrichment with mung beans and sesame seeds is recommended despite their high content of phytic acid, a potent inhibitor of iron and zinc absorption. We have investigated the effect of soaking on the inositol penta‐ (IP5) and hexaphosphate (IP6) (analysed by HPLC), zinc, iron and calcium (via AAS) content of rice‐based complementary foods with and without the addition of mung beans and sesame seeds. Soaking rice flour for 1, 6 and 12 h at 30 °C reduced the content of IP5 + IP6 by 60, 65 and 98% respectively, with only slight changes in zinc, iron and calcium. Levels of IP5 + IP6 were reduced by 10 and 47% by soaking mung bean flour, but not whole beans, for 1 and 6 h respectively. In conclusion, soaking can be used to reduce the IP5 and IP6 content of complementary foods based on mung bean flour and/or rice flour and thus enhance the bioavailability of iron and zinc. © 2002 Society of Chemical Industry     

Modulation of chelating factors,trace minerals and their estimated bioavailability in Italian and African sorghum (Sorghum bicolor (L.) Moench) porridges

Factors able to modulate chelating factors, trace minerals and their bioavailability were investigated in porridges of five sorghum (Sorghum bicolor (L.) Moench) varieties: from Nigeria, Senegal, Burkina Faso and two from Italy. Effects of variety and traditional fermentation and cooking were assessed on iron‐binding phenolic groups, phytates and iron and zinc content and bioavailability. Chelating factors, trace elements as well as the effect of processing (mainly fermentation) were modulated by variety. Fermentation decreased iron‐binding phenolic groups until 49% and phytate content until 72% as well as increased phytase activity 3.4–16.4 fold, leading to enhancement of iron and zinc estimated bioavailability. Cooking alone had almost no effect. The lowest chelating factors content and the highest trace minerals bioavailability were shown by fermented Senegal landrace, whereas the Italian varieties overall showed the worst results. The results indicate that selection of traditional varieties and appropriate processing methods can improve sorghum nutritional value.