Pearl millet malting: factors affecting product quality

Abstract

Pearl millet (Pennisetum glaucum (L.)R. Br.)is a drough tolerant cereal crop grown primarily as a dood grain in southern Africa. In this southern Africa region, the grain is tradidionally processed either by germination or fermentation prior to consumption.Malting involves the limited germination of cereal grain in moist air under controlled conditions. Malts were prepared by malting two varieties of pearl millet, SDMV 89004 and SDMV 91018. The grain was steeped for 8h with a cycle of 2h dry (air rest) and germineted at four temperatures, 20º, 25º, 30º, and 35C overº 5 days. The malts were then dried at 50ºC for 24h. Mobification of starch granules and protein bodies in pearl millet grain structure due to germination was found to start at the germ- floury endosperm interface and move in the direction of the peripheral endosperm. Aleurone layer, cell wall and vitreous endosperm were not greatly involved in modification process. Ungerminated pearl millet grains do not exhibit diastatic power (DP), α - or β – amylase activity. DP, α – and β – amylase activity increase as germination time and temperature increases. DP, total and soluble β – amylase activity increase with germination time and watering treatment probably because high moisture promotes high metabilic activity. Free amino nitrogen (FAN) increase as the germination time, temperature and watering treatment increases. This may be related to the fact that high temperature and moisture promote the growth of roots and shoots, wich are a good of malt FAN. Malt extract increases with germination time and watwring treatment. This increase in hot water extract is an indication of the progress of modification of the malt during the germination process. The increase in malting loss with germination time, temperature and watering treatment observed is related to the high respiratory activity during germination. A germination temperature of 25-30 ºc and germination time of 3-5 days, medium watering treatment are optimun for pearl millet. These conditions result in high DP, FAN, α – and β – amylase activity and malting loss of pearl millet malts, which are similar to sorghum malts, represent an excellent potential for utilisation of pearl millet malt for sorghum beer brewing purposes,. Additionally , pearl millet malt could be a better alternative than sorghum for leger brewing due to the fact that it has higher β – amylase activity. Phytic acid decreases during malting, probably due to phytase activity. Soluble proteins and the Nitrogen solubility index increase due to partial hydrolysis of storage proteins by endogenous proteases. Proteases. This is complimented by an increase in vitro protein digestibility of pearls millet malts. A reduction in the viscisity of flours made fron pearl millet malts, which is due to increased α – and β – amylase, may contribute to the use of this malt to improve the energy and nutrient density of porridges for young children. Germination significant reduces the mousy odour, characteristic of ground pearl millet meals when stored. This is probably due to the grouth of lastic acid bacteria which decrease the PH in the grain affecting the water soluble phenolics which leached out. These phenolcs are belieced to be responsible for the mousy odor of the stored pearl millets meals. Pearl millet malt represents an excellent an potential for utisation of pearl millet for sorghun beer and it appears that it can be used in lager beer brewing. The improved nutritional and funcfional properties of pearl millet malt are an indication that the malting process, a low cost processing technology, usable at both rural and indistrial level, can be successfully aplied to prepare nutrious and funtional food produts