STUDIES ON THE MOISTURE SORPTION ISOTHERMS OF SORGHUM, MILLET AND MAIZE GRAINS AND THEIR MALTS IN RELATION TO MICROBIAL SHELF STABILITY.

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Date
1997-07
Authors
OLALUNMOYE, MUFTAU KOLAWOLE
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Abstract
Moisture equilibrium behaviour for absorption of water by three cereal grains of industrial importance: Sorghum (Sorghum bicolor Sk 5912), millet (Pennisetum americanum EV) and maize (Zea mays Ex-Borno) and their malts were studied at 20, 30 and 37°c over a water activity range of 0.1 - 0.95. The malts were found to exhibit a higher equilibrium moisture content thean the corresponding raw grains at water activity > 0.65 at all temperatures. Analysis of the Isotherms showed that the malts can tolerate more moisture than the grains. Futhermore, the results indicated that the storage stability of both the grains and their malts decreased with increase in temperature. The monolayer values of the grains and their malts were determined and which tended to decrease in relation to increase in storage temperatures. Isoteric heat of desorption was also determined and which was shown to be higher in the grains than the malts; but decreasing in relation to storage temperatures. The microbial load on the raw grains was also estimated. The total count showed that millet had the higher value 5.76x105 cells per gram, followed by sorghu.n 2.38x105 cells/gram while maize had the least value of 1.8x105 cells/gram. Viable counts showed that sorghum had the highest value of 1.81x105 efu/g. followed by millet 1.03x105 cfu/g. and maize had the least value of 3.8x104 cfu/g. respectively. The identity of microbial isolates showed that fungi are the most abundant contaminating/spoilage organism of cereal grains. The mold genera isolated include: Penicillium, Fusarium, Aspergillus, Pythium, Phytophtora, Cladosporium, Colleotrichum, Al ternaria, Mucor, and Curvularia. The yeast isolates include the genera Saccharomyces, Candida and Torula. The mold genera Pythium (AA), Curvularia (DD), Fusarium (GA) and Phytophtora (KA) were isolated from the interior of the grain. viii The bacterial isolated included the genera Pseudomonas, Klebsiella, Staphylococcus, E Coli, Acinetobacter, Bacillus and Proteus. All the isolates are external floral of the cereal grains expect the Pseudomonas SP. The time of appearance of mould was also determined. Mold growth was detected earlier at 95% relative humidity than 85% at all the storage temperatures. But at any particular relative humidity, the time of visual detection of mold increased as temperature increased. It is therefore recommended that cereal grains be stored in the raw state than the malt form at low moisture content <. 6% for good storage stability.
Description
A Thesis submitted to the Postgraduate School, Ahmadu Bello University, Zaria in partial fulfilment of the requirements for the award of Master of Science degree in Microbiology
Keywords
STUDIES, MOISTURE, SORPTION ISOTHERMS, SORGHUM, MILLET, MAIZE GRAINS, RELATIONMICROBIAL SHELF, MALTS, STABILITY.
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