| dc.description.abstract | Corn (Zea mays) is an indigenous crop of Africa, widely eaten in the form of sour meal. Amongst the ten million Yorubas in the Western region of Nigeria, it is the traditional staple cereal and the first native food given to babies as 'Ogi'. It is therefore important that a food such as this should be studied in order to elucidate the microbiological and biochemical changes that take place during its preparation, and to determine to what extent its nutritive value is affected.
Traditionally, the seeds of corn are soaked in lukewarm water for one to two days, after which they are wet milled and sieved with much water to remove the fiber, hulls and such of the germ. The filtrate is then allowed to sediment and become sour. Usually, the sediment may be diluted to 8 to 10 percent total solids in water and boiled into a porridge or pap, or may be turned into a stiff gel for a meal when it is known as 'eko'.
The microflora of the fermentation was determined using the plate dilution method on a peptone, glucose, yeast extract, inorganic salts, agar medium. The important microorganisms were enumerated, isolated and identified by the procedure recommended by Pederson and Albury (1955, 1962).
The moulds isolated consist of Cehalosporis, Fusarium, Aspergilius and Penicilium of the aerobic bacteria, only Corynebacterium and Aerobacter could be identified, Lactic acid bacteria were also isolated and found to be Leuconostoc mesenteroides, and Lactobacillus planterun. There were also yeasts of which Candida mycoderma, Sacchnromyces cerevisise and Rhodotoruis were identified. During the soaking period, the predominant organism was Aerobacter closcae whilst at souring, it was Lactobacillus plantarun.
The dominant organisms, selected on the basis of their relative population were then used to ferment samples of corn mash singly and combined, in order to determine their roles. The various products were then analyzed for nutrient compilation including vitamin and organic acids.
The effects of steeping and fermentation on the sugars of the corn were investigated using paper chromatographic methods (Bond and Glass 1963, Dubios, Gilles, Hamilton, Rebers and Smith, 1956), and on the starch by viscometric measurements.
There was indication that Corynebacterium michiganense excreted alpha amylase enzymes into the mash which hydrolysed the starch of corn into dextrins. The soaked seeds secreted invertase which converted their sucrose to glucose and fructose, and raffinose to mellibiose and fructose was shown to be capable of synthesizing riboflavin and niacin, while Candida mycoderma which predominated at the end of souring period (pH 3.6) increased lightly the calcium, thiamine, niacin and pyridoxine (vit.B6) contents of the corn mash. Both Saccharomyces cerevisiae and Candida mycoderma were found to contribute to the improved flavour of Ogi.
A biological evaluation of the protein quality of whole corn, fermented and unfermented corn flour (Ogi) and soya fortified Ogi at 30 to 70 mixture was carried out using 5 female rats per diet of 8 to 10 percent protein (Goyco 1947). They were compared with a standard case in diet of 10 percent protein while an egg diet of 6 percent protein was used to determine endogenous and metabolic nitrogen (Mitchell and Oarman 1926). The fermentation did not affect significantly the protein quality of corn, but the biological value, the net protein utilization and the protein efficiency ratio of Ogi were inferior to corn because milling and sieving during processing, removed a considerable portion of the hulls, aleurone layer and germ. When Ogi was fortified with full fat Soya at 30 percent level, the protein efficiency ratio was improved three folds giving a value higher than the theoretical and as proving that a high supplemental relationship exists between their proteins.
The traditional fermentation of corn therefore brings about its nutrient enrichment through the synthesis of some B-Vitamins, the dextrinization of the starch, and the development of flavor. The favor of Ogi is related to the pH of the mash and it is usually not acceptable above 3.7. | en_US |
