Effect of soya flour on the lactic fermentation of milled corn.

Corn (Zea mays) is principally eaten in black Africa in the form of a sour meal. The method of preparation in Nigeria consists of steeping corn in water, then wet-milling, and finally allowing it to turn sour (usually about 0.5% total titrable acidity) by natural fermentation. This product, known as "ogi," is then boiled into a porridge or pap called "agidi" having 8' to 10% total solids. Schweigert and Fellingham (2) have shown that the primary acid formed during the production of "mahewu," the favorite corn beverage of the Bantus, was lactic acid. Akinrele (Ph.D. Thesis, Univ. of Ibadan, Nigeria, 1966) has also established that the most important fermenting microorganisms in ogi, the Nigerian equivalent (pap), were the lactobacilli and Saccharomyces cerevisiae. The spontaneous souring of the milled corn which occurs during traditional processing takes too long and proceeds rather irregularly for adaptation into industrial production. During a recent investigation, however, of the protein enrichment of ogi with soya flour, we observed that the mixture of milled corn and raw soya made into a slurry with water brought about a considerable reduction in the souring time of the pure corn mash. Table 1 presents typical results of experiments which illustrate this observation. It is known that lactic fermentation of starchy foods can be favorably influenced by the addition of certain enzyme-rich materials (the Bantus add wheat bran to mahewu) or by the incorporation of low molecular weight nitrogen material that often accompanies protein in natural substances, bringing about enhanced activity of the lactobacilli (1). In the case of soya, it is necessary to find out which of the roles is operative in order to reach' a decision as to whether raw or heat-treated material should be used. The following experiments were then carried out. Nutrient broth having the following composition was prepared: peptone, 0.5 g; yeast extract, 0.3 g; water, 100 ml; and phenol red, two drops. The broth was made slightly alkaline, and 10 ml each was distributed into 12 bijou bottles. Glucose was added to each tube up to a 2% level of the broth, and the bottles were arranged in triplicates of four groups. An 0.05-g amount of raw soya flour was added to each of the bottles in group I. Similarly, 0.05 g of roasted soya flour (heated to 120 C for 2 hr) was added to each bottle in group II, whereas 0.025 g of casein was added to every bottle in group HI, thus keeping the protein levels in all bottles the same. The remaining three bottles were left as the control group. Another set of bottles containing broth was similarly prepared, but dry-milled whole corn was substituted for sugar. After a brief period, all of the bottles were sterilized at 115 C for 15 min and on cooling were inoculated with a drop of the cultured broth of Lactobacillus sp.; these organisms had