Evaluation of natural fermentation and germination to improve the nutritive value of cereal grains
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Natural fermentation was used to improve the nutritional quality of cereal grains. Three lots each of soft wheat, three lots of dent corn and one variety each of barley, oats, millet and rice were ground and separately were fermented by mixing with water (1:4 W/V). These mixtures were fermented at 22 [degrees] C and 37 [degrees] C for 4 and 6 days. The same varieties of wheat, barley, oats and rice were included in the germination study. The type of fermentation was confirmed as lactic acid. The most frequently isolated Lactobacillus was L. fermentum from both wheat and corn. The L. cellobiosus was found only in corn. Pediococcus acidilactici was isolated from both wheat and corn meals. Other organisms in the wheat and corn were enumerated. Challenging the fermenting wheat and corn meals and two model systems (trypticase broth with 1.1% and 1.55% added lactic acid) with five of the most common bacterial pathogens showed that all of these bacteria were inhibited by the acidity developed during fermentation. Aliquots of water and oil extracts of fermented dried wheat and corn meals were not toxic when tested in vivo utilizing chicken embryos. Fermentation improved significantly the relative nutritive values (RNV's) of the cereals, except oats, over the temperature range (22 [degrees] C and 37 [degrees] C) as determined by using Tetrahymena pyriform is W. The biological availability of the limiting amino acids in all cereals increased after fermentation. The available lysine values (mg/gN) of the fermented meals ranged from 45.3 for millet to 113.0 for oats as opposed to a range of 3.0 mg/gN for millet and 23.3 for wheat for the non-fermented meals. Isoleucine also increased due to fermentation. The isoleucine values (mg/gN) for the fermented meals ranged from 121.3 to 204.0 with millet having the lowest and wheat having the highest value. The range for the non-fermented meals of corn and oats was between 11.7 mg/gN and 36.3 mg/gN respectively. The fermentation increased the tryptophan content o f the corn meal (1.7 mg/gN) before fermentation to 18.8 mg/gN after fermentation. The RNV's of bread and chips made from fermented wheat and corn meals were 7% and 8% higher than the products (bread, chips) made from the non-fermented meals. The available amino acids lysine and isoleucine decreased sharply during bread making, but the amount retained in bread made from fermented meal (21.2 mg/gN) was about 10 times the amount retained in bread from non-fermented meal. Bread made of fermented meal had an isoleucine value of 109.0 mg/gN whereas the control bread had an isoleucine content of 8.75 mg/gN. The lysine contents of chips from fermented meal was 18.0 mg/gN as compared to 5.10 mg/gN for the chips from non-fermented meals. The amount of lysine retained in the non-fermented corn chips was only 33% of that in chips from fermented meals. Again, tryptophan retained in fermented chips was 10.25 mg/gN which is about five times the amount of the tryptophan retained in the chips made from non-fermented corn. The riboflavin content, 0.14 mg/100g and 0.21mg/100g sample, of the control and fermented wheat meals, respectively, was fully retained following bread making. Riboflavin content of the bread made from fermented meal was significantly (P [less than] 0.01) higher than that made from non-fermented. The loaf volume made from fermented wheat meal was 687 ml/200g flour, as compared to 1087 ml/200g for loaf made from non-fermented meal. This demonstrated the effect of fermentation on the gluten contents of the wheat. The mean sensory evaluation score (a 5-point hedonic scale) of whole wheat bread made with fermented meal was 3.53 as opposed to 3.68 for whole wheat bread made with non-fermented meal. Both bread samples fell about half-way between "like" and "neither like nor dislike" categories. There was no significant difference between the two samples with regard to taste as determined by the paired sample t-test. The mean score for corn chips made from non-fermented corn meal was 2.95 as compared to 3.13 for the chips made from the fermented corn meal. Both corn chips samples fell in the category "neither like nor dislike". Again, there was no significant difference between the samples with regard to taste as determined by the Paired sample t-test. Although evaluation of both products was based on judging for flavor only, this researcher felt that the products scored low by the influence of other factors such as the dark color of the bread (fermented) and the lack of crispiness in case of the chips. Germination of the cereals improved their nutritive values as did fermentation. The RNV's of the meals and available amino acids, lysine and isoleucine were increased significantly (P [less than] 0.01) following germination. Both natural fermentation and germination appear to be about equal procedures in improving the nutritional quality of cereals. Both of these procedures can be utilized at home as well as by the industry. Both procedures convert readily available but nutritionally poor plant protein into protein sources of higher quality.
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