Isolation And Propagation Of Lactic Acid Bacteria From Fermented Maize Flour For The Optimization Of The Fermentation Process

Abstract

Production of traditional fermented foods especially lactic acid fermented foods has long been practiced for ages in Africa with a variety of products being produced. Lactic fermentation improves the digestibility of proteins and starch, bioavailability of micronutrients, palatability of porridges as well as imparting antimicrobial properties in them. Spontaneous fermentation of the maize flour products involves mixed culture microorganisms, of which only a given microbial community exists under specific conditions. This has resulted in variation in product quality and low standards with no known shelf-life with varied sensory attributes. The right environmental conditions have not been created for these organisms to thrive and proliferate for the fermentation process. Therefore, this study isolated and characterized fermentative bacteria to optimize the fermentation process to improve the uniformity in quality. The study was therefore specifically carried out to formulate and evaluate use of starter cultures and at the same time characterize lactic acid bacteria from traditionally fermented thick porridge (Mkarango) responsible for its sensory attributes. To prepare Mkarango, the composite flours were mixed in various ratios and the mixture was kneaded into a consistent paste and allowed to ferment at the ambient temperatures (15-250C) for about 2 days, the mixture was decanted and then roasted for 30 minutes. The physico-chemical characteristics was determined following standard procedures by AOAC procedures while Microbial profiles in terms of LAB, Enterobacteriaceae, Yeast and molds were evaluated through a ten-fold serial dilutions of fermented cereal flour samples at each day of fermentation. The population of Lactic acid bacteria and yeast was enumerated on plate count agar and Oxytetracycline Glucose Yeast Extract Agar respectively. Cultures of lactic acid bacteria (L. plantarum, and L. brevis and yeast culture (S. cerevisiae) isolated earlier from fermented Mkarango were used to formulate starter cultures which were either tested alone or in a mixture for their ability to ferment maize flour in order to produce Mkarango. Microbial xvii quality and mineral contents of Mkarango was also determined following recommended standards Results showed that pH, titratable acidity and tannin content of mkarango were significantly (p ≤ 0.05) influenced by the period of fermentation, the type of flour and the interaction of the two. The phytic acid content was only influenced significantly (p≤0.05) by the period of fermentation and ranged from 8.5 to 10.1 for the initial period but significantly reduced after the first and the second day. Increasing the period of fermentation considerably increased the titratable acidity to 0.397% from 0.1% while reducing the pH averagely from 5.6 to 5.34.The LAB, yeast and mould and total viable counts significantly increased with increased period of fermentation whereas the population Enterobacteriaceae reduced. The use of starter culture bacteria in combination with yeasts decreased steeping time of the maize flour and produced acceptable pH results and increased the quantity of the titratable acidity. The product with Yeast+ L. Plantarum+ L. brevis (1:2) and Milk+ L. Plantarum+ L. brevis (1:2) had the highest pH readings (5.12) while products with Milk+ L. Plantarum+ L. brevis (2:1) had the least pH readings (4.8). The population of yeast/molds, and LABs were the highest in all the samples while Enterobacteriaceae was the least. The sensory attributes varied for the different products and the overall acceptability was highest for product prepared from Milk +L. Plantarum + L. brevis (2:1) which scored 4.7 on the 5-point hedonic scale. The results show that the product samples were rich in trace minerals, zinc and iron contents which ranged from 2.7mg/100g to 3.9mg/100g and 2.7mg/100g to 16.9mg/100g respectively. The use of starter culture bacteria in combination with yeasts decreased fermentation time of the maize flour and produced acceptable pH and increased the quantity of the titratable acidity thus creating an environment not conducive for enteric bacterial growth thereby increasing the safety xviii and shelf life of the products. Based on the microbial activity exhibited by the isolates, the best starter organism for production of Mkarango consisted of mixed cultures of LAB and yeast. Quality of mkarango is influenced by more than one single culture. The effect of fermentative action on the nutritional and physical attributes of mkarango is dependent on the period of storage and the type of flour used.