Starter culture for corn grist fermentation
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Date
1989-06-26
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Abstract
Microorganisms involved in the Fermentation of corn dough were isolated frog local products using serial dilution and pour plate techniques. The morphological and biochemical characteristics of the Isolates were studied in pure cultures. The dough microflora comprised Saccharomyces cerevisiae, Candida tropicalis, Candida kefyr and Candida krusei. These isolates were tested for their ability to utilize soluble carbohydrates as carbon sources of energy for growth. The isolates as well as combinations of them were inoculated into fresh corn grists at a seeding rate of 1 x 106 cells per ml
Fermentation was monitored for 96 hours for the following parameters: per cent moisture, total nitrogen, total acidity, solubility, total sugars and dough rise. Also pH, viable yeast count, temperature, aroma, taste and texture were determined daily each for 4 days. Glucose, sucrose and galactose gave the Seat growth for Succharomyces cerevisiae, Candida tropicalis and Candida kefyr whilst Candida krusei multiplication was supported by only glucose. Temperature increased from 25oC to 29oC within the initial 24 hours and remained constant; moisture per cent increased progressively throughout the fermentation period. pH decreased significantly ( 0.05) from pH 6.55 to pH 3.70 4.00 at the end of 96 hours. Also acidity per cent increased significantly (P 0.05) from 0.11 to 0.39-0.54 (in terms of lactic acid) with fluctuations due to ester formation. Percentage sugars decreased significantly (P 0.05) from 5.10-5.00 to 1.10-0.70. Viable yeast numbers increased at a rate of 10 - 60 per cent every 2 hours during the first 48 hours but decreased by 13 - 62 per cent within the next 48 hours. Digestibi1ity improved by 41 per cent. Also observed was per cent total nitrogen which increased by 4 – 14 per cent at the end of 96 hours. Volume of corn dough increased by 10 -33 per cent during the first 24 hours but later fall to 9 – 25 per cent. Sactharomyces cervisiae, candida tropicalic and Candida kefyr produced the best acceptable flavours. For starter culture production to be used for controlled fermentation, the three yeasts can be recommended.
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A thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the award of the Degree of Master of Philosophy in Microbiology, 1989