POTENTIALS OF CO-CULTURE OF SACCHAROMYCES CEREVISIAE AND AMYLOLYTIC LACTIC ACID BACTERIA ON CASSAVA AND WHEAT DOUGH FERMENTATION

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Date
2016-05
Authors
AMAPU, TARFENA YOILA
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Abstract
Lactic acid bacteria and yeasts were isolated from fruits, wet milled cereals and cassava using De Man Rogosa Sharpe (MRS) media and Potato Dextrose agar respectively. The Lactic acid bacteria colonies were screened for amylase production on MRS starch agar. Colonies with clear zones of inhibition were identified as Amylolytic Lactic acid bacteria (ALAB) and were selected for further studies. Yeasts and ALAB isolates were morphologically and physiologically characterised and thereafter identified to species level using API 20 C AUX and API50 CHL kits Biomerieux respectively. Results obtained showed that all the isolates grew at 30, 37, 40 and few at 45°C.They all tolerated NaCl at 3, 6 and a few at 10%, they utilised glucose and some produced gas. They also utilised common sugars found in cereals and fruits such as sucrose, maltose, fructose, galactose and some ALAB strains utilised raffinose. The predominat yeasts and ALAB characterised and identified were Saccharomyces cerevisiae (12) 60% and Lactobacillus plantarum 8(57.14%). Fermentation conditions (pH, time and temperature) were optimized for reducing sugars and enzyme activity. The optimum time was found to be 24 h ; pH 6.0 was found to have a strong influence on reducing sugar and on enzyme activity at 0.69mg/ml and 3.11U/ml respectively. Enzyme activity was stable at 70°C. Lactobacillus plantarum (AMz5) from maize and Saccharomyces cerevisiae YSg2 from sorghum showed considerable potentials for leavening ability in wheat flour(94cm3).The leavening potentials of Lactobacillus plantarum and Saccharomyces cerevisiae in co culture were investigated in wheat/cassava composite flour of different ratios. Results showed that there was no significant difference (P < 0.05) among three of the formulations (10, 20%, and Wf (dough started with isolates) in dough rising after four hours of fermentation time. Therewas a significant difference from 30% cassava inclusion. The dough rising capacity of control (commercial yeast) was faster, though dough started with Lactobacillus plantarum and Saccharomyces cerevisiae increased steadily up to four hours. The proximate analysis of the flours and baked products was conducted. Results showed that all the flours met standard specifications for moisture content of less than 14%, carbohydrate and protein 8090% and 1-3% respectively, while ash content for market cassava was at variance with standard specifications of 1.64%. Generally, the proximate (fat, protein and carbohydrate) values of wheat/cassava blended bread decreased with increasing levels of cassava flour substitutions, while moisture and ash contents increased with increase in cassava flour ratios. However, there was no significant difference between the products made from industrial and market cassava flours.The crude protein content of products baked with industrial cassava had higher protein values than the market cassava products. The sensory evaluation which was used to assess the quality of baked products using the five point Hedonic scale, showed a general acceptance of the products. The average scores howeverdecreased as the level of cassava flour substitution increased. There was no significant difference (P > 0.05) in taste, aroma, appearance, texture ratings of the bread samples of 100% wheat bread, 10% and 20%. Wheat bread started with isolates was highly rated by the panelists. A strong correlation existed between dough pH and viable cell growth of the inoculants, where decrease in pH led to increase in viable counts. Bread produced from 10% and 20% wheat cassava rated higher in all the attributes tasted for than those produced with commercial yeast and routine bread
Description
A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES AHMADU BELLO UNIVERSITY, ZARIA, IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF DOCTOR OF PHILOSOPHY IN MICROBIOLOGY DEPARTMENT OF MICROBIOLOGY, FACULTY OF SCIENCE, AHMADU BELLO UNIVERSITY, ZARIA, NIGERIA.
Keywords
POTENTIALS,, CO-CULTURE,, SACCHAROMYCES CERVISIAE,, AMYLOLYTIC LACTIC ACID BACTERIA,, CASSAVA,, DOUGH FERMENTATION,
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