The Microbial Activities Involved in the Alkaline Fermentation of Soybeans into Dawadawa

ABSTRACT

This study was initiated to identify the dominant microbial species and investigate their activities during the fermentation of soybeans to dawadawa.

The dominant microorganisms present in both the boiled and roasted soydawadawa, which were spontaneously fermented for 72 h, were isolated, characterized and identified using an API kit. The proteinase and a-am ylase activities of the microorganisms were determined. Quality indices such as pH, moisture, protein and fat contents of the soydawadawa were measured. The breakdown of proteins during fermentation of soydawadawa was studied using Gel electrophoresis. The trend in the level of sugars during fermentation of soydawadawa was carried out using the Lane and Eynon’s method. Aromatic compounds (GC-MS method) produced by the different types of soydawadawa were also determined.

Results showed that Bacillus species were the dominant micro-organisms found and which increased from 10'’ to 10n cfu/g and 103 to 109 for the boiled and roasted soydawadawa from the start to the end of fermentation respectively. Lactic acid bacteria ( 104 to 106 cfu/g) were also found. Bacillus subliHs accounted for 48% o f the representative isolates taken from various stages of fermentation. Other Bacillus species accounted for 8% to 16% of the isolates. All the identified Bacillus species demonstrated proteolytic activity in the order Bacillus subtilis >Baciflus furmis > Bacillus cerms > Bacillus pumilus. At a = 0.05, proteolytic activity was significantly affected by fermentation time and production method. However, there was no interaction between these two factors a-am ylase activity was positively affected by fermentation time, increasing with increase in fermentation time.

Hydrolysis of proteins during fermentation was confirmed in^soydawadawa bv an increase in the fraction of lower molecular weight proteins and more distinct bands.

The level of sugars increased in the first 24 hours but decreased subsequently as fermentation progressed. Aroma compounds produced were more in the roasted products than the boiled. Both products were dominated by 3-Hexanol and 9, 12-Octadecanoic acid. However, Tetradecanoic acid and 1,2-Benzene dicarboxylic acid were found only in the roasted product.