Isolation and characterization of microorganisms associated with the traditional sorghum fermentation and development of starter culture for production of Sudanese kisra

Sulma Ibrahim Mohammed, Purdue University

Abstract

Sorghum flour of the Dabar variety was obtained from Sudan. The flour was mixed with water in 1:2 (wt/vol) ratio and fermented at 30$\sp\circ$C for 24 h. The bacterial populations increased with fermentation time and reached a plateau at approximately 18 h. At the end of 24 h sorghum batter pH dropped from 5.95 to 3.95 and had a lactic acid content of 0.80%. The microbial population during the 24-h period of fermentation consisted of bacteria (Pediococcus pentosaceus, Lactobacillus confusus, Lactobacillus brevis, Lactobacillus sp., Erwinia ananas, Klebsiella pneumoniae, and Enterobacter cloacae); yeasts (Candida intermedia and Debaryomyces hansenii) and molds (Aspergillus sp., Penicillium sp., Fusarium sp., and Rhizopus sp.). Pediococcus pentosaceus was the dominant microorganism at the end of the 24-h fermentation. When three consecutive fermentations using an inoculum from the previous fermentation were carried out, the bacterial population increase plateaued at 9 h. The lactic acid content and pH were 0.90% and 3.86, respectively, by 9 h and 1.45% and 3.58 by 24 h. The microbial populations in these fermentations were dominated by P. pentosaceus. The end products produced during fermentation of sorghum flour for production of Sudanese kisra were lactic acid, acetic acid, propionic acid, isobutyric acid, butyric acid, ethanol, propyl acetate, and 2-furanmethanol. Lactic, and acetic acids were the major organic acids produced. The total water soluble sugars of sorghum flour consist of high percent of sucrose and maltose and less amounts of fructose and glucose. As the fermentation progresses the amounts and type of water soluble sugar changes. There was an increase in glucose and maltose concentrations, and decrease in the sucrose concentrations during natural fermentation. However, the sucrose, glucose and fructose were not detectable during traditional fermentation. Developed starter cultures that consist of combinations of lactic acid bacteria with different proportion of hetero- to homolactics or combinations of lactic acid bacteria and yeasts did not produce the same amount or types of end products that produced during traditional fermentation of sorghum flour. Sensory evaluation of kisra produced from sorghum fermented by these developed starter cultures remained the important key to choose the best starter combinations.

Degree

Ph.D.

Advisors

Kirleis, Purdue University.

Subject Area

Food science

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