Browsing by Author "Helen, Woldemichael"

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    Development of Starter Culture for Kocho, A Traditional Fermented Food of Ethiopia
    (Addis Ababa University, 2019-07) Helen, Woldemichael; Shimelis, Admassu (Assoc. Prof.)
    Enset fermentation for the production of kocho vary depending on the locality of Ethiopia. In this study, 16 kocho samples originating from four different areas were investigated. They varied both in the fermentation technique and the duration of fermentation. Microbial communities of samples were analysed using culture-independent 16S amplicon high- throughput sequencing. In addition, bacterial strains were isolated and identified using phenotypic and genotypic characteristics. Furthermore, the volatile profiles were characterised by HS-SPME treatment coupled with GC/MS to investigate the correlation of the diversity of the microbiota and volatile profiles. In ordered to select the potential starter culture, the dominant Lactobacillus strains were selected and investigate its growth potential. According to the results of culture-dependent methods LAB and aerobic, mesophilic bacteria constituted the dominant microorganisms. A total of 137 strains were isolated and identified in both phenotypic and genotypic characteristics. Lactobacillus plantarum and Lactobacillus brevis were found abundantly. Lactobacillus paracasei, Lactobacillus fermentum Lactobacillus paracollinoides, Acetobacter pasteurianus and Acetobacter persici/farinalis/malorum were also identified. A total of 18 phyla was identified from kocho samples using culture-independent method. Firmicutes and Proteobacteria phyla were found abundantly (> 90%). Next, to those phyla, Bacteroidetes and Actinobacteria were the dominant ones and the rest were found below 0.01%. Lactobacillus and Acetobacter were the most dominant genera. Clostridium, Bifidobacterium, Enterobacteriaceae, Caproiciproducens and Prevotella were also identified with a relative abundance in some samples. The microbiota of samples from Dilla was mostly (ca. 70% to 80%) dominated by Acetobacter. Wolkite samples was dominated by Lactobacillus, which occurred in all samples in varying abundances. In total, 33 volatile organic compounds were identified from kocho samples. Acetic acid and butanoic acid prevailed in all samples. This could be due to the abundance of Clostridium and acetic acid bacteria. Further, relatively high concentrations of hexanoic acid (caproic acid) were detected in the longer fermented Wolkite samples and especially the samples W6 and W7. This could be due to the presence of Caproiciproducens species in those samples. Different enset processing practices and fermentation period caused a quantitative difference in the volatile profiles of samples. The existence of a high amount of free fatty acid, particularly butanoic acid, acetic acid, and pentatonic acid might give kocho a strong odor. Most L. plantarum showed rapid acidification and the higher growth rate than L. brevis. There were significant differences (P≤ 0.05) in pH reduction between L. plantarum and L. brevis. Based on these results L. plantarum (n=10) and L. brevis (n=3) were selected as possible starter strains and applied to enset pulp in laboratory scale. These starter strains showed fast pH reduction, increased microbial load than the control sample and the possibility of a single strain in the fermentation of enset pulps for the production of kocho. Optimization of enset fermentation using RSM revealed that time, amount of starter culture and types of starter strain affected the sensory attributes of kocho. The pH values were significantly different for the different formulation of kocho products (P ≤ 0.05). The overall acceptability of kocho prepared in the farmer backyard and in laboratory scales was not significantly different (P ≥ 0.05). The preferred sensory quality of kocho was produced using 2% L. plantarum starter strain in 6 days of fermentation time.Kocho samples prepared in different areas and by different processing methods varied both in the composition of the microbiota and in the quantity of volatile profiles. L. plantarum and L. brevis were found to be the most abundent LAB species and could be detected in all samples from the beginning to the later stages of kocho fermetation. The volatile compounds which lead to the characteristic flavor and odor of kocho could be identified as short-chain fatty acids which were presumably produced by the microbial activity. The abundance Firmicutes and Proteobacteria phylum could be the main reason for the detection of a high amount of short-chain fatty acids. Therefore, correlation of microbiota composition and volatile profile of kocho contributes to improving the knowledge of the fermentation process. Moreover, this information also used in the selection and development of starter culture. L. plantarum and L. brevis are the potential starter culture in the production of kocho. Application of starter culture for the production of kocho improve fermentation time and overall consumer acceptability of the product.