Browsing by Author "Nyamwaka, Irene Seila"

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    Determination of fungi and factors associated with their growth on sun dried rastrineobola argentea in Gucha South, Kisii County, Kenya
    (2014) Nyamwaka, Irene Seila
    Micro-fungi are microorganisms that can withstand very low water concentrations. This enables them to grow on substrates where most other microorganisms do not grow. Fish is sun dried to reduce post-harvest deterioration and to provide a microbiologically stable product. In humid climatic conditions like those found in Gucha South due to high amount of rainfall throughout the year, the growth of micro-fungi on sun dried Rastrineobola argentea (Omena) is accelerated due to absorption of moisture from the environment due to poor storage and handling. This leads to creation of a favorable condition for the growth of micro-fungi some of which produce toxins. Continued consumption of these fungi poses a health threat to the consumers. It is therefore necessary to inhibit their growth on this fish. Previous studies have confirmed presence of mycoflora on dried cereals, fruits and meat. However, limited studies have been carried out to establish the fungi present on sun dried R. argentea which is a major source of proteins in many rural areas in Kenya. In this study, mycoflora of sun dried R. argentea were studied to determine the associated micro-fungi that can lead to the production of mycotoxins in the Sun dried fish due poor handling and storage in Gucha South district. The study also sought to determine the relationships between moisture content and colony forming units and between salt concentration and colony forming units. Samples were collected randomly and systematically from five wholesalers and thirty retailers in six markets. A sample of about 50 grams of R. argentea was collected from each participant during the period between September and December 2012. Moisture content of the samples was determined by oven drying while the salt concentration was determined by titrimetric method. The samples were cultured on dichloran 18 % glycerol (DG 18) agar to identify the fungi growing on the sun dried R. argentea. Identification keys by Barnett, Pitt and Hocking and Samson et al. were used to identify the fungi. Fungal image atlases were also used. The results obtained showed that thirteen different fungal species were isolated. These were; Absidia sp., Aureobasidium sp., Alternaria sp., Cladosporium sp., Aspergillus niger, Aspergillus flavus, Aspergillus fumigatus, Fusarium sp., Trichoderma sp., Rhizopus sp., Yeasts, Penicillium sp. and Mucor sp. The moisture content in all the samples obtained from retailers in different markets ranged from 12.24 to 23.54 percent with that of wholesalers ranging from 17.88 to 24.5 while the CFU ranged from 8.34 x 10 2 to 3.123 x 10 3 per gram with a significant difference in CFU between the different markets (p˂ 0.05). The correlation between moisture content and CFU was 0.69. The findings of this study showed that salting significantly reduced the number of CFU in the samples with 20 % salt concentration being the best. The correlation between CFU and salt concentration was 0.72. The findings from the control experiment showed that the high moisture content of the samples can be reduced if the wholesalers and retailers dried their fish to the recommended moisture content of 10 % and observed proper storage and handling measures. The presence of mycotoxin producing species such as Aspergillus, Penicillium and Fusarium in the samples showed that the fish sold in Gucha South district could be a threat to the health of the consumers. It is therefore recommended that the fish should be dried and maintained at about 10 % moisture content by drying it for seven to ten days during the rainy season and four to five days during the dry season after harvesting in order to make it safe for human consumption.
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    Diversity of Moulds, Sources of Contamination, Moisture Content and Aflatoxin Levels in Fish and Fish Feeds in Kisii County, Kenya
    (Kenyatta University, 2024-02) Nyamwaka, Irene Seila
    Aflatoxins are toxic substances produced by some members of Aspergillus species which commonly invade foodstuffs as well as animal feeds. When consumed in quantities exceeding 10 µg/kg, they cause nephrotoxic and hepatotoxic effects in humans and other animals. Data on the levels of aflatoxins in fish and fish feeds sold in Kisii County is not available. This study was carried out to assess the diversity of moulds associated with fresh, sundried fish and fish feeds sold in selected markets in Kisii County, determine aflatoxin levels in sundried fish and fish feeds, evaluate the relationship between aflatoxin levels and moisture content in sundried fish and fish feeds and assess sources of fungal contamination of sundried and fresh fish sold in selected markets in Kisii County. Samples of sundried and fresh fish from retailers in four main markets in Kisii County were obtained by random sampling. Samples from fish farmers in Kisii County and shores of Lake Victoria were obtained to serve as control. Commercial and home-made fish feeds were purposively obtained from five main outlets and three self-help groups respectively. Moisture content of all samples was determined by oven drying and the levels of aflatoxin in sundried fish and fish feeds determined by ELISA. Isolated moulds were identified using macroscopic and microscopic characteristics and Sanger sequencing technique. Sources of fish contamination were determined using a structured questionnaire and level of contamination expressed as cfu/g. Data on aflatoxin levels and colony forming units in different types of fish and fish feed samples was analysed using one-way analysis of variance. The means that were significantly different were separated using Tukey’s HSD test. Two-way analysis of variance was used to analyse the interactions between markets and type of fungi, types of fish feeds and fungal species, markets and types of fish. Data from molecular work was analysed using MEGA version 4. Relationship between moisture content and aflatoxin levels in fish and fish feed samples was analysed using regression analysis. Thirty fungal species from fourteen genera namely; Acremonium, Alternaria, Aspergillus, Candida, Cladophialophora, Cladosporium, Cunninghamella, Fusarium, Microporum, Mucor, Penicillium, Phoma, Trichoderma and Verticillium species were isolated from fresh and sundried fish samples. Eighteen fungal species were isolated from commercial and home made fish feeds. They comprised of eleven genera; Alternaria, Aspergillus, Aureobasidium, Cladosporium, Eurotium, Fusarium, Mucor, Penicillium, Stachybotrys, Trichoderma and Rhizopus species. Aflatoxin levels in sundried fish ranged from 20-840 ng/kg and 80-500 ng/kg in fish feeds. The cfus/g from control samples were significantly low compared to those from fresh and dried fish samples (p < 0.05). Transportation, handling and storage were found to be sources of fish contamination. The relationship between moisture content and fish, moisture content and fish feed was statistically significant (R2 = 0.942, p = 0.000) and (R2 = 0.797, p = 0.000) respectively. The findings of this study offer new insights into the levels of aflatoxins and associated fungi in fish and fish feeds sold in Kisii County. Therefore, there is need for frequent surveillance on aflatoxin levels in dried fish and fish feeds sold in this County.