Determination of fungi and factors associated with their growth on sun dried rastrineobola argentea in Gucha South, Kisii County, Kenya
Nyamwaka, Irene Seila
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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.