MICROBIOLOGICAL QUALITY ASSESSMENT OF DRIED YAM CHIPS (Dioscorea rotundata) DURING STORAGE

Abstract

Microbiological and physico-chemical analyses of dried yam chips (gbodo) retailed in four markets in Ilorin and its environs alongside a laboratory – prepared control were carried out over a six month period. Microbiological assay consisted of total viable and coliform counts as well as microbial isolation. A total of 11 fungi and 5 bacteria were isolated from the different samples which included Acremonium sp., Aspergillus fumigatus., A. niger, A. ochraceus, Fusarium solani, Mucor hiemalis, Mucor racemosus, Penicillum notatum, Rhizopus oryzae, Rhizopus stolonifer, Syncephalastrum racemosum and Bacillus cereus, Bacillus subtilis, Erwinia carotovora, Escherichia coli and Staphylococcus aureus respectively. Total Viable Counts ranged from 3.0-120.0 cfu g-1 and coliform counts ranged from 0.00 - 18.80 cfu g-1 pre-storage to 0.10-219 cfu g-1 and 0.0-31.0 cfu g-1 post storage respectively. The physico-chemical parameters analysed were moisture content which ranged between 14.38-17.10% pre-storage to 13.43-24.96% post-storage; crude protein: 5.81-7.53% and 2.11-6.75%; crude fat: 0.35-0.71% and 0.07-0.61%; ash content: 3.30-5.18% and 1.17-4.77%; crude fibre: 0.77-1.45%; carbohydrate: 70.18-74.00% and 70.93-75.17% pre-storage and post-storage content respectively. Levels of Aflatoxin B1 were also monitored throughout the storage period. Insect infestation of the samples occurred during the storage period. Four species were identified; these were Tribolium casteneum, Dinoderus porcellus, Rhyzopertha dominica and Sitophilus zeamais. The traditional practice of open air sun-drying of yam chips should be discouraged, rather oven drying is recommended to minmize microbial contamination. In addition, sorting to exclude extreneous material and minimize mouldiness and insect infestation is suggested.