BIOACTIVITY OF THREE SELECTED BOTANICALS AGAINST Dermestes maculatus DEGEER AND MICROORGANISMS IN SMOKED CATFISH, Clarias gariepinus BURCHELL.

Abstract

Fish, a major source of protein is mainly preserved by smoking in many developing countries. However, insect pests and micro-organisms constitute economic and health challenges to fish farmers and consumers. Three medicinal plant materials from Zingiber officinale rhizome, Allium sativum bulb and Moringa oleifera seed were evaluated for progeny inhibition in fish beetle, Dermestes maculatus, and incidence of bacteria and fungi in smoke-dried Clarias gariepinus. Cleaned C. gariepinus were separately soaked in extracts of the plants (50g/1000ml) for 60mins before smoke-drying in a mud kiln at 105ºC. Proximate analyses and sensory evaluation were conducted on un-infested fishes in lot A while fishes in lot B were artificially infested with 5 pairs of newly emerged adult D. maculatus for 10 days. Number of emerged larvae, pupae, adult insects and incidence of micro-organisms before and following 90 days in storage after infestation were used as indices of potency of the extracts. Results obtained showed that all the treated un-infested smoked-dried C. gariepinus retained high scores for taste, texture, aroma and appearance within the first five weeks of storage after smoking when compared with the control. This implied that the tested extracts had no negative effect in terms of sensory attributes on the treated fish during storage and can therefore be used for fish preservation. Larvae emerged in untreated fish much earlier (2 days) after artificial infestation than an average of 8 days in extract-treated fish. Mean numbers of developmental stages of D. maculatus were highest in untreated fish having 36.00±2.00 larvae, 21.00±0.58 pupae and 40.00±1.73 adults. Fish treated with extract of A. sativum had significantly (p < 0.05) lowest value of 17.67±1.45, 12.00±0.58 and 21.00±1.53 for larvae, pupae and adult respectively. The extracts reduced the type and load of fungi and bacteria in treated fish compared with the control. Untreated fish had higher moisture content and crude fat, and lower ash, crude fibre and crude protein contents. Meanwhile, A. sativum among all the selected extracts had the least number of larvae (17.67±1.45), adult (21.00±1.53), fungi (9.00x10²±0.53sfu/ml) and bacteria counts (11.33x10²±0.33cfu/ml) following 90 days in storage after infestation. Therefore, A. sativum proved to be most effective among the tested extracts followed by Z. officinale and M. oleifera, hence it could be recommended for control of D. maculatus and microorganisms in smoked C. gariepinus. The plant extracts could play a major role in inhibiting insect feeding and development, incidence and growth of micro-organisms thus extending the shelf-life of smoked fish. Most importantly it will reduce occurrence of food infestation and infection thereby enhancing consumer safety.