Growth response of microorganism to powdered neem leaves (Azadirachta indica) and vegetable oil on smoked dried fillets of African Catfish (Chrysichthys nigrodigitatus)

Abstract

Fillets of 50 g ± 5 treated with 30% brine and hot smoked to constant weight in an enclosed coal oven were divided into three parts; X was dusted with air dried powdered neem leaves, Y with freshly extracted vegetable oil, and Z was untreated. Products were packaged in airtight polythene containers, stored and monitored for microbial development for 12 weeks. Nutrient quality was determined. Microbial organisms were detected from the second week of storage. Mean fungal growth on X, Y and Z were 1.5 x 10 3 cfu/g ± 0.2x10 3 , 5.3x10 2 cfu/g ± 0.08x10 3 and 0.9 x 10 3 cfu/g ± 0.091 x10 3 at moisture contents 22.36±0.16, 23.61±0.67 and 23.13±0.52 respectively. Population growth pattern varies with the different treatments; it doubles every fourth week in X, it continues geometrically to stabilise between the eight and tenth week in Y and less gradual in Z. Microbial development was significantly different among various treatments (p< 0.05). Fungi associated with powdered neem leaves on fillets were Aspergillus flavus, Penicillium citrium, A. parasiticus and A. Niger in order of importance. Though neem was found to inhibit fungal growth on mustard seeds, growth seems not to have been inhibited on C. nigrodigitatus, however mycotoxin production ability could have been reduced. There is need to determine the mycotoxin production level of fungi associated with dried fish preserved with powdered neem leaves. Fillets of 50g ± 5 treated with 30% brine and hot smoked to constant weight in an enclosed coal oven were divided into three parts; X was dusted with air dried powdered neem leaves, Y with freshly extracted vegetable oil, and Z was untreated. Products were packaged in airtight polythene containers, stored and monitored for microbial development for 12 weeks. Nutrient quality was determined. Microbial organisms were detected from the second week of storage. Mean fungal growth on X, Y and Z were 1.5 x 10 3 cfu/g ± 0.2x10 3 , 5.3x10 2 cfu/g ± 0.08x10 3 and 0.9 x 10 3 cfu/g ± 0.091 x10 3 at moisture contents 22.36±0.16, 23.61±0.67 and 23.13±0.52 respectively. Population growth pattern varies with the different treatments; it doubles every fourth week in X, it continues geometrically to stabilise between the eight and tenth week in Y and less gradual in Z. Microbial development was significantly different among the various treatments (p< 0.05). Fungi associated with powdered neem leaves on fillets were Aspergillus flavus, Penicillium citrium, A. parasiticus and A. Niger in order of importance. Though neem was found to inhibit fungal growth on mustard seeds, growth seems not to have been inhibited on C. nigrodigitatus, however mycotoxin production ability could have been reduced. There is need to determine the mycotoxin production level of fungi associated with dried fish preserved with powdered neem leaves.