Toxicity of Cassia mimosoides Leaf Extracts Against the Weevil Callosobruchus maculatus and Nutritional and Organoleptic Quality Assessment of the Treated Vigna subterranea (L.) Verdc

Aims: This present study aimed to assess the toxicity, the inhibition of progeny production and the reduction of weight losses of Cassia mimosoides (L.) leaf extracts against Callosobruchus maculatus (FAB.) on the bambara groundnut grains as well as the physico-chemical, sensorial and organoleptic characterization of that grains 3 months post-storage.

Place and Duration of Study: The toxicity tests were done from April to August 2016 in the laboratory of Applied Zoology of the Department of Biological Sciences, University of Ngaoundere. The physico-chemical, sensorial and organoleptic characterization of bambara groundnut were determined in the laboratory of Food Chemical Engineering of the University Institute of Technology, University of Ngaoundéré from October to December 2016.

Methodology: Toxicity of the plant extracts was evaluated by exposing 20 adult weevils to 5, 10, 15 and 20 g/kg concentrations of the plant extracts mixed with bambara groundnut grains and the mortality of C. maculatus was monitored at 1, 3 and 6 days post-infestation. The inhibition effect of the plant products was assessed on the production of bambara groundnut pea beetle progeny F1. After 3 months of storage, the influence of V. subterranea post-storage losses including weight loss, biochemical, sensorial and taste characteristics were also evaluated.

Results: C. mimosoides extracts caused a significant mortality of the weevil and also significantly reduced the progeny F1 production. The hexane extract was revealed the most effective causing 73.65% mortality, reduced completely the progeny F1 production at the lowest concentration of 5 g/kg. At the same concentration, hexane extract also protected completely bambara groundnut grains up to 3 months from the attack of pea beetle. After 3 months post-storage with the plant extracts, the nutritional value of the bambara groundnut was preserved since no variation in protein, sugar and mineral contents was recorded. Moreover, an improvement in taste, tenderness and crispness of bambara groundnut grains after processing was also noticed.

Conclusion: Thus, C. mimosoides products especially hexane extract could be used as a natural safe and biodegradable plant product to protect bambara groundnut grains from the weevil attacks in the storage for at least 3 months without its significant nutritional value degradation and taste change.