Evaluating the Potential of Liquid Smoke in Protecting Cocoa Beans against Storage Pest (Corcyra cephalonica)

Abstract

Cocoa is a very important crop all over the world. For the countries that grow it, it has become a major export commodity and foreign exchange earner. To importing countries, it is also considered a valuable raw material for the manufacturing of various products. The postharvest handling of cocoa bean is critical because of its ability to affect the final quality of products. Storage as an aspect of postharvest handling is very critical and must be carried out well to reduce risk factors like insect attacks on beans. Efforts to curb it using synthetic pesticides have ended up with other serious problems such as pesticide residue in food products, depletion of the ozone layer, and development of resistance by target pests. In the meantime, improper disposal of the cocoa pod husk (CPH) waste after pod breaking has also been found to be serving as alternate hosts and hideout for cocoa plant disease pathogens such as Phytophthora spp. The resulting disease causes a reduction in the quantity and quality of beans harvested. The nature of the problem described above inspired the design of this research to investigate the possible use of CPH to produce wood vinegar/ liquid smoke (LS) as a biopesticide for controlling the storage pests of cocoa beans. In this study, the third instar larva of Corcyra cephalonica was used model insect. The specific objectives include ; 1, determining the compounds present in CPH liquid smoke. 2, ascertaining the toxicity, repellence and feeding deterrence effects of the liquid smoke against Corcyra cephalonica, and 3, investigating the effect of CPH liquid smoke treatment on the quality of cocoa beans. The study was set up in a Completely Randomized Design (CRD) with four replications. There were five treatments representing various concentration rates of liquid smoke :10%; 20%; 50%; 100 % concentrations and control (0 %) distilled water. The treatment was applied to the outer surface of mini jute sacks containing cocoa beans. The GCMS analysis of the LS detected 20 compounds. The compounds with higher concentrations were Butanamine (27%), Acetic acid (8.23%), 2-Pyrrolidinone (7.25%), Butanoic acid (6.96%), 2,5-Pyrrolidinedione (6.93%), 2H-Pyran-2-on (6.45%) and Cyclopropyl carbinol (5.62%). Allyl N butanoate and Hydrazine compounds were found to have a strong odour hence possess high potential for use as an insect repellent. In the test for mortality, LS did not cause enough mortality effect against Corcyra cephalonica. At the undiluted concentration of 100%, the LS could kill just half (52.5 %) of the insect population after five days (120hrs) of treatment. However, from the repellency test, 100% concentration of LS repelled as much as 90% of the insect population. The feeding deterrence index (FDI) was also highest at the 100% treatment. This, however, was not significantly different from the performance of the 50% concentration, which also deterred 90% of feeding activity. The FDI effect also caused a reduction in bean damage: 7.65% damage for beans treated with 100% LS as against 22% damage in beans without treatment. Weight loss was also reduced from 2.13% in control to 0.11 % in beans treated with 100% LS. Further quality tests on the beans showed that LS treatment did not cause any significant change in the FFA and pH content of the beans. The organoleptic test also suggested that LS treatment did not cause any substantial change in the flavour and overall acceptance of beans taste and aroma. In conclusion, liquid smoke from the pyrolysis of cocoa pod husk has the potential to be used for protecting cocoa beans against pest attack