Moisture content, insect pest infestation and mycotoxin levels of maize in markets in the northern region of Ghana

Authors: MANU, NAOMI - Kwame Nkrumah University Of Science And Technology; OPIT, GEORGE - Oklahoma State University; OSEKRE, ENOCH - Kwame Nkrumah University Of Science And Technology; Arthur, Franklin; MBATA, GEORGE - Fort Valley State University; Armstrong, Paul; DANSO, JAMES - Kwame Nkrumah University Of Science And Technology; MCNEILL, SAMUEL - University Of Kentucky; Campbell, James - Jim

Submitted to: Journal of Stored Products Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2018
Publication Date: 1/1/2019
Citation: Manu, N., Opit, G., Osekre, E., Arthur, F.H., Mbata, G., Armstrong, P.R., Danso, J.K., McNeill, S.G., Campbell, J.F. 2019. Moisture content, insect pest infestation and mycotoxin levels of maize in markets in the northern region of Ghana. Journal of Stored Products Research. 80:10-20. https://doi.org/10.1016/j.jspr.2018.10.007.
DOI: https://doi.org/10.1016/j.jspr.2018.10.007

Interpretive Summary: In developing countries around the world there is often limited reliable quantitative data on losses to stored grain after harvest and the factors that contribute to these losses, but this information is fundamental to developing and implementing improved grain storage programs. In Ghana corn (maize) is often stored and traded in markets, so the presence of insects and damaged kernels caused by insect feeding, and mycotoxin levels associated with fungal contamination were assessed over a storage season in multiple markets in the Northern Region of Ghana. Across all the markets and sampling periods grain temperature was greater than 30°C, which is favorable for stored-product insect development, although corn moisture tended to be low which should inhibit insect and mold growth. The primary stored product insects collected from the corn samples were red flour beetle, weevils, lesser grain borer, and rusty grain beetle. As the equilibrium moisture content increased the total number of insects recovered also tended to increase, but there was no relationship between corn temperature and the total number of insects. The average percentage of insect-damaged kernels (IDK) in the corn sampled across all the markets and sampling periods was approximately 3%, with a range between 0 and 21%. Using all the market and sampling month data, levels of insect damage tended to increase with corn moisture, but not with temperature, and levels of insect damaged corn also increased with number of stored product insects recovered. The action threshold for aflatoxin in maize in Ghana is 15 ppb, but overall mean aflatoxin level in the markets was approximately 20 ppb and aflatoxin levels ranged from 0.3 to 132 ppb, with 53% of the samples having levels above the threshold of 15 ppb. The mean fumonisin level was approximately 1 ppm, which is below the 4.0 ppm action threshold for Ghana. Our results show that aflatoxin levels were high in the market maize in Northern Region of Ghana and insects were prevalent, even though grain moisture tended to be relatively low, especially compared to the Middle Belt of Ghana where corn is also grown and stored.

Technical Abstract: Reliable quantitative data on maize post-harvest losses and factors that cause them in northern Ghana are limited. In this study we assessed maize at six markets in the Northern Region of Ghana, in and around Tamale, during the harvest and storage period of October 2015–June, 2016. Across all the markets and sampling periods grain temperature was 32.6±0.2°C and equilibrium moisture content (EMC) was 9.5±0.2%. EMC tended to decrease to a low in January and February and then increased again, while mean maize temperature was above 30°C in all months. The primary stored product insects collected from the samples were Tribolium castaneum (Herbst), Sitophilus spp., Rhyzopertha dominica (Fauvel), and Cryptolestes ferrugineus (Stephens). Using all the market and sampling month data, there was a significant correlation between EMC and total number of insects recovered, but not between total number of insects and temperature. The average percentage of insect-damaged kernels (IDK) in the maize sampled across all the markets and sampling periods was 2.7±0.2%, with a range between 0 and 21.4. Using all the market and sampling month data, levels of insect damage tended to be positively correlated with maize moisture, but not temperature, and levels of insect damage increased with number of stored product insects recovered. The action threshold for aflatoxin in maize in Ghana is 15 ppb, but overall mean aflatoxin level was 19.8±1.5 ppb and aflatoxin levels ranged from 0.3 to 132.2, with 53% of the samples having levels above 15 ppb. The mean fumonisin level was 1.2±0.0 ppm, which is below the 4.0 ppm action threshold for Ghana. Our results show that aflatoxin levels were high in the market maize in Northern Region of Ghana and insects were prevalent, even though grain moisture tended to be relatively low, especially compared to the Middle Belt of Ghana.