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

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 ppb, 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.