EFFECTIVENESS OF DENSITY SORTING IN REDUCING AFLATOXIN B1 AND FUMONISINS IN MAIZE GRAIN

Maize is a staple food in Kenya. About 75% of the maize production is provided by small scale farmers out of the 90% produced by households in the rural areas (Kang’ethe, 2011) while 25% is produced by large scale farmers. Maize contributes to most households as a main food source and as an income earner especially in Western and Rift valley regions of Kenya. Statistics from Kenya Maize Development Program show that maize consumption levels are at 103 kg per person per year contributing to 35% of the dietary consumption per day (Kang’ethe, 2011). Maize production has been fluctuating in Kenya over the last 10 years, with the production levels being 24 million bags to 33 million bags per annum. The consumption levels are estimated at over 36 million bags. Maize farming is faced by major challenges at the pre-harvest stages which include pests and diseases such as Maize Lethal Necrosis Disease and Fall Army Worm whereas post-harvest challenges are majorly inclined to fungi producing mycotoxins (Hell and Mutegi, 2011). Mycotoxins pose threats to food safety, requiring great interventions as food safety enhances people’s health and productivity.

Mycotoxins are secondary metabolites produced by many species of fungi during the pre-and post- harvest periods. High levels of contamination cause the maize to be very unsafe for animal and human consumption (Wagacha and Muthomi, 2008). Currently the issue of mycotoxins is of primary concern in the Kenyan maize value chain. The major fungi of interest are Aspergillus and Fusarium species causing aflatoxins and fumonisins respectively (Kang’ethe, 2011). Aflatoxins are classified as B1, B2, G1 and G2 with Aflatoxin B1 being the most prevalent and the most potent (Kang’ethe, 2011).

Many fungi attack maize in the field which include Aspergillus, Fusarium, Alternaria, Cladosporioum and Cochlioboulus. Some fungi start attacking maize in the field and in storage causing major threats to food safety as well as serious post-harvest losses (Mutiga et al., 2015). Aspergillus spp. and Fusarium spp. are major threats to maize causing Aspergillus and Fusarium ear rots respectively, which reduce grain quality. In storage they tend to cause discoloration and shriveling. In addition these fungi produce mycotoxins as their secondary metabolites (Wagacha and Muthomi, 2008). Aspergillus flavus produces aflatoxin which is highly toxic and carcinogenic. Chronic exposure to aflatoxins is associated with liver cancer and currently Kenya ranks 76th globally for this type of cancer (Chai and Jamal, 2012). Acute exposure to aflatoxins in humans leads to hepatic failure and can kill very fast. In 2010, 2.3 million bags of maize were declared unsafe for human consumption by the Kenyan government due to high levels of aflatoxins (Mutegi, Cotty and Bandyopadhyay, 2018). Over 60% of maize produced in Eastern Kenya has unsafe levels of aflatoxins in some years (Mutegi, Cotty and Bandyopadhyay, 2018). Major aflatoxicosis outbreak was reported in Kenya in 2004 with minor outbreaks being reported in 2005, 2006 and 2009 (Muthomi et al., 2009).

Fusarium verticilloides is associated with production of fumonisins which are also carcinogenic. Chronic toxicity arising from exposure of small amounts in humans over a long period of time leads to esophageal cancer (Mutiga et al., 2015). They have also been associated with disruption of sphingolipid metabolism. Currently, Kenya ranks 8th globally in esophageal cancer cases (Chai and Jamal, 2012). Fumonisins have been associated with blind staggers a condition known as leukoencephalemalocia in animals (Cardwell and Henry 2004). Co-exposure of aflatoxins and fumonisins have been shown to increase human morbidity and stunted growth in children (Smith et al., 2012).Aspergillus and Fusarium require high moisture content to thrive especially in storage (Kang’ethe, 2011). Grain damage in the field facilitates fungal colonization which can be prevented by interventions at the pre-harvest and post-harvest stages. Interventions have been attempted in Kenya by improving storage conditions which are not always enhanced by farmers, so the two fungi tend to thrive (Kang’ethe, 2011). Visual sorting has been attempted by most farmers as they believe that visual characteristics can enable them distinguish between the clean and infected samples, which is not always possible. It has been documented that maize kernels that look very clean can be highly toxic with either aflatoxins or fumonisins or both (Mutiga et al., 2015). Maize samples that are traded in the local markets can be very toxic and are then sold to the millers who sell the flour for household consumption. The rate of maize flour consumption in Kenya is very high, which can lead to continuous exposure to the toxins present. Farmers as well as millers do not have a specific way of distinguishing between the clean and infected maize grains. In some cases, some of the grains tend to have a natural co-occurrence of both Aspergillus and Fusarium, being highly contaminated with fumonisins and aflatoxins increasing the negative health effects of consumption (Kimanya et al., 2015). Mycotoxins remain be a major threat to human and animal health and their great impact has informed several approaches to lowering their levels to below the acceptable limit for consumption. The present study adds onto the knowledge gap in the area of sorting maize grains for fungal and mycotoxin contamination.

Food safety is vital in any society and ensuring that food consumed enhances nutritional status rather than causing harm. Food that is contaminated only leads to predisposing factors that can lead to chronic illnesses or even death. Continuous intake of aflatoxins in small quantities is suspected to have implications for human nutrition and can lead to chronic problems such as stunted growth and liver cancer. Fumonisins have been associated with esophageal cancer. Fumonisins also affect sphingolipid metabolism. The threats posed to human health by intake of aflatoxins and fumonisins in humans either in small quantities over time or in high quantities at once are very high. It is important to reduce this intake in economically viable ways so that everyone can have access to safe maize. Management of the fungi at the farming and storage levels has not guaranteed safe and clean maize. Several approaches have been applied in trying to reduce the toxicity levels in maize to ensure that the maize is safe for consumption. Mitigation processes that have been tried at pre- and post- harvest periods include;

Harvesting practices are highly critical and most farmers have tried harvesting when the maize is fully mature and dry (Kang’ethe, 2011). The approach seeks to ensure that the maize has the right moisture content to reduce the prevalence of any fungal development. However, most farmers don’t have the right information as to when they are supposed to harvest. Some of the approaches such as harvesting at the onset of rain causes most of the maize to accumulate moisture creating a favorable environment for the fungi producing mycotoxins to infect the maize during storage (Alakonya et al. 2009). Climatic conditions that tend to change over time really affect planting and harvesting seasons (Santiago et al. 2015).

Maize drying is one of the most critical steps in reducing moisture content in maize, which reduces probabilities of fungal growth and consequently, fumonisins and aflatoxin production (Hell and Mutegi, 2011). However, some farmers tend to harvest maize when natural sun drying is not highly effective and when moist maize is placed into storage, fungal development is very high. Other regions have very high relative humidity combined with high temperatures. In such places maize is not fully dried and in storage, mycotoxin accumulation is very high. This approach has not been very effective in curbing the problem of mycotoxins.

Maize sorting has also been practiced by farmers whereby most farmers sort the maize during the harvesting process as they get rid of the rotten maize cobs (Kang’ethe, 2011). The cobs that are classified as highly rotten are shelled separately and their grains used to make animal feeds. The maize cobs that pass through the grading system as clean are shelled separately and considered fit for consumption or sale. The sorting approach has a limitation in that not all maize kernels that are highly contaminated are visibly moldy. Some of the highly contaminated samples appear clean when observed visually, so contaminated maize is still consumed in the Kenyan households. The maize grain lots tend to be heterogeneous for the toxins. Most of the toxins tend to be in a minority of the kernels thus mycotoxin contamination is highly skewed greatly reducing sorting effectiveness (Stasiewicz et al. 2017).

Mycotoxins, as a major threat to food safety and human health, have attracted significant interest. In this context, this project seeks to come up with a cost effective intervention method at a farmer’s and miller’s level to reduce toxicity in the maize set for consumption. The project seeks to test the effectiveness of density sorting in reducing toxicity caused by aflatoxin B1 and fumonisins in maize grain. The approach is because maize grain with high levels of toxins has a lower density compared to the maize grains with lower levels of toxins (Shi et al. 2014; Morales et al. 2019). The difference is attributed to the fact that the fungi in the maize grains feeds on the sugars and carbohydrates in the maize, which lead to the production of secondary metabolites which are the mycotoxins (Nelson, 2016; Lewis et al., 2005). This reduces the bulk density of the kernel thus sorting out a portion of the lighter maize grain from a larger sample may reduce toxicity of the maize.

The broad objective of the study was to evaluate a low-cost sorter as a possible technology in reducing mycotoxin contamination in maize that is used for consumption at a household and consumer level through sorting thus enhancing food safety in Kenya.

The specific objectives were: