**5. Post-harvest management**

ment. A. flavus and A. parasiticus are unable to grow or produce aflatoxin at water activity of less than 0.7 (relative humidity below 70% or temperature below 100C, however under stress condition such as drought, aflatoxin contamination can be higher [17]. Various strat‐ egies have been suggested in management of aflatoxins. The strategies should adhere to the following: a) aflatoxin must be transformed to non-toxic products, b) fungal spores and my‐ celia should be destroyed to prevent formation of new toxins, c) the food or feed material should retain its nutritive value and palatability, d) the physical properties of raw material

The Physical and chemical treatment of contaminated commodities include detoxification of aflatoxins using physical means such as removal of contaminated commodities or inactiva‐ tion of the toxin in the commodity. These methods include mechanical sorting and separa‐ tion, washing, density segregation, solvent extraction, irradiationand oxidation [5]. However,efficiency of these techniques will depend on level of contamination. Furthermore, results obtained are often uncertain and relatively costly and could remove or destroy essen‐ tial nutrients in feed [41]. Also some of the methods have disadvantages such as nutritional loss, toxic, limited efficiency and high cost therefore limiting practical application. Various natural and synthetic agents could prevent growth of toxigenic fungi and formation of my‐ cotoxins and these have been reviewed by Mahoneyet al. [47]. Chemical methods of deacti‐ vating mycotoxins in feeds and also clay products that could be used in deactivating mycotoxins have been extensively been reviewed by Kolosova and Stroka [41]. Management

**a.** Good agricultural practices (GAP) that involve adequate fertilizer application and crop

**b.** Management of insect pests that predispose crops to fungal infection through availabili‐

**c.** Optimal harvest time so that crops are not left in the field exposed to environmental factors that predispose crops to pathogen infection. Harvesting immediately after phys‐ iological maturity is recommended since aflatoxin level can increase with delayed har‐

**d.** Suitable management of crop residues as they harbor pathogens that are able to survive

**e.** Management with fungicides has challenges due to environmental pollution and also emergence of resistant pathogen populations and also chemical residue in food prod‐ ucts. Of fundamental valueare environmentally friendly strategies. Polysaccharides and glycoproteins particularly β-glucans from basidiomycetes Lentinulaedodes (edible

should not change significantly d) it must be cost efficient [5, 16, 64].

strategies can be divided into Pre-harvest and Post-harvest strategies.

ty of infection channels such as wounds and other entry points.

**4. Pre- harvest strategies**

44 Aflatoxins - Recent Advances and Future Prospects

rotation with non-host.

vest interval [35].

saprophytically [5].

These include;

Reduction of moisture in grains is very important. There are a number of technologies that could be used to dry maize fast. Such technologies have extensively been reviewed by Lut‐ fyet al., [46]. These technologies are expensive and most African farmers may not be able to acquire them. However some of the post-harvest strategies that could be used in Africa in‐ clude the following: Rapid and proper drying of maize to moisture level of 13% or below. This will halt growth of fungi in the product. Products stored with high moisture increase growth of fungi in the stored product and this leads to increase of aflatoxin in the product [27]. Post-harvest insect control can prevent damage to maize. Clays such as Novasil could bind to aflatoxin in animal feeds [36]. Other control strategies have been reviewed by Ker‐ stin and Mutegi, [40]. Quality management systems for Hazard Analysis Critical Control Point (HACCP) should be employed for management of mycotoxins [65).

**5.** There should be surveillance of aflatoxin testing in food and feed products

in Africa should be able to perform these tests during surveillance survey.

RNA interference (RNAi) refers to post-transcriptional gene silencing mediated by either degradation or translation arrest. This mechanism was first discovered in plants where transgene and viral RNAs guide DNA methylation [74, 34, 52]. The process is a naturally occurring biological process that is highly conserved among multicellular organisms includ‐ ing plants. The process is mediated by small interfering RNAs (siRNAs) that are produced from long dsRNA of exogenous or endogenous origin by an endonuclease (an enzyme) called a dicer. The resulting siRNAs are about 21-24 nucleotides long with 2 nucleotide sin‐ gle stranded 3' end overhangs on each strand. The siRNAs are then incorporated into a nu‐ clease complex called the RNA-induced silencing complex (RISC), which then targets and

In plants, RNAi plays a role in cellular defense, protecting the cell from inappropriate ex‐ pression of repetitive sequences, transposable elements and viral infections [43]. RNAi has

**8. RNA interference Strategy and its mechanisms**

cleaves mRNA that is complementary to the siRNA [86].

**7. Current status of aflatoxins in Africa.**

non-toxigenic strains. This will assist in formulation of appropriate policies.

**6.** Government officials should be sensitized on aflatoxins and advantages of using local

A New Approach in Aflatoxin Management in Africa: Targeting Aflatoxin/Sterigmatocystin Biosynthesis in Aspergillus

Species by RNA Silencing Technique http://dx.doi.org/10.5772/51440 47

In 2010 the level of aflatoxin in maize stored by farmers in Kenya were found to be 1776ppb while in the markets the concentration was 1632ppb [49]. These levels are likely to cause acute toxicity if contaminated products are consumed. In 2011, 40% of samples that were taken from farmers' fields in Eastern and Western Kenya were found with aflatoxin level of >10ppb. In Mali between 2009- 2010 aflatoxin level in peanuts were found to be >10ppb in 35-61 % of samples from farmers' fields and 39-91% samples from farmers stores [73]. Pea‐ nut paste in Mali had high aflatoxin level of >300ppb. Apparently the levels of aflatoxins in West Africa have been quite high. Maize in Benin had 4,000ng/g, In Ghana aflatoxin level in peanuts was reported to be 216ng/g while peanut paste had 3,278ng/g and peanut sauce 943ng/g, cashew paste, 366ng/g. In Nigeria Peanut oil had 500ng/g while yam flour had 7600ng/g [7]. This an indication that Ghana urgently needs intervention strategies to miti‐ gate the aflatoxin challenges. In Kenya,aflatoxin M1 has been reported in milk [37]. There have been re-occurrence of outbreaks of acute aflatoxicoses in Eastern province that causes various deaths [57, 58].The S strain morphotype of A.flavus was identified as the cause of aflatoxicoses in 2004 and 2006 [57]. Apparently the high incidence of S strain of A. flavush‐ ighly correlated with acute aflatoxicosis in Eastern region of Kenya [56, 58, 57]. A simple test for Aflatoxin in maize kernels is the Bright greenish-yellow fluorescence (BGYF) or the black light test. Kernels are viewed under UV lamp (365 nm) for characteristic BGYF. This indi‐ cates a possible presence of aflatoxin producing fungi or mycotoxin itself [84] Laboratories

## **6. Cost effectiveness of aflatoxin reduction strategy in Africa**

It is important to consider economic impacts of food contaminants such as aflatoxins as it imposes enormous socio-economic cost to human society. Wu and Khlangwiset [80] ana‐ lyzed two potential aflatoxin control strategies in Africa, 1) pre-harvest control using atoxi‐ genic strains of Aspergillusflavus competitively to exclude toxigenic strains in maize and 2) post-harvest intervention in a package to reduce aflatoxin contamination in peanuts in Guinea. Health benefit was gained from each intervention in terms of fewer aflatoxin-in‐ duced cases compared to cost of implementing the intervention. Both interventions were found to be cost-effective if applied widely in Africa. The monetary value of life saved and quality of life gained by reducing aflatoxin induced hepatocellular carcinoma exceeds the cost of either bio-control or post-harvest intervention package. The estimated cost-effective‐ ness ratio (CER: gross domestic product multiplied by disability adjusted life years saved per unit cost) for bio-control in Nigerian maize ranged from 5.10 - 24.8 while estimated CER for post-harvest intervention package in Guinea peanut ranged from 0.21 - 2.08. Any inter‐ vention with a CER >1 is considered by world Health Organization (WHO) to be very cost effective while intervention with CER > 0.33 is considered cost effective [80]. The way for‐ ward with toxigenic strains of Aspergillusflavusis therefore:-

