## 3 Results and Discussion
### Impurities and Aflatoxins of Paddy Rice  
Figure 9 shows the impurities in fresh and dried paddy rice collected from each drying batch. Among the batches, the amount of impurities in fresh paddy rice was different because it was dependent on the field conditions and the harvesting activities. A significant difference was observed in all batches between the impurities in the fresh paddy rice and those in ISD or sun-dried paddy rice (\(p\leq 0.05\)). In batch 1, the impurities were significantly higher in the paddy rice dried in the ISD than for the paddy rice dried under the sun at \(p\leq 0.05\). The reason could be because the fans sucked a lot of dusty air into the dryer due to the low position of the ISD inlets near to the ground. Since the experiments were conducted on sandy soils, the dust was easily generated by people walking nearby. However, when the ISD inlets were covered in batch 2, the amount of impurities was significantly lower than for paddy  
Figure 8: Moisture content over time of paddy rice dried in the inflatable solar dryer (ISD) and under the sun in each drying batch (20, 21 and 22 November, 2017).  
rice dried under the sun at \(p\leq 0.05\). This suggests that the ISD inlets should be placed at a higher position from the ground or covered, especially for drying operations on sandy soils. Besides dust, other impurities found included leaves, straw, stones and other unwanted materials [35]. Remarkably, most of these materials were found amidst the paddy rice in batch 3.  
The content of aflat in fresh paddy rice, along with paddy rice dried in the ISD and under the sun in batch 1, is presented in Figure 10. Fresh paddy rice had a much higher AFB1 than dried paddy rice. The AFB1 of fresh paddy rice was 1.06 \(\mu\)g/kg, which was already under 5 \(\mu\)g/kg as the maximum limit regulated by European Commission-EC [11]. The paddy rice dried in the ISD showed higher AFB1, AFB2 and AFG1 contents than under the sun. Moreover, no content of AFG1 was detected from the paddy rice dried under the sun. The content of AFG2 of fresh paddy rice was 0.22 \(\mu\)g/kg, but no trace of AFG2 was detected in dried paddy rice. It could be hypothesized that drying seemed to affect the content of AFG2. To the best of our knowledge, no studies have been reported the thermal stability of AFG2 [6; 36]. In general, the total aflat content for all samples revealed that the levels of aflat were still under the threshold of the EU regulation, namely, 10 \(\mu\)g/kg [11].  
Aflatoxins can be found in tropical and subtropical countries due to the higher temperatures and humidity that induce the growth of the moulds. However, this does not seem to be the case for Burkina Faso. This might be related to the high solar radiation in this country, which leads to substantial photodecomposition of aflat [36]. Although the level of aflat was at a safe limit, it should be monitored during long-term storage [6].  
Figure 9: Impurities in paddy rice dried in the inflatable solar dryer (ISD) and under the sun, compared to fresh paddy rice. Different small letters (a, b and c) within groups (batch 1, batch 2 and batch 3) indicate a significant difference at \(p\leq 0.05\).