Optimization of low-temperature nitrogen plasma in reducing fungi and aflatoxin human exposure through maize

Abstract

Globally, aflatoxin contamination in maize remains a huge burden despite many interventions put in place. The use of low-temperature plasma to decontaminate the maize is a potential solution for ensuring the safety and extended shelf life of the grain. This study optimized the parameters and investigated the efficacy of low-temperature nitrogen plasma (LTNP) in destroying fungi and reducing exposure to aflatoxins in naturally contaminated maize from an endemic region. The study generated 17 experimental runs using the Response Surface Methodology (RSM) of the Box Behnken Design (BBD) with exposure time, pressure, and ionization density as independent variables. Quantitative exposure assessment was conducted using Monte Carlo simulations followed by sensitivity and scenario analysis to study factors influencing exposure and best aflatoxin-reducing plasma parameters. The best-fitting RSM model, the linear model, indicated that increased exposure time but not pressure and power led to a corresponding statistically significant decrease in the fungal load and aflatoxin content. LTNP reduced aflatoxin contamination to levels below all the main global regulatory limits. Numerical optimization of the percent reduction in aflatoxin and fungal load indicated that an exposure time of 1793.4 s, pressure of 0.98 pascal and ionization power of 189.8 W are required to achieve an optimal reduction of aflatoxin content of 82.6% and fungal load of 96.9%. Exposure assessment indicated high exposure especially for populations with lower body weight with ρ = -0.46 between body weight and exposure. The best LTNP combinations achieved aflatoxin exposure reduction results comparable to but with markedly less variation than existing practically used decontamination methods. Further optimization studies during upscaling are recommended, incorporating independent factors such as temperature and processing volume and outcomes such as organoleptic, physical, and chemical changes in the food matrices after treatment.

Keywords: Aflatoxin; Box Behnken design; Fungi; Low-Temperature nitrogen plasma (LTNP); Maize; Quantitative exposure assessment; Response surface methodology (RSM).

Fig. 1

(a) Perturbation plot showing the main effect of individual factors (time, pressure and ionization power) on reduction in aflatoxin (A = time in seconds, B = pressure in pascal, C = power in watts) and (b) combined effect of pressure and time on percent reduction in aflatoxin content.

Fig. 2

(a) Perturbation plot showing the main effect of individual factors (time, pressure and ionization power) on reduction in fungal load (A = time in seconds, B = pressure in pascal, C = power in watts) and (b) combined effect of pressure and time on percent reduction in fungal load.

Fig. 3

Optimal points for aflatoxin and fungal load reduction as generated using the RSM methodology.

Fig. 4

Aflatoxin and fungal concentrations in maize kernels before and after plasma treatment.

Fig. 5

Cumulative probability distribution and distribution of exposure to aflatoxin from maize presented as total daily aflatoxins and the contribution of consumption during breakfast, lunch and dinner to this exposure.

Fig. 6

Tornado chart depicting sensitivity analysis results on important factors affecting daily exposure to aflatoxins. Values adjacent or inside the bars indicate the Spearman’s correlation coefficient explaining the magnitude each of the model inputs has on exposure to aflatoxins.

Fig. 7

Principal component analysis (PCA) of the factor combinations and percent aflatoxin reduction labelled by ordinal reduction levels.

Fig. 8

Reduction in aflatoxin exposure by plasma treatment for ordinal categories of percent reduction in aflatoxin concentrations using plasma in maize.