Modeling of low-temperature plasma inhibition and mechanism of Aspergillus flavus on corn kernels surface

Figures & data

Figure 1. Schematic diagram of the experimental low-temperature plasma generator.

1 – gas supply control unit, 2 – vacuum chamber, 3 – plasma generator, 4 – controller, and 5 – vacuum pump

Figure 2. Schematic diagram of the vacuum chamber.

1 – door, 2 – seal ring, 3 – window, 4 – negative electrode, 5 – positive electrode, 6 – negative electrode, and 7 – vacuum chamber

Table 1. Levels of independent variables chosen for the experimental design.

		Levels
Variable	Unit	−1	0	+1
Plasma-treated time	s	30	60	90
Plasma-treated power	W	300	400	500
Vacuum degree	Pa	85	90	95

Table 2. Box–Behnken design: effects of process variables on decontamination effect parameters.

Exp	Input variables			Response
	Plasma treatment time/s	Plasma treatment power/W	Vacuum degree/Pa	A. flavus spores/log(cfu/g)
1	0	−1	+1	6.43
2	0	0	0	4.70
3	0	0	0	4.58
4	−1	0	−1	5.33
5	+1	−1	0	4.31
6	−1	+1	0	4.43
7	+1	0	+1	4.66
8	−1	0	+1	6.55
9	−1	−1	0	6.44
10	0	−1	−1	5.19
11	0	+1	+1	4.56
12	0	0	0	4.50
13	+1	0	−1	4.58
14	0	+1	−1	4.44
15	0	0	0	4.60
16	+1	+1	0	4.13
17	0	0	0	4.53

The response variable data represent the mean ± standard deviation of three measurements.

Table 3. Results obtained in the assays for validation of the conditions optimized for low-temperature plasma decontamination of corn kernels.

	Process variables optimum point values			Responses
Experimental assay	Plasma treatment time/s	Plasma treatment power/W	Vacuum degree/Pa	A. flavus/log (cfu/g)
1	90	500	90	3.98
2	90	500	90	3.92
3	90	500	90	4.01
Average				3.97
Results predicted by statistical analysis				4.03

Figure 3. Predicted values versus experimental values of A. flavus counts.

Figure 4. Response surface of the independent variables on A. flavus counts.

Figure 5. Effects of plasma treatment on the extracellular conductivity of A. flavus.

Figure 6. The changes of (a) SOD and (b) CAT activity after different plasma-treated time.

Figure 7. A schematic of plasma sterilization mechanism on antioxidant enzyme.

Figure 8. Effect of different durations of plasma-treated time on the values of MDA.

Figure 9. SEM images of the surface of control and low-temperature, plasma-treated A. flavus spores. (a) Control , (b) 300 W-30 s, (c) 400 W-30 s, and (d) 500 W-30 s. 1, change in the shape of cells; 2, disruption of spore’s coat; and 3, spore debris due to the bursting of spores.