Degradation of Toxins Derived from Foodborne Pathogens by Atmospheric-Pressure Dielectric-Barrier Discharge

Abstract

Foodborne diseases can be attributed not only to contamination with bacterial or fungal pathogens but also their associated toxins. Thus, to maintain food safety, innovative decontamination techniques for toxins are required. We previously demonstrated that an atmospheric-pressure dielectric-barrier discharge (APDBD) plasma generated by a roller conveyer plasma device is effective at inactivating bacteria and fungi in foods. Here, we have further examined whether the roller conveyer plasma device can be used to degrade toxins produced by foodborne bacterial pathogens, including aflatoxin, Shiga toxins (Stx1 and Stx2), enterotoxin B and cereulide. Each toxin was spotted onto an aluminum plate, allowed to dry, and then treated with APDBD plasma applied by the roller conveyer plasma device for different time periods. Assessments were conducted using a competitive enzyme-linked immunosorbent assay (ELISA) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results demonstrate a significant time-dependent decrease in the levels of these toxins. ELISA showed that aflatoxin B₁ concentrations were reduced from 308.6 µg/mL to 74.4 µg/mL within 1 min. For Shiga toxins, Stx1 decreased from 913.8 µg/mL to 65.1 µg/mL, and Stx2 from 2309.0 µg/mL to 187.6 µg/mL within the same time frame (1 min). Enterotoxin B levels dropped from 62.67 µg/mL to 1.74 µg/mL at 15 min, and 1.43 µg/mL at 30 min, but did not display a significant decrease within 5 min. LC-MS/MS analysis verified that cereulide was reduced to below the detection limit following 30 min of APDBD plasma treatment. Taken together, these findings highlight that a range of foodborne toxins can be degraded by a relatively short exposure to plasma generated by an APDBD using a roller conveyer device. This technology offers promising advancements in food safety, providing a novel method to alleviate toxin contamination in the food processing industry.

Keywords: Shiga toxin; aflatoxin; bacterial toxin; cereulide; discharge; disinfection; enterotoxin; gas plasma; mycotoxin; roller conveyer; sterilization; verotoxin.

Figure 1

Quantitative measurement of aflatoxin B₁ by ELISA after APDBD treatment. Dried spots of aflatoxin B₁ were exposed to plasma for 0, 1, 2, 5, 15, and 30 min. The concentration of aflatoxin B₁ in each sample was then determined by competitive ELISA. The concentration of aflatoxin B₁ was quantified by comparison to a reference standard. Values were considered significantly different from the untreated sample (0 min) when verified by non-repeated measures analysis of variance (ANOVA), followed by a Tukey test (** p < 0.01).

Figure 2

Quantitative measurement of Shiga toxins (Stx1 and Stx2) by ELISA after APDBD treatment. Samples of Stx1 (A) and Stx2 (B) were treated with APDBD plasma for 0, 1, 2, 5, 15, and 30 min. Recovered samples after plasma treatment were subjected to an immunoassay using a RIDASCREEN^® Verotoxin kit (R-Biopharm AG, Darmstadt, Germany) to determine the concentrations of Stx1 and Stx2. Values were considered significantly different from the untreated sample (0 min) when verified by a non-repeated measures ANOVA, followed by a Tukey test (** p < 0.01).

Figure 3

Dried spots of enterotoxin type B derived from Staphylococcus aureus were subjected to APDBD treatment for 0, 5, 15, and 30 min using a roller conveyer plasma instrument. The amount of enterotoxin type B in the recovered samples was subsequently determined by ELISA. Values were considered significantly different from the untreated sample (0 min) when verified by a non-repeated measures ANOVA, followed by a Tukey test (** p < 0.01). NS: not significantly different from the untreated sample (0 min).

Figure 4

Cereulide derived from Bacillus cereus was subjected to treatment with APDBD plasma for 0, 5, 15, and 30 min using a roller conveyer plasma device. The recovered samples were analyzed by liquid chromatography–tandem mass spectrometry. Representative chromatograms are shown. Peaks corresponding to cereulide (assigned to m/z 1171→357) are indicated (▼). X-axis, retention time (min); Y-axis, signal intensity; cps, counts per second.

Figure 5

Schematic representation of the atmospheric-pressure dielectric-barrier discharge (APDBD) plasma treatment of bacterial toxins. (A) Toxins were applied to an aluminum plate and subjected to APDBD treatment using a roller conveyer plasma device consisting of high-voltage electrodes and earth electrodes. (B) Both electrodes comprise a plastic rod (30 mm diameter) covered with an aluminum sheet (0.02 mm thick) and a silicone sheet (0.5 mm thick). A high-voltage power supply (10 kHz, 10 kV (V_peak-to-peak)) was used to generate the APDBD plasma. Modified from Figure 6 in Sakudo and Yagyu [38], published under an open access Creative Commons CC BY 4.0 license.