Atmospheric Cold Plasma Interaction with Allergens in Food Processing

Approximately 5-15% of allergen recalls are associated with consumer reactions, which are largely attributed to cross contamination with allergens. Therefore, it is essential to mitigate against allergen cross-contamination during food processing, distribution and storage. Atmospheric Cold plasma (ACP) was found to effect functionality and modify proteins such as enzymes, owing to the chemical and bioactive radicals generated known collectively as reactive oxygen (ROS) and nitrogen species (RONS), together with physical stress such as electric field and UV irradiation. Allergens are comprised of proteins; thus, ACP was investigated as a promising tool to mitigate allergen cross-contamination in food processing sectors. The aim of this work is to understand and develop ACP based approaches for control and prevention of allergen cross-contamination within food processing. This program of research focused on developing a mechanistic understanding of how ACP interacts with food allergens and affects the antigenicity of food allergens. RSS systems, which comprised two modes of tunable plasma discharge, spark discharge (SD) and glow discharge (GD), were used as plasma source for the liquid application environment. To optimise the efficacy of application, diagnostics studies of the plasma devices and the chemical composition of plasma activated water (PAW) generated by RSS system were investigated. SDPAW predominantly contains H2O2 and NO3-. GDPAW predominantly contains peroxide, NO2- and NO3-. The concentration of ROS and RNS was dependent on applied voltage and frequency of the plasma. To understand the mechanism of plasma in gas-phase, the ignition and propagation of air discharges of SD and GD were examined using fast imaging diagnostic techniques in collaboration with the University of Liverpool. SD drives both anode-directed and cathode-directed streamers, while GD drives only anode directed streamers. SD had higher OH emission than GD at both positive and negative half-periods. The effect of SD and GD on the antigenicity reduction of milk-derived and wheat-derived allergens were then studied. Casein, a-lactalbumin and ß-lactoglobulin are the major allergens in bovine milk while gliadin is the major allergen in wheat gluten. These allergen solutions were treated directly by SD and GD. The antigenicity of caseins, a-lactalbumin and gliadin decreased while ß-lactoglobulin increased. The results showed the modification of chemical structure of plasma treated allergens. A concentration dependence also emerged across the different studies. For example, indirect PAW treatment reduced casein antigenicity but only at low concentrations of 0.01 mg/ml, when applied in combination with a mild heat treatment at 60 °C. The ROS generated in SDPAW is attributed to antigenicity reduction of casein, while RNS generated in either SDPAW or GDPAW was not involved. The mode of application was probed, where liquid mediated direct SD and GD RSS were compared with indirect PAW treatment, and further compared to direct gaseous dry plasma approaches of dielectric barrier discharge (DBD) in-package system and plasma brush (PB) system. The antigenicity reduction of milk-derived and wheat-derived allergens were studied in terms of sample concentrations and plasma process duration. The results showed the conformational and linear epitopes of plasma treated allergens were altered. The efficacy for antigenicity reduction is correlated with protein composition, sample concentration and plasma process duration. Overall, dry or liquid mediated plasma processes can be tailored to mitigate allergen residues in food processing. The food allergens from two important foods were investigated to reveal the universality of ACP. The effectiveness of antigenicity reduction was well explained by the modification of conformational and linear structures of allergens treated by ACP.