# Non-Thermal Technologies in Food Processing: Implications for Food Quality and Rheology
## 6 Cold Plasma (CP)
This study concluded that voltages between 80 and 100 kV and treatment durations of 4 to 5 min are recommended for the shelf-life assessment of plasma-treated chopped carrots to maximise the inhibition of spoilage microflora and preserve the quality [173]. Additionally, it has been demonstrated that CP inactivates the enzymes Peroxidase (POD) and Polyphenol Oxidase (PPO), which are typically found in the majority of fruits and vegetables and cause browning reactions by forming o-quinones following a series of reactions that are deemed undesirable because they ultimately result in a deterioration in the flavour and colour [167]. [PERSON] et al. [174] investigated the kinetics of the inactivation of tomato peroxidase as a model enzyme at 30, 40, and 50 kV, using atmospheric air dielectric barrier discharge plasma treatments up to 5\({}^{\prime}\). They found that both the treatment time and voltage reduced the POD enzyme activity, with the former having a stronger effect. CP has also been assessed for efficacy in controlling key microbial indicators encountered in the food industry effluent. In the study by [PERSON] et al. [175], it was found that microbial counts in synthetic dairy and meat effluents were significantly reduced within 120 s of ACP treatment and completely annihilated after 300 s. In addition, 20 min of ACP treatment provided a \(\geq\)2 Log\({}_{10}\) reduction of _Bacillus megaterium_ endospores in the wastewater effluent. For the determination of the potential toxicity, the study used two fish cell lines (PLHC-1 and RTG-2) and a crustacean model (_Daphnia magna_) for bioassays. While untreated effluents were toxic to the aquatic models, ACP treatment inhibited the toxic effects. However, the observed toxic effects were dependent on the concentration and treatment period of the ACP-treated effluent, with 30% cytotoxicity in _Daphnia magna_ and fish cells seen after 24 h of exposure to the ACP-treated effluent for concentrations up to 5%. This study demonstrates ACP's potential as a highly effective wastewater treatment agent while emphasising the need to control treatment parameters to prevent environmental toxicity [175]. In the food industry, several unit operations including mixing, shaping, kneading, moulding, pasteurisation, filling, etc., are highly influenced by the rheological properties of food products [176]. It has been reported that the interaction of plasma species with starch causes chemical, enzymatic, and physical modifications through three different plausible mechanisms such as cross linking, depolymerisation, and plasma etching [177]. Hence, the response of the food rheological characteristics to plasma species during treatment would be of interest to the food industry as they determine the design of food processing and handling equipment. Review articles on the application of cold plasma as a potentially useful technology to improve the rheological properties of food and starch modification have been published [176; 177; 178]. The summarised findings of these reviews showed that cold plasma could be a promising technique for modifying starch to achieve the desired rheological characteristics. In an informative study, the interaction of plasma species with corn starch changed the rheological behaviour from pseudo-plastic to non-Newtonian due to molecular weight degradation [179]. This resulted in the decreased viscosity of the CP-treated starch, affirming that CP can modulate the rheological properties of starch food products. On the other hand, CP processing has proven to improve the gelling characteristics of plant proteins by modifying their structure through oxidation and crosslinking [180]. Also, from a study on the effect of cold atmospheric-pressure plasma on the rheological properties of gum Arabic, it was shown that CP treatment improved its viscosity and elastic-like behaviour [181].