# Non-Thermal Technologies in Food Processing: Implications for Food Quality and Rheology
## 6 Cold Plasma (CP)
Similarly, [PERSON] and [PERSON] [182] investigated and reported the effect of atmospheric-pressure CP on the rheological and gelling properties of high-methoxyl apple pectin using a pin-to-plate plasma reactor at a 1 kHz frequency, 190 V, 210, and 230 V voltages and 3, 6, 9, 12, and 15 min treatment time. The results showed that after CP treatment, the pseudoplastic pectin dispersions transitioned towards a Newtonian-like behaviour, while the decreasing stability and strength of pectin dispersions and gels were observed with the increasing voltage (\(\geq\)210 V). Though improved rheological properties were observed for low voltage-time combinations (190 V/9 min and 210 V/6 min), prolonged exposure at higher voltage processing (210 and 230 V) negatively impacted both the rheological and gelling properties. In another study, the changes in the structural morphology and rheological properties of pectin fractions isolated from okra pods under CP treatment were studied at a plasma flow of 3 L/min, pulse frequency of 20 kHz, power consumption of 750 W, and treatment time of 5 to 30 s [183]. A slight change in the rheological behaviour of the fluid from dilatant towards Newtonian was observed for chelator-soluble pectin and diluted alkali-soluble pectin, and pseudoplastic behaviour for water-soluble pectin. In the investigation of the effect of atmospheric CP (N2-O2/N2 plasma species) treatment on the acid gelation properties of skim milk, it was found that the viscosity increased as the treatment time increased from 0 to 5 min and there was a significant impact on the storage/elastic modulus [180]. Similarly, the study of the impact of CP processing on the rheological properties of pear millet flour at different power levels (20-30 kV) for 10-20 min, found that CP-treated samples exhibited a higher storage modulus (G\({}^{\prime}\)), demonstrating an elastic behaviour [184]. Consequently, the CP-processed pearl millet flours possess higher values of flow behaviour indices than those observed in the control, suggesting higher shear-thinning behaviour. A similar increase in the shear-thinning behaviour was observed for CP-treated gum Arabic dispersions [181]. In general, it is obvious from the review of the literature that CP processing can strengthen the elastic (storage modulus) features of food products as a result of increased intermolecular interactions. This will also aid in determining the possible applications of CP in the food industry. The industrial application of CP technology requires further studies on process optimisation and the effect on food components. This study by [PERSON] et al. [185] investigated the effect of different process times (5, 10, and 15 min) and flow rates (10, 20, and 30 mL/min) of CP treatment on the physicochemical properties, bioactive compounds, fatty acid composition, and volatile profile of chocolate milk drinks. The findings showed that mild (a lower flow rate and shorter duration) and severe (a higher flow rate and longer duration) plasma conditions led to the reduction of bioactive compounds such as the total phenolic content and ACE-inhibitory activity. In addition, these conditions altered the fatty acid composition, increasing the amount of saturated fatty acids and decreasing the amount of monounsaturated and polyunsaturated fatty acids, resulting in less favourable health indices (increased atherogenic, thrombogenic, and hypercholesterolemia fatty acids). A decrease in volatile compounds was also observed. On the other hand, intermediate cold-plasma conditions maintained an optimal balance of bioactive compounds, preserved a desirable fatty acid profile, and improved the volatile profile by increasing the ketones, esters, and lactones. These results suggest that cold plasma technology could be a promising processing method for chocolate milk drinks, but the optimisation of the treatment parameters is necessary to preserve nutritional and sensory properties [185].