Effect of plasma activated water on Escherichia coli disinfection and quality of kale and spinach.

Plasma activated water (PAW) is one of the promising technologies for fresh food disinfection. In this study, PAW was generated by activating water under nonthermal plasma for 10, 20, 30, 45 and 60 min. The effectiveness of Escherichia coli inactivation by PAW treatment on kale and spinach samples was assessed. The differences between kale and spinach samples in terms of the product quality and nutritional characteristics upon PAW treatment was also investigated. Further, changes in leaf structure and surface morphology upon PAW treatment was also evaluated through FTIR cuticle analysis and SEM imaging of leaf surfaces. Results showed that, around 6 log CFU/g reduction in E. coli population was observed in PAW-45 min treatment. However, PAW treatment significantly reduced the total chlorophyll content in both kale and spinach. The total phenolic content, flavonoid content and ascorbic content were altered according to the PAW activation time. Further, kale and spinach behaved differently in terms of antioxidant activity and membrane electrolytic leakage values upon PAW treatment. Clear changes in the cuticular layer and the surface morphological characteristics of the leaf samples were observed after PAW which could be the reason for the significant differences between kale and spinach characteristics in response to PAW treatments.

Influence of plasma activated water treatment on enzyme activity and quality of fresh-cut apples.

Plasma activated water (PAW) is a new approach to disinfecting surfaces including fresh-cut foods while maintaining their quality attributes. The aim of this study was to evaluate the effect of PAW on enzyme activity, microbial and physicochemical quality of fresh-cut apples. PAW was produced at different production activation times of 10 min, 20 min, 30 min, 45 min and 60 min and the fresh-cut apple slices were washed with PAW for 5 min and stored at 4 °C for 12 days. Results showed that PAW treatments reduced the polyphenol oxidase activity immediately after treatment and the lowest activity was recorded in PAW-20 min (5.10 ± 0.16 U/g FW) after 12 days. Conversely, peroxidase activity of the samples increased immediately after PAW treatment and the samples treated with PAW activated for 30 min had the lowest peroxidase activity at the end of 12 days of storage. No significant changes in the total phenolic content and FRAP antioxidant activity of the fresh-cut apple samples after PAW treatments. The results from firmness, membrane permeability, respiration rate and microstructural imaging showed that at higher PAW activation times (45 min and 60 min) had adverse effects on the quality of fresh-cut apples. Significant reductions in the total aerobic bacteria and total yeast and molds were observed in all PAW treatments except PAW activated for 10 min. The results suggests that plasma activated water could maintain the quality of the fresh-cut apples during storage for plasma activation times of 20 min and 30 min for up to 12 days of storage.

Nonthermal Plasma-Liquid Interactions in Food Processing: A Review.

Nonthermal processing methods are often preferred over conventional food processing methods to ensure nutritional quality. Nonthermal plasma (NTP) is a new field of nonthermal processing technology and seeing increased interest for application in food preservation. In food applications of NTP, liquid interactions are the most prevalent. The NTP reactivity and product storability are altered during this interaction. The water activated by NTP (plasma-activated water [PAW]) has gained considerable attention during recent years as a potential disinfectant in fruits and vegetable washing. However, detailed understanding of the interactions of NTP reactive species with food nutritional components in the presence of water and their stability in food is required to be explored to establish the potential of this emerging technology. Hence, the main objective of this review is to give a complete overview of existing NTP-liquid interactions. Further, their microbial inactivation mechanisms and the effects on food quality are discussed in detail. Most of the research findings have suggested the successful application of NTP and PAW for microbial inactivation and food preservation. Still, there are some research gaps identified and a complete analysis of the stability of plasma reactive species in food is still missing. By addressing these issues, along with the available research output in this field, it is possible that NTP can be successfully used as a food decontamination method in the near future.