Impact of Atmospheric Pressure Microwave Plasma Treatment on Quality of Selected Spices

A new 915 MHz coaxial-line-based microwave plasma source

Microwave plasma is known for its versatility in providing tailored operating conditions (pressure, working gas composition and residence time of reagents) for specific applications. Microwave plasma sources (MPSs) are vital in modern applications, demanding continuous improvement. This work introduces a coaxial-line-based nozzleless MPS that operates at atmospheric pressure at an unique frequency of 915 MHz. The measured electrodynamic characteristics in nitrogen of the MPS highlighted the need for improved energy efficiency of the device. The main novelty of this work lies in improving an energy efficiency of the presented MPS, which led to an advanced new version of the device. To achieve this, a dual strategy is employed. Firstly, numerical simulations are used to design a construction modifications to the MPS, which should increase the efficiency of transferring microwave energy from the microwave source to the generated plasma. In this step, a standard model for homogeneous plasma and a two-port equivalent method were used. Then, the theoretical results were experimentally validated by manufacturing a new energy improved version of the MPS. In the new MPS the achieved reflected microwave power (losses) was less than 3% of incident microwave power in the tested range of nitrogen flow rate (50-100 Nl/min). Compared to the MPS before improvement, this means a two-fold decreasing the reflected microwave power. To test the new MPS, the electrodynamic characteristics of the new device version and properties of the microwave plasma generated in nitrogen, using optical emission spectroscopy (OES), were investigated. The OES was used to determine the vibrational Tvib and rotational Trot temperatures of nitrogen molecules and molecular ions. In this work, the estimated Tvib and Trot temperatures for nitrogen molecules ranged from 4000 to 5300 K, depending on discharge conditions, while for nitrogen molecular ions, the temperatures changed between 4700 and 6100 K, respectively. Both the Tvib and Trot temperatures decrease linearly along the plasma flame.

The casein in sheep milk processed by cold plasma technology: Phosphorylation degree, functional properties, oxidation characteristics, and structure

Cold plasma is a nonthermal process used for modification of proteins. The objective of this study was to investigate the effect of cold plasma technology on the phosphorylation degree, functional and oxidation properties, and structure of casein in sheep milk. Cold plasma treatment for 3-4 min significantly increased the phosphorylation degree and enhanced functional properties, including water-holding capacity, solubility, foaming capacity and stability. Besides, plasma treatment time profoundly influenced protein oxidation, and treatment for 2 and 3 min could be the preferred conditions to minimize protein change. The protein conformation became unstable with the extension of treatment time. Particle size, polymer dispersity index, and microscopy images confirmed alterations in the protein structure following 3 min of processing. Consequently, using cold plasma treatment at 10 kHz 20 kV for 3 min could be suggested for milk protein modification, providing a basis for the application of high-quality caseins in food processing.

Potential use of cold plasma treatment for disinfection and quality preservation of grape inoculated with Botrytis cinerea

Gray mold caused by Botrytis cinerea is a serious disease of grape (Vitis vinifera) during storage. The aim of this study is to evaluate the effect of atmosphere cold plasma (a novel and nonthermal technology) on inactivation of B. cinerea and preservation of chemical, physical, and mechanical characteristics of grape inoculated with B. cinerea. Herein, different time of cold plasma (0, 10, 20, and 40 s) was firstly considered to be the main factors, besides different storage time (1, 2, 3, 4, and 5 weeks) at 4°C. According to the results, plasma treatment exhibited inhibitory effect on gray mold percentage and microbial load of B. cinerea (log CFU g-1) during postharvest storage. So, in the last week, the gray mold percentage and microbial load in the control were 100% and 3.6 log CFU g-1, and in 40-s plasma were 4.5% and 2.53 log CFU g-1, respectively. Although the minimum infection and microbial load were observed in 40-s plasma, better postharvest quality preservation was observed in short-time cold plasma treatment (≤20 s). Forty-second plasma caused fruit tissue destruction and negatively decreased mechanical indices (Emod: 0.0028, Fmax = 1.78, and W = 3.18) and weight loss (91.9) in comparison with ≤20-s plasma, in which mechanical indices (Emod =0.0077, Fmax = 3.6, and W = 10.06) and weight loss (1/1) were higher. The long-time cold plasma treatment (40 s) had also maximum effects on color changes (10) and surface temperature (2.8°C). Although the highest TSS and TA were observed in 40-s Plasma, but different time of plasma treatments had no effect on pH. Altogether, these results indicate that the short-time cold plasma treatment can inactivate B. cinerea on grape berries and preserve crop quality properties.

Effect of pin-to-plate atmospheric cold plasma (ACP) on microbial load and physicochemical properties in cinnamon, black pepper, and fennel

The current study aimed to investigate the influence of pin-to-plate atmospheric cold plasma treatment (ACP) on the microbial decontamination efficacy, physical (water activity, color, texture), and bioactive (total phenolic and anti-oxidant capacity, volatile oil profile) of three major spices cinnamon, black pepper, and fennel at three different voltages (170, 200, 230 V) and exposure time (5, 10, 15 min). The surface etching and oxidative reactions of cold plasma is anticipated to cause microbial decontamination of the spices. In accordance with this, the ACP treatment significantly reduced the yeast and mold count of cinnamon, black pepper, and fennel, resulting in 1.3 Log CFU/g, 1.1 Log CFU/g, and 1.0 Log CFU/g, respectively even at the lowest treatment at 170 V-5 min. While at the highest treatment of 230 V-15 min, complete decontamination in all the samples was observed due to the plasma-induced microbial cell disruption. The water activity of samples reduced post-treatment 0.69 ± 0.02 to 0.51 ± 0.03 for cinnamon, 0.61 ± 0.03 to 0.49 ± 0.01 for pepper, and 0.60 ± 0.02 to 0.43 ± 0.02 for fennel which further reassures better microbial stability. The color and textural properties were significantly unaffected (p > 0.05) preserving the fresh-like attributes. The total phenolic content was increased for cinnamon (2.26 %), black pepper (0.11 %), and fennel (0.33 %) after plasma treatment at 230 V-15 min due to the cold plasma surface etching phenomenon. However, the essential oil composition revealed no significant variation in all three spices' control and treated samples. Thus, the study proves the potential of the atmospheric pressure cold plasma for the complete decontamination of the investigated spices (cinnamon, pepper, fennel) without remarkable changes in the volatile oil profile.

Advancements in Plasma Agriculture: A Review of Recent Studies

This review is devoted to a topic of high interest in recent times-the use of plasma technologies in agriculture. The increased attention to these studies is primarily due to the demand for the intensification of food production and, at the same time, the request to reduce the use of pesticides. We analyzed publications, focusing on research conducted in the last 3 years, to identify the main achievements of plasma agrotechnologies and key obstacles to their widespread implementation in practice. We considered the main types of plasma sources used in this area, their advantages and limitations, which determine the areas of application. We also considered the use of plasma-activated liquids and the efficiency of their production by various types of plasma sources.

The Sensitivity of Fungi Colonising Buckwheat Grains to Cold Plasma Is Species Specific

Fungi are the leading cause of plant diseases worldwide and are responsible for enormous agricultural and industrial losses on a global scale. Cold plasma (CP) is a potential tool for eliminating or inactivating fungal contaminants from biological material such as seeds and grains. This study used a low-pressure radiofrequency CP system with oxygen as the feed gas to test the decontamination efficacy of different genera and species commonly colonising buckwheat grains. Two widely accepted methods for evaluating fungal decontamination after CP treatment of seeds were compared: direct cultivation technique or contamination rate method (%) and indirect cultivation or colony-forming units (CFU) method. For most of the tested fungal taxa, an efficient decrease in contamination levels with increasing CP treatment time was observed. Fusarium graminearum was the most susceptible to CP treatment, while Fusarium fujikuroi seems to be the most resistant. The observed doses of oxygen atoms needed for 1-log reduction range from 10²⁴-10²⁵ m^-2. Although there was some minor discrepancy between the results obtained from both tested methods (especially in the case of Fusarium spp.), the trends were similar. The results indicate that the main factors affecting decontamination efficiency are spore shape, size, and colouration.

Nonthermal Plasma Effects on Fungi: Applications, Fungal Responses, and Future Perspectives

The kingdom of Fungi is rich in species that live in various environments and exhibit different lifestyles. Many are beneficial and indispensable for the environment and industries, but some can threaten plants, animals, and humans as pathogens. Various strategies have been applied to eliminate fungal pathogens by relying on chemical and nonchemical antifungal agents and tools. Nonthermal plasma (NTP) is a potential tool to inactivate pathogenic and food-contaminating fungi and genetically improve fungal strains used in industry as enzyme and metabolite producers. The NTP mode of action is due to many highly reactive species and their interactions with biological molecules. The interaction of the NTP with living cells is believed to be synergistic yet not well understood. This review aims to summarize the current NTP designs, applications, and challenges that involve fungi, as well as provide brief descriptions of underlying mechanisms employed by fungi in interactions with the NTP components.

Cold plasma technology: An insight on its disinfection efficiency of various food systems

Cold plasma technology is considered as one of the novel potential non-thermal techniques for food disinfection. The acceptability of any food product depends upon its physicochemical properties and shelf life. Recent studies have confirmed that plasma can effectively reduce the pathogenic microbes in various food systems. Further, there are reports that cold plasma showed minimal or no effect on the physicochemical and sensory properties of the foods owing to its low-temperature operation. The present review explores the recent reports on cold plasma technology emphasizing its disinfection efficacy on different food categories. Various researchers have demonstrated that plasma successfully reduced the microorganisms on cereals, milk, meat, fish and spices. Therefore, based on the current research, it can be suggested that cold plasma is an effective disinfectant technology for the inactivation of pathogenic microorganisms, and its non-thermal and environmentally friendly nature is an added advantage over traditional processing technologies.

Application of Non-Thermal Plasma to Fungal Resources

In addition to being key pathogens in plants, animals, and humans, fungi are also valuable resources in agriculture, food, medicine, industry, and the environment. The elimination of pathogenic fungi and the functional enhancement of beneficial fungi have been the major topics investigated by researchers. Non-thermal plasma (NTP) is a potential tool to inactivate pathogenic and food-spoiling fungi and functionally enhance beneficial fungi. In this review, we summarize and discuss research performed over the last decade on the use of NTP to treat both harmful and beneficial yeast- and filamentous-type fungi. NTP can efficiently inactivate fungal spores and eliminate fungal contaminants from seeds, fresh agricultural produce, food, and human skin. Studies have also demonstrated that NTP can improve the production of valuable enzymes and metabolites in fungi. Further studies are still needed to establish NTP as a method that can be used as an alternative to the conventional methods of fungal inactivation and activation.

Dual-Frequency Microwave Plasma Source Based on Microwave Coaxial Transmission Line

A dual-frequency plasma source has many advantages in applications. In this paper, a dual-frequency microwave plasma source is presented. This microwave plasma source is based on a coaxial transmission line without the resonator, and it can be operated in a wide band frequency region. Two microwaves are inputted from two ports into the plasma reactor: one is used firstly to excite the plasma and the other one is used to adjust plasma characteristics. Based on the COMSOL Multiphysics simulation, the experiment is carried out. In the experimental investigation, the plasma electron density and electron temperature can be controlled, respectively, by feeding in different frequencies from the second port, causing the particles at different energy levels to present different frequencies. This exploratory research improves the operation frequency of dual-frequency microwave plasma sources from RF to microwave.

Effect of nonthermal treatments on selected natural food pigments and color changes in plant material

In recent years, traditional high-temperature food processing is continuously being replaced by nonthermal processes. Nonthermal processes have a positive effect on food quality, including color and maintaining natural food pigments. Thus, this article describes the influence of nonthermal, new, and traditional treatments on natural food pigments and color changes in plant materials. Characteristics of natural pigments, such as anthocyanins, betalains, carotenoids, chlorophylls, and so forth available in the plant tissue, are shortly presented. Also, the characteristics and mechanism of nonthermal processes such as pulsed electric field, ultrasound, high hydrostatic pressure, pulsed light, cold plasma, supercritical fluid extraction, and lactic acid fermentation are described. Furthermore, the disadvantages of these processes are mentioned. Each treatment is evaluated in terms of its effects on all types of natural food pigments, and the possible applications are discussed. Analysis of the latest literature showed that the use of nonthermal technologies resulted in better preservation of pigments contained in the plant tissue and improved yield of extraction. However, it is important to select the appropriate processing parameters and to optimize this process in relation to a specific type of raw material.

Impact of cold plasma on the biomolecules and organoleptic properties of foods: A review

Cold plasma is formed by the nonthermal ionization of gas into free electrons, ions, reactive atomic and molecular species, and ultraviolet (UV) radiation. This cold plasma can be used to alter the surface of solid and liquid foods, and it offers multiple advantages over traditional thermal treatments, such as no thermal damage and increased output variation (due to the various input parameters gas, power, plasma type, etc.). Cold plasma appears to have limited impact on the sensory and color properties, at lower power and treatment times, but there has been a statistically significant reduction in pH for most of the cold plasma treatments reviewed (p < 0.05). Carbohydrates (cross linking and glycosylation), lipids (oxidation), and proteins (secondary structure) are more significantly impacted due to cold plasma at higher intensities and longer treatment times. Although cold plasma treatments and food matrices can vary considerably, this review has identified the literary evidence of some of the influences and impacts of the vast array of cold plasma treatment parameters on the biomolecular and organoleptic properties of these foods. Due to the rapidly evolving nature of the field, we have also identified that authors prioritize the presentation of different information when publishing from different research areas. Therefore, we have proposed a number of key physical and chemical cold plasma parameters that should be considered for inclusion in all future publications in the field.

Effect of Selected Drying Methods and Emerging Drying Intensification Technologies on the Quality of Dried Fruit: A Review

Drying is one of the oldest methods for food preservation that removes the water from fruit and makes it available for consumption throughout the year. Dried fruits can be produced by small- and large-scale processors, which makes them a very popular food among consumers and food manufacturers. The most frequent uses of drying technology include osmotic dehydration, vacuum drying, freeze-drying and different combinations of other drying technologies. However, drying may provoke undesirable changes with respect to physiochemical, sensory, nutritional and microbiological quality. Drying process energy efficiency and the quality of dried fruits are crucial factors in fruit drying. Recently, innovative technologies such as ultrasound, pulsed electric field and high pressure may be used as a pretreatment or in combination with traditional drying technologies for process intensification. This could result in quality improvements of dried fruits and enhanced efficiency and capacity of the production process, with a positive impact on environmental and economic benefits.