Effects of dielectric barrier discharge cold plasma on the quality of dandelion root infusions

Abstract

Since ancient times, humans have sought solutions to their illnesses from plants. In the past 30 years, consumers' dietary preferences and interest in healthy nutrition have significantly changed, leading to increased research on medicinal plants. The health effect of medicinal plants primarily stems from their rich sources of bioactive compounds and antioxidants. Taraxacum officinale, commonly known as dandelion, stands out due to its bioactive properties due to its bioactive compounds. The root of Taraxacum officinale, which often emerges as waste in the food industry, is an intriguing plant root due to its bioactive compounds. The compounds found in the root may exhibit antioxidant effects and help prevent cellular damage caused by oxidative stress. Before food products are commercialized, they need to undergo processing to minimize health risks, provide convenience and usability, enable long shelf life, reduce food waste, and offer variety. Traditional food processing methods that have been widely used since ancient times and they are temperature-dependent. However, heat-dependent conventional processing techniques can result in nutrient losses or physical demage in food. Cold plasma, charged and reactive gas molecules and these molecules inactivate harmful microorganisms which present in foods and food packaging materials, is a promising green and appropriate technique for heat-sensitive foods. This method can help preserv the bioactive compounds in foods. Currently, cold plasma (CP) technology is used for various purposes, including extraction of volatile oils, promotion of seed germination, modification of surface structures, inactivation of enzymes and microorganisms, and degradation of pesticides. Antioxidants are bioactive compounds that naturally found in foods and they can reduce the risk of various diseases. However, these most of the bioactive compounds are recognised as sensitive to thermal processing. DBD cold plasma processing will enable food processing without the loss of antioxidant capacity in food due to its operation at low temperatures. Understanding the interaction between plasma types and bioactive compounds is crucial to prevent nutrient degradation and other undesirable effects. Cold plasma is a form of plasma consisting of high-energy ions, electrons, free radicals, and other reactive molecules. This plasma can interact with bioactive compounds and alter their properties. While there are many studies in the literature on the antimicrobial effects of DBDCP application, research on improving the process efficiency is limited. This study focus to analyze the effects of subjecting dandelion roots to cold plasma treatment during tea brewing, specifically focusing on the changes of the exposure time on the antioxidant activity, color concentration and total phenolic content. For this study, dried dandelion roots were obtained from a local vendor in Izmir and ground using a coffee grinder, and samples to be used in the study were separated through the sieves of 212 micrometers and 450 micrometers and samples called ground. Subsequently, a dielectric barrier discharge cold plasma (DBDCP) was generated using a pulsed direct current power supply (400W, 40 kV , 56 kHz, and 1 mA). The process was conducted as follows: Both ground and unground samples underwent treatment with 40 kV DBDCP for 10 min and 20 min. Untreated samples were used as the control. All treatments were repeated three times. The electrode gap was set at 1.1 cm. The samples subjected to cold plasma were prepared for the brewing process. The prepared samples were brewed at 95±2 0C for 4 minutes. During the brewing process, 2 grams of sample and 200 milliliters of distilled water were used. For grounded samples, 2 grams of ground dandelion root was added to 200 mL of distilled water at 95±2 0C and allowed to steep for 4 minutes, followed by centrifugation through 4000 rpm, 5 minutes at a controlled temperature of 4°C. For unground samples: 2 grams of dandelion root was immersed in 200 mL of distilled water at 95±2 0C using a metal sieve and allowed to steep for 4 minutes. After the infusion process, the metal sieves were removed from the water and the samples were cooled to room temperature. Subsequently, the necessary analyses were performed. The first analysis conducted was color measurement to evaluate the brewing efficiency. Color intensity during brewing has positive effects on consumers. In the color measurement results, a statistically difference (p<0.05) was observed only for the b* value. The b* value represents the yellowness. The brewed dandelion roots transitioned from transparent to yellow throughout the brewing process. Thus, it is possible to say that DBDCP can increase the color intensity. Total phenolic content (TPC) analysis is a commonly used method to calculate the amount of phenolic compounds present in a products, reflecting their antioxidant capacity. In the analysis of samples ground into powder, a significant increase was observed only in the 20 min-treated samples (p<0.05). In unground samples, a decrease at the 10th minute and a slight increase at the 20th minute were observed. The observed increase in antioxidants after processing in ground samples can be attributed to an increase in surface area and enhanced interaction with reactive compounds. This phenomenon may be linked to the increased ability of antioxidants to neutralize free radicals through their interaction. However, in unground samples, a decrease followed by a slight increase through processing time can be observed. This may be due to the initial decrease in the amount of antioxidants on the outer surfaces of larger particles. With the application of DBDCP for a longer time, bioactive compounds in the cell can be reached by breaking down the cell wall in the samples. Accordingly, the total phenolic content of the all samples were as followed: 0.122 mg GAE/mL for ground samples without cold plasma treatment, 0.128 mg GAE/mL for ground samples which implied cold plasma for 10 min, 0.140 mg GAE/mL for ground samples treated with cold plasma for 20 min, 0.045 mg GAE/mL for unground samples without cold plasma treatment, 0.027 mg GAE/mL for unground samples treated with cold plasma for 10 min, and 0.036 mg GAE/mL for unground 20 min cold plasma treated samples for. 2,2-diphenyl-1-picrylhydrazyl (DPPH) is a free radical compound that undergoes a change in color when interacts with substances exhibiting antioxidant properties. In the analysis of samples ground into powder, a significant DPPH radical scavenging activity increase was observed only in the 20 min-treated samples compared to the control (p<0.05), while no significant difference was observed in unground samples (p>0.05). Accordingly, the DPPH radical scavenging activity of the samples were as follows: 0.668 mg TE/mLfor ground samples without cold plasma treatment, 0.695 mg TE/mL for ground samples applied with cold plasma for 10 min, 0.774 mg TE/mL for ground samples applied with cold plasma for 20 min, 0.290 mg TE/mL for unground samples without cold plasma treatment, 0.218 mg TE/mL for10 min cold plasma applied ungrounded samples, and 0.241 mg TE/mL for unground samples which treated with cold plasma for 20 minutes. 2,2'-azinobis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) radical scavenging assay is a commonly used method for evaluating the antioxidant activity. Accordingly, the ABTS radical scavenging activity of the samples were as follows: 0.119 mg TE/mL for ground samples without cold plasma treatment, 0.124 mg TE/mL for ground samples that applied cold plasma for 10 min, 0.135 mg TE/mL for ground samples treated with cold plasma for 20 minutes, 0.049 mg TE/mL for unground samples without cold plasma treatment, 0.036 mg TE/mL for unground samples which cold plasma applied for 10 minutes, and 0.044 mg TE/mL for unground samples which cold plasma applied for 20 minutes Ferric reducing antioxidant power (FRAP) assay is a rapid evaluation of antioxidant activity method. Accordingly, the antioxidant activity as assessed by FRAP assay were as follows: 0.358 mg TE/mL for ground samples without cold plasma treatment, 0.374 mg TE/mL for ground samples cold plasma applied for 10 minutes, 0.387 mg TE/mL for ground samples cold plasma applied for 20 minutes, 0.144 mg TE/mL for unground samples without cold plasma treatment, 0.090 mg TE/mL for unground samples cold plasma treated for 10 minutes, and 0.118 mg TE/mL for unground samples cold plasma treated for 20 minutes. The sensory analysis was conducted by a panel of 12 individuals from the Department of Food Engineering at ITU. The samples were placed in screw-capped test tubes, labeled with randomLy assigned three-digit numbers. Subsequently, the samples were presented to the panelists and evaluated using a 7-point hedonic scale. The scale was used to assess odor intensity, color intensity, clarity, and overall impression. All measurements were reported as means and standard deviations. Minitab software was used for statistical analysis, applying analysis of variance (ANOVA) and Tukey's test for comparisons. No significant differences were observed among any of the samples in the sensory analysis (p>0.05). This study investigates the effect of DBDCP treatment on the process efficiency and antioxidant activity during the brewing process of Taraxacum officinale roots as tea. The study shows that cold plasma treatment can enhance the process efficiency by preserving the antioxidant activity of Taraxacum officinale roots. It can be said that dielectric barrier discharge cold plasma treatment can be utilized in the brewing process of Taraxacum Officinale roots as tea, leading to an improvement in the process efficiency with the preservation or even enhancement of antioxidant activity.