The effect of non-thermal plasma on physicochemical and microbial properties of ginger and sumac powder

Background: Spices are widely used in food preparation and formulation as flavoring, and when stored in unhygienic settings, they can harbor various bacteria. Cold plasma, a safe method for non-thermal equilibrium discharge production at atmospheric pressure, is an innovative solution for producing healthy food. Cold plasma is one of the new non-thermal methods in maintaining maximum bioactive compounds and minimal changes.
Aims: This research investigated the suitability of cold plasma technology for disinfecting spices.
Methods: In this study, the effect of atmospheric cold plasma using argon gas for 3 minutes on chemical (antioxidant capacity (DPPH) and color), microbial (total form count, total and mold count), sensory evaluation and microstructure of ginger and sumac powder, in order to determine the effectiveness of the plasma effect, the prepared samples were compared with the control sample.
Results: The results showed that by applying 3 minutes of plasma treatment in both samples, cold plasma had no significant effect on the antioxidant capacity of the treated samples compared to the control (p>0.05). Under the scanning electron microscope, sumac and ginger samples had a rough, raised and heterogeneous surface before being exposed to plasma, and after being exposed to plasma with argon gas, they had a smooth and uniform surface. By applying 3 minutes of plasma treatment, the amount of mold growth in sumac from 949 cfu/g to 109 cfu/g and ginger from 2495.6 cfu/g to 1000.2 cfu/g, the total amount of form in the treated samples of ginger from cfu/g 6.96 to 7 cfu/g and sumac from 97 cfu/g to 8 cfu/g and also, the total count value in treated ginger samples from 566666 cfu/g to 29000 cfu/g and sumac from 593333 cfu/g to 29666 cfu/g decreased (p<0.05). In terms of sensory evaluation, no significant impact was observed in the samples (p>0.05).
Conclusion: Considering the importance and use of spices in the food and pharmaceutical industry, the use of cold plasma process in reducing the microbial load of spices is possible with the least changes.
Introduction: Spices are used as one of the most common flavors in preparing food stuff .Spices represent a prevalent category of natural flavors extensively employed in culinary practices and food formulation. To increase food's nutritional and sensory quality while simultaneously ensuring the products' microbiological safety, one of the key targets is finding alternatives to current food processing and preservation technologies. Preparing, storing and consuming food safely and while preserving nutrients is one of the most important parts of maintaining food health and hygiene. The suitability of food for the growth of microbes can lead to spoilage and ultimately pathogenicity. Emerging innovations in food science and engineering have developed consistently and quickly over the past 20 years. The innovative food processing method called "cold plasma" uses energetic reactive gases to inactivate contaminating bacteria in spices. Ginger is an edible plant, a spice and a medicinal plant. Ginger is one of the medicinal plants that is used as a spice with strong antibacterial and antioxidant properties around the world. In addition to treating indigestion, ginger is used as a pleasant and appetizing spice in the food industry.Sumac (Rhus coriaria L.) is a pistachio genus of small shrubs 1 to 5 meters high, with 9 to 15 leaflets, covered with hairs and toothed. Employing thermal processes for spices sterilization may cause in destruction of bioactive materials, so it is necessary to recommend employing non-thermal processes which preserve the most amount of bioactive ingredients and cause less alternation. One of these techniques is cold plasma which is a non-thermal process providing microbial safety with minimum destruction. Cold plasma decontamination techniques are significantly safer and more efficient than previous ones .The purpose of this investigation is to study the influence of atmospheric cold plasma (DBD), with the use of argon gas, on chemical and microbial features of ginger and sumac in 3 minutes' time.

Material and methods: The examined elements of these spices were: color, scanning electron microscopy(SEM), counting coliform, mold, and counting total microbial. In order to show the proficiency of plasma influence, the prepared samples were compared to the controlled sample(non-plasma). In order to prepare samples for plasma treatment, DBD plasma device of Faculty of Physics, Faculty of Science and Research, Azad University of Tehran was used in this process. By adjusting the gas current and voltage by 10 kV and frequency of 40 kHz and power of 100 watts, plasma irradiation was performed for 3 minutes using argon gas. Samples were stirred several times during treatment Antioxidant capacity was measured using 2 and 2 diphenyl 2 picryl hydrazyl solution (DPPH).
In a test tube, 600 μl of DPPH solution was poured and 60 μl of the spice extract was added and 5.34 ml of methanol was added to the tube.After 15 minutes at room temperature and in a dark environment, the absorbance of both test tubes was read by a spectrophotometer at 517 nm, zeroing the device with methanol solvent.
The morphological study of the cross section of the spice sample was performed using SEM (manufactured by Tescan, Czech Republic).Bombarding the sample causes electrons to be released from the sample toward the positively charged plate, where these electrons become signals. The movement of the beam on the sample provides a set of signals on the basis of which the microscope can display an image of the sample surface on a computer screen.To evaluate the microbial load of the samples, including total count from PCA sterile culture medium, coliform count from VRB culture medium, mold count from DG18 culture medium were used. 2 replicates were cultured from each treatment. After incubation, the plates were counted. ). In this study, Sumac and ginger spices were exposed to cold plasma processing with argon gas to examine their microbiological, chemical, physical, and organoleptic qualities.

Results and discussion: The results demonstrated that, with the use of plasma, the reduction of mold growth in sumac was 5/8 and in ginger 5/2. The reduction of coliform was 92% in the treated ginger sample and 91% in the treated sumac sample compared to the control. The total count was significant at the 5% probability level(p<0.05). In both treated spices, compared to the control samples, a 20-fold reduction in the microbial population was observed. In investigating the antimicrobial effect of Enterococous, Salmonella and saffron mold mold, similar results showed that the rate of decrease in saffron mold population was less than Enterococous, Salmonella. Plasma had no effect on the antioxidant capacity of control samples. Scanning electron microscopy images to examine the morphology of the samples before plasma exposure showed a rough, prominent, and inhomogeneous surface and after exposure to plasma with argon gas with a smooth and uniform surface, which increased the solubility. In the study of the effect of plasma on onion powder, it was reported that the samples treated with cold air plasma had a smoother surface than the samples treated with hot air . Also, no organoleptic changes were observed in the samples. In a study, they reported that the type of gas used did not differ significantly from the color indices of turmeric samples.
Conclusion:
The non-thermal nature of cold plasma makes it a valuable alternative to traditional chemical methods, offering an option that minimizes the use of chemical substances while maintaining the quality of the food ingredients. This presents an innovative and potentially more sustainable approach to ensure food safety and longevity without compromising the essential characteristics of spices.
1-In both types of spices, by applying 3 minutes of treatment time, the total number of bacteria and also the amount of mold count was significantly reduced. This reduction in the total bacterial count and the amount of mold count for sumac spice is more than ginger spice.
2- Examination of coliform counts showed that by applying plasma for 3 minutes in two spices (ginger, sumac), it was reduced by 92%.
3- Changes in the level of inhibition of antioxidant compounds after exposure to cold plasma have been reported for a long time in other studies. The reasons for the lack of change in antioxidant capacity in this study can be attributed to the short plasma time.
4-Morphological evaluation of control and cold plasma treated samples shows that the treated sumac has a smooth structure and a smooth surface and the treated ginger is rougher and spongy compared to sumac.
5- The results of color parameter analysis showed that there is no color reduction in control samples and after treatment.