## 4 Discussion
It has been reported that the inactivation of viruses using low-temperature plasma has successfully deactivated various viruses, such as the norovirus [49], adenovirus [50], and HAV. RT-qPCR was used to detect HAV. RT-qPCR quantification is used as a detection method for diverse microorganisms, including viruses [51; 52]. However, this method has the disadvantage of detecting both infectious and noninfectious viruses by amplification [53]. Nucleic acids from damaged viruses can persist for several months after the inactivation process [54; 55], and RT-qPCR can eventually overestimate the number of viruses [56]. Therefore, it is necessary to distinguish between infectious and noninfectious viruses. In this study, a fluorescent dye, PMA, was used to distinguish between infectious and noninfectious viruses. PMA can only penetrate dead or membrane-damaged cells, and covalently binds to cell nucleic acids through photolysis. Consequently, nucleic acids become insoluble and the PCR amplification of nucleic acids from dead or membrane-damaged cells is inhibited [57]. In this study, the infection power was confirmed by the PMA treatment of the samples. In viral suspensions, there was a significant difference in titers between the PMA-treated and the non-PMA-treated samples in the 30-60 min treatment, and in the oysters infected with HAV, there was a significant difference at 60 min. PMA treatment allowed a distinction between infectious and non-infectious viruses, and an observation of the effect of DBDP treatment. Previous studies have reported that plasma treatment sufficiently damages the viral capsid, and thus, the PMA dye is well-attached to the inside to detect only infectious viruses, and it is effective against bacteria [58]. [PERSON] et al. [31] also showed that the DBDP treatment of norovirus in oysters greatly helps to inactivate infectious viruses, and PMA preprocessing is an indirect method suitable for estimating the infectivity of viruses. Since the 1980s, the consumer's interest in safe food has increased [59]. Therefore, the challenge in the food industry is to prevent or minimize quality degradation to produce high-quality products. pH and texture (hardness) are major factors that affect the quality of food. The pH affects the pigment, taste, texture, and shelf life of food, and rapid changes can have undesirable effects on food [60; 61]. Texture (hardness) is an important factor that influences the perception of the sensory attractiveness of food. It represents freshness and contributes to the enjoyment of eating [62]. DBDP treatment did not affect the pH of oysters. Previous studies also reported that oysters and sea squirt did not have pH changes when treated with DBDP [47; 49], and considering the results of this study, DBDP does not affect the pH of food. The hardness was significantly different from that in the control group. [PERSON] et al. [63] treated blueberries with atomic cold plasma and determined that plasma did not directly affect quality changes, such as texture. A number of studies using plasma reported no change in apples [64], melons [65], pork, beef [66], minced pork [67], and oysters [31]; the results of this study were different. This is could be due to the differences between individual oyster and the influence of the surrounding environment, and it is difficult to determine whether it is the effect of DBDP.