# Study of the Effects of Plasma Pretreatment on the Microstructure of Peanuts
## 3 Results and Discussion
### Effects of Plasma on the Structure of Peanut Seed Coat
#### 3.1.3 Impact of Plasma Treatment Gas Type on the Structure of Peanut Seed Coat  
The results are presented in Figure 3. Figure 3c,e,g are SEM images at 500\(\times\) magnification, corresponding to plasma treatments with helium (He), oxygen (O\({}_{2}\)), and argon (Ar), respectively, at 200 W for 60 s. Interestingly, the structure in Figure 3c,d closely resembles the peanut seed coat morphology observed after plasma treatment at 200 W. In contrast, in Figure 3e, interconnected pores gradually form cracks on the seed coat surface. Lipid particles evade from these cracks and are distributed evenly around the cracks. Decomposed protein particles and polymers are covered by lipid particles. The surface exhibits increased irregular wrinkles, and cell structures are less distinct. As depicted in Figure 3g, numerous quadrilateral cell structures with clear boundaries are evident. Cross-linking results in deep grooves, distinct textures, and wrinkle superpositions. Although cracks form on the cell surface, there is no significant lipid particle exudation around the cracks or within the pores, and only a small amount of protein body particles and polymers escape the cells.  
Comparisons between treatment groups show large differences in the apparent phenomena produced by the different gas species. The different ions and free radicals produced during the ionization of He, O\({}_{2}\), and Ar gases result in varying etching effects on the peanut seed coat surface. It is speculated that O\({}_{2}\), as an oxidative reactant, generates reactive plasma ions upon ionization, which readily interact with the surface, forming new functional groups and generating novel substances. Due to the oxidation susceptibility of lipid bodies, the ionization of O\({}_{2}\) generates highly reactive species such as oxygen atoms (O\({}^{\bullet}\)), negative oxygen ions (O\({}^{-}\)), and ozone (O\({}_{3}\)). These species interact with the seed coat surface, leading to an etching effect that accelerates lipid oxidation. Consequently, cell walls rupture, causing lipid particles to escape from the cracks and altering cell membrane permeability and porosity, which aligns with research findings by [PERSON] et al. [35] and [PERSON] et al. [36]. In contrast, He and Ar are inert gases, and their ionized ions are non-reactive plasma that only excite the material surface. Consequently, the ionization of different gases exerts distinct apparent phenomena on the peanut seed coat.  
Figure 2: Appearance of peanuts under scanning electron microscope after different treatment durations. Note: The left column shows SEM images at 500\(\times\) magnification. (**a**) Corresponds to the control group peanuts. (**c.e,g,i,k**) Correspond to peanuts treated with cold plasma for 30 s, 60 s, 90 s, 120 s, and 150 s, respectively. The right column shows SEM images at 2000\(\times\) magnification. (**b**) Corresponds to the control group peanuts. (**d,f,h,j,l**) Correspond to peanuts treated with cold plasma for 30 s, 60 s, 90 s, 120 s, and 150 s, respectively.  
Figure 3: \(Cont\).