# 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  
#### 3.1.1 Impact of Plasma Treatment Power on the Structure of Peanut Seed Coat  
As shown in Figure 1, Figure 1a,b are the SEM images of the untreated peanut seed coat at 500\(\times\) and 2000\(\times\) magnifications, respectively. According to the figures, the surface of the peanut seed coat appears smooth, with slightly wide but shallow protrusions, clear and irregularly shaped textures, indistinct cell boundaries, and no cracks or obvious concavities. However, small micropores are present, likely serving as channels for material exchange within peanut cells. The changes were highly significant when comparing the control and treated groups. Figure 1c depicts the peanut seed coat treated with a plasma device at 100 W for 60 s and observed at 500\(\times\) magnification. Compared to Figure 1a, fine cracks appear along the micropores on the seed coat.  
As the power increases from 100 W to 300 W in Figure 1c,e,g, the surface cracks gradually widen along with the micropores, evolving from small cracks to small holes and eventually clustering into longer cracks. The surface textures of the seed coat transform from irregular shapes to quadrilaterals or trapezoids, becoming deeper and denser withclear cell boundaries arranged in a tight and orderly manner. Nevertheless, the cellular structure and shape distribution remain largely intact. Cross-linking of these boundaries results in grooves, creating a tough protective layer that shields the interior of the seed from external environmental factors, consistent with findings reported by [PERSON] et al. (2014). As the power gradually increases from 300 W to 500 W, Figure 1i,k reveal that the cracks on the seed coat gradually transform into holes. At 2000\(\times\) magnification under SEM (Figure 1j,i compared to Figure 1d,f,h), lipid particles exude and cover the peanut seed coat, causing the polygonal structure of the cells to become shallower and looser until the morphological changes in the seed coat become unobservable.  
This is attributed to the increasing number of high-energy reactive particles released per unit time as the plasma treatment power increases. These high-energy particles penetrate the peanut seed coat through the formed holes, reaching the embryo layer and reacting vigorously with the macromolecular compounds on the surface of the embryo. This leads to the disintegration of these macromolecules, damaging the cellular structure of the embryo layer and causing the cytoplasm to leak out. The higher the treatment power, the more lipid particles exude around the holes, eventually covering the entire seed coat, consistent with the findings of [PERSON] et al. (2016). Low-power cold plasma treatment creates cracks on the surface of the seed coat, enhancing water absorption and stimulating seed germination. Conversely, high-power cold plasma treatment damages the surface of the seed coat, breaking down the barrier for material exchange and disrupting the structural morphology of peanuts, potentially having adverse effects on peanut processing, storage, and breeding. [PERSON] et al. (2016) analyzed the breakage of the seed coats of mechanically shelled peanuts with different degrees of drying and found that peanut seed coats with low water content and prolonged storage time are extremely easy to break. Additionally, etching after cold plasma pretreatment increases the pore-like structures and material exchange channels; however, the quality and characteristics of the subsequent peanut should be analyzed further to provide guidance.  
Figure 1: Cont.  
Figure 1: \(Cont.\)