## 3 Results and Discussion  
### Washing Performance Test of Different Proteases  
The washing effect of different proteases on protein fouling cloths and dirty blood cloths was analyzed. [PERSON] et al. [29] reported the capability of protease to digest and convert the insoluble form of egg white and blood clot into their soluble forms. [PERSON] et al. [30] reported that adding protease to detergent has a better washing effect. Through the above washing method, different proteases were used to clean protein-fouling cloths and blood-dirty cloths under the conditions of 80 U, 50 \({}^{\circ}\)C, and 50 min (Table 1). In the washing of protein stains, the highest reflectivity was obtained when trypsin was added, equivalent to 1.3 times upon the addition of alkaline protease, followed by keratinase. In the washing of bloodstains, the highest reflectivity was obtained when trypsin was added, equivalent to 1.6 times upon the addition of alkaline protease, followed by keratinase. Neutral protease and aminopeptidase have the worst washing effects. In washing blood-stained cloths with protease, some proteases could not completely decompose hemoglobin on the cloth piece, which caused hemoglobin to be retained by the fibers on the surface of the cloth piece and redeposited on the surface of the cotton cloth. [PERSON] et al. [13] reported that crude keratinase could effectively remove blood and egg yolk stains and can be added to detergent products as a washing aid. In addition, the sewage used for washing does not pollute water resources. [PERSON] et al. [31] reported that alkaline protease is the most commonly used protease in detergents because of its good thermal stability and compatibility with detergents. However, continuing research and development on detergents is important to find proteases with better effects. Commercial keratinase and trypsin have become promising choices. As a protease added to detergents, commercial keratinase is a more promising option. Trypsin has better detergent effects but is limited by price and production conditions and can be added to special detergents as appropriate. The stain residue on the surface and interior of the protein fouling cloth and blood-dirty cloth before cleaning and after protease washing was observed under an ultra-depth-of-field microscope and a desktop scanning electron microscope (Figure 1). A large number of stains were attached to the fiber surface and between the fibers before washing, and the amount of residual stains on the surface and between the fibers of the experimental group after washing with enzymes was significantly reduced, and the fibers were arranged loosely and smoothly. The cleaning effect of the cloth after washing with trypsin and keratinase was better than that after washing with alkaline protease. The total reflectance of the protein-fouling cloth and blood-dirty cloth before and after washing with different proteases was analyzed using FTIR in the wavenumber range of 500-4000 cm\({}^{-1}\). [PERSON] et al. (2016) reported that the special spectral characteristics of protein detected by FTIR can reflect the residual protein stains on the surface of the fabric and the interior of the fabric fiber. ATR-FTIR analysis before washing the dirty cloth showed significant infrared absorption peaks at 1640 and 1526 cm\({}^{-1}\), which represent the two infrared absorption peaks in the protein-peptide bond C=O stretching vibration absorption peaks and \(\beta\)-sheet conformation amide III band characteristic absorption band (Figure 2). The area of absorption peaks at 1640 and 1526 cm\({}^{-1}\) of the stained cloth washed with enzymes was significantly reduced, indicating that protein stains were separated from the cloth after being decomposed by enzymes. Alkaline protease, keratinase, and trypsin can all decompose proteins to different degrees, but trypsin and keratinase were better than alkaline protease in decomposing proteins.