## 3 Results and Discussion
### Toxicity of Degradation Products  
The quantitative structure-activity relationship (QSAR) for AFB\({}_{1}\) was studied. Double bonds between C8 and C9 carbons in the furan ring, lactone ring, cyclopentenone, and methoxy structures are critical for toxicity and carcinogenicity. Any change in these structures might significantly reduce biological activity and toxicity [49]. Therefore, according to QSAR, it was assumed that the toxicity of AFB\({}_{1}\) degradation products would be lower than AFB\({}_{1}\). As Figures 2 and 4 show, the 8, 9 double bonds of the furan rings of the degradation Products 1, 2, 3, and 4 have been opened; the keto groups of P1, P2, and P3 have been converted to single bonds; and the methoxy groups of P3 and P4 have been replaced. In addition, the degradation Product 5, which changes only the keto group on the AFB\({}_{1}\) cyclopentenone to a hydroxyl group, has been proven to be only 1/18 as toxic as AFB\({}_{1}\)[50]. Product 6 (AFD\({}_{1}\)) is a non-fluorescent compound with phenolic properties, which has been verified as less toxic and mutagenic than AFB\({}_{1}\)[51; 52; 53; 54]. The Ames test and the chick embryo test have been conducted by [PERSON], [PERSON], [PERSON], and [PERSON] [52] to study the toxicity of AFD\({}_{1}\) and AFB\({}_{1}\)[51]. Similarly, an MTT assay was performed using chicken liver cancer cells, and animal toxicity experiments were performed using mice to verify that the toxicity of AFD\({}_{1}\) was less than AFB\({}_{1}\)[55]. Moreover, the products P7, P9, and P6 have the same skeleton structure; hence, we hypothesized that the toxicity of P7 and P9 is close to that of P6, and that of both is less than that of AFB\({}_{1}\). The degradation molecule P8 (aflatoxin D\({}_{2}\)) is a nonfluorescent phenol that retains the difuran molecule but lacks the cyclopentenone ring and the lactone carbonyl structure within the AFB\({}_{1}\) molecule. [PERSON], [PERSON], and [PERSON] [51] demonstrated that AFD\({}_{2}\) is less toxic than AFB\({}_{1}\) using cellular experiments, and the degradation molecule P10 is structurally close to P8, with fewer hydroxyls, double bonds on the benzene ring, and methoxyl. Therefore, we hypothesized that the toxicity of P10 was similarly lower than that of AFB\({}_{1}\). Based on the QSAR analysis, the degradation products, theoretically, are less toxic than AFB\({}_{1}\). Figure 4: Proposed degradation pathways for 10 AFB\({}_{1}\) degradation products. In this study, the MTT cellular assay was further used to evaluate the cytotoxicity of AFB1 and its degradation products. After mixing 20 \(\upmu\)L of different concentrations of AFB1 working solution or degradation samples after strain treatment with 180 \(\upmu\)L of Hep G2 cells and incubating for 72 h, the relative viability of Hep G2 cells decreased significantly with an increase in AFB1 concentration (Figure 5A). Compared with untreated cells, the cell viability of Hep G2 cells treated with 100 \(\upmu\)g/mL AFB1 working solution decreased to nearly 50%, which was consistent with the results of Hep G2 cells cultured for 24 h [38]. However, the cell viability results were significantly lower than the AFB1 concentration, corresponding to the IC50 of Hep G2 cells cultured for 72 h (200 \(\upmu\)M) [56]. This difference might be because AFB1 has different effects on the same cell but in different cell growth states. In addition, as shown in Figure 5B, the survival rate of Hep G2 cells treated with the degradation products of AFB1 after four days of treatment with the strain increased to 62.09 \(\pm\) 3.71%, which was significantly higher than the relative cell viability of 46.36 \(\pm\) 1.678% treated with the same concentration of AFB1. This indicated that the cytotoxicity of the samples treated with the strain was lower than that of AFB1.