## 3 Results and Discussion
### Identification of AFB\({}_{1}\) Degradation  
Further analysis via HPLC-Q Exactive MS was performed to determine the unknown degradation products. AFB\({}_{1}\) was detected in both the control group and the degraded extraction group. Ten degradation products (P1-P10) were determined in the extracted samples from AFB\({}_{1}\) treated with the strain for 4 days. Relative double bond equivalent (RDBE) values are calculated indications of the number of double bonds or rings in the structures of the unknown compounds. In this study, the RDBE value of AFB\({}_{1}\) was 12.0, and the RDBEs of P1, P2, and P3 were 11, 12, and 10, respectively. The RDBEs of the degradation products 1 and 3 were lower than those of AFB\({}_{1}\), indicating that the probability of their double bonds being disrupted was higher. Among the 10 degradation products, P8 and P10 had the lowest RDBE values of 7 and 6, respectively, i.e., these two substances had the fewest double bonds or rings compared to several other substances. The retention time, molecular formula, adduct form, theoretical mass-to-charge (\(m/z\)) ratio of adducts, measured mass-to-charge ratio of adducts, mass error, and ion fragment information of 10 degradation molecules are summarized in Table 1. The retention time of these 10 degradation molecules is mainly concentrated in 24-33 min, and the adduct form is [M+H]\({}^{+}\). The measured mass-to-charge ratio values of all of the molecular adducts are very close to the values of the theoretical mass-to-charge ratio, and the mass errors are much lower than 5 ppm, indicating that the obtained molecular formula has high accuracy. To further analyze the structure of the 10 degradation products, Q Exactive MS was simultaneously used to fragment the 10 parent ions, and the molecular formula of the fragment ions was obtained according to the accurate mass of the parent ions and their main fragment ions. The structural formulae of 10 degradation substances are shown in Figure 2.  
The mass spectra of 10 degradation products, including the fragmentation pathway of the fragment ions, are shown in Figure 3. The measured \(m/z\) values of the fragment ions (labeled with orange arrows) of the degradation molecules P1-P10 in Figure 3 were successfully matched with the theoretical \(m/z\) values. The fragment ions \(m/z\) 313.0702, \(m/z\) 287.0910, \(m/z\) 285.0752, and \(m/z\) 259.0959 of P1 all correspond to the theoretical values of the fragment ion library, and the structural formula is shown in Figure 3. The fragment ions \(m/z\) 313.0702 were obtained from P1 after \(\alpha\)- and \(\beta\)-charge-site rearrangement. The fragment ion \(m/z\) 287.0910 was mainly formed by P1 through ring contraction and inductive cleavage, and the rest of the fragment ions were mainly formed by P1 through electron sharing and Retro Diels-Alder (RDA) formation. The fragmentation pathway of the fragmentation ion \(m/z\) 313.0702 is shown in Figure 3 (blue arrow). The fragmentation ion of P2 was obtained from P2 via electron transfer, including electron sharing, charge  
Figure 1: FTIR-ATR analysis of AFB\({}_{1}\) degradation by _Kocuria rose_ at wavenumber 4000–400 cm\({}^{-1}\). A, B, C, and D represent _Kocuria rose_ cultured with AFB\({}_{1}\) for different days (0, 2, 4, and 5 days). resonance, and radial resonance. The fragmentation ion of P3 was mainly obtained via charge resonance, radical cleavage, and hydrogen rearrangement. The fragment ions of P4 were formed mainly by charge resonance and Retro Diels-Alder and were also identified in AFB\({}_{2}\) degradation products [41]. Moreover, the fragment ion \(m/z\) 287.0908 of P5 is formed mainly by inductive cleavage, and the fragment ion \(m/z\) 269.0801 is formed mainly by electron sharing and H rearrangement, inductive cleavage, and removal of the carbonyl group (-C=O). The fragment ion \(m/z\) 259.0954 was formed via charge resonance and RDA. The degradation molecule P5 was identified as aflatoxinoid (AFL).