Top ten high-quality MSL samples evaluated by the CRITIC method.

#### **4. Conclusions**

There have been many studies on the chemical composition of mulberry leaves. However, due to the potential existence of isomeric skeletons in MSLs, there were possible attribution errors in the identification of homologous compounds. This study constructed an IS-CID−TCC-CID strategy based on UHPLC-ESI-QTOF-MS/MS that showed the advantage of being able to solve this problem by accurately comparing the skeleton MS/MS spectra of analogous compounds. Meanwhile, semiquantitative determination combined with PLS-DA analysis showed that the major flavonoids (rutin, que-mal-glu 1, kae-rut, and kae-mal-glu 1), chlorogenic acid, and amino acids (isoleucine, phenylalanine, valine, *N*-isobutyrylglycine, proline, and asparagine) were important indicators of qualitative differences between MSL cultivars. Then, the high-quality MSLs were comprehensively screened in 90 *Morus* cultivars based on the CRITIC method, which will provide excellent genetic resources for further utilization of MSLs in food and supplement fields.

**Author Contributions:** Y.-J.H. and X.-Y.Z. conceived and designed the experiments; X.-Y.Z. and Y.-J.H. performed the experiments, analyzed the data, and wrote the paper; Y.-H.Y. and Z.-B.L. prepared the materials; X.-P.Y. participated in the coordination of the experiments; H.Y. helped revise the manuscript. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was supported by the Natural Science Foundation of Hunan Province (grant number: 2020JJ4043).

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Data are available in the article.

**Conflicts of Interest:** The authors declare no conflict of interest.
