**4. Conclusions**

The chemical profile of monofloral buckwheat, clover, heather, linden, rapeseed, willow, and polyfloral honey samples of Latvian origins was assessed by IRMS, UHPLC-HRMS, and NMR methods in order to find suitable indicators that could be used for the classification of botanical origin of honey. The depletion in δ15N values in honey proteins was suggested as indicator for heather honey (δ15N = −2.3 ± 1.0 ‰). Moreover, the total N in proteins indicated potential distinctiveness between the pairs of willow and rapeseed honey, and buckwheat and heather honey. After the data treatment using PCA, the total nitrogen and total carbon in honey proteins were taken into account for recognition of heather honey origins. Out of 31 organic compounds quantified by UHPLC-HRMS, rutin showed a selective difference as a buckwheat honey indicator. p-Hydroxybenzoic acid, p-coumaric acid, pantothenic acid (B5), quercetin, and vanillic acid were found to have statistically different concentration levels within different monofloral honey types and could be used as specific indicators for monofloral honey purity. The polyphenol profile comes in good agreemen<sup>t</sup> with other studies, with the exception of the few compounds that were reported with higher concentrations in foreign country honey. The NMR qualitative analysis showed distinguishment among monofloral buckwheat, heather, and linden honey. Using NMR tyrosine, proline, alanine, and lactic acid, we found characteristic chemical shifts in buckwheat honey, with monosubstituted benzene derivatives and ethanol in heather honey and CDCA derivatives in linden honey. This study proves the validity of the combination of multiple analytical methods, statistical data treatment, and PCA to differentiate various natural monofloral honey classes, thus guaranteeing botanical authentication and the honey quality and origin.

**Supplementary Materials:** The following are available online at https://www.mdpi.com/article/10 .3390/foods11010042/s1, Figures S1 and S2: Tukey simultaneous 95% confidence intervals differences of mean for δ13C and δ15N. Figure S3: Fisher simultaneous 95% confidence interval differences of mean for total N (%). Figures S4–S6: PCA scree plots (δ13C, δ15N, total C and N in proteins; 27 organic compound quantified by UHPLC-HRMS; 1H-NMR spectra intervals 9.0–6.0 and 3.0–0.5 ppm). Figure S7: 1H-NMR spectra interval (0.5–3.0 and 4.5–8.5 ppm) overlayed comparison of monofloral buckwheat, clover, willow, linden, heather, and rapeseed honey. Supplementary workbook.

**Author Contributions:** Conceptualization and resources, K.D.L., J.R. and A.V.; methodology, validation, formal analysis, and investigation, K.D.L., M.B., J.N. (IRMS), J.R. (UHPLC-HRMS), R.K., M.S. (NMR), I.E. (Melissopalynology); writing—original draft preparation, K.D.L. and V.R.; visualization, K.D.L. and R.K.; writing—review and editing, V.R., L.B., J.R., R.K., M.B. and A.V.; supervision, K.D.L., V.R. and A.V.; project administration and funding acquisition, A.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the gran<sup>t</sup> "Recognition of monofloral honey of Latvian origin using nuclear magnetic resonance, chromatographic, isotope ratio mass spectrometry and chemometric methods" gran<sup>t</sup> no. LZP-2020/2-0200.

**Data Availability Statement:** Data are contained within the article or Supplementary Material.

**Acknowledgments:** "Strengthening of the capacity of doctoral studies at the University of Latvia within the framework of the new doctoral model", identification no. 8.2.2.0/20/I/006.

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