Purity & Lab Tests
Proline and HMF in Honey Explained
Last updated: 2026-09-28
Short answer
Proline is an amino acid used as a quality and ripeness indicator; very low values can signal sugar-syrup feeding. HMF rises with heating and long or poor storage; the EU Honey Directive generally caps it at 40 mg/kg.
Proline
Proline is an important quality criterion in honey assessment.[1] Proline below about 300 mg/kg in blossom honey has been proposed as a possible indicator of bee colonies overfed with industrial sugar syrups.[2]
There is no single universal threshold: 180 mg/kg is the commonly cited international reference,[3] while Turkish studies cite 300 mg/kg with reference to the national honey communiqué.[1] In 48 honeys produced in Türkiye, proline ranged from 34.6 to 662.6 mg/kg, so it varies widely by honey type.[1]
HMF (hydroxymethylfurfural)
HMF forms when honey is heated or stored for a long time. The EU directive generally allows up to 40 mg/kg,[5] and Turkish studies also use 40 mg/kg.[1] Together with diastase activity, HMF is used as an indicator of freshness and excessive heating.[6]
Diastase
Diastase is a natural enzyme activity. The directive generally requires at least 8 (Schade scale); honeys naturally low in enzymes (e.g. citrus) need at least 3 together with HMF ≤ 15 mg/kg.[5]
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Frequently asked questions
What proline level should honey have?+
There is no single figure: 180 mg/kg (international reference) and 300 mg/kg (Turkish studies) are both cited, and it varies by honey type.
Is high HMF dangerous?+
The sources here treat HMF as a marker of heating and storage history rather than as a stand-alone hazard.
Related articles
Sources
- Türkiye'de Üretilen Balların Bazı Fizikokimyasal Özellikleri (48 bal örneği; HMF ve prolin değerlendirmesi) — Ondokuz Mayıs Üniversitesi açık erişim arşivi
- Study of honey from colonies overfed with industrial sugar syrups (proline, electrical conductivity) — Kafkas Üniversitesi Veteriner Fakültesi Dergisi 23(2):259–268 (2017)
- Harmonised Methods of the International Honey Commission — Bogdanov S. (ed.), International Honey Commission (2009)
- Türk Gıda Kodeksi Bal Tebliği (Tebliğ No: 2020/7) ve 2023/37 sayılı değişiklik duyurusu — T.C. Tarım ve Orman Bakanlığı, Gıda ve Kontrol Genel Müdürlüğü
- Council Directive 2001/110/EC relating to honey — Annex II (composition criteria) — European Union
- Evaluation of factors affecting crystallization of disparate set of multi-flower honey samples — Grégrová A. et al. — Agronomy Research 13(5):1215–1226 (2015)