Influence of proline and methylglyoxal on the formation of 5-hydroxymethylfurfural in manuka honey

Manuka honey, originating from the nectar of Leptospermum scoparium, is known for its antibacterial activity, which is due to the presence of methylglyoxal (MGO). As every honey, manuka honey has to fulfil legal requirements, e.g. must not be heat treated in a way that affects composition or quality changes and may not contain more than 40 mg/kg 5-hydroxymethylfurfural (HMF). To study the influences of MGO and proline as the most abundant amino acid in honey on the HMF formation, artificial honeys with up to 500 mg/kg MGO and up to 1000 mg/kg proline, as well as authentic honeys spiked with MGO, have been stored for 10 weeks at 37 °C and the formation of HMF and its precursor 3-deoxyglucosone (3-DG) have been analysed via HPLC-UV. For both MGO-spiked authentic honeys and artificial honeys, the content of HMF increased to significantly higher concentrations, depending of the added amount of MGO. Higher MGO levels induced an increased HMF formation due to higher 3-DG levels present in the honey. The addition of proline led to the contrary effect. Lower HMF levels were observed, although an addition of proline induced higher 3-DG levels, indicating a scavenging effect on the conversion of 3-DG to HMF. Based on these findings, it seems appropriate to review the current limit of 40 mg/kg for MGO-containing manuka honey.