*2.1. Chemicals*

Glycerol (pure per analysis grade, ppa grade), gelatine (ppa grade), sodium hydroxide 0.1 M analytical weighed amount, sodium acetate trihydrate (ppa grade), potassium hexacyanoferrate (II) trihydrate (ppa grade), and zinc acetate dihydrate (ppa grade) were purchased from Chempur (Piekary Sl ˛ ´ askie, Poland). The Phadebas Honey Diastase Test tablets were bought from Magle Life Sciences (Malmö, Sweden) and glacial acetic acid (ppa grade) from Pol-Aura (Zawroty, Poland). Methanol and hydroxymethylfurfural were obtained from J.T. Baker (Gliwice, Poland) and Merck (Darmstadt, Germany), respectively, and were of HPLC grade. For the analyses, distilled or ultrapure water from the Milli-Q system (Merck, Darmstadt, Germany, resistivity 18.3 MΩ cm) was used.
