*3.4. Free Acidity*

The free acidity of honey is determined by the presence of organic acids and other compounds such as esters, lactones and inorganic ions found in its composition [11]. Contribution to this parameter also presents the composition of protein, phenolic acids and vitamin C, which are chemical components that act as H<sup>+</sup> donors [40]. Determining the acidity helps to appreciate the freshness of the honey. As the composition of honey deteriorates, an increase of free acidity occurs as a result of the fermentation of sugars into organic acids. According to the EU legislation [41], for this parameter a maximum of 50 milliequivalents of acid per 1000 g is allowed [2]. In our study, the highest acidity was determined in sunflower (31.63 meq·kg−1) honey and the lowest (16.01 meq·kg−1) in rape honey (Table 2). The botanical origin of honey had a significant influence on this parameter (*p* < 0.01), while the year of production determined no significant variation between samples (*p* > 0.05). Lazarevi´c et al. [42] observed similar results, they determined the highest free acidity (27.2 meq/kg) in sunflower honey and the lowest values of the parameter (11.6 meq·kg−1) in acacia honey. Significant di fferences in the function of the botanical origin of honey were also reported for the free acidity of acacia and hay honey [43]. Oroian and Ropciuc [44] reported that free acidity varied between 6.63 meq·kg−<sup>1</sup> in tilia honey, 13.02 meq·kg−<sup>1</sup> in sunflower honey and reached the maximum value in the case of polifloral honey (20.83 meq·kg−1).

### *3.5. HMF Content*

The HMF content is a chemical parameter that can be used to study the degree of freshness of honey and consequently its degree of deterioration. The causes of honey deterioration could be due to strong or prolonged thermal treatment and inadequate storage conditions [45]. As seen in Table 2, honey samples had an HMF content between a minimum of 8.26 mg HMF·kg−<sup>1</sup> (sunflower honey) and a maximum of 50.8 mg HMF·kg−<sup>1</sup> (thyme honey). Botanical origin had a significant influence (*p* < 0.001) on this parameter. For some of the samples of mint (two samples) and thyme honey (one sample) that were analyzed, the HMF content was above the maximum concentration (40 mg·kg−1) allowed by European legislation [41]. In the case of these samples, it is possible that there was an overheating during processing and/or storage, which might have influenced the HMF content in honey.

Rodríguez et al. [46] observed that the avocado honey had a maximum level of HMF of 27.1 mg·kg−1. Another study, focused on the quality of honey from Rio Grande do Sul State (Brazil), reported values of 0.47–22.72 mg HMF·kg−<sup>1</sup> of honey, which met the quality requirements established by both Brazilian legislation (upper limit of 60 mg HMF·kg−1) and international standards (Codex, 2001—maximum of 40 mg HMF·kg−1) [47].
