*3.4. Free Acidity and pH Value*

According to the national regulation [36], the maximum allowable value of free acidity in any type of honey is set at 50 mEq/kg (with the exception of baker's honey). All examined samples of sunflower honey had free acidity less than 50 mEq/kg (Table 1). These findings showed that unfavorable fermentation was absent. The studied samples had an average acidity value of 28.48 mEq/kg. All examined samples of sunflower honey after storage had free acidity less than 50 mEq/kg.

The reference value for pH value is not prescribed by the regulations. According to our research, the tested samples of honey had pH values that ranged from 3.46 to 3.99 (on average, 3.66 ± 0.14) (Table 1). The mean acidity value and pH value in the examined samples after storage for 18 months (Table 3, Figures 2 and 3) were very similar to results obtained immediately after sampling (28.48 ± 5.09 mEq/kg versus 28.07 ± 4.88 mEq/kg and 3.66 ± 0.14 versus 3.56 ± 0.11). The differences between mean values for free acidity were not statistically significant (*p* = 0.78). However, differences between mean values for pH values in honey after sampling and 18 months later were statistically significant (*p* = 0.01).

**Figure 2.** Effect of storage time on acidity in sunflower honey.

**Figure 3.** Effect of storage time on pH in sunflower honey.

Organic acids (tartaric, citric, oxalic, acetic, etc.), nectar, or bee secretions all contribute to the acidity of honey [48]. The pH value measurement (total acidity) or a titration with sodium hydroxide (free acidity) can be used to measure the acidity of honey. The acidity values (total and free acidity) obtained in our investigation of sunflower honey before storage were similar to the results published by Devillers et al. [43], Lazarevi´c et al. [38], Sari and Ayyildiz [9], Prica et al. [21], and Ðogo Mraˇcevi´c et al. [46]. The pH of sunflower honey decreased after 18 months of storage at room temperature (Figure 3). Differences in honey pH before and after storage were significant. However, changes in free acidity during storage for 18 months were not significant (*p* > 0.05). Although the honey's pH level changed during storage, it is important to emphasize that the acidity values (free acidity and pH) were in accordance with the values considered as normal for fresh honey. The normal pH value for fresh honey in the range of 3.2 to 4.5 (free acidity maximum 50 mEq/kg) inhibits most microorganisms and ensures that honey is safe for consumption [4]. Similar results that the pH value decreases during honey storage were reported by Seraglio et al. [41], Da Silva et al. [4], Soares et al. [11], and Evahelda et al. [13]. Czipa et al. [5] have reported that the pH value of honey did not change after a two-year storage. Seraglio et al. [41], Da Silva et al. [4], and Chou et al. [19] found that free acidity increased during storage time.
