*3.7. Electrical Conductivity*

Another physical parameter that serves as a means to authenticate honey, and particularly the monofloral types, is electrical conductivity. Electrical conductivity is a parameter included in the new international standards regarding the di fferentiation between honeydew and flower honey. The limits of this parameter that were specified by standards are 500 to 800 <sup>μ</sup>S·cm<sup>−</sup><sup>1</sup> for mixed honey and <500 <sup>μ</sup>S·cm<sup>−</sup><sup>1</sup> in the case of pure floral honey with some exceptions [51]. Values greater than 800 <sup>μ</sup>S·cm<sup>−</sup><sup>1</sup> are specific to honeydew and therefore are not acceptable for floral honey, and can confirm an adulteration with inverted sugar [52–54]. In the work of Kaskoniene et al. [55] it was shown that floral honey has an electrical conductivity that was lower than that of honeydew, confirming that this parameter is a quality indicator that can be used as a means to distinguish honeydew from floral honey [56].

As the values in Table 2 show, the honey samples analyzed had an electrical conductivity of less than 500 <sup>μ</sup>S·cm<sup>−</sup>1, so they can be classified as pure floral honey. Mint honey had the highest electrical conductivity (474.05 <sup>μ</sup>S·cm<sup>−</sup>1) followed by raspberry honey (446.16 <sup>μ</sup>S·cm<sup>−</sup>1). Polyfloral and sunflower honey presented close values of electrical conductivity (354.09 <sup>μ</sup>S·cm<sup>−</sup><sup>1</sup> and 362.27 <sup>μ</sup>S·cm<sup>−</sup>1) and rape and thyme honey were characterized by the lowest values of electrical conductivity (162.5 <sup>μ</sup>S·cm<sup>−</sup><sup>1</sup> in rape honey and 244.28 <sup>μ</sup>S·cm<sup>−</sup><sup>1</sup> in thyme honey). Botanical origin had a significant influence (*p* < 0.001) on the variation of this parameter. Boussaid et al. [36] reported for Tunisian mint honey an electrical conductivity of 430 <sup>μ</sup>S·cm<sup>−</sup>1, which was similar to our results for mint honey. In the case of thyme honey, the value reported for Tunisian honey was higher than the electrical conductivity measured for the Romanian thyme honey. Oroian and Ropciuc [44] reported, in the case of sunflower honey, an electrical conductivity value of 346.1 <sup>μ</sup>S·cm<sup>−</sup><sup>1</sup> and 431.4 <sup>μ</sup>S·cm<sup>−</sup><sup>1</sup> for the polyfloral honey. Usually, monofloral rape honey has low electrical conductivity, 130 to 580 <sup>μ</sup>S·cm<sup>−</sup><sup>1</sup> [57] and 110–270 <sup>μ</sup>S·cm<sup>−</sup><sup>1</sup> [58], which indicates that this type of honey has a lower mineral content [55]. By comparing these reported values to the values we have determined for the electrical conductivity of our rape honey samples, it can be concluded that the samples analyzed in this study were of pure rape honey.

Regarding the influence of other parameters on the electrical conductivity of honey, it was found that the variation of this parameter positively correlated with an increased ash and acid content [8]. The pollen collected by bees is a major source of minerals, and consequently, in the case of monofloral honey the electrical conductivity correlated with the pollen content [55] and may serve as a means to identify the botanical origin of honey [59]. This parameter was included in international standards to replace the ash content determination [2]. The electrical conductivity is a good criterion for identifying the botanical origin of honey and is also used for its routine control [60].

### *3.8. Total Phenolic Content*

The functional properties of honey are related to the number of natural antioxidants from pollen collected by bees and other floral nectars [61]. The antioxidant e ffects of honey were attributed to the presence of phenolic acids, flavonoids, ascorbic acid, carotenoids, catalase, peroxidase, as well as Maillard reaction products in the composition of honey [62,63]. Table 2 presents the total phenolic content (TPC) of raspberry, mint, thyme, rape, sunflower and polyfloral honey samples. TPC varied between 18.91 mg GAE ·100 g<sup>−</sup><sup>1</sup> (thyme honey) and 23.71 mg GAE ·100 g<sup>−</sup><sup>1</sup> (mint honey); no significant di fferences were determined by botanical origin and year.

Chua et al. [64] reported in their study that the TPC of the analyzed honey samples ranged from 110.39 to 196.500 mg GAE ·100 g<sup>−</sup>1. In their study on four types of honey, Marghita¸s et al. [37] reported that sunflower honey had the highest value of total polyphenol content (40 mg GAE ·100 g<sup>−</sup>1), while acacia honey had values between 2 and 39 mg GAE ·100 g<sup>−</sup>1. The total phenolic content of Indian honey was found in the range of 47 mg GAE ·100 g<sup>−</sup><sup>1</sup> of honey to 98 mg GAE/100 g of honey [51]. The TPC

values determined for Romanian monofloral honey in our study were lower than those obtained by other authors when analyzing honey of different origin.

### *3.9. Flavonoids Content*

The flavonoids of honey may originate from pollen, nectar or propolis [65]. In general, the main flavonoids found in honey are pinocembrin, apigenin, campferol, quercetin, pinobanksin, luteolin, galangin, hesperetin, and isorhamnetin [15]. Flavonoids have low molecular weight and are vital components of honey and its antioxidant properties [66]. Table 2 shows the values determined for flavonoids content by botanical origin and year of honey production. As in the case of total polyphenols, in this study the thyme honey samples had the lowest flavonoid content (17.45 mg QE·100 g<sup>−</sup>1). The highest flavonoid content was identified in raspberry honey (33.58 mg QE·100 g<sup>−</sup>1) followed by mint honey (25.73 mg QE·100 g<sup>−</sup>1), polyfloral honey (24.14 mg QE·100 g<sup>−</sup>1), sunflower honey (22.86 mg QE·100 g<sup>−</sup>1) and rape honey (20.25 mg QE·100 g<sup>−</sup>1). The flavonoids content was influenced by year (*p* < 0.05), but not by botanical origin (*p* > 0.05).

<sup>M</sup>ărghita¸s et al. [37] reported that the total flavonoid content of honey samples ranged between 0.91–2.42 mg QE·100 g<sup>−</sup><sup>1</sup> in acacia honey, 4.70–6.98 mg QE·100 g<sup>−</sup><sup>1</sup> in tilia honey, and 11.53–15.33 mg QE·100 g<sup>−</sup><sup>1</sup> in sunflower honey. Boussaid et al. [36] reported higher total flavonoids content in mint honey (22.45 mg QE·100 g<sup>−</sup>1), and lower in the case of rosemary (16.24 mg QE·100 g<sup>−</sup>1), thyme (14.77 mg QE·100 g<sup>−</sup>1), orange (11.12 mg QE·100 g<sup>−</sup>1), horehound (11.02 mg QE·100 g<sup>−</sup>1), and eucalyptus (9.58 mg QE·100 g<sup>−</sup>1) honey.
