Effects of the Carbohydrate Sources Nectar, Sucrose and Invert Sugar on Antibacterial Activity of Honey and Bee-Processed Syrups

Abstract

Honey is a functional food with health-promoting properties. Some types of honey are used in wound care for the treatment of acute and chronic infected wounds. Increased interest in using honey as a functional food and as a base for wound care products causes limited availability of raw honey. Numerous studies suggest that the protein content of honey is mainly comprised of bee-derived proteins and peptides, with a pronounced antibacterial effect. Therefore, the aim of our study was to characterize for the first time the antibacterial activity of raw honeys and bee-processed syrups which were made by processing sucrose solution or invert sugar syrup in bee colonies under field conditions. Furthermore, we compared the contents of glucose oxidase (GOX) and the levels of hydrogen peroxide (H₂O₂) in honey samples and bee-processed syrups. These parameters were also compared between the processed sucrose solution and the processed invert sugar syrup. Our results clearly show that natural honey samples possess significantly higher antibacterial activity compared to bee-processed syrups. However, no differences in GOX contents and accumulated levels of H₂O₂ were found between honeys and bee-processed syrups. Comparison of the same parameters between bee-processed feeds based on the two artificial carbohydrate sources revealed no differences in all measured parameters, except for the content of GOX. The amount of GOX was significantly higher in bee-processed sucrose solutions, suggesting that processor bees can secrete a higher portion of carbohydrate metabolism enzymes. Determination of honey color intensity showed that in bee colonies, bee-processed syrups were partially mixed with natural honey. Further research is needed to identify the key botanical compounds in honey responsible for the increased antibacterial potential of honey.

Keywords: bacteria; functional food; glucose oxidase; honeybee; medical-grade honey.

Figure 1

Antibacterial activity of Styrian honey samples (n = 25) and manuka honey UMF 15+ (M) against Staphylococcus aureus and Pseudomonas aeruginosa isolates. Activity was determined with a minimum inhibitory concentration (MIC) (A) and a minimum bactericidal concentration (MBC) assay (B). MIC and MBC were defined as the lowest concentrations of honey solution (%) inhibiting bacterial growth and killing the bacteria, respectively. Data are expressed as the mean values with SD.

Figure 2

Antibacterial activities of raw honey samples and bee-processed syrups (B-PS) from bee colonies (n = 10) against Staphylococcus aureus (A,B) and Pseudomonas aeruginosa (C,D) isolates. Honey and bee-processed syrups were subsequently collected from the same colonies. Activity was determined with a minimum inhibitory concentration (MIC) assay. (B,D) Average MIC values for honey samples and bee-processed syrups. Data are expressed as the mean values with SD. * p < 0.05 (Wilcoxon test).

Figure 3

GOX contents and H₂O₂ levels in raw honey samples and bee-processed syrups (B-PS) from bee colonies (n = 10) (A,C). Honey and bee-processed syrup were subsequently collected from the same colonies. (B,D) Average GOX content and levels of H₂O₂ for honey samples and bee-processed syrups. Data are expressed as the mean values with SD.

Figure 4

Correlation between the content of GOX and H₂O₂ production capacity in (A) raw honey samples and (B) bee-processed syrups. A Pearson correlation test was used for analysis.

Figure 5

Antibacterial activity of bee-processed syrups (B-PS) and GOX contents and H₂O₂ levels in B-PS collected after processing sucrose (n = 11) or invert sugar (n = 8) feeds in the bee colony. Average antibacterial activities of B-PS against Staphylococcus aureus (A) and Pseudomonas aeruginosa (B). Average GOX contents (C) and levels of H₂O₂ (D) in BP-S. Data are expressed as the mean values with SD. * p < 0.05 (unpaired t-test).

Figure 6

Total protein contents of bee-processed syrups. Protein content was determined using the Quick Start Bradford protein assay. (A) Protein content in individual bee-processed syrup after processing sucrose solution (n = 11) or invert sugar syrup (n = 8). (B) Average protein content in both analyzed groups of bee-processed syrups.

Figure 7

Color analysis of honey samples and bee-processed syrups. The color-grading system consisted of seven different colors (water white, extra white, white, extra light amber, light amber, amber and dark amber).

Figure 8

Honey sampling locations in Styria (Austria). Honey samples (n = 25) were collected in the year 2020. Red color–honey samples; green color–honey samples and paired bee-processed syrups.