Investigation of the effects of grapefruit peel extract on bee health and nosema infection

The aim of this study was to investigate the effects of grapefruit peel extract on bee health and its anti-nosemal activity. In this study, dried grapefruit peels were optimized by classical and microwave-assisted extraction methods using the response surface method with the highest yield. The optimum conditions for both extractions were determined, and Central Composite Design was used for optimization. The highest content of total phenolics (TPC), total antiradical activity (TAA-DPPH), and total flavonoids (TFC) were obtained by optimization. For classical solvent extraction, the solvent ratio was 74.336%, the solvent/solids ratio was 20 ml/g, time was 20 hours, and temperature was 50 °C. For microwave-assisted extraction, the solvent ratio was 65%, the solvent/solid ratio was 30 ml/g, the time was 5 min, and the microwave power was 525 W. The polyphenolic substance contents of the optimum extracts were determined by high performance liquid chromatography (HPLC). The effects of optimum extracts on honey bees were determined by acute and chronic toxicity studies. The effects of the extracts on intestinal health were evaluated by histopathological examination. Antinosemal activity of the optimum extracts (1%) was evaluated. In acute and chronic toxicity studies, it was determined that the addition of the extracts to sugar syrup had no adverse effects on intestinal health in histopathological examinations, and there was no statistically significant difference between the groups. In chronic toxicity studies, it was determined that 10-day feeding with the optimized extracts did not cause a significant difference between the life spans. In the survival test studies, the survival times for both extracts were significantly different. At the end of the feeding of 1% of the classical extract to sugar syrup, honey bees showed a longer life span than the control group. Optimal extracts showed nosema spore-reducing activity compared to the control group, but this difference was not statistically significant. In conclusion, the use of grapefruit peel extracts against nosema infection requires further studies.