The bioactive and phytochemical composition of the range of Australian honeys and their potential implications in health

INTRODUCTION
Honey is one of the most common food products used in a variety of different cuisines and has been used as a sweetener for over a millennium. Honey is also a supersaturated sugar solution derived from the plant nectars. Its physicochemical composition is largely influenced by several factors such as geographical position, predominant floral availability, and climate and temperature variations. Furthermore, the region of the individual hives (top and bottom) and the different comb (new and old) play an important characteristic in the overall honey composition. The potential implication of honey consumption in health will depend on the honey composition. This project aimed to determine the phytochemical composition of some of the commercially available Australian honey. Furthermore, we intended to examine the polyphenolic and antioxidant variation in the different comb (new and old) of the same hive.

MATERIALS AND METHODS
In total, 28 commercially available Australian honeys were obtained from local shops and chain supermarkets. These honeys were transported to the Institute of Apicultural Research (China) for analysis. In addition, 8 honey samples (using variation in combs) from one hive were donated by the local honey grower and analysed at the FFNR Laboratory (Australia). Honeys were analysed for physical properties (moisture, total soluble solids, Baumé, pH, electrical conductivity and colour), carbohydrate composition (sucrose, maltose, fructose, glucose), quality (5-hydroxymethylfurfural (5-HMF)), acidity (free acid, lactone total acid), enzymatic activity (diastase), antioxidant profile including antioxidant radical scavenging capacity (2,2-Diphenyl-1-picrylhydrazyl (DPPH)), Cupric reducing antioxidant capacity (CUPRAC) assay and Ferric reducing antioxidant power (FRAP) assay. Furthermore, we also analysed total phenolic content (Folin-Ciocalteur method) and total flavonoid content. Data were expressed as mean ± standard error and plotted as bar graphs using GraphPad Prim 8 (GraphPad Software, San Diego, CA, USA). Differences between groups were analyzed using one-way ANOVA and Duncan's post hoc test (p < 0.05) in SPSS 17.0 (Chicago, IL, USA).

RESULTS
The selection of samples from the commercially available Australian honeys had a range of values for total polyphenolic content (226.93±1.52 to 475.74±3.49 mgGAE/kg), total flavonoid (28.62±0.10 to 87.76±0.57 mgCE/kg), DDPH (0.03±0.01 to 0.47±0.02 mmolTE/g; 8.09±2.26 to 43.18±2.97 %), FRAP (0.55±0.04 to 1.58±0.06 mmolTE/g), CUPRAC (1.92±0.05 to 4.12±0.05 mmolTE/g), total sugar (64.43±2.36 to 78.62±3.17 %), total acid (17.47±1.41 to 45.02±1.77 mg/kg), color (L*: 19.80±0.26 to 27.13±0.38; a*: -0.33±0.15 to 2.37±0.31; b*: 2.50±0.00 to 8.83±0.42). Samples from the same hive have exhibited total polyphenolic (320.60±4.03 to 430.57±2.49 mgGAE/kg), DDPH (0.37±0.05 to 0.53±0.03 mmolTE/g; 15.55±5.64 to 35.12±3.94 %,), FRAP (0.74±0.06 to 1.50±0.18 mmolTE/g), CUPRAC (4.51±0.42 to 6.51±0.68 mmolTE/g), color (L*: 13.47±0.32 to 16.04±0.70; a*: 1.69±0.82 to 3.27±0.76; b*: 4.17±0.73 to 6.69±2.10).

DISCUSSION AND CONCLUSION
All honey samples have exhibited relatively high total polyphenolic content and antioxidant properties. All other values remained relatively consistent between the samples while total acidity levels have shown highest range. This could be due to the geographical positioning of the sample’s origin. Future studies, using these samples are orientated towards the taste determinations and potential anti-diabetic properties in vitro and in human participants.