The compositions of floral and honeydew honeys differ, inter alia, in that honeydew honey typically has higher oligosaccharide and acid contents. Honeydew honey is made from honeydew excreted as a byproduct of plant sap digestion by aphids, including the Giant Willow Aphid (GWA), an invasive pest insect in New Zealand and other countries. GWA honeydew honey is problematic to apiarists, as it crystallizes in the comb, reducing yield and making it commercially unacceptable. This crystallization has been ascribed to high levels of the oligosaccharide melezitose.
Some oligosaccharides are prebiotic; that is, indigestible to humans but selectively fermented by beneficial colonic bacteria, conferring a health benefit. This research used NMR, HPLC and GC-MS methods for identification and quantitation of carbohydrate fractions in Beeotic®, an Australian honey marketed as prebiotic, and in some New Zealand honeydew honeys, and developed methods to extract melezitose crystals and to make palatable candy from GWA honeydew honey. The acid and enzyme lability of melezitose were also determined, as an indication of its prebiotic potential.
Analysis of Beeotic® showed it to contain 2.73 ± 0.36% oligosaccharides, 12.06 ± 0.10% disaccharides, 23.11 ± 0.59% glucose, and 49.16 ± 0.82% fructose. It was estimated that to ingest a dose capable of providing a prebiotic effect, a consumer would have to eat a minimum of 73.18 ± 9.67 g of Beeotic® daily, perhaps more if the oligosaccharides present in Beeotic® have lower prebiotic activity. This mass of honey contains 64 g digestible sugars: more than double the WHO-recommended daily maximum.
Analysis of a New Zealand beech honeydew honey showed it to contain 13.83 ± 0.01% oligosaccharides, 14.56 ± 0.10% disaccharides, 22.29 ± 0.23% glucose, and 44.61 ± 0.29% fructose. The minimum daily dose to confer a prebiotic effect would be 14.46 ± 0.44 g of beech honeydew honey, which includes 11 g digestible sugars.
Analysis of GWA honeydew honey, in the first known carbohydrate profile of this honey, showed it to contain 37.74 ± 0.19% oligosaccharides (of which 27.4% of the honey mass was melezitose), 37.11 ± 0.27% disaccharides, 16.54 ± 0.82% glucose, and 24.68 ± 1.13% fructose. The minimum daily dose to confer a prebiotic effect would be 5.30 ± 0.03 g of GWA honeydew honey, which includes 4 g digestible sugars.
Preliminary methods were developed for making GWA honeydew honey into a palatable candy, and for extracting melezitose from GWA honeydew honey. Enzyme digestion of melezitose caused minimal hydrolysis, and acid digestion no significant hydrolysis; this indicates that melezitose may fulfil the prebiotic criterion of human indigestibility and therefore GWA honeydew honey may, pending a full prebiotic activity assay, be an appropriate prebiotic functional food. This would add value to what is currently a waste product and offset the impact of GWA honeydew on New Zealand apiarists.
