Enzymes
Honey can contain a number of different enzymes. Some of these are introduced by bees, and some are found in the nectar. As with most aspects of honey, different nectar/honey sources have widely varying enzyme activity. Typically enzymes are proteins of complex structure that catalyze a specific chemical reaction. They are sensitive to heat, visible and UV light and other forms of energy such as microwaves.
Of all the enzymes in honey, Diastase and Invertase have received the most attention. They are introduced to honey by bees but their presence [in fresh honey] is variable. Factors that affect their presence are thought to be nectar composition and concentration, the age of the bees, and the intensity of the nectar flow. e.g. an intense flow of nectar with a high concentration usually yields low values for diastase and Invertase activity.
Diastase
In simplistic terms, this enzyme is responsible for converting starch to dextrins and sugars and is introduced into honey by the bees. Its main point of interest is as an indicator of heating - much like HMF and is usually used in conjunction with HMF. It is measured with an empirical scale - the Gothe scale. Some honeys are naturally very low in Diastase. The Codex standard has a minimum of 8 on the Gothe scale for Diastase and a special category for honeys low in Diastase of 3. However in the case of honeys low in Diastase, the HMF must not be more than 10 mg/kg (compared with the more normal 80 mg/kg).
| Half Life of Diastase in Honey | |
|---|---|
| 20°C | 1,480 days |
| 30°C | 200 days |
| 40°C | 31 days |
| 50°C | 5.38 days |
| 60°C | 1.05 days |
| 70°C | 5.3 hours |
| 80°C | 1.2 hours |
Invertase
Invertase is the most significant enzyme in honey in relation to the amount of work done, and is primarily responsible for converting sucrose in a nectar source to glucose and fructose. Since most ripe honey has very little sucrose (usually less then 5%) this enzyme's work is done very early on in the life of honey.
| Half Life of Invertase in Honey | |
|---|---|
| 20°C | 820 days |
| 30°C | 83 days |
| 40°C | 9.6 days |
| 50°C | 1.28 days |
| 60°C | 4.7 hours |
| 70°C | 47 minutes |
| 80°C | 8.6 minutes |
Glucose Oxidase
Glucose Oxidase (GOX) is of interest in relation to antibacterial properties in honey. It catalyses glucose to form gluconic acid and Hydrogen Peroxide (H2O2) - the main agent responsible for antibacterial activity in most honeys. GOX activity (usually measured by its production of H2O2) is highly variable in differing honeys. It appears that GOX activity is related to specific honey sources e.g. beech honeydew usually has a high level of activity.
The activity of GOX is reduced by heat, light and other forms of energy such as microwaves. Some honeys appear to lose GOX activity with even small amounts of visible light while other honeys can retain their GOX activity with exposure to strong sunlight.
GOX is thought to be mostly added to honey by bees. There is some evidence that there are at least two variants of this enzyme coming from different parts of the bee - and this may explain the apparent variance in some GOX's sensitivity to heat/light etc. GOX is also produced by various other sources (e.g. Aspergillus niger is a common source of commercially available GOX) and it is possible that some of these may find their way into honey under some circumstances.
Gluconic acid is the main acid found in honey and usually accounts for most of a honey's acidity. The production of gluconic acid and H2O2 is very slow in ripe honey and most of this production takes place as the honey is being ripened and dried by the bees. If honey is diluted then this reaction speeds up again. This is an important factor that greatly affects the antibacterial property of a honey. At this time we have no published data on the half life of GOX, but references to its stability indicate that this is highly variable.
Catalase
Catalase is recorded in some honeys and its presence is thought to be derived from the nectar i.e. a plant source. Catalase decomposes H2O2 so its presence will produce a decrease in the antibacterial activity produced from GOX activity. It is possible that some of the variability of apparent H2O2 production is due to the presence or absence of catalase in the nectar from a particular plant species.