Honey is the sweet liquid produced by honeybees from the nectar of flowers. Honey is rich in antioxidants because the flowers from which the nectar is gathered have plant antioxidants. Human evidence on the effects of honey antioxidants is limited, although they may have antibacterial, antiviral, anti-inflammatory actions. However, pasteurization of honey may alter its antioxidant content.
Honey has a mixture of different antioxidant compounds called polyphenols. These mainly include quercetin, kaempferol, luteolin, apigenin, glangin and chrysin, among others. The antioxidant content depends on several factors; the species of bee, plant varieties, season, environment and processing methods. Depending on the type of honey, the antioxidant content can range from as little as 56 to as much as 500 milligrams of antioxidants per kilogram of honey. Buckwheat honey, which is a high antioxidant variety of honey, has similar amounts of antioxidants per gram as fruits and vegetables, although the serving size is much smaller.
Honey is sold either raw or pasteurized. It is pasteurized both to prevent unwanted honey crystal formation and to destroy harmful microorganisms. During pasteurization, the heat causes a type of browning referred to as the Maillard reaction. The sugars in honey -- fructose and glucose -- bind to free proteins and form brown-colored pigments called Maillard reaction products. This process causes losses in the amount of natural honey antioxidants as Maillard reaction products form.
In 2004, X.-H. Wang of the University of Illinois and others. studied the effects of heat processing on the antioxidants in buckwheat and clover honey. Pasteurization had no effect on the antioxidant capacity --the ability to protect against oxidation -- of clover honey. However, pasteurization decreased the antioxidant capacity of buckwheat honey by approximately one-third compared with raw buckwheat honey. After six months of storage, the antioxidant capacity of the raw and pasteurized buckwheat honey were similar. The antioxidant loss that occurs during honey storage likely occurs mainly within the first six months, so only very recently produced buckwheat honey would possibly have higher antioxidant levels.
The changes in antioxidant capacity of the honeys during processing were due to alterations in the antioxidant profile, or the concentrations of the different antioxidants. This may be because different antioxidant structures break down less during pasteurization. For example, pasteurization increased the levels of quercetin and galangin antioxidants in clover honey, while reducing the amount of galangin in buckwheat honey.