Antibacterial capacity

The factors responsible for the antimicrobial activity of honey are high osmolarity, acidity and particularly hydrogen peroxide, which is formed from the oxidation of glucose by the enzyme glucose oxidase, during the period when honey is ripening. Glucose oxidase originates from the hypopharyngeal glands of honeybees. When hydrogen peroxide is removed by adding catalase, some honeys still show significant antibacterial activity and this activity is referred to as non-peroxide antibacterial activity. The non-peroxide factors of honeys include lysozyme, phenolic acids and flavonoids . Bogdanov suggested that the main part of the non-peroxide antibacterial activity might be of honeybee origin, while part may be of plant origin. Wahdan also suggested that flavonoids and phenolic acids might be a part of the antibacterial activities of honey. The nonperoxide antibacterial activity is more heat- and lightinsensitive than the hydrogen peroxide, and remains intact after storage of honey for long periods. Therefore, some authors have found that the non-peroxide antibacterial activity is more important than the hydrogen peroxide in terms of antibacterial effects . However, the contribution to antibacterial properties of non-peroxide antibacterial activity may be smaller than that of hydrogen peroxide . Thus, for optimum antibacterial activity, honey should be stored in a cool, dark place and be consumed when fresh.

Furthermore, it was reported that honey has also been shown to inhibit the Rubella virus in vitro , three species of the Leishmania parasite and Echinococcus .

Nevertheless, there are differences in the antibacterial activity of different unifloral honeys . Notably, the greatest activity is from manuka honey (Leptospermum scoparium), originating from New Zealand, particularly the East Cape region of the North Island. The high antibacterial activity of New Zealand manuka honey is in many cases due entirely to the non-peroxide components. Manuka honey contains several phenolic compounds, including methyl syringate and syringic acid . By examining the antimicrobial activity against Staphylococcus aureus, methyl syringate was found to possess significant antibacterial activity. An Australian honey from a very similar source (Leptospermum polygalifolium) has also recently been found to possess a high level of non-peroxide antibacterial activity , though the cause of the non-peroxide antibacterial activity is still unclear and requires further investigation.

Antioxidant capacity

Antioxidant activity, or simply antioxidant capacity, is the ability and potential of honey to reduce oxidative reactions within the food systems and human health. This another one of the important benefits from honey usage. Notably, these oxidative reactions can cause deleterious reactions in food products (e.g., lipid oxidation in meat, and enzymic browning in fruits and vegetables) and adverse health effects, such as chronic diseases and cancers . The antioxidants that naturally occur in honey contribute to its antioxidant capacity. These compounds are flavonoids, phenolic acids and some enzymes (e.g., glucose oxidase, catalase), ascorbic acid, carotenoid-like substances, organic acids, Maillard reaction products, amino acids and proteins .

Honey's oxidative power is second only to certain whole grains and pulses, such as beans, wheat and millets. The bean horse gram, also known as Macrotyloma uniflorum, is one of the most powerful anti-oxidants, and as such, this property is an important benefit of horse gram consumption.

Lots of methods for determining the antioxidant activity in honey have been used, e.g., determination of active oxygen species (viz. the superoxide anion, peroxyl and hydroxyl radicals), their radical scavenging ability , the 1,1-diphenyl-2-picrylhydrasyl (DPPH) antioxidant content , enzymatic or nonenzymatic measurements of lipid peroxidation inhibition , the ferric reducing/antioxidant power assay (FRAP) and the TEAC (Trolox equivalent antioxidant capacity) assay .

Gheldof et al. found that while phenolic compounds contribute significantly to the antioxidant capacity of honey, they are not solely responsible for it. However, the antioxidant capacity varies greatly depending on the honey floral source, possibly due to the differences in the content of plant secondary metabolites and enzyme activity.

The influence of honey ingestion on the antioxidant capacity of plasma was tested in two studies . In the first one, healthy subjects were given maize syrup or buckwheat honeys with a different antioxidant capacity in a dose of 1.5 g/kg body weight. In comparison to the sugar control, honey caused an increase of both the antioxidant and the reducing serum capacity. In the second study volunteers received a diet supplemented with a daily honey serving of 1.2 g/kg body weight. Honey increased the body antioxidant agents: blood vitamin C concentration by 47%, ß-carotene by 3%, uric acid by 12% and glutathione reductase by 7% . These data support the concept that phenolic antioxidants from processed honey are bioavailable and that they increase the antioxidant activity of plasma.

The protective activity of honey from different floral sources in a cultured endothelial cell line (EA.hy926) subjected to oxidative stress was studied. The results reported that honey, especially native honey, showed strong quenching activity against lipophilic cumoxyl and cumoperoxyl radicals, with significant suppression/ prevention of cell damage, complete inhibition of cell membrane oxidation and intracellular ROS production, and recovery of intracellular GSH . It can be speculated that the phytochemicals present in honey may augment defences against oxidative stress and might be able to protect humans, thus creating a potentially protective antioxidant barrier. Given that the average sweetener intake by humans is estimated to be over 70 kg/year, the substitution of traditional sweeteners by honey in some foods could result in an enhanced antioxidant defence system in healthy adults.