Gluconic honey

Mato, I., Huidobro, J. F., Sanchez, M. P., Muniategui, S., Fernandez-Muino, M. A., and Sancho, M. T. (1997). Enzymatic determination of total o-gluconic acid in honey. /. Agric. Food Chem. 45, 3550-3553. 

Galacturonic, gluconic, tartaric, pyruvic, quinic, malic, isocitric, succinic, fumaric, propionic, dimethylglyceric, 2-oxopentanoic, glutaric Honey Spherisorb ODS (250 X 4.6 mm) 5 fan H2S04, pH 2.45 UV, 210 26... 

Determination of gluconic acid in honey samples using an integrated electrochemical biosensor based on self-assembled monolayer modified gold electrodes... 

D-Gluconic acic/o-glucono-ii-lactone test combination kit (10428 191035 (R-Biopharm )) for the comparison of the obtained results in honey samples. 

Fig. 16.2. Current-time recordings obtained for (a) five successive additions of 20 fj.L of a 0.005 M gluconic acid stock solution and (b) honey-diluted samples.

The presence of glucose, fructose, galactose, arabinose and citric, malic and tartaric acid did not produce interference on the quantification of gluconic acid. Only ascorbic acid yielded an amperometric response under the working conditions, due to the electrochemical oxidation of this compound at the applied potential. Nevertheless, the content of gluconic acid in honey samples is remarkably higher than the possible content of ascorbic acid. Consequently, no significant interference should be expected in the analysis of the proposed real samples. 

The biosensor was used for the analysis of gluconic acid in honey samples. No matrix effect was observed and, therefore, the determination was carried out by interpolation of the corresponding amperometric responses into an appropriate calibration graph. 

The results obtained with the biosensor for five different honey samples were compared with those obtained with a commercial enzyme kit from R-biopharm using spectrophotometric detection (Table 16.1). This method is based on the phosphorylation of gluconate by gluconate kinase in the presence of ATP, then the 6-phospho-D-gluconate produced was oxidized with NADP+ by 6-phosphogluconate dehydrogenase. The reduced form of NADP, NADPH, formed in this oxidation reaction is measured spectrophotometrically at 340 nm. 

Results obtained for the determination of gluconic acid in honey samples by using the biosensor and a commercial enzyme kit... 

Organic acids are responsible for the acidity of honey and contribute considerably to its unique flavor (Anklam, 1998). Organic acid content of about 0.57% consists primarily of gluconic acid. It is a by-product of the enzymatic action of glucose oxidase on glucose (Olaitan et ah, 2007). Other organic acids identified up to the present are the pyruvic acid, malic acid, citric acid, succinic acid, and fumaric acid. 

The pH of honey ranges between 3.4 and 6.1 with an average of 3.9 (Iurlina and Fritz, 2005). However, the pH is not directly related to acidity, due to the buffering action of acids and minerals found in honey (de Rodriguez et ah, 2004). Its acidity is due to the presence of organic acids, particularly gluconic acid, pyruvic acid, malic acid, and citric acid. These are in equilibrium with lactones or esters, as well as to inorganic ions, such as, phosphate or chloride (Anklam, 1998). 

The first step is searching out a flower to pick up some nectar. Nectar is a mixture of sugar and water. Specifically, the sugar in nectar used to make honey is sucrose, a disaccharide (see Biochemistry ). A honeybee produces enzymes in its body that Ctm break down the sucrose into monosaccharides, fructose, and glucose as well as gluconic acid. These sugars are the primary constituents of honey. Most of the water evaporates, which is what makes honey so viscous and sticky. 

Glucose oxidase presence in honey is also derived from bees. Its optimum pH is 6.1. The enzyme oxidizes glucose (100%) and mannose (9%). The enzymatic oxidation by-product, hydrogen peroxide, is partly responsible for a bacteriostatic effect of nonheated honey, an effect earlier ascribed to a so-called inhibine . The enzymatic oxidation yields gluconic acid, the main acid in honey. Glucose oxidase activity and thermal stability in honey vary widely (limit values were given in Ta-... 

The principal organic acid in honey is gluconic acid, which results from glucose oxidase activity. 

In honey gluconic acid is in equilibrium with its gluconolactone. The acid level is mostly dependent on the time elapsed between nectar collection by bees and achievement of the final honey density in honeycomb cells. Glucose oxidase activity drops to a negligible level in thickened honey. Other acids present in honey only in small amounts are acetic, butyric, lactic, citric, succinic, formic, maleic, malic and oxalic acids. 

Gluconic acid naturally occurs in plant, fruit, and foodstuffs, such as wine (up to 0.25%) and honey (up to 1%). Similar to other outstanding properties, gluconic acid has a good chelating capacity in alkaline pH its action is comparatively better than ethylenediaminetet-raacetic acid, nitrilotriacetic acid, and other chelators. Calcium, iron, copper, aluminum, and other heavy metals are firmly chelated in alkaline solution. It has been extensively used in the cleaning and construction industries as an additive to increase cement resistance and stability under extreme climatic conditions (Ramachandran et al., 2006). 

Gluconic acid has several applications in the food industry due to its mild organic acid nature. As stated earlier, gluconic acid naturally occurs in fruit juices and honey and is used... 

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