Determination of Total D-Gluconic Acid in Honey

To synthesize functionalized poly(lactic acid-co-glycolic acid)-based polyesters for biomedical and pharmaceutical applications such as controlled drug delivery, d-gluconic acid was considered as an interesting source of comonomer. Accordingly D-Gluconic-acidwas used to synthesize novel 1,4-dioxane-2,5-diones with protected hydroxyl groups, namely 3-dioxane-2,5-dione and 3-methyl-6-dioxane-2,5-dione.

The solution of honey was adjusted to pH 10.5 with 0.1 N KOH; 10 min at room temperature was allowed for hydrolysis of D-glucono-δ-lactone to D-gluconic acid. After this, it was necessary to adjust to test pH (7. with 0.1 N HCl. With these conditions, there were no observed interference effects.

The enzymatic determination was measured spectrophotometrically at 340 nm, using gluconate kinase and 6-phosphogluconate dehydrogenase. The method combines precision (% CV was 0.30, at worst), good recovery (99.8%), simplicity, and low cost because this cost was reduced by 60% using a microtest. The total D-Gluconic-acidcontent of the honeys analyzed ranges between 3.91 and 11.71 g/kg (mean = 7.37 g/kg), which is in keeping with value ranges obtained by other authors using HPLC methods.