Ageing of honeys (part II) – What happens with the acidity?
1Moreira, R. F. A..; 1De Maria, C. A. B.; 2Trugo, L. C. ; 2Pietroluongo, M.
1DCF, IB, UNIRIO, ricfelipe@terra.com.br; 1IQ, UFRJ.
Sometimes, honeys have to be stored during one year before consumption. So, many physicochemical parameters used in their quality control may change. Based on this information, the aim of this work is to study the changes in the acidity of two honeys stored under tropical conditions using five systems: 1 - fresh samples; 2 and 3 - samples heated during 3 and 6 months under 35 – 40oC; 4 and 5 – similar to systems 2 and 3, but containing sodium metabisulfite (3 ppm/g of honey). The free, lactone and total acidity were measured according to the standard AOAC method. A significant reduction (p<0.05) in the free acidity of systems 2 and 3 was observed when compared to fresh honeys. This reduction in both honeys was followed by an increase of the lactone acidity. The total acidity of systems 2 and 3 of cashew honey could not be considered statistically different from its fresh form. Honey acidity is a result of the glucose oxidase action that converts glucose to gluconolactone, which in turn is hydrolysed to render the gluconic acid. Thus, there is a balance between the concentrations of these two last compounds. So, it seems that the hydrolysis reaction of the lactone was only displaced in the direction of its production. In the marmeleiro honey, the increase in the lactone acidity of systems 2 and 3 was not proportional to the free acidity reduction. This process produced a significant increase in the total acidity of the marmeleiro honey system 3 in relation to system 1. Such tendency could already be observed in marmeleiro honey system 2. Therefore, part of the lactone generated in these last systems must be produced from the glucose oxidation catalysed by a more active enzyme. This high activity in marmeleiro honey could be related to its greater moisture content [(20.50 ± 0.28) g/100g of honey], when compared to the cashew honey [(17.10 ± 0.40) g/100g of honey]. The free, lactone and total acidity of both honeys in systems 4 and 5 did not change statistically when compared to systems 1. Probably, the internal esterification reaction is being blocked by sulfite, that also seems to block the gluconolactone production from glucose. Supported by: FAPERJ, CAPES, CNPq . …In memorian
|