Assessing the non-specific hydroxyl radical scavenging properties of melanoidins in a Fenton-type reaction system

Soluble high molecular weight fraction (>10 kDa, named melanoidins) was isolated from Maillard reaction model systems, coffee, beer and sweet wine by ultrafiltration. Deoxyribose method was adjusted for measuring the hydroxyl radical scavenging properties of melanoidins. The presence of competitive melanoidins with deoxyribose for OH decrease the rate of deoxyribose degradation. Possible interferences to the deoxyribose method have been evaluated. Most of isolated melanoidins exhibited a variable and measurable non-site-specific hydroxyl scavenging activity in a Fenton-type reaction system. The iron reducing properties of melanoidins at the reaction conditions were evaluated with ferrozine. It has established a kinetic approach to assess the second rate constants of hydroxyl radical scavenging reactions of melanoidins. This approach may be a valuable tool for addressing the structure-activity relationships of melanoidins in a future. There is no correlation between browning (absorbance at 420 nm) and efficiency for scavenging hydroxyl radicals in solution.     

Ingenious bioorganic adsorbents for the removal of distillery based pigment-melanoidin: preparation and adsorption mechanism

Melanoidins are composite biopolymers which consist of amino carbonyl compounds which are the major coloring and polluting elements of distillery effluent. In this study, a synthetic melanoidin was used as a model for natural melanoidins, the chief colorant of the effluent. Deportations of melanoidins were investigated using both natural adsorbents and constructed microbial consortia based adsorbents and denoting it using the adsorption isotherms and SEM analysis. A review enabled us to assess about the valuation of the prepared low cost adsorbent and microbial coated adsorbents and for the treatment of the synthetic melanoidin solution. Based on the performances, both Microbial Coated Commercially Activated Carbon (MCCAC) and Commercially Activated Carbon (CAC) were better when compared with the other adsorbents at lower melanoidin concentrations; however, at higher melanoidin concentration, MCCAC performed better. The utilization of CAC for the removal of melanoidins may be cost competitive; hence Microbial Coated Procured Prosopsis Activated Carbon (MCPPAC) can be used as a substitute for the removal systems. Therefore, the microbial coated adsorbents can be a remedy for the removal of color through expatriation of melanoidin from the distillery effluents.     

Role of melanoidins in sweet wines

Melanoidins from several Spanish sweet wines were isolated by dialysis. Browning indexes (absorbances at 420 and 345 nm) and CIELab parameters of the wines and their dialysed fractions were measured. The antioxidant activity, which was expressed as Trolox equivalent antioxidant activity (TEAC), was determined using the N,N-dimethylphenylene diamine dihydrochloride (DMPD) method.Results showed a good correlation of colour parameters L^∗, h^∗ and absorbances at 345 and 420 nm between the dialysed fractions and the original sweet wines. However, the TEAC of dialysed fractions did not show any significant correlation with TEAC of the original wines. So brown polymers of high molecular weight (>12000 Da) isolated by dialysis, which could be mainly melanoidins, play an important role on the colour of these sweet wines, but not in their antioxidant activity.