Description: Coomassie stainable particles (CSP) are protein-containing transparent particles that can be stained with Coomassie brilliant blue (CBB) and are found abundantly in aquatic systems; however, their distribution and role remain poorly known, in part due to the lack of an efficient method to study them. We developed a new, simple, and low cost semi-quantitative spectrophotometric method for determination of CSP in aquatic systems. The method is analogous to that used to quantify polysaccharide-rich gel particles called transparent exopolymeric particles (TEP). CSP concentration is determined relative to bovine serum albumin (BSA) standard aggregates (in a manner similar to how TEP is quantified relative to xanthan gum). The method is based on the linear relationship between CSP concentration and the absorbance of the eluted dye from a CBB-protein complex, which has an absorbance maximum (λmax) at 615 nm. The limit of detection and the precision (%RSD) for the proposed method are 6 μg BSA equivalent and 11%, respectively. The new spectrophotometric method was validated with the existing microscopic method. This new method to quantify CSP is simple, enables rapid measurements, and allows a more efficient comparison with TEP concentrations than the present microscopic method. The spectrophotometric analyses will further the investigation of the abundance, distribution, and role of CSP in the biogeochemistry of the ocean.

Description: Melanoidins, condensation products of sugars and amino acids, are thought to represent a key link in the transformation of polysaccharides and proteins to humic material in the marine environment. We investigated adsorption behaviour of melanoidins prepared in equimolar solutions of glucose and amino acids of choice (glutamic acid, valine and lysine) and pseudomelanoidins which were prepared from glucose only. Melanoidins were prepared using different condensation times (2, 4, 16 and 32 days). Synthesized melanoidins were separated into different molecular mass fractions. Fractionation of melanoidins by sorption on the macroreticular resin XAD-8 separated melanoidins into hydrophobic neutral, hydrophobic acid and hydrophilic fractions. Adsorption of melanoidins and their different fractions was studied at a mercury electrode by directly measuring the change of the double layer capacitance caused by the adsorption of organic molecules on the electrode surface through phase sensitive alternating current voltammetry. The hydrophobic acid fraction of melanoidins accounted for most of the adsorption behaviour of melanoidins. Consequently, the higher molecular mass fraction of melanoidins (〉10 kDa) exhibits a stronger adsorption in comparison to the lower molecular mass fraction (〈3 kDa) of the same melanoidin. The good fit of adsorption data of melanoidins and pseudomelanoidins to the same adsorption isotherm supports the idea that melanoidins are comprised of a sugar derived “backbone” that is responsible for the adsorption behaviour of melanoidin, while the presence of nitrogen atoms is responsible for the complexation of copper ions. Adsorption characteristics and complexation ability of melanoidins and natural organic matter were similar. Our results suggest that in the process of humification, selective adsorption of condensation products on aqueous surfaces may lead to a progressive immobilization of certain fractions, i.e., it is probable that higher molecular mass components accumulate at aquatic surfaces, while lower mass components remain in solution.