Ascorbic acid-induced browning of (+)-catechin in a model wine system.

The ability of ascorbic acid to induce browning of (+)-catechin in a model wine system has been studied. A significant increase in absorbance at 440 nm was observed over 14 days when ascorbic acid was incubated at 45 degrees C with (+)-catechin in a model wine base. The onset of browning was delayed for about 2 days, although the length of the lag period was dependent on the amount of molecular oxygen in the headspace of the reaction system. The lag period was not observed when a preoxidized solution of ascorbic acid was used, suggesting that a product of ascorbic acid oxidation is responsible for the onset of browning. Hydrogen peroxide, when added directly to (+)-catechin in the model system, was not capable of producing the same degree of browning as that generated by ascorbic acid. Liquid chromotography evidence is presented to show that different reaction products are produced by ascorbic acid and hydrogen peroxide.

Size fractionation of metals in wine using ultrafiltration.

Ultrafiltration has been used to examine the size fractionation of lead, copper, iron, aluminium, calcium, potassium and sodium in white and red wines. Fractionation patterns demonstrated that the behaviour of lead is significantly diferent to the other metals considered. In red wine, there was a sudden decrease for lead between 100 000 and 30 000 nominal molecular weight cut off (NMWCO) and in white wine, a gradual decrease in the lead concentration was observed from 100 000 NMWCO. Iron was the only other metal which showed, for red wine, a size distribution pattern with a reduction in the iron concentration between 30 and 50% from 100 000 to 1000 NMWCO. Potential binding agents for lead and iron are discussed. The absence of any fractionation pattern for the other metals examined has been interpreted in terms of the metals existing as aquated cations (potassium and sodium), metal tartrate complexes (aluminium, copper and calcium) and either tartrate or phosphate for iron in white wine. The possibility of ultrafiltration disturbing kinetically facile processes, particularly for copper and calcium, is identified.

Determination of sulfur dioxide in wines and beverages by flow injection analysis with reductive amperometric detection and electrolytic cleanup.

A new flow injection method is described for the determination of sulfur dioxide in red and white wines and other beverages. A dual-electrode electrochemical detector eliminates interferences by reduction at an upstream coulometric electrode before reductive detection of sulfur dioxide at the amperometric electrode. The data for free and total sulfur dioxide in wines and other beverages agree well with those obtained by the standard aspiration-oxidation method.

The interaction of phosphine with haemoglobin and erythrocytes.

1. Phosphine progressively converts oxyhaemoglobin to methaemoglobin and hemichrome species, with the product formed being time- and concentration-dependent. 2. The reaction of phosphine with oxyhaemoglobin leads to the formation of phosphite and phosphate. 3. Incubation of rat erythrocytes with various concentrations of phosphine results in the progressive uptake of phosphine by the erythrocytes in a temperature-dependent first-order process. 4. Uptake of phosphine by erythrocytes causes crenation, but conversion of oxyhaemoglobin to methaemoglobin and hemichrome could not be demonstrated.

Determination of calcium in waters, milk and wine by discontinuous-flow analysis.

The flow-based analysis method, discontinuous-flow analysis (DFA), was used for the determination of total calcium in drinking water, milk and wine by titration with ethyleneglycoltetraacetic acid. The detector is a coated-wire calcium-selective electrode. The titration can be cycled continuously with a cycle time of about 1 min. This can be carried out with a single sample or with different samples using an autosampler. The method for waters and wine is simple, fast and highly reproducible. For milk, a back-titration method was used because of the complex matrix of the sample.