Abstract: Glycerol, the most important secondary product of alcohol fermentation, contributes to the smoothness and viscosity of wines with favorable effects on taste. An electrochemical biosensor was developed for online monitoring of glycerol biosynthesis. Anal. parameters as pH, buffer composition, and cofactor concentration. were optimized. The lifetime of the sensor in working conditions was also evaluated. The biosensor was assembled by immobilizing glycerol-3-phosphate oxidase on polymeric membranes and glycerokinase on aminopropyl glass beads. The enzymatic membrane was placed in contact with the surface of a Pt electrochemical transducer for H2O2 detection. Glass beads with immobilized glycerokinase were packed to form a reactor connected with the enzyme electrode in a flow system. A cell with a wall-jet configuration was used to monitor glycerol levels by flow-through and flow injection analysis (FIA) in a 10^-5 to 10^-3 mol/L concentration. range. This system was used to measure glycerol levels during alcohol fermentation at different temperatures and pH values.

Abstract: Alternatives to the Monier-Williams assay for sulfites are outlined. In one procedure, a Kjeltec distillation app. is used to produce SO2, which is then trapped and titrated with NaOH. Alternatively, flow-injection anal. and colorimetry may be used. The reagents employed are either pararosaniline (which forms a complex with SO2 that absorbs at 560 nm) or malachite green (decolorization by SO2, monitored at 615 nm). When applied to food and wine, all 3 alternative procedures gave values that were consistent with the Monier-Williams method. (SFS)