An antiserum raised against whole cells of Thiobacillus ferrooxidans was allowed to react with a variety of acidophilic and nonacidophilic bacteria in an enzyme-linked immunosorbent assay and an indirect immunofluorescence assay. Both experiments demonstrated that the antiserum was specific at the species level. This preparation was used to evaluate the role of T. ferrooxidans in the microbial desulfurization process. Leaching experiments were performed, and the numbers of T. ferrooxidans cells and other bacteria were estimated by using a combined immunofluorescence-DNA-fluorescence staining technique that was adapted for this purpose. Nonsterile coal samples inoculated with T. ferrooxidans yielded high concentrations of soluble iron after 16 days. After this period, however, T. ferrooxidans cells could no longer be detected by the immunofluorescence assay, whereas the DNA-fluorescence staining procedure demonstrated a large number of microorganisms on the coal particles. These results indicate that T. ferrooxidans is removed by competition with different acidophilic microorganisms that were originally present on the coal.

A method for the quantitative determination of riboflavin levels in beer was developed. The method is based on the quenching of riboflavin fluorescence, which occurs when riboflavin binds to the aporiboflavin-binding protein from egg white. The method does not require any pretreatment of the beer before analysis, other than dilution, and proved to be simple, reliable, and sensitive. The lowest concentration that could be detected was approximately 10 nM riboflavin. The possible interference of flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) with the determination of the riboflavin content of beer was excluded, because beer contains only a very small amount of FAD (0.03 microM) and no FMN. The riboflavin levels of the types and brands of beer investigated were in the range of 0.5-1.0 microM. The origin of the riboflavin in beer proved to be the malt. Hop and yeast hardly contributed to the riboflavin content of beer. Besides its use in the determination of riboflavin levels, the aporiboflavin-binding protein also provides a way to remove riboflavin from beer, which reduces the light sensitivity and the related lightstruck off-flavor formation in beer.

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Tlte effect of riboflavin and riboflavin binding proteins on the light-induced formation of reactive oxygen species and sunstruck off-flavour was studied in model beer solutions. Under model beer conditions (pH 4.0, 1 ppm riboflavin, 5% ethanol and traces of O2) hydroxyl and hydroxyethyl radicals were formed upon illumination. Radical formation was measured with the spin traps N-t-butyl-a-phenylnitrone (PBN) and 5,5-dimethyl-l-pyrroline-N-oxide (DMPO). DMPO appeared to be a better spin trap than PBN for sttidying the effect of light exposure, since PBN is photochemically active by itself. Addition of isohumulones to the model beer reduced the amount of riboflavin-induced radicals. Two different riboflavin binding proteins were tested both for their ability to scavenge riboflavin and how in turn this influenced free radical formation. The apoform of egg white riboflavin binding protein (RfBP) was more efficient in reducing radical formation than an apo-flavodoxin protein isolated from Azotobacter vinelandii. Organoleptic assessment clearly indicated that the addition of apoRfBP to model beer solutions, containing stiochiometric amounts of riboflavin as well as isohumulones and cysteine, reduced sunstruck off-flavour formation. The dual role of riboflavin and ethanol as radical propagators in oxidiatve flavour change is discussed. From these anaerobic stock solutions, samples were prepared in an anaerobic glove box (20% H2 and 80% N2).All samples were freshly prepared and well protected against light prior to illumination.Samples for flavour evaluation were prepared as described above, except that 12 ml GC sealable vials were The EPR experiments were performed immediately after illumination. EPR analysisAll EPR experiments were performed at room temperature on a Bruker ER 200D EPR spectrometer.The following parameters were used: field (