Biomedical subjects

K J Verstrepen

Publications and source records attributed to K J Verstrepen.

3 recordsLinked to original sources

PubMed2003

Effects of CO2 on the formation of flavour volatiles during fermentation with immobilised brewer's yeast.

Immobilised-cell fermentors offer great benefits compared to traditional free-cell systems. However, a major problem is unbalanced flavour production when these fermentors are used for the production of alcoholic beverages. One of the keys to obtaining better control over flavour formation may be the concentration of dissolved CO2, which has inhibitory effects on yeast growth and metabolism. This article demonstrates that the presence of immobilisation matrices facilitates the removal of CO2 from the liquid medium, which results in a low level of dissolved CO2 during fermentation. Moreover, the formation of volatile higher alcohols and esters was greatly enhanced in the immobilised-cell system when compared to the free cell system. By sparging a CO2 flow (45 ml/min) into the immobilised-cell system, cell growth was reduced by 10-30% during the active fermentation stage, while the fermentation rate was unaffected. The uptake of branched-chain amino acids was reduced by 8-22%, and the formation of higher alcohols and esters was reduced on average by 15% and 18%, respectively. The results of this study suggest that mismatched flavour profiles with immobilised-cell systems can be adjusted by controlling the level of dissolved CO2 during fermentation with immobilised yeast.

Alcoholic Beverages↗

PubMed2003

Bioflavoring and beer refermentation.

Various techniques are used to adjust the flavors of foods and beverages to new market demands. Although synthetic flavoring chemicals are still widely used, flavors produced by biological methods (bioflavors) are now more and more requested by consumers, increasingly concerned with health and environmental problems caused by synthetic chemicals. Bioflavors can be extracted from plants or produced with plant cell cultures, microorganisms or isolated enzymes. This Mini-Review paper gives an overview of different systems for the microbial production of natural flavors, either de novo, or starting with selected flavor precursor molecules. Emphasis is put on the bioflavoring of beer and the possibilities offered by beer refermentation processes. The use of flavor precursors in combination with non-conventional or genetically modified yeasts for the production of new products is discussed.

Beer↗

PubMed2003

Yeast flocculation: what brewers should know.

For many industrial applications in which the yeast Saccharomyces cerevisiae is used, e.g. beer, wine and alcohol production, appropriate flocculation behaviour is certainly one of the most important characteristics of a good production strain. Yeast flocculation is a very complex process that depends on the expression of specific flocculation genes such as FLO1, FLO5, FLO8 and FLO11. The transcriptional activity of the flocculation genes is influenced by the nutritional status of the yeast cells as well as other stress factors. Flocculation is also controlled by factors that affect cell wall composition or morphology. This implies that, during industrial fermentation processes, flocculation is affected by numerous parameters such as nutrient conditions, dissolved oxygen, pH, fermentation temperature, and yeast handling and storage conditions. Theoretically, rational use of these parameters offers the possibility of gaining control over the flocculation process. However, flocculation is a very strain-specific phenomenon, making it difficult to predict specific responses. In addition, certain genes involved in flocculation are extremely variable, causing frequent changes in the flocculation profile of some strains. Therefore, both a profound knowledge of flocculation theory as well as close monitoring and characterisation of the production strain are essential in order to gain maximal control over flocculation. In this review, the various parameters that influence flocculation in real-scale brewing are critically discussed. However, many of the conclusions will also be useful in various other industrial processes where control over yeast flocculation is desirable.

Fermentation↗