Philippe Perpete

Retention of sulfur flavours by food matrix and determination of sensorial data independent of the medium composition

Interactions between food matrix and sulfur compounds (thioesters, sulfides, disulfides, pentanethiol and 2-ethoxythiazole) were studied in a real food system composed of fresh cheese, triolein or inulin, and water. Results obtained with the lipidic medium confirm that 10% of triolein is enough to significantly affect flavour perception. The lipophilicity index, log k(W), appears as an interesting physicochemical property allowing assessment of the aroma retention intensity. Results obtained with inulin indicate how different the retention will be when a polysaccharide is used as a fat-mimic. Formulation of dietetic products has to take that discrepancy into account. GC-odour port evaluation of diluted solutions appears as an interesting method for easy acquisition of best estimated GC-lower amounts detected by sniffing (BE-GC-LOADS), threshold values independent of the medium composition

How to improve the enzymatic worty flavour reduction in a cold contact fermentation

Although much more efficient at 28 degrees C than at low temperature, enzymatic removal of Strecker aldehydes by brewers yeast, Saccharomyces cerevisiae, is always limited to 60-85% of the: initial concentration, whatever the fermentation conditions. This asymptotic reduction pattern leads to residual concentrations imparting the well-known unpleasant worty taste to alcohol-free beers. Low-energy binding to flavanoids is shown to hinder more complete enzymatic reduction in the cold contact fermentation process

Fate of the worty flavours in a cold contact fermentation

3-Methylbutanal, 2-methylbutanal and 3-methylthiopropionaldehyde are described in the literature as preponderantly responsible for the worty taste of alcohol-free beers. Even in a cold contact process, such aldehydes are reduced through fermentation. The chemical removal of aldehydes by amino acids or proteins does not exceed 20% of the initial concentration, although such mechanisms appear much more effective at 28 degrees C. The role of Saccharomyces cerevisiae brewers yeast, in the reduction of wort aldehydes, is confirmed here. Only viable yeasts allow a significant decrease in carbonyl level. Unfortunately, residual concentrations are higher for Strecker aldehydes among which 3-methylthiopropionaldehyde is characterized by a very low flavour threshold. Effects of yeast strain, pitching rate and inhibitors have been assessed