Influence of water on the generation of Strecker aldehydes from dry processed foods

Completeness of extraction, losses during isolation and, in particular, the formation of new constituents are challenges during the enrichment of volatiles for GC analysis. Especially the isolation of volatiles by simultaneous steam distillation/extraction has long been known to generate artifacts due to the hot water treatment. However, even a simple treatment of dry foods with cold water may already lead to the release of odour-active volatiles. After treatment of chocolate or cocoa beans with water, the concentrations of the four Strecker aldehydes 2- and 3-methylbutanal, 3-(methylthio)propanal and phenylacetaldehyde were increased by factors between 10 and 100. Also in other dry processed foods, such as malt or crackers, the concentrations of the Strecker aldehydes were substantially increased upon water addition. Although a physical release of the aldehydes weakly bound to, e.g. proteins or starch is possible, in a further experiment, it could be shown that a yet unknown precursor of 3-(methylthio)propanal and phenylacetaldehyde could be isolated by solvent extraction from caramalt and Munich malt. As a consequence, the presence or absence of water during the work-up procedure might either lead to an over- or underestimation of the relevance of the respective aroma compounds, which might also effect aroma formation and perception during the process of eating.