Application of property-activity relationships and structure-activity relationships to flavour research. part ii. correlation of calculated octanol/water partition coefficients with the flavour thresholds of compounds in beer.
Relationships of property/activity and structure/activity which are widely used in the pharmaceutical industry to correlate the relative biological activities of drugs, have now been applied to the flavour threshold values of beer constituents. The relative biological activities of many drugs have been correlated with their octanol/water partition coefficients by means of different mathematical expressions. The logarithm of the octanol/water partition coefficient (log P) can be calculated for a series of homologues such as aliphatic compounds from information already available and the values obtained have been compared with the flavour threshold values of the compounds in beer available in the literature. Calculation of log l/T where T = threshold value of the compound in ppm in beer were made and showed good agreement with the estimated log P values. Such relationships were calculated for saturated aliphatic alcohols and esters, unsaturated aliphatic alcohols and esters, aromatic alcohols and esters and saturated aliphatic aldehydes and ketones. Besides relationships in a homologous series, activity measurements also apply to substituents of the compounds within a series. In the case of the analogues of hulupone there was less satisfactory agreement between log l/T and the estimated log P. Generally for saturated aliphatic compounds agreement was good but for unsaturated and aliphatic substances the percentage fit fell to 77%. The method shows sufficient promise for further practical and theoretical use on beer flavour.
Keywords: alcohol beer carbonyl compound ester flavour volatile compound water