Identification of taste-and-odor compounds in drinking water
Authors:   , Khiara Djanette 
Published: July 2024

The perception of tastes and odors constitutes the main criterion for the public acceptance of drinking water quality. For the general public the presence of objectionable odors is often associated with an unsafe water. To respond to this concern and improve the public's confidence in drinking water, water authorities have to make great efforts to understand the nature of taste-and-odor problems of their drinking water supplies and develop a sound strategy for the control and removal of the chemicals that cause them. The essential step to the development of such a strategy begins with the identification of these taste-and-odor causing chemicals. Drinking water is an extremely complex mixture of several compounds covering a wide range of chemical structures as well as organoleptic characteristics. Sensory analysis of whole water samples does not always provide a reliable characterization because of the complex interactions between the chemicals present. Taste-and-odor causing compounds generally occur at concentrations so low that it is very difficult to identify them by the traditional instrumental methods. It is therefore necessary to develop appropriate methods and focus on individual compounds using a combination of chemical and sensory methods. This study developed and applied specific sensory methods and used them in tandem with instrumental methods in order to identify taste-and-odor causing compounds. The following unique analytical developments were completed: (1) Development and optimization of methods suitable to the study of organoleptic compounds. These methods included isolation/concentration techniques and identification of organoleptic compounds by coupled instrumental-sensory analyses. (2) Assessment of the contribution of individual odorous compounds to the overall odor description. (3) Identification of chemicals present in natural odor reference standards for the standardization of the flavor profile analysis method. (4) Confirmation of the presence of odorous compounds in natural waters. (5) Identification of taste-and-odor chemicals during taste-and-odor events, such as chemicals causing cucumber, burnt rubber and fishy odors in natural waters. Two extraction techniques, closed loop stripping analysis (CLSA) and simultaneous distillation extraction (SDE) have been examined and found suitable for the isolation of most organoleptic compounds from water. SDE was determined to be a valuable alternative to CLSA for compounds of higher volatility and polarity. This study has also demonstrated that sensory gas chromatography (sensory GC) is a highly sensitive method for the detection of individual odorous compounds. The application of these methods allowed the determination of grassy, decaying vegetation, and septic odor reference standards. Grassy odors were found to be caused by cis-3-hexenyl acetate and its corresponding alcohol, cis-3-hexen-1-ol. Decaying vegetation odors were found to be associated with a combination of dimethyl disulfide, dimethyl trisulfide, 2-isobutyl-3-methoxypyrazine. Dimethyl trisulfide and indole have been shown to be associated with septic odors. All these chemicals were also identified in field samples that were described as presenting decaying vegetation and septic characteristics by flavor profile analysis (FPA). Two unsaturated aldehydes (trans-4-heptenal and trans, trans-2,4-heptadienal) have been confirmed by chemical and sensory analyses as some of the chemicals responsible for causing fishy/swampy type of odors in the water supply. An unsaturated ketone (1-penten-3-one)was tentatively identified as a fishy odor causing compound. The elucidation of the chemical composition of these odorous compounds is an important step toward a better understanding of the nature of taste-and-odor problems. It will assist drinking water authorities in the choice of the appropriate treatment for the removal of these compounds.