Factors Affecting the Stability and Behavior of Grassy Odors in Drinking Water

The presence of grassy-type odors in drinking water has frequently been determined by flavor-profile analysis (FPA). Previous work (Khiari et al., 1995) has identified cis-3-hexen-1-ol and cis-3-hexenyl acetate as the causes of these odors in laboratory experiments. Both chemicals possess very similar characteristics; however, cis-3-hexenyl acetate has a much lower odor threshold concentration (OTC) than its corresponding alcohol. In this study, both chemicals were identified by both sensory and chemical analyses separately or in combination in natural and treated waters. It was also found that the sensory and chemical characteristics of samples with grassy odors have a tendency to change upon storage and shipment. Hydrolysis was determined to be a major controlling mechanism for the degradation of cis-3-hexenyl acetate and the formation of cis-3-hexen-1-ol in aqueous solution. The kinetics of the hydrolysis of cis-3-hexenyl acetate to cis-3-hexen-1-ol was evaluated in bench-scale experiments. These studies showed the concentration of cis-3-hexen-1-ol and cis-3-hexenyl acetate to be strongly pH-dependent. This study shows that preservation by refrigeration and adjustment of pH to 4.6 were important steps to be taken when quantitation of the compounds is needed. However, the samples should be analyzed as quickly as possible.