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International symposium on off-flavours in the aquatic environment
Ware," Res ;or. l-. No. l t. pp tTt3-1+la+ 1983 Printed :n Great Britain
0043-t35 -t $3 53 00 - 0.00 Pergamon Press ktd
TECHNICAL REPORT I N T E R N A T I O N A L S Y M P O S I U M ON OFF-FLA VOURS IN THE AQ UA TIC E N V I R O N M E N T E s p o o , F i n l a n d , I 4 - 1 8 June, i982 The taste and odour of drinking water and aquatic products are important in severat respects. The sensory characteristics of food are the only ones that can be directly evaluated by consumers, and the decision of acceptance or rejection of a food item is largely based on this evaluation. Water is the essence of life, and fishery products are important protein sources in many countries. Offensive tastes and odours in water and aquatic products cause consumer dissatisfaction, resulting in high treatment costs for water supplies, economic losses to fisheries and decreased value of real estate. Although tastes and odours in water supplies and fisheries have been known for a long time, research on these problems has suffered from a low official status. However, significant scientific advances have been made in the last few years in this field. Because of increasing public and scientiiic interest, a scientific meeting on taste and odour problems in natural waters was deemed necessary. The first International Symposium on Off-Flavours in the Aquatic Environment was held in Espoo. Finland. on 14-18 June, 1982, under the auspices of the International Association on Water Pollution Research and Control and the International Association of Theoretical and Applied Limnology. Financially and organizationally, the event was supported by several national sponsors. The meeting was attended by 90 participants from t3 countries, and it discussed all aspects of offensive tastes and odours in water and aquatic organisms. The papers were arranged under the following headings: (1) (2) (3) (4)
Sensory characterization of flavour problems. Chemistry of flavour problems. Biology and biochemistry of flavour problems. Technology of off-flavour abatement.
In dealing with taste and odour problems, the usefulness of sensory methods as screening methods was widely acknowledged. When evaluating the quality of drinking water, there is a definite need to assess consumer reactions. The large consumer taste panels used by the Rotterdam water works have proved to be inexpensive, accurate and reliable for routine monitoring of water quality. Studies comparing laboratory and consumer panels would be needed. Generally, the refinement of quantitative sensory techniques (e.g. threshold techniques) for routine application in water works is needed. Many different offensive tastes and odours occur in water and fish. A standardization of current descriptive techniques is clearly needed. As a first step, specific odorous compounds and the corresponding verbal descriptions, representing the most common off-flavours in water and fish, should be assembled. Such standard odour reference kits would be very useful for training panelists. At the symposium, a working group was set up to continue work in this area. Chemical analytical instrumentation and technology is needed to isolate, identify and characterize taste and odour compounds in natural waters. It is also needed for the elucidation of the sources of these compounds. Chemical and sensory methods are complementary: the tastes and
odours must be described by sensory methods, and the corresponding compounds identified by chemical means, In some cases, the compounds responsible for specific ofl'-flavours in natural waters have been identified, although it is evident that much more work is needed in this area. For example, muddy odour is caused by geosmin, musty odour by 2-methytisoborneo[, iodine flavour by obromophenol, mushroom-like odours by oct-l-en-3-ol and 1,3-octadiene, tobacco-like by fl-cyctocitral and onion flavour in crustaceans by dimethyltrisulphide. Major difficulties in the analysis of odorous compounds in natural waters are the isolation, concentration and separation or purification of the compounds. At the symposium, various extraction and stripping techniques were discussed. Using closed loop stripping analysis and a gas chromatograph-mass spectrometer system, several odorous compounds could be an:dyzed at concentrations of 2 - S n g I -t (at or below their threshold odour concentrations). In spite of this, there is still a definite need tbr the development of less expensive chemical analytical methods, applicable to routine monitoring of water quality. Biogenic off-fiavours--i.e, tastes and odours produced by algae and bacteria--are common in water supplies and fisheries around the world. At the symposium, criteria for establishing biogenic odour production were discussed. Existing lists of taste and odour producing algae were considered inaccurate. To prove odour production by an alga, sensory and chemical studies in the field and in the laboratory are needed. Extreme care must be taken to exclude artel:acts and sources of contamination. Several studies establishing the odour production by several algae were presented at the symposium. For the first time, evidence for simultaneous production of geosmin and 2-methylisoborneol by a blue-green alga was presented. There is a large variation in the odour production by different algal strains. The reasons for this variability need more study, as does the ecology of odour-producing organisms generally. It should be emphasized that both p[anktic and benthic algae may produce odours. The importance of the latter group was evident from several contributions to the symposium. Work on the biosynthesis of taste and odour compounds is still in infancy, and more research in this area is urgently needed. In Calitbrnia, an early warning system for the prediction of odour problems in reservoirs was developed. By monitoring odour compounds chemically below their threshold odour concentrations and the growth of benthic blue-green algae, the problem was predicted one month in advance, allowing time for preventive action. Practical abatement of flavour problems in water supplies and fisheries was discussed in several papers at the symposium. In Japan, sand filtration and active carbon filtration was effective in removing geosmin and 2-methylisoborneol from water. In Finland and France, ozonization and carbon filtration was effective in removing odorous compounds. It is evident that more work is needed in this area. The elucidation of off-flavours in natural waters requires an integration of sensory, chemical and biological research. When the information thus obtained is coupled to tech-
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171 o,
Technical Report
noloNcal research, rational abatement techniques may result. The proceedings of the symposium are scheduled for publication as Parts 6 and 7 of Volume 15 of Water Science and Technology, I983 and will simultaneously' appear as a book to be published by Pergamon Press in 1983, entitled
"'Taste and Odour in Waters and Aquatic Organisms".
PER-EDvlN PERSSON
Programme Chairman. Symposium Editor
0043-t35 -t $3 53 00 - 0.00 Pergamon Press ktd
TECHNICAL REPORT I N T E R N A T I O N A L S Y M P O S I U M ON OFF-FLA VOURS IN THE AQ UA TIC E N V I R O N M E N T E s p o o , F i n l a n d , I 4 - 1 8 June, i982 The taste and odour of drinking water and aquatic products are important in severat respects. The sensory characteristics of food are the only ones that can be directly evaluated by consumers, and the decision of acceptance or rejection of a food item is largely based on this evaluation. Water is the essence of life, and fishery products are important protein sources in many countries. Offensive tastes and odours in water and aquatic products cause consumer dissatisfaction, resulting in high treatment costs for water supplies, economic losses to fisheries and decreased value of real estate. Although tastes and odours in water supplies and fisheries have been known for a long time, research on these problems has suffered from a low official status. However, significant scientific advances have been made in the last few years in this field. Because of increasing public and scientiiic interest, a scientific meeting on taste and odour problems in natural waters was deemed necessary. The first International Symposium on Off-Flavours in the Aquatic Environment was held in Espoo. Finland. on 14-18 June, 1982, under the auspices of the International Association on Water Pollution Research and Control and the International Association of Theoretical and Applied Limnology. Financially and organizationally, the event was supported by several national sponsors. The meeting was attended by 90 participants from t3 countries, and it discussed all aspects of offensive tastes and odours in water and aquatic organisms. The papers were arranged under the following headings: (1) (2) (3) (4)
Sensory characterization of flavour problems. Chemistry of flavour problems. Biology and biochemistry of flavour problems. Technology of off-flavour abatement.
In dealing with taste and odour problems, the usefulness of sensory methods as screening methods was widely acknowledged. When evaluating the quality of drinking water, there is a definite need to assess consumer reactions. The large consumer taste panels used by the Rotterdam water works have proved to be inexpensive, accurate and reliable for routine monitoring of water quality. Studies comparing laboratory and consumer panels would be needed. Generally, the refinement of quantitative sensory techniques (e.g. threshold techniques) for routine application in water works is needed. Many different offensive tastes and odours occur in water and fish. A standardization of current descriptive techniques is clearly needed. As a first step, specific odorous compounds and the corresponding verbal descriptions, representing the most common off-flavours in water and fish, should be assembled. Such standard odour reference kits would be very useful for training panelists. At the symposium, a working group was set up to continue work in this area. Chemical analytical instrumentation and technology is needed to isolate, identify and characterize taste and odour compounds in natural waters. It is also needed for the elucidation of the sources of these compounds. Chemical and sensory methods are complementary: the tastes and
odours must be described by sensory methods, and the corresponding compounds identified by chemical means, In some cases, the compounds responsible for specific ofl'-flavours in natural waters have been identified, although it is evident that much more work is needed in this area. For example, muddy odour is caused by geosmin, musty odour by 2-methytisoborneo[, iodine flavour by obromophenol, mushroom-like odours by oct-l-en-3-ol and 1,3-octadiene, tobacco-like by fl-cyctocitral and onion flavour in crustaceans by dimethyltrisulphide. Major difficulties in the analysis of odorous compounds in natural waters are the isolation, concentration and separation or purification of the compounds. At the symposium, various extraction and stripping techniques were discussed. Using closed loop stripping analysis and a gas chromatograph-mass spectrometer system, several odorous compounds could be an:dyzed at concentrations of 2 - S n g I -t (at or below their threshold odour concentrations). In spite of this, there is still a definite need tbr the development of less expensive chemical analytical methods, applicable to routine monitoring of water quality. Biogenic off-fiavours--i.e, tastes and odours produced by algae and bacteria--are common in water supplies and fisheries around the world. At the symposium, criteria for establishing biogenic odour production were discussed. Existing lists of taste and odour producing algae were considered inaccurate. To prove odour production by an alga, sensory and chemical studies in the field and in the laboratory are needed. Extreme care must be taken to exclude artel:acts and sources of contamination. Several studies establishing the odour production by several algae were presented at the symposium. For the first time, evidence for simultaneous production of geosmin and 2-methylisoborneol by a blue-green alga was presented. There is a large variation in the odour production by different algal strains. The reasons for this variability need more study, as does the ecology of odour-producing organisms generally. It should be emphasized that both p[anktic and benthic algae may produce odours. The importance of the latter group was evident from several contributions to the symposium. Work on the biosynthesis of taste and odour compounds is still in infancy, and more research in this area is urgently needed. In Calitbrnia, an early warning system for the prediction of odour problems in reservoirs was developed. By monitoring odour compounds chemically below their threshold odour concentrations and the growth of benthic blue-green algae, the problem was predicted one month in advance, allowing time for preventive action. Practical abatement of flavour problems in water supplies and fisheries was discussed in several papers at the symposium. In Japan, sand filtration and active carbon filtration was effective in removing geosmin and 2-methylisoborneol from water. In Finland and France, ozonization and carbon filtration was effective in removing odorous compounds. It is evident that more work is needed in this area. The elucidation of off-flavours in natural waters requires an integration of sensory, chemical and biological research. When the information thus obtained is coupled to tech-
1713
171 o,
Technical Report
noloNcal research, rational abatement techniques may result. The proceedings of the symposium are scheduled for publication as Parts 6 and 7 of Volume 15 of Water Science and Technology, I983 and will simultaneously' appear as a book to be published by Pergamon Press in 1983, entitled
"'Taste and Odour in Waters and Aquatic Organisms".
PER-EDvlN PERSSON
Programme Chairman. Symposium Editor