Flavor Evaluation by Triangle and Hedonic Scale Tests of Fish Exposed to Pulp Mill Effluents F. A. Farmer, H. R. Neilson and D. Esar School of Food Science Macdonald College of McGill University Montreal, P.Q.
Abstract Tainting was found in perch exposed to Barometric well, Foul water condensate, Peabody wash water and Seal tank effluents as judged by triangle tests. Treatment of 4 point, 3 point and 2 point sources of the above effluents with aerated lagoon and with decreasing effectiveness with acti'vated sludge and turbulent contact absorber methods, reduced the objectionable flavor in the fish as judged by hedonic scale testing. Fish taken from the St. Lawrence River below the Domtar Fine Papers Ltd. mill in Cornwall, showed no flavor tainting in a triangle test when compared to fish taken from the river above the dam.
Resume Des degustations selon la methode consistant it choisir entre trois poissons ont demontre Ie mauvais gout de perches exposees aux effluents du puits barometrique, du condensat d'eau residuaire, de l'eau de rin<;age du Peabody et du reservoir. Le traitement it l'origine en 4, 3 et 2 points des effluents ci-dessus au moyen d'un bassin d'aeration et, avec une efficacite moindre par boues activees et par des procedes d'absorption it contact par turbulence ont permis d'ameliorer la saveur du poisson comme I'a prouve I'opinion de personnes appelees it y gouter. Le poisson preleve dans Ie fleuve St-Laurent en avant de l'usine des Papiers fins Domtar Ltee de Cornwall ne presente aucune trace de gout douteux si on Ie donne it deguster au milieu d'autres poissons preleves dans Ie fleuve en amont du barrage.
Introduction In the past, Canadians have accepted pollution of our waterways with industrial waste as an unavoidable accompaniment of prosperity. Now we are beginning to ask whether the wealth produced justifies the contamination of drinking water and the loss of fresh fish which inevitably follows the introduction of industrial waste into rivers and lakes. The pulp and paper industry is one of the greatest contributors to the Canadian economy, but it also contributes significantly to the pollution of our waterways. This industry is to be commended however, for undertaking research 011 fish tainting at a time when profits were low due to an overall economic recession. Moreover, since ninety percent of exported newsprint paper goes to the United States (Canada Yearbook, 1970-71) this was one of the industries badly hit when the Canadian dollar was floated in 1970. The research undertaken was financed by the Department of Fisheries and Forestry and the Department of Energy, Mines and Resources under the Water Pollution Abatement Research Program. The total program was under the direction of Dr. G. H. Tomlinson II, Vice-president, Research and Environmental Technology, Domtar Ltd. The bulk of the work was done at Domtar Fine Papers Ltd., Cornwall Mill, but the section reported herein was carried out in the School of Food Science at Macdonald College of
McGill University. The object :of the largerstndy was to locate sources of effluent from the pulp and paper mill operation which might cause significant odor and taste problems for drinking purposes or flavor of fish, downstream from the mill in the St. Lawrence River. The study also attempted to determine practical treatments to prevent such pr,oblems. The present paper deals with one aspect only of the total study, Le. the flavor panel studies used to detect flavor changes in fish resulting from exposure to various pulp mill effluents and to effluents treated to remove odor and taste. The samples for tasting were obtained in collaboration with T. W. Beak Consultants TAd., working at the mill in Cornwall, Ontario. About forty years ago Thayson and Pentelow (1936), demonstrated that fish can acquire unusual flavors or taints from the water in which they are living. Since that time fishermen from various localities have suggested that fish become tainted when exposed to waters receiving pulp and paper mill effluent. The Michigan Water Resources Commission in 1963 initiated a study to define the problem. One of the tests used in their research was a taste panel for detection of undesirable flavor in trout. Their panel members were able to distinguish between trout held upstream and downstream of the known waste sources of industries around Muskegan Lake. Amerine et al. (1965) gave a review of methods available for organoleptic testing. Two types of laboratory tests can be used: those which determine simple differences between treated samples and those which determine directional differences. The triangle test, a true difference test, lends itself to statistical analysis (Roessler et at 1956). Hedonic scaling measures likes and dislikes on a scale with a continuum of preference. The meaning of the results of hedonic testing is not always apparent. The descriptive analysis method, such as the flavor profile, records analysis in which all flavor components can be considered in perspective. This method has the disadvantage that it does not lend itself to statistical analysis. No one method 'of evaluation can be used exclusively, for each has its strengths and weaknesses. It is necessary to determine what information is desired and then select the appropriate method that will yield reliable and reproducible data (Amerine et al. 1965). The taste panel studies done at 'Macdonald College served as an independent evaluation of the results obtained by Domtar Fjne Papers Ltd. at Cornwall. Can. lrist. Food ScI. Techno!. J. Vol. 6. No. I, 1973
Expedmental Methods 'l'he flavor tests were carried out in three phases. 'The first was to determine which effluent sources were causing fish tainting. This was accomplished by means of the triangle test method which is used for -detecting simple differences in flavor. The second was to compare the effectiveness of the treatments applied to the effluents in removing the source of fish tainting. A. hedonic scale test was used for this purpose because it tests degrees of difference of flavor rather than simple differences. The third phase was a study of the river samples taken above and below the mill. Triangle tests were used in this phase. Perch (Perce flavescens) taken from the St. Lawrence River were kept in holding tanks in Cornwall and subjected to the following effluent sources: TME (Total mill effluent) was used at three levels of concentration: 10%, 5% and 0.33%. The latter concentration was used at three durations: one week, six weeks and }ong term. Barwell (Barometric well) was the evaporator condensate from the Kraft IMill - Old Recovery Sewer. F'WC
(Foul water condensate) was the digester effluent from the Kraft Mill - Main Sewer. Peabody wash water was the Recovery Furnace Flue Gas Condensate. Seal Tank was the Evaporator Condensate from the Kraft Mill - Old Recovery Sewer. 4 lJoint Barwell (1.9%), FWC (1%), Peabody wash water (7.3%) and Seal Tank (1.4%). Numbers in brackets indicate proportions normally found in the TME. This source was used at two conce;ntrations, 11.6% and 6%. 3 lJoint Barwell (1.9%), FWC (1%) and Seal Tank (1.4%) used at the 2% and 1% concentration. 2 point FWC (1%) and Seal Tank (1.4%) used in hedonic scale tests only, at the 1% concentration. Three different treatments were then applied to these effluent sources: ActivMed Sludge with clarification and sludge recycle - 4, 7 and 24 hI's. Aerated Lagoon - low intensity (4, 5 and G.5 days). TCA (Turbulant Contact Absorber) to provide a counter-current flow of gas and liquid. 1 or 7.3 cycles. The fish were then filletted, frozen and delivered to Macdonald College. Details of the methods used in the treatment of fish prior to delivery are reported elsewhere (Cook et al., 1972). Samples of fish were thawed completely, wrapped in aluminum foil packages containing about eight fillets each and placed on a cooky sheet in an oven preheated to 425°F. When the fish was judged to be cooked, in approximately ten minutes, it was removed J. Inst. Can. Sci. Techno!. Aliment. Vo!. 6, No I, 1973
from the oven and cut up into small bite-sized pieces, each one of which was wrapped individually in aluminum foil. These small packets were kept warm over hot water, in a double boiler, labelled inside with the sample number and on the lid with a code symbol. The code symbols were allotted to samples using random numbers (Cochran and Cox, 1957). In the authors' opinion, the important factors to be considered in selecting a taste panel are: availability, honesty and motivation. These are of greater significance than acuity of taste since flavor testing may become very monotonous to S'omeone not motivated to perform honestly to the best of his ability. The tests reported herein were carried out two or three times a week over a nine month period. Eight graduate students at Macdonald Oollege served on each panel used in these studies. They were selected in a manner similar to that used in previous studies (MacLeod et al. 1969). The room in which the tests were held was a large classroom located adjacent to the preparation laboratory. It was a well ventilated, well illuminated room having individual tables and chairs. The panelists were seated so that they could not read the score sheets of those next to them. Each table had on it a paper placemat marked off in squares and labelled with code symbols according to the type of test to be performed. The tables were set with a score sheet, a serviette, fork, waste disposal bag, a glass for water and also, in some cases, a cup for hot Chinese tea. The samples to be tasted were put on the placemat over the corresponding code symbols so that the panelists could identify a sample only by its code symbol. After all the panelists had completed the first te~t of each session, the score sheets were collected and new sheets and samples for the second test were distributed in a similar way. The fish for duplicate tests for each treatment was all cooked at once and kept hot in the double boiler until needed. In the triangle tests three packages were offered to the panelists - the contents of two were identical, one was different. They were asked to pick out the unmatched sample and to circle the corresponding code symbol on the score sheet. Then if they detected any undesirable flay-or, they had to state whether this flavor was more or less pronounced in the unmatched sample. Finally, if possible, they described the flavor in words. After each pair of tests the panel discussed, as a group, any unusual flavor and tried to suggest words to describe what they had tasted. In the hedonic scale test six samples were used for each test. One of these was a known control, one an unidentified control and the other four were treatment samples. The known control was arbitrarily assigned a value of "seven" on an eight point scale with "one" being the poorest. The flavor of the other five samples was compared relative to this control and to each other. Each sample was identified by a code symbol (,6 0 0 * =) rather than a number. The score sheet for the hedonic scale test also allowed for comments from the panelists. 13
The perch for the third series of tests were taken from the river above and below the Cornwall dam. Fi~h ,,'ere caught by angling in May, June and August, 1911, from three locations below the mill: Windmill Point (3 miles downstream), Glen Walters (5 miles downstream) and Summerstown area (10 miles down>1t!·eam). Triangle tests were used for this phase of the research. The control samples were fish taken froIll the river above the dam. In addition to these tests, triangle tests were also carded out on fish held in pools to which mud from upstream or downstream was added and also on fish held in the river in a cage suspended three feet a1>O\'e the river bed. The significance of the results of the triangle tests ('rable 1) was judged by comparing the number of correct judgements (i.e. the number of panelists \\'ho could correctly select the unmatched sample and theu identify the effluent treated sample as having the more objectionable taste) to the values in Table 2 (Roessler et al., 1956) for p = 1/6 in a one-tail test. The hedonic scale values were anaylzed in several ways. Since the 2 point source was not given the aerated lagoon treatment, an orthogonal set of treatment comparisons was not available. Several analysis of variance tests (Table 2) involving partial use of the data were therefore made. Significance of treatment effects was judged from an "F" table (Steel and Torrie, 1960). In addition to these analyses, the hedonic scale values were ranked (Table 3) for use in the Friedman two-way analysis of variance by ranks (Siegel, 1956). The TME treatments (Table 2) weI'e compared by means of a "t" test (Siegel, 1956) using the standard error calculated in the analysis of variance for average hedonic scale values for 4 point and 3 point sources of treated effluent (Table 2) .
Results and Discussion It is evident from Table 1 that total mill effluent imparted an objectionable flavor to fish when it was llsed at the level of 10% of the water entering the tanks in which fish were held. This is a greater concentration (three times the normal) than is likely to occur in the river, even if fish live at the mill outfall. This table also shows that the total mill effluent sometimes imparted objectionable flavor to fish at the 5% level but not at the 0.33% level except in long term trials. The 0.33% level is about what could be expected if a diffuser were installed in the river for the mill effluent. The 4 point source of effluent (Barwell, FWC, Peabody wash water and Seal tank) tainted fish when used at either the 11.6% or the 6% level. The 11.6% level is the proportion of the four effluent sources normally present in the total mill effluent. However, since even the 6% level imparted taint to fish, one must conclude that some objectionable factor is present in the 4 point source. Removal of the Peabody wash water, to provide a 3 point source however, gave insufficient improvement since the panelists were still able to detect taint in fish when the 3 point source was used at the 2% level.
Panel success 0 in trian~le tests used to identify effluent sources likely to cause fish tainting.
Untreated Source TME
4 point source 3 point source Barwell
FW.C. Peabody wash water Seal tank Paper machines #6 & #7 Seal tank #9 Seal tank #11 Sulphite waste liquor Vanillin main Caustisizing agent Kraft west sewer Sherbrooke thickener North Woodroom Sulphite bleach main
Concentration TME EquivalentO 0
of Tests Significant at
P = .05
10 5 0.33 (long term) 0.33 (six weeks) 0.33 (one week) 11.6 6 2 1.9 0.95 2.2 1.1 0.55 14.4 7.2 3.6 1.4 0.7 8.0
6 2 2
o o o o
o o o o o o o o o o 1 o
2 2 2 4 2 2 2 2 2 4 2 4 2 6
2 2 2 2
o o o o
o o o o o o
2 2 1 1 4 1 4 2 1
o o o
o Number of tests in which panel selected and correctly identified effluent source as having more objectionable flavor than control. 00 TME used at the 10% level means 10% TME 90% town water. 4 point used at the 11.6% level means 11.6% 4 point 88.4% town water, but this is equivalent (based on the 4 point effluent sources only) to 100% TME because the 4 point sources normally constitute 11.6% of the TME. Thus 6% level of 4 point source is helf normal cpncentration.
This is only half the normal level for these effluent sources. These results are understandable in view of the fact that when the individual components of the 4 point source were tested the panelists had little difficulty detecting a dif~erence due to Barwell and no difficulty detecting a difference due to FWC, Peabody wash water or Seal tank at the levels normally found in the total mill effluent (1.9%, 1.0%, 7.3 and 1.4% respectively). The panel also rceognized an objectionable flavor in sulphite waste liquor at the 0.7% level. When preliminary studies of sewer water were carried out at Cornwall, these same five sources were found to be contributing strong odor to the effluent. However, it was felt that the odor contribution from Can. Inst. Food ScI. Techno!. J. Vol. 6, No.1, 1973
sulphite waste liquor to the TME a,fter mixing was substantially reduced. For this reason, no further tests were done on this source. F1VC and Seal tank, on the other hand, were found to be major contributors also to taste of sewer water. In addition to these sources, three others, paper machines #6 and #7 at the 8% level, seal tank #9 at 1.2% and seal tank #11 effluent at the 1.2% level also imparted an objectionable flavor but panel results suggested that it was less pronounced than in the five effluents first mentioned. No further tests were done on these sources or on the six samples with which the panel failed to associate an objectionable flavor. The design of the hedonic scale tests provided an opportunity to compare the assigned value for control samples with the average value for unidentified control suggested by the panelists. Analysis of variance showed no significant differences between fourteen tests or between eight panelists. In contrast to this, it was possible to show a highly significant difference between hedonic scale scores for unidentified control and untreated 4 point plus 3 point plus 2 point effluent s'ources. The lower scores for untreated effluent sources indicate that they were contributinO' an undesirable flavor to fish. Table 2 shows that there is a highly significant difference between scores for the 4 point and for the 3 point sources of untreated effluent with the 3 point being higher (better). As in the case of the triangle tests this is interpreted to mean that removal 'of the Peabody wash water from the 4 point source improved the untreated effluent. Since there was a significant difference between the 4 point and the 3 point plus 2 point source, but no difference in hedonic scale scores between the 3 point and the 2 point sources of untreated effluent, one can assume that removal of the Barwell effluent from the 3 point source gave no further improvement. Earlier it was pointed out that the panelists had more difficulty detecting differences due to Barwell than to the other components of the 4 point source in triangle tests. The 3 point and the 2 point sources (in hedonic scale tests) were used at the 1 % concentrati'on. For the 3 point source this was only 1/4 of the normal concentration in the TME whereas for the 2 point source it was 1/2 of the normal concentration. In considering the difference observed between tainting from the 4 point and the 3 point sources, it becomes evident that the Peabody wash water was responsible for this difference. As stated previously, the panelists had no difficulty distinguishing (Table 1) between control fish and those subjected to Peabody wash water effluent at the 7.2% level. However, 'l'able 1 also shows that when the concentration was dropped to 3.6%, the panelists could still detect an objectionable flavor in the fish. Chemical analysis, carried out at the Domtar Research Centre in connection with this project revealed a high content of phenolics (13.4 ppm) in this effluent source. This chemical may have been responsible for the objectionable flavor imparted to fish. However, even when this J. Inst. Can. Sci. Technol. Aliment. Vol. 6, No 1, 1973
Summary of mean hedonic scale scores 1 for fish exposed to various pulp mill effluents.
Effluent source Untreated effluent: Unidentified control 4 point untreated 6% 3 point untreated 1% 2 point untreated 1% Untreated and treated effluent: Untreated Activated sludge Aerated lagoon TCA Treated effluent: Activated sludge Aerated lagoon TCA Short duration Long duration Untreated and treated TME 0.33% 10% 10% Lagoon 5 days 13.5% Lagoon 4 days 24% Lagoon 4 days 25% Lagoon 5 days 42% + Lagoon 4 days 50% Lagoon 5 days
+ + + + +
No. of Tests
14 6 4 4
6.408 a 1.423b 3.407 c 2.895 c
10 10 10 10
2.217x 3.912Y 5.049z 2.975 x
14 10 12 20 16
4.537m 5.049 m 3.406 n 3.179d 5.706e
2 4 2 2 2 2 2 2
6.430p 3.323q 5.785p 6.070p 5.135 3.855 3.055 2,855
Control assigned a value of seven on an eight point scale with one the poorest. a Mean scores with different superscript letters are significantly different (P = .05). 1
was removed, the panelists still f'ound the remaining effluent (3 point source) objectionable. Since removal of the Barwell effluent to provide a 2 point source did not materially improve the resultant flavor in fish, one can assume that the objectionable flavor in the 3 point source came from either the FWC or the Seal tank. Since FWC is almost as high in phenolics (11.6 ppm) as the Peabody wash wateJ;,FWC may have contributed significantly to the objectionable flavor. On the other hand, FWC also contains a high level of dimethyl disulfide (4.7 ppm) which may have been responsible for tainting the fish. If this were so, then Seal tank may also have made a significant contribution since it too contains a high level of dimethyl disulfide (2.2 ppm). This conclusion seems justified since three of the effluent sources making up the 4 point source (FWC, Peabody wash water and Seal tank) when used individually, rendered the fish unpalatable to the point where the panelists were able to select the unmatched sample in a triangle test, with a high degree of accuracy. Hedonic scale testing was the only type of flavor test used for the effluent treatment studies. When all durations of treatment were lumped together, (Table 2) the untreated effluent, was found to have the lowest (poorest) score, the TCA to be slightly higher (not significantly different) followed by activated sludge, with aerated lagoon having the highest (best) value. The Friedman two-way analysis of variance by ranks (Table 3) on the same data, also showed a highly significant difference between treatments with the untreated lowest, TCA next, ac-
Average ranks of hedonic scale scores" for treated effluent using Friedman analysis.
No. of Tests
Untreated Activated sludge Aerated lagoon TeA
10 10 10 10
Average ranks 1.20 3.10 3.55 2.15
" 4 point and 3 point sources only
tivated sludge third and aerated lagoon again in the preferred position. An analysis of variance for types and also for duration of effluent treatments, (Table 2) which combined 4: point and 3 point plus 2 point values, which are known to be different, nevertheless showed a highly significant difference between effluent treatments (untreated was omitted from this analysis) and mean values suggest again that TCA is the poorest, activated sludge next and aerated lagoon the best treatment, although the latter two are not statistically different. When short and long duration treatments were compared, the 4 hour and 7 hour activated sludge samples were combined. This analysis suggests that in each case, the longer the duration of the treatment (up to 24 hours for activated sludge, 6.5 days for aerated lagoon and 7.3 cycles for TCA) the better the effluent treatment. The total mill effluent at 10% (Table 2) gave such a low score that TME at 0.33% was significantly higher as was lagoon treatment of the 10% TME for 5 days. Lagoon treatment apparently removed some of the objectionable flavor. Even when TME was used at 13.5% and lagoon treatment was carried on for only 4 days, there was a significant improvement over the 10% TME untreated. A limited number of tests carried out on TME at 24-50% concentration with 4 or 5 days lagoon treatment tended to give progressively lower (poorer) scores on the hedonic scale with increasing concentrations of TME but this could not be substantiated statistically because of the limited number of tests. This research was undertaken originally because local fishermen complained that fish taken from the S1. Lawrence river below the dam were tainted in flavor by effluent from the mill. However, in the present tests, not more than two panelists out of seven in each 'of 18 different triangle tests were able to correctly select and identify the downstream sample as having a more objectionable flavor than the control (taken from the river above the dam). vVhen fish were held in the river in a cage suspended three feet above the river bed, a highly significant change in flavor developed in those fish which survived the test. However since few fish did survive, there may have been factors other than tainting by which the panel correctly selected the odd sample.
Conclusions By means of triangle tests for flavor, Barometric well, Foul water condensate, Peabody wash water and Seal tank effluents were identified as the problem sources causing flavor tainting in fish exposed to pulp mill effluents. The problem sources, Barometic well, Foul water condensate, Peabody wash water and Seal tank when used as the 4 point source equivalent to 6% of the total mill effluent caused taint in fish as judged in a hedonic scale test. Removal of the Peabody wash water to provide the 3 point source of effluent used at a level equivalent to 1% total mill effluent gave a significant improvement in flavor as judged by the hedonic scale test. Removal of the Barometric well to provide the 2 point source of effluent, used at a level equivalent to 1% of the total mill effluent gave no further improvement. Fish exposed to effluent sources, treated with Activated Sludge plus Aerated Lagoon plus Turbulent Contact Absorber considered together were less objectionable than fish exposed to the untreated 4 point, 3 point and 2 point effluents as judged by the hedonic scale test. Activated Sludge (24 hours) Aerated Lagoon (6.5 days) and Turbulent Contact Absorber (7.3 cycles) considered together were significantly better than the same effluent treatments used for a shorter time, as judged by the hedonic scale test. .. . The effective effluent treatments III Illcreasmg order of value were Turbulent Contact Absorber, Activated Sludge and Aerated Lagoon. Fish taken from the St. Lawrence River below the mill showed no flavor tainting by the triangle test method.
References Amerine, M. A., Pangborn, R. M. and Roessler, E. B. 1965. Principles of Sensory Evaluation of Food. Academic Press, New York. Cochran, W. G. and Cox, G. M. 1957. Experimental DeSIgns. John WHey and Sons Inc. 2nd ed. New York. . . Cook, W. H., Farmer, F. A., Kristiansen, O. E., ReId, K., ReId, J. and Rowbottom, R. 1972. The effect of pulp and paper mIll effluents on the taste and odour of receiving water and the fIsh therem. (In press). MacLeod, C. M., Farmer, F. A. and Neilson, H. R. 1969. Organoleptic evaluation of low-dose Irradiated chicken stored under refrigeration conditions. Food Techno!. 23: 104. Michigan Water Resources Commission. 1963 Fish Off-Flavor problems In Saginaw Bay, Lake Huron, ~Ith a summary of factors which Influence the palatablllty of fIsh. A paper presented by C.N. Fetterolf, Jr. to the American Fisheries Society, Mlnneapolls. Sept. 12, 1963. 0 T 11 d Roessler, E. B., Baker, G. A. and Amerine, M. A. 1956. ne- a e and Two-Tailed Tests In Organoleptic Comparisons. Food Res., 21: 117. Siegel, S. 1956. Non parametric statistics for the behavioral sciences. McGraw-Hlll Book Co., Inc. Toronto. Steel. R. G. D. and Torrle, J. H. 1960. Principles and Procedures of Statistics. McGraw-Hll1 Book Co., Inc. Toronto. . Thaysen, A. C. and Pentelow. F. T. K. 1936. The orlgm of an earthy or muddy taint In fish. II. The effect on fish of the taint produced by an odoriferous species of actinomyces. Ann. App!. Blo!. 22: 105. Received JUly 3, 1972
Can. Inst. Food ScI. Techno!. J. Vo!. 6, No. I, 1973