- Email: [email protected]
Development of a Modified Mattson Bean Cooker Procedure Based on Sensory Panel Cookability Evaluation
Con Inst. Food Sci. Technol. J. Vo!. 20, No. 1, pp. 9-14, 1987
RESEARCH
Development of a Modified Mattson Bean Cooker Procedure Based on Sensory Panel Cookability Evaluation J.R. Proctor and B.M. Watts Department of Foods and Nutrition University of Manitoba Winnipeg, Manitoba R3T 2N2
ability" refers to the cooking time required to reach that texture (Moscoso et al., 1984). Poor cookability, caused either by long cooking time required to soften the majority of beans within a sample, or by extended cooking time required for a small but significant proportion of hard-to-cook beans in an otherwise good cooking sample, is a major problem with pulses. Poor cookability can cause loss of nutrients, increased consumption of energy and consumer rejection (Bressani et al., 1963). The phenomenon of within-sample variability complicates cookability measurement and the comparison of bean samples. The testing of large numbers of beans is required to ensure statistical reliability (Silva et al. , 1981). Methods which attempt to ensure statistical reliability by testing large samples rather than individual beans, can mask the very important effect of individual bean cooking time on the overall sample cooking time (Bourne, 1972). Therefore, testing methods must be able to measure the cooking time of the individual beans within a sample. The Mattson Bean Cooker (MBC) (Mattson, 1946) was developed to assess cookability by measuring the time required to cook large numbers of individual beans to a defined degree of softness (Morris, 1964; Jackson and Varriano-Marston, 1981). The MBC as first developed by Mattson (1946) and as used by Morris (1964) consisted of 100 plungers held in position by supporting racks so that the plunger points rested on the supported uncooked beans. Burr (1976) modified this version of the MBC, so that plunger dropping times would be automatically recorded. A 25 plunger model was described by Jackson and Varriano-Marston (1981), and Chhinnan (1985) reported a prototype 25 plunger model with an electronic device to monitor plunger movement. These instruments are designed to test the cooking time of individual beans by measuring the time required for plungers of specific weight and diameter to puncture single beans while they are actually cooking in the cooking water. Plunger types reported in the literature are either 82 g, 2 mm (Jackson and Varriano-Marston, 1981) or 90 g, 2 mm (Morris, 1964; Burr et al., 1968).
Abstract The Mattson Bean Cooker (MBC) is widely used to measure relative cooking times of bean samples, but MBC values have not been related to values determined by sensory evaluation. In order to obtain instrumental values that reflected sensory assessment of cookability, MBC plungers of four weights and two tip diameters were tested. Plots of percent beans cooked versus cooking times, produced by the 48 g 5 mm diameter MBC plungers, corresponded closely to the cookability curves resulting from evaluation by a trained, nine member sensory panel. The optimum cooked point, as identified by this panel, was 93.75070. This corresponded to the drop of the twentythird plunger for the 25 plunger model of the MBC (92070 cooked point or CT92). MBC CT92 values gave better discrimination among freshly harvested navy bean samples than did the commonly employed CT 50 values.
Resume Le cuiseur a haricots Mattson (MBC) est tres utilise pour mesurer les temps de cuisson relatifs d'echantillons d'haricots, mais les valeurs MCB n'ont pas ete correlees aux valeurs determinees par I'evaluation sensorielle. Dans le but d'obtenir des valeurs instrumentales qui soient representatives des evaluations sensorielles de l'aptitude a la cuisson, des plongeurs MBC de quatre pesanteurs et deux diametres de pointe ont ete essayes. Les traces des pourcentages d'haricots versus temps de cuisson, obtenus avec les plongeurs MBC de 48 g et de diametre de 5 mm, ont ete etroitement correles aux courbes d'aptitude a la cuisson obtenues de l'evaluation par un jury sensoriel exerce de neuf membres. Le point de cuisson optimum, tel qu'indique par ce jury fut de 93.75070. Ceci a correspondu a la chute du vingt-troisieme plongeur du modele MBC de 25 plongeurs (92070 point de cuisson ou CT 92)' Les valeurs MBC CT 92 ont permis de mieux differencier entre les echantillons d'haricots blancs fraichement cueillis que ce fut possible avec les valeurs CT 50 couramment utilisees.
Introduction Edible dry beans ("grain legumes or pulses") play a major role in human nutrition. Navy beans (PhaseoIus vulgaris L.), grown commercially in Western Canada, are consumed by Canadians and have a large potential export market. Plant breeders and legume marketers have expressed interest in improving the quality of navy beans grown in Western Canada. Cooking time is one of the major criteria involved in the evaluation of pulse quality. Each type of edible dry bean has a particular cooked texture which is considered acceptable by consumers and the term "cookCopyright
Cl
1987 Canadian Institute of Food Science and Technology
9
The MBC tests large numbers of beans individually and provides an indication of within sample variability. Cooking times of different bean samples have been compared using the cooking time required to reach the 50070 cooked point (CTso) as the reference point (Morris, 1964; Jackson and Varriano-Marston, 1981). However, cooking time as measured by the MBC has not been related to the cooking time as determined by sensory analysis, which is the ultimate method of calibrating instrumental methods of measuring texture (Bourne, 1982). The objectives of this study were to design MBC plungers that would consistently reproduce the results determined by sensory analysis and to devise a method for calculating comparative cooking times, based on sensory panelists' cooking point preference.
..
E
u
'"'"
J
Materials and Methods
--1~mm
ExperitnentalSequence In the first experiment, using one sample of navy beans, MBC cookability curves produced with plungers of different designs were compared to the sensory cookability curve determined by a five member sensory panel. In the second experiment, three stored navy bean samples were tested by the MBC using a plunger selected on the basis of the results of experiment one. The aim of the second experiment was to determine whether the plunger design consistently reproduced the sensory cookability curves determined by a five member sensory panel. In the third and final experiment, cookability curves for three freshly harvested bean samples were determined by the MBC using a slightly adjusted plunger design. The reproducibility of sensory cookability curves by instrumental curves was verified. In this experiment a preference test was also conducted to determine the most appropriate reference point for cooking time comparison.
Materials One sample of navy beans was purchased at a local supermarket ("commercial" sample), three were obtained from the Manitoba Department of Agriculture Research Station, Brandon, Manitoba and two were obtained from the Plant Science Department of the University of Manitoba. Samples were refrigerated at 4°C. Storage conditions for the "commercial" (cultivar unknown), Seafarer '77 - Brandon and Seafarer '78 - Brandon samples, prior to receipt, were not known.
MBC Apparatus and Method of Operation The MBC used consisted of a brass rack with 25 identical plungers as described 'by Jackson and Varianno-Marston (1981), but with smaller, 3 mm diameter perforations in the lowest plate of the rack (Figure I). The 5 mm diameter brass plungers had threaded upper ends to which hollow brass cylinders of different weights could be attached. Lead shot placed inside the cylinders was used to standardize weights precisely. Plunger tips were flat faced and were 5 mm or 2 mm in diameter. Plungers used had the follOWing weights and tip diameters: 65 g, 2 mm; 35 g, 10 I Proctor and Watts
Fig. I. Dimensions of rack and plungers of Mattson Bean Cooker.
2 mm; 49.75 g, 5 mm; and 48 g, 5 mm. The force exerted by these plungers was 20.7, 22.9, 2.5 and 2.4 g/mm 2 respectively. For each replication of the MBC test, 25 beans, which had been soaked in distilled water (1:4 beans to water ratio) at 20°C for approximately 16 h, were placed on the perforations in the bottom plate. The plungers, when inserted, were positioned at right angles to the cotyledon face. The rack was then placed in a . 2 L beaker or Pyrex coffee pot (Model 7759) which was filled to 34 mm above the level of the bottom plate with distilled water at 20°C. The apparatus was placed over direct heat and water brought quickly to a boil. The time boiling commenced was recorded (0 time) and heat was reduced to maintain slow boiling throughout the cooking period. The number of plungers which had dropped were counted at 10 min intervals until either all had dropped, or until 70 min had elapsed in the second experiment and 90 min had elapsed in the third experiment. Four replications were conducted for each test.
Sensory Methods Panelists were selected from staff and graduate students of the Department of Foods and Nutrition, University of Manitoba because of their availability, interest and experience in sensory evaluation. Training sessions, with discussion, were conducted using bean samples cooked to varying degrees, to enable the panelists to identify cooked navy bean texture characteristics. Two separate panels were used. The first, consisting of five members, carried out the preliminary sensory testing to establish the plunger design. The second panel, composed of nine members, was used in the final experiment to evaluate the 48 g, 5 mm plunger and to identify the preferred cooked texture. Although preference ratings for industrial food products would usually be determined using a consumer panel, the use of the nine member trained panel J. Inst. Can. Sci. Technal. Aliment. Vol. 20, No. 1, 1987
was considered acceptable for this particular application. Two replications were performed by the five meIl1ber panel, and three by the nine member panel. At each panel session panelists were presented with beans from one treatment only, cooked for six cooking times. The Seafarer '83 - Brandon samples were cooked from 10 to 60 min, with cooking times spaced at 10 min intervals. The "commercial", Seafarer '78 _ Brandon and Seafarer '83 - Winnipeg were cooked from 20 to 70 min; and the Seafarer '77 - Brandon and Exrico '83 - Winnipeg were cooked from 30 to 80 min. These times were based on previously conducted preliminary experiments and were considered to represent a range of cooking times resulting in uncooked to completely cooked products. Panelists were asked to test 20 beans individually from each cooking time and to indicate the number of beans cooked and the number uncooked. Panelists were instructed to include in the "cooked" category all beans from those just cooked to those overcooked. Split, as well as whole beans, were to be included for assessment. The nine member panel was asked to indicate which of the six samples had the preferred texture. For panel assessment, beans were soaked in the same manner as were the samples to be tested by the MBe. Soaked beans were divided into six equal portions and placed in six pyrex cooking pots each containing distilled water in an approximately 1:2 bean to water ratio. Start of cooking time was staggered so that all samples reached the end of their cooking period at the same time. Twenty-five to thirty beans from each of the six cooking times were presented to the individual panelists. Samples were presented in a random order in coded opaque red coloured pyrex sample cups, which were used to maintain the warmth of the samples. Evaluations were conducted in a sensory panel room equipped with individual testing booths and with controlled lighting and testing conditions. Results were plotted as the percent of cooked beans at each cooking time, to produce cookability curves.
Statistical Methods For the MBC results obtained using the 49.75 g, 5 mm plunger and the 48 g, 5 mm plunger, the cumulative mean "percent cooked" and standard error of the mean (SEM) for each cooking time for four replications were calculated. For the sensory panel results, the mean percent cooked value and SEM for all panelists for all replications were calculated at each of the six cooking times. For the preference test, conducted by the nine member sensory panel, the percent cooked for each of the preferred samples was obtained. The mean percent cooked based on of all 81 judgements (9 panelists x 3 treatments x 3 replications) and standard deviation were calculated.
Results and Discussion
Comparison of Plungers In the initial experiment, MBC plungers of three different designs (65 g, 2 mm; 37.5 g, 2 mm; 49.75 g, 5 mm) were tested on the sample of "commercial" beans, and the cookability curve produced by each of Can. Inst. Food Sci. Technol. J. Vol. 20, No. I, 1987
100 90
0
80
:.:: 0 0
70
W
U
60
~
50
W
40
Z
U Cl: W
Q.
30 20 10 0
10
I
I
I
I
60
70
80
90
COOKING TIME (m;n)
Fig. 2. Cookability curves for "commercial" navy beans as determined by a 5 member sensory panel and by the MBC using 3 plunger types. ... - plunger - 65.00 g; 2mm • - plunger - 37.50 g; 2 mm • - plunger - 49.75 g; 5 mm o - 5 member sensory panel
the plungers was compared to the curve as determined by a 5 member sensory panel (Figure 2). The 65 g, 2 mm plunger represented the lightest of the plunger types described in the literature. The 37.5 g, 2 mm and 49.75 g, 5 mm plungers were tested because preliminary studies indicated that these plungers might prove to be more predictive of sensory panelists' assessment of cookability than the heavier plungers. Values for percent beans cooked at each cooking time, when determined with the 65 g, 2 mm diameter plungers were much greater than when percent cooked values were determined by the sensory panel. It was, therefore, concluded that this plunger did not reproduce the sensory cookability curves as effectively as the two lighter plungers, which both gave values close to the sensory values at each cooking time. The 37.5 g, 2 mm diameter plunger produced a cookability curve which intersected the sensory curve at the 95070 cooked point. The 49.75 g, 5 mm plungers gave a cookability curve similar in shape to the curve determined by sensory analysis. Thus, from the designs tested, the 49.75 g, 5 mm plunger was considered to provide the best indication of sensory percent cooked values for navy beans.
Comparison of Instrumental and Sensory Cookability Curves of a Commercial and of Stored Samples In the second experiment, "commercial", Seafarer'77-Brandon and Seafarer'78-Brandon were tested with the MBC using the 49.75 g, 5 mm plunger and were also evaluated for cookability by the five member sensory panel. The Seafarer samples, which had undergone long term storage, were expected to have extended cooking times. This experiment was conducted to determine whether the instrumentally determined cookability curves would conform to the pattern of the sensory curves for these samples as well as for the commercial sample. The MBC curves obtained in this experiment again corresponded with the curves obtained using sensory analysis (Figure 3). In addition, curves obtained for Proctor and Watts / 11
80
100 92 80
60
60
100
40
40
SEAFARER '77 BRANDON
20
EXRICO '83 WINNIPEG
20
0 C
100
~
80
()
60
c
w
W
0 0
~
Z
W
0
a: W a.
~
o o() ~
40
Z
SEAFARER '78 BRANDON
20 0
W
()
a: w a.
100 92 80 60 40
OL.---I.
80
':
60
60
100
40
SEAFARER '83 WINNIPEG
20
...L.-_L.---I._-..L_...L..----.JL---I
~------- ----
40 , COMMERCIAL'
20
SEAFARER '83 BRANDON
20
0'----'--------'---'----'---1----'---'----1
10 20 30 40
50
60
70
80 90
COOKING TIME (min)
10
20
30 40
50
60
70 80
90
COOKING TIME (min)
Fig. 3. Cookability curves for three samples of navy beans as determined by the MBC with 49.75 g, 2 mm plungers and by a 5 member sensory panel. • - MBC - "Commercial" o - Panel - "Commercial" .. - MBC - Seafarer-'78 6, - Panel - Seafarer-'78 • - MBC - Seafarer-'77 D - Panel - Seafarer-'77
Fig. 4. Cookability curves for 3 samples of navy beans as determined by the MBC with 48 g, 5 mm plungers and by a 9 member sensory panel. • - MBC - Seafarer-1983-Brandon o - Panel- Seafarer-1983-Brandon .. - MBC - Seafarer-1983-Wpg 6, - Panel- Seafarer-1983-Wpg • - MBC - Exrico-1983-Wpg D - Panel - Exrico-1983-Wpg
each sample were distinctly different. Times to cook, when compared at CT so, were approximately 30, 38 and 48 min for the "commerical", Seafarer'78Brandon and Seafarer '77-Brandon samples respectively. It was concluded that for the quick cooking (30 min) sample as well as for the slower cooking 38 and 48 min samples, the MBC with 49.75 g, 5 mm plungers could effectively reproduce sensory curves. Comparative cookability of the samples could be assessed by comparing CT 50 values, but for these values the standard errors were high. At higher percent cooked values the standard errors of the means were much lower (Table 1). This suggested that it would be more appropriate to use a higher percent cooked value as the point of comparison in future experiments.
Comparison of Instrumental and Sensory Cookability Curves ofFreshly Harvested Samples
12 / Proctor and Watts
In experiment three, sensory and instrumental curves for three freshly harvested navy bean samples (Seafarer'83-Brandon, Seafarer'83-Winnipeg and Exrico'83-Winnipeg) were compared. Plunger weight was adjusted from 49.75 g, as used in experiment two, to 48 g to try to bring instrumental values even closer to sensory values. Sensory assessment was carried out by a nine member trained sensory panel with three replications of each test. Cookability curves determined for these three samples using the MBC and the sensory panel are shown in Figure 4, and means and standard errors for the percent cooked values are shown in Table 2. MBC and J. Inst. Can. Sci. Technol. Aliment. Vol. 20, No. I, 1987
Table I. Mean percentage of cooked beans as measured by sensory and instrumental methods at different cooking times for "commercial", Seafarer '78-Brandon and Seafarer '77-Brandon navy beans. Sensory· Instrumental 2 Cooking Mean Mean Time 0J0 cooked SEM SEM 3 010 cooked (min) Commercial 8.50 3.50 20 44.50 15.49 30 78.50 1.49 40 93.50 2.50 50 96.00 2.00 60 99.50 0.50 70 Seafarer '78 Brandon 1.25 0.00 20 28.13 4.38 30 42.50 13.75 40 83.13 0.62 50 93.13 4.38 60 95.63 2.91 70 Seafarer '77 Brandon 14.25 6.75 30 37.38 40 3.63 48.63 7.62 50 71.50 60 3.50 70 86.25 1.25 89.13 2.13 80 Ifive member sensory panel 2MBC using 49.75 g, 5 mm plungers 3Standard error of the mean.
2.00 51.00 88.00 98.00 100.00 100.00
1.16 3.42 3.27 1.16 0.00 0.00
0.00 15.00 61.00 83.00 95.00 97.00
0.00 1.00 3.00 3.42 1.92 1.00
1.00 23.00 62.00 77.00 88.00
1.00 4.44 9.59 7.73 3.27
sensory panel values were in close agreement. This was the case particularly in the 80 to 100070 cooked range, where in all but one instance, mean values were within 3 percentage points of each other. In this experiment the sensory panelists were also asked to select the sample with the preferred degree of cooking, from among the six cooking time samples presented to them at each panel session. The mean per-
Table 2. Mean percentage of cooked beans as measured by sensory and instrumental methods at different cooking times for Seafarer '83-Brandon, Seafarer '83-Winnipeg and Exrico '83-Winnipeg navy beans. SensoryI Instrumental 2 Cooking Mean Time Mean (min) 0J0 cooked 0J0 cooked SEM SEM 3 Seafarer '83 Brandon 4.62 0.00 0.00 3.34 10 20 32.59 5.00 1.92 5.31 79.44 30 66.00 5.29 4.49 97.57 96.00 1.62 0.18 40 50 98.14 99.00 1.00 0.49 99.63 100.00 0.00 0.18 60 Seafarer '83 Winnipeg 20 14.06 4.27 1.00 1.00 30 51.11 39.00 6.41 3.26 40 86.67 1.92 2.42 81.00 97.04 50 96.00 1.64 0.49 99.07 98.00 0.49 1.16 60 70 99.44 99.00 1.00 0.32 Exrico '83 Winnipeg 24.64 7.21 14.00 2.58 30 4.89 40 59.22 7.68 56.00 83.61 81.00 2.52 50 3.63 1.92 90.18 2.13 93.00 60 70 97.22 97.00 1.00 1.39 98.99 98.00 1.16 0.55 80 Inine member sensory panel 2MBC using 48 g, 5 mm plungers 3Standard error of the mean.
cent cooked values for the selected samples were used to calculate the mean percent cooked preferred for each sample and also the overall mean. Preferred values were 94.4070 for Seafarer'83-Brandon, 94.1070 for Seafarer'83-Winnipeg and 92.6070 for Exrico'83Winnipeg. The overall percent preferred was 93.7070 (Table 3).
Table 3. Percentage of beans identified as cooked in the preferred sample by a nine member sensory panel for Seafarer '83-Brandon, Seafarer '83-Winnipeg and Exrico '83-Winnipeg navy beans. Type of Navy Bean Seafarer '83 Seafarer '83 Exrico '83 Brandon Winnipeg Winnipeg Panelist Panelist Mean l SEM Mean SEM Mean Mean SEM 2 SEM I 96.11 1.11 95.00 2.89 98.33 1.67 95.00 5.01 2 5.01 94.44 0.56 95.00 93.33 1.67 95.00 2.89 3 6.02 95.56 2.42 100.00 91.67 0.00 95.00 0.00 4 78.33 1.67 80.00 0.00 5.01 80.00 75.00 10.42 5 100.00 0.00 0.00 100.00 0.00 100.00 0.00 100.00 6 1.67 97.77 0.55 96.67 98.33 1.67 98.33 1.67 7 0.99 7.51 93.05 95.00 91.67 4.42 92.50 2.89 8 8.34 96.67 2.55 91.66 98.33 1.67 100.00 0.00 1.72 9 6.52 92.50 93.33 5.01 89.17 3.34 95.00 Sample Mean SEM Overall Mean SEM
94.81 2.53
94.07 2.71
92.59 3.63
93.70 0.93
lmean of three replications 2Standard error of the mean Can. Inst. Food Sci. Technol. J. Vo!.
20,
No. I, 1987
Proctor and Watts / 13
Comparisons of bean cookability using data obtained with the MBC have been based previously on CTso values (Morris, 1964; Jackson and VarrianoMarston, 1981). The appropriateness of using CTso for cookability comparison must be questioned, as panelists clearly indicated their preference for the texture of beans cooked to the 80-100% range. Since cookability is defined in terms of the cooking time required for beans to reach a texture at which panelists consider the beans to be "cooked" or "done" (Moscoso et al., 1984), then it would be appropriate to use an MBC value corresponding to the 93.70/0 preference point. For the 25 plunger MBC, the fall of the 23rd plunger represents the 92% cooked point. Use of the 92% cooked or CTn values for comparison of bean cookability would ensure that the cooking time values used were close to the actual cooking times necessary to achieve the cooked texture and degree of doneness preferred by the sensory panel. Cooking times of the three harvested samples tested in experiment three, determined by using CT n rather than CTso values, were not only longer but also more widely spread. CT92 values were 58, 48 and 35 min, while the corresponding CTso values were 38, 32 and 28 min, for the Exrico'83-Winnipeg, Seafarer'83-Winnipeg and Seafarer'83-Brandon samples respectively. The order of cookability did not change, but the difference in cooking time of the fastest and slowest cooking samples doubled. CTn therefore provided a better indication of differences in cookabilities. If samples being tested by the MBC were less homogeneous than were the freshly harvested samples used in the final experiment of this study, having either a wide range of within-sample cooking times, or having a significant proportion of hard-to-cook beans, then the use of CTso values for comparative purposes could give misleading results. Determination of CTn values, on the other hand, would enable rapid identification of samples with over 8% hard cooking beans, and examination of MBC cookability curves would indicate the extent of the hard cooking problem.
Conclusions Cookability curves for navy beans, determined by sensory evaluation, were essentially duplicated using a Mattson Bean Cooker with 48 g, 5 mm plungers. Use
14 / Proctor and Watts
of CT n rather than CTso values provided better discrimination among samples. For other types of beans, the MBC plungers could be adjusted to give values consistent with those obtained by sensory evaluation, and the modified MBC could then be used to provide a reference testing method that could be used to evaluate the reliability of rapid screening tests for cookability assessment.
Acknowledgements The support of this project by Agriculture'Canada is gratefully acknowledged. Appreciation is expressed to J. Tsukamoto, Manitoba Department of Agriculture, and to Dr. P. McVetty, Department of Plant Science, University of Manitoba for samples used. References Bourne, M.C. 1972. Texture measurement of individual cooked dry beans by the puncture test. J. Food Sci. 37:751. Bourne, M.C. 1982. Food Texture and Viscosity: Concept and Measurement. Academic Press Inc. New York, NY. Bressani, R., Elias, L.G. and Valiente, A.T. 1963. The effect of cooking and of amino acid supplementation of black beans. Br. J. Nutr. 17:69. Burr, H.K. 1976. Adapting an experimental bean cooker for automatic recording. J. Food Sci. 41:218. Burr, H.K., Kon, S. and Morris, H.J. 1968. Cooking rates of dry beans as influenced by moisture content and temperature and time of storage. Food Technol. 22:336. Chhinnan, M.S. 1985. Development of a device for quantifying hardto-cook phenomenon in cereal legumes. Trans. Am. Soc. Agric. Eng. 335. Jackson, G.M. and Varriano-Marston, E. 1981. The hard-to-cook phenomenon in beans: effects of accelerated storage on water absorption and cooking time. J. Food Sci. 46:799. Mattson, S. 1946. The cookability of yellow peas. Acta. Agric. Suecana H. 2:185. Morris, H.J. 1964. Changes in cooking qualities of raw beans as influenced by moisture content and storage time. Proceedings of the 7th Dry Bean Conference. USDA Agric. Res. Service. 74:37. Moscoso, W., Bourne, M.C. and Hood, L.F. 1984. Relationship between the hard-to-cook phenomenon in red kidney beans and water absorption, puncture force, pectin, phytic acid and minerals. J. Food Sci. 49:1577. Silva, C.A.B., Bates, R.P. and Deng, J.C. 1981. Influence of soaking and cooking upon the softening and eating quality of black beans (Phaseolus vulgaris). J. Food Sci. 46:1716.
Submitted December 23, 1985 Revised July 11, 1986 Accepted September 17, 1986
J. Inst. Can. Sci. Technol. Aliment. Vo!. 20. No. I, 1987
RESEARCH
Development of a Modified Mattson Bean Cooker Procedure Based on Sensory Panel Cookability Evaluation J.R. Proctor and B.M. Watts Department of Foods and Nutrition University of Manitoba Winnipeg, Manitoba R3T 2N2
ability" refers to the cooking time required to reach that texture (Moscoso et al., 1984). Poor cookability, caused either by long cooking time required to soften the majority of beans within a sample, or by extended cooking time required for a small but significant proportion of hard-to-cook beans in an otherwise good cooking sample, is a major problem with pulses. Poor cookability can cause loss of nutrients, increased consumption of energy and consumer rejection (Bressani et al., 1963). The phenomenon of within-sample variability complicates cookability measurement and the comparison of bean samples. The testing of large numbers of beans is required to ensure statistical reliability (Silva et al. , 1981). Methods which attempt to ensure statistical reliability by testing large samples rather than individual beans, can mask the very important effect of individual bean cooking time on the overall sample cooking time (Bourne, 1972). Therefore, testing methods must be able to measure the cooking time of the individual beans within a sample. The Mattson Bean Cooker (MBC) (Mattson, 1946) was developed to assess cookability by measuring the time required to cook large numbers of individual beans to a defined degree of softness (Morris, 1964; Jackson and Varriano-Marston, 1981). The MBC as first developed by Mattson (1946) and as used by Morris (1964) consisted of 100 plungers held in position by supporting racks so that the plunger points rested on the supported uncooked beans. Burr (1976) modified this version of the MBC, so that plunger dropping times would be automatically recorded. A 25 plunger model was described by Jackson and Varriano-Marston (1981), and Chhinnan (1985) reported a prototype 25 plunger model with an electronic device to monitor plunger movement. These instruments are designed to test the cooking time of individual beans by measuring the time required for plungers of specific weight and diameter to puncture single beans while they are actually cooking in the cooking water. Plunger types reported in the literature are either 82 g, 2 mm (Jackson and Varriano-Marston, 1981) or 90 g, 2 mm (Morris, 1964; Burr et al., 1968).
Abstract The Mattson Bean Cooker (MBC) is widely used to measure relative cooking times of bean samples, but MBC values have not been related to values determined by sensory evaluation. In order to obtain instrumental values that reflected sensory assessment of cookability, MBC plungers of four weights and two tip diameters were tested. Plots of percent beans cooked versus cooking times, produced by the 48 g 5 mm diameter MBC plungers, corresponded closely to the cookability curves resulting from evaluation by a trained, nine member sensory panel. The optimum cooked point, as identified by this panel, was 93.75070. This corresponded to the drop of the twentythird plunger for the 25 plunger model of the MBC (92070 cooked point or CT92). MBC CT92 values gave better discrimination among freshly harvested navy bean samples than did the commonly employed CT 50 values.
Resume Le cuiseur a haricots Mattson (MBC) est tres utilise pour mesurer les temps de cuisson relatifs d'echantillons d'haricots, mais les valeurs MCB n'ont pas ete correlees aux valeurs determinees par I'evaluation sensorielle. Dans le but d'obtenir des valeurs instrumentales qui soient representatives des evaluations sensorielles de l'aptitude a la cuisson, des plongeurs MBC de quatre pesanteurs et deux diametres de pointe ont ete essayes. Les traces des pourcentages d'haricots versus temps de cuisson, obtenus avec les plongeurs MBC de 48 g et de diametre de 5 mm, ont ete etroitement correles aux courbes d'aptitude a la cuisson obtenues de l'evaluation par un jury sensoriel exerce de neuf membres. Le point de cuisson optimum, tel qu'indique par ce jury fut de 93.75070. Ceci a correspondu a la chute du vingt-troisieme plongeur du modele MBC de 25 plongeurs (92070 point de cuisson ou CT 92)' Les valeurs MBC CT 92 ont permis de mieux differencier entre les echantillons d'haricots blancs fraichement cueillis que ce fut possible avec les valeurs CT 50 couramment utilisees.
Introduction Edible dry beans ("grain legumes or pulses") play a major role in human nutrition. Navy beans (PhaseoIus vulgaris L.), grown commercially in Western Canada, are consumed by Canadians and have a large potential export market. Plant breeders and legume marketers have expressed interest in improving the quality of navy beans grown in Western Canada. Cooking time is one of the major criteria involved in the evaluation of pulse quality. Each type of edible dry bean has a particular cooked texture which is considered acceptable by consumers and the term "cookCopyright
Cl
1987 Canadian Institute of Food Science and Technology
9
The MBC tests large numbers of beans individually and provides an indication of within sample variability. Cooking times of different bean samples have been compared using the cooking time required to reach the 50070 cooked point (CTso) as the reference point (Morris, 1964; Jackson and Varriano-Marston, 1981). However, cooking time as measured by the MBC has not been related to the cooking time as determined by sensory analysis, which is the ultimate method of calibrating instrumental methods of measuring texture (Bourne, 1982). The objectives of this study were to design MBC plungers that would consistently reproduce the results determined by sensory analysis and to devise a method for calculating comparative cooking times, based on sensory panelists' cooking point preference.
..
E
u
'"'"
J
Materials and Methods
--1~mm
ExperitnentalSequence In the first experiment, using one sample of navy beans, MBC cookability curves produced with plungers of different designs were compared to the sensory cookability curve determined by a five member sensory panel. In the second experiment, three stored navy bean samples were tested by the MBC using a plunger selected on the basis of the results of experiment one. The aim of the second experiment was to determine whether the plunger design consistently reproduced the sensory cookability curves determined by a five member sensory panel. In the third and final experiment, cookability curves for three freshly harvested bean samples were determined by the MBC using a slightly adjusted plunger design. The reproducibility of sensory cookability curves by instrumental curves was verified. In this experiment a preference test was also conducted to determine the most appropriate reference point for cooking time comparison.
Materials One sample of navy beans was purchased at a local supermarket ("commercial" sample), three were obtained from the Manitoba Department of Agriculture Research Station, Brandon, Manitoba and two were obtained from the Plant Science Department of the University of Manitoba. Samples were refrigerated at 4°C. Storage conditions for the "commercial" (cultivar unknown), Seafarer '77 - Brandon and Seafarer '78 - Brandon samples, prior to receipt, were not known.
MBC Apparatus and Method of Operation The MBC used consisted of a brass rack with 25 identical plungers as described 'by Jackson and Varianno-Marston (1981), but with smaller, 3 mm diameter perforations in the lowest plate of the rack (Figure I). The 5 mm diameter brass plungers had threaded upper ends to which hollow brass cylinders of different weights could be attached. Lead shot placed inside the cylinders was used to standardize weights precisely. Plunger tips were flat faced and were 5 mm or 2 mm in diameter. Plungers used had the follOWing weights and tip diameters: 65 g, 2 mm; 35 g, 10 I Proctor and Watts
Fig. I. Dimensions of rack and plungers of Mattson Bean Cooker.
2 mm; 49.75 g, 5 mm; and 48 g, 5 mm. The force exerted by these plungers was 20.7, 22.9, 2.5 and 2.4 g/mm 2 respectively. For each replication of the MBC test, 25 beans, which had been soaked in distilled water (1:4 beans to water ratio) at 20°C for approximately 16 h, were placed on the perforations in the bottom plate. The plungers, when inserted, were positioned at right angles to the cotyledon face. The rack was then placed in a . 2 L beaker or Pyrex coffee pot (Model 7759) which was filled to 34 mm above the level of the bottom plate with distilled water at 20°C. The apparatus was placed over direct heat and water brought quickly to a boil. The time boiling commenced was recorded (0 time) and heat was reduced to maintain slow boiling throughout the cooking period. The number of plungers which had dropped were counted at 10 min intervals until either all had dropped, or until 70 min had elapsed in the second experiment and 90 min had elapsed in the third experiment. Four replications were conducted for each test.
Sensory Methods Panelists were selected from staff and graduate students of the Department of Foods and Nutrition, University of Manitoba because of their availability, interest and experience in sensory evaluation. Training sessions, with discussion, were conducted using bean samples cooked to varying degrees, to enable the panelists to identify cooked navy bean texture characteristics. Two separate panels were used. The first, consisting of five members, carried out the preliminary sensory testing to establish the plunger design. The second panel, composed of nine members, was used in the final experiment to evaluate the 48 g, 5 mm plunger and to identify the preferred cooked texture. Although preference ratings for industrial food products would usually be determined using a consumer panel, the use of the nine member trained panel J. Inst. Can. Sci. Technal. Aliment. Vol. 20, No. 1, 1987
was considered acceptable for this particular application. Two replications were performed by the five meIl1ber panel, and three by the nine member panel. At each panel session panelists were presented with beans from one treatment only, cooked for six cooking times. The Seafarer '83 - Brandon samples were cooked from 10 to 60 min, with cooking times spaced at 10 min intervals. The "commercial", Seafarer '78 _ Brandon and Seafarer '83 - Winnipeg were cooked from 20 to 70 min; and the Seafarer '77 - Brandon and Exrico '83 - Winnipeg were cooked from 30 to 80 min. These times were based on previously conducted preliminary experiments and were considered to represent a range of cooking times resulting in uncooked to completely cooked products. Panelists were asked to test 20 beans individually from each cooking time and to indicate the number of beans cooked and the number uncooked. Panelists were instructed to include in the "cooked" category all beans from those just cooked to those overcooked. Split, as well as whole beans, were to be included for assessment. The nine member panel was asked to indicate which of the six samples had the preferred texture. For panel assessment, beans were soaked in the same manner as were the samples to be tested by the MBe. Soaked beans were divided into six equal portions and placed in six pyrex cooking pots each containing distilled water in an approximately 1:2 bean to water ratio. Start of cooking time was staggered so that all samples reached the end of their cooking period at the same time. Twenty-five to thirty beans from each of the six cooking times were presented to the individual panelists. Samples were presented in a random order in coded opaque red coloured pyrex sample cups, which were used to maintain the warmth of the samples. Evaluations were conducted in a sensory panel room equipped with individual testing booths and with controlled lighting and testing conditions. Results were plotted as the percent of cooked beans at each cooking time, to produce cookability curves.
Statistical Methods For the MBC results obtained using the 49.75 g, 5 mm plunger and the 48 g, 5 mm plunger, the cumulative mean "percent cooked" and standard error of the mean (SEM) for each cooking time for four replications were calculated. For the sensory panel results, the mean percent cooked value and SEM for all panelists for all replications were calculated at each of the six cooking times. For the preference test, conducted by the nine member sensory panel, the percent cooked for each of the preferred samples was obtained. The mean percent cooked based on of all 81 judgements (9 panelists x 3 treatments x 3 replications) and standard deviation were calculated.
Results and Discussion
Comparison of Plungers In the initial experiment, MBC plungers of three different designs (65 g, 2 mm; 37.5 g, 2 mm; 49.75 g, 5 mm) were tested on the sample of "commercial" beans, and the cookability curve produced by each of Can. Inst. Food Sci. Technol. J. Vol. 20, No. I, 1987
100 90
0
80
:.:: 0 0
70
W
U
60
~
50
W
40
Z
U Cl: W
Q.
30 20 10 0
10
I
I
I
I
60
70
80
90
COOKING TIME (m;n)
Fig. 2. Cookability curves for "commercial" navy beans as determined by a 5 member sensory panel and by the MBC using 3 plunger types. ... - plunger - 65.00 g; 2mm • - plunger - 37.50 g; 2 mm • - plunger - 49.75 g; 5 mm o - 5 member sensory panel
the plungers was compared to the curve as determined by a 5 member sensory panel (Figure 2). The 65 g, 2 mm plunger represented the lightest of the plunger types described in the literature. The 37.5 g, 2 mm and 49.75 g, 5 mm plungers were tested because preliminary studies indicated that these plungers might prove to be more predictive of sensory panelists' assessment of cookability than the heavier plungers. Values for percent beans cooked at each cooking time, when determined with the 65 g, 2 mm diameter plungers were much greater than when percent cooked values were determined by the sensory panel. It was, therefore, concluded that this plunger did not reproduce the sensory cookability curves as effectively as the two lighter plungers, which both gave values close to the sensory values at each cooking time. The 37.5 g, 2 mm diameter plunger produced a cookability curve which intersected the sensory curve at the 95070 cooked point. The 49.75 g, 5 mm plungers gave a cookability curve similar in shape to the curve determined by sensory analysis. Thus, from the designs tested, the 49.75 g, 5 mm plunger was considered to provide the best indication of sensory percent cooked values for navy beans.
Comparison of Instrumental and Sensory Cookability Curves of a Commercial and of Stored Samples In the second experiment, "commercial", Seafarer'77-Brandon and Seafarer'78-Brandon were tested with the MBC using the 49.75 g, 5 mm plunger and were also evaluated for cookability by the five member sensory panel. The Seafarer samples, which had undergone long term storage, were expected to have extended cooking times. This experiment was conducted to determine whether the instrumentally determined cookability curves would conform to the pattern of the sensory curves for these samples as well as for the commercial sample. The MBC curves obtained in this experiment again corresponded with the curves obtained using sensory analysis (Figure 3). In addition, curves obtained for Proctor and Watts / 11
80
100 92 80
60
60
100
40
40
SEAFARER '77 BRANDON
20
EXRICO '83 WINNIPEG
20
0 C
100
~
80
()
60
c
w
W
0 0
~
Z
W
0
a: W a.
~
o o() ~
40
Z
SEAFARER '78 BRANDON
20 0
W
()
a: w a.
100 92 80 60 40
OL.---I.
80
':
60
60
100
40
SEAFARER '83 WINNIPEG
20
...L.-_L.---I._-..L_...L..----.JL---I
~------- ----
40 , COMMERCIAL'
20
SEAFARER '83 BRANDON
20
0'----'--------'---'----'---1----'---'----1
10 20 30 40
50
60
70
80 90
COOKING TIME (min)
10
20
30 40
50
60
70 80
90
COOKING TIME (min)
Fig. 3. Cookability curves for three samples of navy beans as determined by the MBC with 49.75 g, 2 mm plungers and by a 5 member sensory panel. • - MBC - "Commercial" o - Panel - "Commercial" .. - MBC - Seafarer-'78 6, - Panel - Seafarer-'78 • - MBC - Seafarer-'77 D - Panel - Seafarer-'77
Fig. 4. Cookability curves for 3 samples of navy beans as determined by the MBC with 48 g, 5 mm plungers and by a 9 member sensory panel. • - MBC - Seafarer-1983-Brandon o - Panel- Seafarer-1983-Brandon .. - MBC - Seafarer-1983-Wpg 6, - Panel- Seafarer-1983-Wpg • - MBC - Exrico-1983-Wpg D - Panel - Exrico-1983-Wpg
each sample were distinctly different. Times to cook, when compared at CT so, were approximately 30, 38 and 48 min for the "commerical", Seafarer'78Brandon and Seafarer '77-Brandon samples respectively. It was concluded that for the quick cooking (30 min) sample as well as for the slower cooking 38 and 48 min samples, the MBC with 49.75 g, 5 mm plungers could effectively reproduce sensory curves. Comparative cookability of the samples could be assessed by comparing CT 50 values, but for these values the standard errors were high. At higher percent cooked values the standard errors of the means were much lower (Table 1). This suggested that it would be more appropriate to use a higher percent cooked value as the point of comparison in future experiments.
Comparison of Instrumental and Sensory Cookability Curves ofFreshly Harvested Samples
12 / Proctor and Watts
In experiment three, sensory and instrumental curves for three freshly harvested navy bean samples (Seafarer'83-Brandon, Seafarer'83-Winnipeg and Exrico'83-Winnipeg) were compared. Plunger weight was adjusted from 49.75 g, as used in experiment two, to 48 g to try to bring instrumental values even closer to sensory values. Sensory assessment was carried out by a nine member trained sensory panel with three replications of each test. Cookability curves determined for these three samples using the MBC and the sensory panel are shown in Figure 4, and means and standard errors for the percent cooked values are shown in Table 2. MBC and J. Inst. Can. Sci. Technol. Aliment. Vol. 20, No. I, 1987
Table I. Mean percentage of cooked beans as measured by sensory and instrumental methods at different cooking times for "commercial", Seafarer '78-Brandon and Seafarer '77-Brandon navy beans. Sensory· Instrumental 2 Cooking Mean Mean Time 0J0 cooked SEM SEM 3 010 cooked (min) Commercial 8.50 3.50 20 44.50 15.49 30 78.50 1.49 40 93.50 2.50 50 96.00 2.00 60 99.50 0.50 70 Seafarer '78 Brandon 1.25 0.00 20 28.13 4.38 30 42.50 13.75 40 83.13 0.62 50 93.13 4.38 60 95.63 2.91 70 Seafarer '77 Brandon 14.25 6.75 30 37.38 40 3.63 48.63 7.62 50 71.50 60 3.50 70 86.25 1.25 89.13 2.13 80 Ifive member sensory panel 2MBC using 49.75 g, 5 mm plungers 3Standard error of the mean.
2.00 51.00 88.00 98.00 100.00 100.00
1.16 3.42 3.27 1.16 0.00 0.00
0.00 15.00 61.00 83.00 95.00 97.00
0.00 1.00 3.00 3.42 1.92 1.00
1.00 23.00 62.00 77.00 88.00
1.00 4.44 9.59 7.73 3.27
sensory panel values were in close agreement. This was the case particularly in the 80 to 100070 cooked range, where in all but one instance, mean values were within 3 percentage points of each other. In this experiment the sensory panelists were also asked to select the sample with the preferred degree of cooking, from among the six cooking time samples presented to them at each panel session. The mean per-
Table 2. Mean percentage of cooked beans as measured by sensory and instrumental methods at different cooking times for Seafarer '83-Brandon, Seafarer '83-Winnipeg and Exrico '83-Winnipeg navy beans. SensoryI Instrumental 2 Cooking Mean Time Mean (min) 0J0 cooked 0J0 cooked SEM SEM 3 Seafarer '83 Brandon 4.62 0.00 0.00 3.34 10 20 32.59 5.00 1.92 5.31 79.44 30 66.00 5.29 4.49 97.57 96.00 1.62 0.18 40 50 98.14 99.00 1.00 0.49 99.63 100.00 0.00 0.18 60 Seafarer '83 Winnipeg 20 14.06 4.27 1.00 1.00 30 51.11 39.00 6.41 3.26 40 86.67 1.92 2.42 81.00 97.04 50 96.00 1.64 0.49 99.07 98.00 0.49 1.16 60 70 99.44 99.00 1.00 0.32 Exrico '83 Winnipeg 24.64 7.21 14.00 2.58 30 4.89 40 59.22 7.68 56.00 83.61 81.00 2.52 50 3.63 1.92 90.18 2.13 93.00 60 70 97.22 97.00 1.00 1.39 98.99 98.00 1.16 0.55 80 Inine member sensory panel 2MBC using 48 g, 5 mm plungers 3Standard error of the mean.
cent cooked values for the selected samples were used to calculate the mean percent cooked preferred for each sample and also the overall mean. Preferred values were 94.4070 for Seafarer'83-Brandon, 94.1070 for Seafarer'83-Winnipeg and 92.6070 for Exrico'83Winnipeg. The overall percent preferred was 93.7070 (Table 3).
Table 3. Percentage of beans identified as cooked in the preferred sample by a nine member sensory panel for Seafarer '83-Brandon, Seafarer '83-Winnipeg and Exrico '83-Winnipeg navy beans. Type of Navy Bean Seafarer '83 Seafarer '83 Exrico '83 Brandon Winnipeg Winnipeg Panelist Panelist Mean l SEM Mean SEM Mean Mean SEM 2 SEM I 96.11 1.11 95.00 2.89 98.33 1.67 95.00 5.01 2 5.01 94.44 0.56 95.00 93.33 1.67 95.00 2.89 3 6.02 95.56 2.42 100.00 91.67 0.00 95.00 0.00 4 78.33 1.67 80.00 0.00 5.01 80.00 75.00 10.42 5 100.00 0.00 0.00 100.00 0.00 100.00 0.00 100.00 6 1.67 97.77 0.55 96.67 98.33 1.67 98.33 1.67 7 0.99 7.51 93.05 95.00 91.67 4.42 92.50 2.89 8 8.34 96.67 2.55 91.66 98.33 1.67 100.00 0.00 1.72 9 6.52 92.50 93.33 5.01 89.17 3.34 95.00 Sample Mean SEM Overall Mean SEM
94.81 2.53
94.07 2.71
92.59 3.63
93.70 0.93
lmean of three replications 2Standard error of the mean Can. Inst. Food Sci. Technol. J. Vo!.
20,
No. I, 1987
Proctor and Watts / 13
Comparisons of bean cookability using data obtained with the MBC have been based previously on CTso values (Morris, 1964; Jackson and VarrianoMarston, 1981). The appropriateness of using CTso for cookability comparison must be questioned, as panelists clearly indicated their preference for the texture of beans cooked to the 80-100% range. Since cookability is defined in terms of the cooking time required for beans to reach a texture at which panelists consider the beans to be "cooked" or "done" (Moscoso et al., 1984), then it would be appropriate to use an MBC value corresponding to the 93.70/0 preference point. For the 25 plunger MBC, the fall of the 23rd plunger represents the 92% cooked point. Use of the 92% cooked or CTn values for comparison of bean cookability would ensure that the cooking time values used were close to the actual cooking times necessary to achieve the cooked texture and degree of doneness preferred by the sensory panel. Cooking times of the three harvested samples tested in experiment three, determined by using CT n rather than CTso values, were not only longer but also more widely spread. CT92 values were 58, 48 and 35 min, while the corresponding CTso values were 38, 32 and 28 min, for the Exrico'83-Winnipeg, Seafarer'83-Winnipeg and Seafarer'83-Brandon samples respectively. The order of cookability did not change, but the difference in cooking time of the fastest and slowest cooking samples doubled. CTn therefore provided a better indication of differences in cookabilities. If samples being tested by the MBC were less homogeneous than were the freshly harvested samples used in the final experiment of this study, having either a wide range of within-sample cooking times, or having a significant proportion of hard-to-cook beans, then the use of CTso values for comparative purposes could give misleading results. Determination of CTn values, on the other hand, would enable rapid identification of samples with over 8% hard cooking beans, and examination of MBC cookability curves would indicate the extent of the hard cooking problem.
Conclusions Cookability curves for navy beans, determined by sensory evaluation, were essentially duplicated using a Mattson Bean Cooker with 48 g, 5 mm plungers. Use
14 / Proctor and Watts
of CT n rather than CTso values provided better discrimination among samples. For other types of beans, the MBC plungers could be adjusted to give values consistent with those obtained by sensory evaluation, and the modified MBC could then be used to provide a reference testing method that could be used to evaluate the reliability of rapid screening tests for cookability assessment.
Acknowledgements The support of this project by Agriculture'Canada is gratefully acknowledged. Appreciation is expressed to J. Tsukamoto, Manitoba Department of Agriculture, and to Dr. P. McVetty, Department of Plant Science, University of Manitoba for samples used. References Bourne, M.C. 1972. Texture measurement of individual cooked dry beans by the puncture test. J. Food Sci. 37:751. Bourne, M.C. 1982. Food Texture and Viscosity: Concept and Measurement. Academic Press Inc. New York, NY. Bressani, R., Elias, L.G. and Valiente, A.T. 1963. The effect of cooking and of amino acid supplementation of black beans. Br. J. Nutr. 17:69. Burr, H.K. 1976. Adapting an experimental bean cooker for automatic recording. J. Food Sci. 41:218. Burr, H.K., Kon, S. and Morris, H.J. 1968. Cooking rates of dry beans as influenced by moisture content and temperature and time of storage. Food Technol. 22:336. Chhinnan, M.S. 1985. Development of a device for quantifying hardto-cook phenomenon in cereal legumes. Trans. Am. Soc. Agric. Eng. 335. Jackson, G.M. and Varriano-Marston, E. 1981. The hard-to-cook phenomenon in beans: effects of accelerated storage on water absorption and cooking time. J. Food Sci. 46:799. Mattson, S. 1946. The cookability of yellow peas. Acta. Agric. Suecana H. 2:185. Morris, H.J. 1964. Changes in cooking qualities of raw beans as influenced by moisture content and storage time. Proceedings of the 7th Dry Bean Conference. USDA Agric. Res. Service. 74:37. Moscoso, W., Bourne, M.C. and Hood, L.F. 1984. Relationship between the hard-to-cook phenomenon in red kidney beans and water absorption, puncture force, pectin, phytic acid and minerals. J. Food Sci. 49:1577. Silva, C.A.B., Bates, R.P. and Deng, J.C. 1981. Influence of soaking and cooking upon the softening and eating quality of black beans (Phaseolus vulgaris). J. Food Sci. 46:1716.
Submitted December 23, 1985 Revised July 11, 1986 Accepted September 17, 1986
J. Inst. Can. Sci. Technol. Aliment. Vo!. 20. No. I, 1987