SENSORY EVALUATION OF SELECTED WALNUT CULTIVARS Chuck Ingels, Gale McGranahan and Ann Noble ABSTRACT A sensory evaluation study was performed at UC Davis to determine if taste differences could be detected among several English walnut (Juglans regia) cultivars. Differences were tested using the duo-trio method, in which 'Hartley' was compared to seven other cultivars. No differences were found when 'Hartley' was compared to 'Vina', 'Scharsch Franquette' and 'Mayette', however 'Chandler', 'Chico', 'Howard' and 'Sunland' were significantly different. Paired comparisons were then used to compare the four latter cultivars to 'Hartley' in terms of several taste charac- teristics. No differences in astringency and "walnut" flavor were detected, however 'Chandler' was judged to be sweeter, and 'Howard' less sweet than 'Hartley'. In comparison of sweetness and firmness among the four cultivars, 'Chandler' was found to be sweeter than 'Howard' and 'Chico' was found to be the firmest cultivar. OBJECTIVES It has been stated by many people familiar with walnuts that certain cultivars are "better" in terms of flavor and/or texture than others. However, few people agree upon which cultivar is sweetest, least astringent, most flavorful, etc. Furthermore, there has been some concern among consumers that flavor charac- teristics are ignored in breeding of many horticultural crops. In the walnut breeding program at the University of California, nut flavor has not been used as a criteria for evaluating culti- vars. The results obtained from this study may show whether or not it would be desirable to perform sensory tests when evalu- ating new cultivars. No previous sensory evaluation of walnuts on the basis of vari- etal differences has been reported. The objectives in this experiment were therefore, 1) to determine if differences between selected popular walnut cultivars can be detected by members of a taste panel, and 2) to have the panel members evaluate each of these cultivars on the basis of certain descriptors if differ- ences were detected in the first step. It is possible that the results of this sensory evaluation may be correlated with physical and/or chemical characteristics such as oil or sugar content. If any such correlation can be found, chemical or physical tests may give an indication as to the sensory qualities of the cultivar in question (Heintz and Kader, 1983) . 4 ---
Transcript
SENSORY EVALUATION OF SELECTED WALNUT CULTIVARS
Chuck Ingels, Gale McGranahan and Ann Noble
ABSTRACT
A sensory evaluation study was performed at UC Davis to determineif taste differences could be detected among several Englishwalnut (Juglans regia) cultivars. Differences were tested usingthe duo-trio method, in which 'Hartley' was compared to sevenother cultivars. No differences were found when 'Hartley' wascompared to 'Vina', 'Scharsch Franquette' and 'Mayette', however'Chandler', 'Chico', 'Howard' and 'Sunland' were significantlydifferent. Paired comparisons were then used to compare the fourlatter cultivars to 'Hartley' in terms of several taste charac-teristics. No differences in astringency and "walnut" flavorwere detected, however 'Chandler' was judged to be sweeter, and'Howard' less sweet than 'Hartley'. In comparison of sweetnessand firmness among the four cultivars, 'Chandler' was found to besweeter than 'Howard' and 'Chico' was found to be the firmestcultivar.
OBJECTIVES
It has been stated by many people familiar with walnuts thatcertain cultivars are "better" in terms of flavor and/or texturethan others. However, few people agree upon which cultivar issweetest, least astringent, most flavorful, etc. Furthermore,there has been some concern among consumers that flavor charac-teristics are ignored in breeding of many horticultural crops.In the walnut breeding program at the University of California,nut flavor has not been used as a criteria for evaluating culti-vars. The results obtained from this study may show whether ornot it would be desirable to perform sensory tests when evalu-ating new cultivars.
No previous sensory evaluation of walnuts on the basis of vari-etal differences has been reported. The objectives in thisexperiment were therefore, 1) to determine if differences betweenselected popular walnut cultivars can be detected by members of ataste panel, and 2) to have the panel members evaluate each ofthese cultivars on the basis of certain descriptors if differ-ences were detected in the first step.
It is possible that the results of this sensory evaluation may becorrelated with physical and/or chemical characteristics such asoil or sugar content. If any such correlation can be found,chemical or physical tests may give an indication as to thesensory qualities of the cultivar in question (Heintz and Kader,1983) .
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PROCEDURE
Preparation of nuts. Nuts from all Juglans regia cultivars usedin the experiment were harvested in September and October, 1988at approximately 80% husk split from healthy commercial orchardsin the Gridley/Live Oak area of California. The nuts were imme-diately dried and stored at room temperature for approximately 1-2 weeks, after which they were transferred to UC Davis and storedin plastic bags at OOC. Moisture content was calculated bydrying 100g of kernels at 70°C in a vacuum oven for 36 hours andthen reweighing. Kernel moisture content was found to be vari-able among cultivars and for most cultivars exceeded the optimumrange of 3.2-3.8% (R.E. Gunnerson, personal communication). Thewhole nuts were therefore redried at 43°C for 3-6 hours, cooledat room temperature and then refrigerated in plastic bags forseveral days to equalize nut moisture content. The nuts werethen retested and the moisture content was determined to beacceptable (Table 1). J. hindsii nuts, used in the training ses-sion, were dried and stored in the same manner, but were nottested for moisture content. Nuts of each cultivar were crackedthe day before they were to be tested and the kernels were brokeninto pieces approximately one-sixth the size of a kernel half.The kernels were then stored overnight in a plastic bag at 2°C.
Sensory evaluation. Twenty-one people associated with the Pomol-ogy Department at UC Davis, who were selected on the basis ofmotivation and availability, participated as judges. The panel-ists were advised to chew several kernel pieces and to expector-ate and rinse with water between each sample. However, due toindividual preferences and the small number of nuts being sam-pled, they were given the choice to swallow or expectorate thenuts and to rinse two times after each sample or only after eachtrio. In either case, they were told to use the same techniquefor the entire experiment. All evaluations were conducted in aconference room in Wickson Hall (approx. 22°C) using a six-persor.booth setup on a table; each booth was illuminated with a 25W redlight.
In the initial difference testing, 'Hartley' was compareQ to
Table 1. Kernel moisture content of cultivars evaluated.
CuI ti var ________HartleyVinaScharsch FranquetteMayetteChandlerChicoHowardSunland
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Moisturecon t~n!:__L~L
3.03.13.43.13.23.43.03.0.-".---.-
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seven other cu1tivars using the duo-trio method (Institute ofFood Technologists, 1981). Each day, one cu1tivar was testedagainst 'Hartley' (identified as "control") with four replica-tions. One bowl of 'Hartley' kernels was placed on each panelmember's tray along with four pairs of portion cups (coded withrandom 3-digit numbers) which contained approximately 6-8g ofkernels. In each pair, 'Hartley' kernels and the other testcu1tivar were presented in a random order. Panel members wereasked to indicate which sample in each pair was identical to the"control" sample. The first day of testing was used as a prac-tice session, in which black walnuts (J. hindsii) were testedagainst 'Hartley'. Formal testing began on day two of the exper-iment and continued through day eight. The last day of thisperiod was used for makeups.
Pair tests were conducted during the third week to compare cu1-tiv.ars on the basis of firmness, astringency, sweetness andoverall walnut flavor. All testing was performed under the sameconditions as those used for difference testing. Eleven of thepanelists were selected, on the basis of scores in the differencetesting and availability, to participate in this period of test-ing. Training consisted of one day in which panel members werepresented with mildly sweet (5g/1 sucrose) and astringent (50mg/1 aluminum sulfate) solutions; then in separate paired testsall judges correctly identified the sweeter and more astringentsolutions. Judges were also asked to sample walnut pelliclematerial to taste astringency. No training was performed forfirmness and walnut flavor. 'Hartley' was then compared to'Chandler', 'Chico', 'Howard' and 'Sun1and' in paired comparisonsin duplicate (eight pairs). Judges were asked to identify thefirmer and more astringent sample in each pair one day, and thesample which was sweeter and had greater overall walnut flavorthe second day. The four cu1tivars were also compared to eachother on the basis of firmness and sweetness in duplicate, withone replication performed per day (six pairs) .
Data analysis. Results were interpreted from a table constructedfrom binomial probability where p=0.5, one-tailed (Roessler eta1.,1978).
RESULTS AND CONCLUSIONS
The results of the difference tests are summarized in Table 2.In the training session, J. hindsii was highly significantlydifferent from 'Hartley' (P<0.001). Of the seven J. regia cu1-tivars tested against 'Hartley', only 'Chandler', 'Chico', 'How-ard' and 'Sun1and' differed significantly (P<O.OOl).
Pair testing was performed to determine how these four cu1tivarsdiffered from 'Hartley' and from each other. As summarized inTab1~ 3, no differences in astringency or overall walnut flavorwere detected between 'Hartley' and the four other cu1tivars.Differences in sweetness and firmness were found, however.'Chandler' was sweeter than 'Hartley' (P<0.05), while 'Hartley'
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was sweeter than 'Howard' (P<0.05). All four of the cultivarstested were firmer than 'Hartley'. Pair tests comparing the fourcultivars for sweetness and firmness are summarized in Tables 4and 5, respectively. The only significant difference in sweet-ness found was that 'Chandler' was significantly sweeter than'Howard' (P<O.OOl). Although 'Chico' nuts were slightly higherin moisture content, they were nonetheless firmer than the otherthree cultivars which did not differ among themselves.
In this study, the cultivar 'Hartley' was shown to be signifi-cantly different in sensory properties from 'Chandler', 'Chico','Howard' and 'Sunland', while not differing from 'Vina','Scharsch Franquette' and 'Mayette'. In pair tests, all fourcultivars were found to be firmer than 'Hartley', while twodiffered in sweetness. None of the four cultivars differed from'Hartley' in astringency nor in walnut flavor. The results ofthis study dispute informal claims that 'Hartley' is less flavor-ful than other cultivars, especially the French-types, 'Mayette'and 'Scharsch Franquette', which were shown to not differ from'Hartley' .
The majority of walnuts are used as ingredient items (e.g., inbaked goods), in which case the difference in hardness or sweet-ness of these cultivars may not be an important parameter. Inwalnuts sold for consumption directly, however, consumer pref-erence for harder or sweeter nuts would have to be assessedbefore either parameter should be used as a criterion for influ-encing cultivar selection. Although intensity of walnut flavordid not differ for these cultivars, in new cultivars it may be animportant parameter to assess.
We thank Bill Stuke for providing the walnuts used in this study.This work was partially supported by USDA/ARS Specific Coopera-tive Agreement number 58-91H2-8-131.
LITERATURE CITED
Gunnerson, R.E. Diamond Walnut Cooperative. Personal communica-tion.
Heintz, C.M. and A.A. Kader. 1983.evaluation of horticultural crops.
Procedures for the sensoryHortScience 18(1)18-22.
Institute of Food Technologists. 1981. Sensory evaluation guidefor testing food and beverage products. Sensory Evaluation Div.tInst. Food Technologists. Food Tech. 35(11) :50-59.
Roessler, E.B., R.M. Pangborn, J.L. Sidel and H. Stone. 1978.Expanded statistical tables for estimating significance inpaired-preference, pair-difference, duo-trio and triangle tests.J. Food Sci. 43(3)940-943.
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Table 2. Number and significance of correct responses in dif-ference tests of Hartley vs. other cultivars (n = 21 judges x 4reps) .
Cultivar comparedto Hartley
J. hindsii (in trainingVinaScharsch FranquetteMayetteChandlerChicoHowardSunland
