- Email: [email protected]
Influence of Composition and Processing on Sensory Properties of Nonfat Milk
Influence of Composition Properties of Nonfat
a n d Processing o n S e n s o r y
Milk MARIANNE LANG 1, R. FORMENT 2 , and W. L. DUNKLEY Department of Food Science and Technology University of California, Davis 95616
selection of conditions for subsequent use in studies of consumer acceptance.
ABSTRACT
Variations in pasteurization temperature and increases of 1 and 2% solids-notfat resulted in significant detection of differences by trained judges in triangle testing of nonfat milk. Pasteurization, particularly at 79.4 and 85 C, produced a heated flavor which decreased in intensity during storage (9 days). Changes in fat content within the range studied (.1 to .5%) did not produce detectable flavor or mouthfeel differences, nor did variations in homogenization pressure. Judges detected differences between samples with and without 200 and 300 ppm additions of stabilizers when the milk was pasteurized at 85 C, but not at 73.8 C. The ability of judges to detect 400 p p m additions of emulsifiers depended upon the composition of the nonfat milk, with .5% fat inhibiting detection of added emulsifiers. Addition of stabilizers increased viscosity, but addition of emulsifiers did not.
MATERIALS AND METHODS
INTRODUCTION
Added fat, solids-not-fat (SNF), or both influence the appearance, flavor, and mouthfeel of milk, but o p t i m u m percents have not been determined (4). Effects of pasteurization and homogenization on heated and oxidized flavors have been studied extensively in relation to whole milk (8, 13), but relatively little information is available regarding their effects on nonfat milk. We used triangle testing by trained judges to detect differences in flavor or mouthfeel associated with fat, SNF, pasteurizing temperature, homogenizing pressure, and additions of stabilizers and emulsifiers. The results were to guide
Received March 9, 1976. l Clorox Technical Center, Pleasanton, CA 94566. 2Carnation Research Laboratories, Van Nuys, CA 91412.
Samples were prepared from milk 1 to 2 days old produced by cows in the University herd. The milk was separated into skim milk and cream by a farm-type separator (DeLaval model 518). Condensed skim milk (approximately 24% SNF and .3% fat) was obtained from Crystal Cream and Butter Co., Sacramento, and was packaged in half-gallon plastic containers, frozen, and stored at - 2 6 C. When needed, it was thawed in water not exceeding 60 C. The ingredients were blended in proportions to give milks with desired compositions. Emulsifiers were dispersed in cold skim milk before addition to the mixtures. Stabilizers were added slowly with continuous agitation to skim milk at 50 C and were dissolved b y stirring 5 to 10 rain. Milks were pasteurized and homogenized with the desired conditions by pilot-scale equipment (APV Junior Paraflow heat exchanger and Crepaco homogenizer model 3 DDL fitted with a two-stage micro-shear homogenizing valve, and set to a capacity of 57 liters/h). The homogenizer served as the timing pump and provided a calculated holding time of 18 s. The cooled milks were packaged in 1.9-liter plastic bottles and stored at 1 C, protected from light, until time of tasting. Fat and total solids were determined in duplicate by the Mojonnier method, and SNF was calculated by difference. Viscosity determinations were in triplicate at 10 C with a Brookfield viscometer (Model LTV, fitted with a U.L. adapter). One series of experiments included comparis o n s of variables related to processing and composition o f the milks. The processing variables were pasteurization at 73.8, 79.4, and 85 C with 18 s holding time, and homogenization at 0, 1400, and 2800 N/cm 2. Composition variables were .1, .25, and .5% fat, and 9, 10,
1560
SENSORY PROPERTIES OF NONFAT MILK and 11% SNF. To reduce the numbers of combinations, reference treatments were selected. Processing variables were compared on two milk compositions, .1% fat, 9% SNF; and .5% fat, 11% SNF. To compare compositional differences, two processing conditions were pasteurization at 73.8 C without homogenization and pasteurization at 85 C with homogenization at 1400 N/cm 2. In all experiments, homogenization was two-stage with one-fourth of the total pressure on the second stage. All samples were evaluated after storage for 1, 3, and 9 days. In another series of experiments, effects of stabilizers and emulsifiers were studied. For experiments with stabilizers, three fractions of carrageenan (lambda, kappa, iota) were used at concentrations of 0, 200, and 300 ppm in milks with three compositions .1% fat, 9% SNF; .1% fat, 11% SNF; and .5% fat, 11% SNF. Processing treatments were pasteurization at 73.8 and 85 C, each without homogenization, and with homogenization at 1400 N/cm 2. For the emulsifier experiments, four emulsifiers were used at 400 ppm. Compositions of the milks were as for the stabilizer experiments, and all samples were pasteurized at 73.8 C and homogenized at 1400 N/cm 2 . The samples were stored 4 days at 1 C before sensory evaluation. For triangle tests, a panel of 15 judges was selected on prior experience and ability to distinguish by taste differences between milks pasteurized at 73.8 and 85 C. For a triangle test, the judges were given a set of three samples, two of which were the same, and they were asked to choose the different sample. Each day the judges were given six triangles which provided triplicate comparisons of one milk treatment or composition with two others. To prepare samples for triangle tests, 30-ml portions of milk were placed in 50-ml coded, brown, narrow-necked bottles. Six groups of three bottles each, for the six triangle tests, were placed in trays. The order of the six triangle tests was randomized as was the order within each triangle. The trays were covered with aluminum foil and were tempered 90 rain at 10 C. For the tests, the trays were served to judges in individual booths with red illumination to mask visual differences. Significance of differences between numbers of correct responses was determined from tables (1). The judges were asked to characterize their
1561
basis for differentiation (e.g., heated flavor, viscosity, etc.). For triangles in which the odd sample was identified correctly, the number of times each differentiating characteristic was mentioned was calculated as a percentage of the correct responses. Results were recorded only for characteristics used in 20% or more of the correct responses. RESULTS A N D DISCUSSION Processing
Table 1 summarizes results of the trials in which the principal variables were processing conditions. In trials 1 and 2 (which were duplicates to check reproducibility), the judges readily detected differences between samples pasteurized at 73.8 and 85 C at all storage times. For samples pasteurized at 73.8 and 79.4 C, differences were significant (P<~.01) on all 3 days in trial 1 but only on the 1st day in trial 2. In trial 3, the intermediate pasteurization temperature was compared with the two extreme temperatures. Results of this comparison between the 73.8 and 79.4 C samples were intermediate between those of trials 1 and 2. Differences between samples pasteurized at 79.4 and 85 C were detected readily after storage for 1 and 3 days (P~.001), but not so readily after 9 days (P~.05). In trial 4, the milks had increased percentages of fat and SNF, and the results were similar to those of trials 1 and 2. In trial 5, homogenization of the milks did not influence detection of differences between samples pasteurized at the different temperatures. In trials 6 and 7, effects of different homogenization treatments were compared for milks of two compositions. There were no significant differences related to homogenization treatments. In trials 1 to 5, heated flavor was the predominant characteristic for differentiation; oxidized flavor was next in frequency. Comments about heated flavor decreased in frequency with increase in storage time. In trials 6 and 7, although no differences were significant in triangle tests, watery was the dominant characteristic the judges used in selecting the odd sample when they were correct. Oxidized flavor was second in frequency in comparisons of samples homogenized at 0 and 2800 N/cm 2, Journal of Dairy Science Vol. 59, No. 9
Ox tJ
TABLE 1. Effect of pasteurization temperature and homogenization pressure of nonfat milks on detection of differences by triangle tests. (See footnotes for significance of differences.) O3
<
Q
Trial
Variable
Processing conditions Past temp f Homo pressg (C) (N/cm 2)
Composition Fat SNF (%) (%)
Day 1
Triangle test, correct judgments e Day 3 Day 9
Past temp (C) 1
73.8 vs. 79.4 h 73.8 vs. 85
0 0
.1 .1
9 9
23/42 c 32/42 d
26/45 d 31/45 d
25/45 c 24/45 c
2
73.8 vs. 79.4 73.8 vs. 85
0 0
.1 .1
9 9
27/42 d 33/42 d
19/42 a 34/42 d
11/42 a 28/42 d
3
79.4 vs. 73.8 79.4 vs. 85
0 0
.1 .1
9 9
32/42 d 38/42 d
21/42 b 34/42 d
21/42 b 20/42 b
4
73.8 vs. 79.4 73.8 vs. 85
0 0
.5 .5
11 11
20/39 b 37/39 d
23/39 d 27/39 d
15/45 a 22/45 b
5
73.8 vs. 79.4 73.8 vs. 85
1400 1400
.5 .5
11 11
26/39 d 23/39 d
14/36 a 24/36 d
17/42 a 21/42 b
6
0 vs. 1400 0 vs. 2800
73.8 73.8
.1 .1
9 9
13/42a 14/42 a
17/42 a 17/42 a
13/36 a 12/36a
7
0 vs. 1400 0 vs. 2800
73.8 73.8
.5 .5
11 11
20/45 a 14/45 a
1 5/42 a
19/45 a 12/45 a
Homo press (N/cm 2 )
a'b'c'dsignificance of differences: a, not significant; b, c, and d, significant at P<.O 5, .01, and .001, respectively. eNumber correct/total number of judgments. fHolding time, 18 s. gTwo stage, with one-fourth of total on second stage. hFirst number indicates the reference sample in each pair, compared in triplicate with the other two.
12/42 a
Z ~q
SENSORY PROPERTIES OF NONFAT MILK but there were no comments concerning oxidized flavor in comparisons of 0 and 1400 N/cm 2 . The results with different pasteurization temperatures (trials 1 to 5) were generally in accord with the expected increase in intensity of heated flavor with increase in pasteurizing temperature and decrease in intensity during storage (3, 7, 8). Differences between milks pasteurized at the low and high pasteurizing temperatures (73.8 and 85 C) were detectable up to 9 days of storage whereas with samples pasteurized at the lower and intermediate temperatures (73.8 and 79.4 C) differences were detected readily after 1 day but inconsistently after 3 and 9 days of storage. Because of the well known influence o f heat treatments (8, 10, 13) and homogenization (8, 13) on development of oxidized flavor in milk, special attention was given to identifying this characteristic. At the time the milks were in the triangle tests, they also were scored by three judges with 5 or more y r experience in scoring milk and were tested by TBA test (5). Generally the flavor scores indicated no or only slight oxidized flavor, and results of the TBA tests were low. Also, the results were inconsistent with oxidized flavor comments in the triangle tests. We concluded that the milks were so resistant to oxidized flavor that the results did not indicate whether pasteurizing and homogenizing treatments influenced development of the flavor. Composition
Differences between samples with the different fat percentages compared in trials 8 and 9 (.1 v s . . 2 5 , and .1 v s . . 5 , Table 2) were not detected in the triangle tests. However, varying SNF (trials 10 to 12) resulted in differences that were detected significantly. In samples containing 9 and 10% SNF, both with .1% fat (trials 10 and 11), differences were not detected after 3 and 9 days of storage when the milks were pasteurized at 73.8 C but were evident when the milks were pasteurized at 85 C and homogenized. The predominant characteristic for correct differentiation of samples that differed in fat (trials 8 and 9) was watery followed by heated and oxidized. These comments must be discounted, however, because the judges were not
1563
able to differentiate the samples significantly, but they were required to state the basis for their differentiation. For the samples that differed in SNF, watery was the dominant differentiating characteristic, and heated was the second most frequently mentioned term. In early studies of effects of milk composition on flavor, Kelly (9) and Foust (6) noted that differences in fat were not detected as readily as differences in SNF. Pangborn and Dunkley (11) found that the concentration of SNF influenced the minimum difference in fat that was detectable in nonfat milk. Minimum detectable differences in nonfat milks containing 8.5 and 10% SNF were, respectively, .3 and .8% fat. By interpolation of these results to those in trials 8 and 9 of our study, the minimum detectable difference in milk containing 9% SNF would be .4% fat. Our panel did not detect this difference. However, there was a difference in the percentage of fat in the reference milk in the two studies. In the study by Pangborn and Dunkley (11), the skim milk for the sample with the lower fat content was separated with an efficient commercial separator whereas the farm-type separator used in our study left about .1% fat in the skim milk. The detection of 1 and 2% differences in SNF in trials 10 to 12 is consistent with (4, 11). Stabilizers
Additions of stabilizers at both 200 and 300 ppm were detected readily in samples pasteurized at 85 C but not at 73.8 (Table 3, trials 13 to 21). Two results with carrageenan at 300 ppm appear inconsistent, which may have resulted from sample errors. In general, heat treatment was the only significant variable with no differences among results of the triangle tests attributable to stabilizer fraction or concentration, milk composition, or homogenization. Increases in viscosity in centipoises from additions o f the carrageenans at 200 and 300 ppm, respectively, were lambda, 1.2 and 1.8, kappa, 2.3 and 7.0, and iota, 1.0 and 3.3. The most frequent characteristics used to distinguish differences were watery and heated, with few designations of mouthfeel characteristics. Experience in the earlier trials may have attuned the judges to look principally for differences in flavor. However, additions of stabilizers could change flavor more than they Journal of Dairy Science Vol. 59, No. 9
Ox ~o
e~
TABLE 2. Effect o f fat and SNF concentration in nonfat milk on detection of differences by triangle tests. (See footnotes for significance of differences.)
< o
Trial
Variable
Processing conditions Past temp f Homo pressg
Composition Fat SNF
(C)
(N/cm ~)
(%)
Triangle test, correct judgments e
(%)
Day 1
Day 3
Day 9
0 0
9 9
14/45 a 16/45 a
16/45 a 20/45 a
18/45 a 21/45 b
1400 1400
9 9
20/42 b 18/42 a
15/39 a 10/39 a
15/45 a
Fat (%) 8
.1 vs..25 h .1 vs..5
73.8 73.8
9
.1 vs..25 .1 vs.. 5
85 85
SNF (%) 10
9 vs. 10 9 vs. 11
73.8 73.8
0 0
.1 .1
26/42 d 26/42 d
20/45 a 32/45 d
12/36 a 19/36 b
11
9 vs. 10 9 vs. 11
85 85
1400 1400
.1 .1
26/39 d 30/39 d
26/39 d 27/39 d
26/42 d 34/42 d
12
9 vs. 10 9 vs. 11
85 85
1400 1400
.5 .5
22/39 d 21/39 c
25/39 d 28/39 d
17/36 a 24/36 d
a'b'c'dsignificance of differences: a, not significant;b, c, and d, significant at P<.05, .01, and .001, respectively. eNumber correct/total number o f judgments. fHolding time, 18 s. gTwo stage, with one-fourth of total on second stage. hFirst number indicates the reference sample in each pair, compared in triplicate with the other two.
TABLE 3. Effect of additions of stabilizers to n o n f a t milk on detection of differences by triangle tests. (See f o o t n o t e s for significance of differences.)
Processing conditions Trial
Stabilizer
Past t e m p f (C)
13 14 15 16 17 18 19 20 21
lamb d a h kappa kappa iota iota lambda lambda lambda iota
85 85 85 85 85 73.8 73.8 73.8 73.8
Triangle test, correct j u d g m e n t s e
Composition
H o m o pressg ( N / c m 2)
Fat (%)
SNF (%)
0 vs. 200 p p m
0 vs. 300 p p m
1400 0 1400 0 1400 0 1400 0 0
.5 .1 .5 .1 .5 .1 .5 .1 .1
11 11 11 11 11 11 11 9 9
31/45 d 27/42 d 26/45 d 24/36 d 24/42 c 16/45 a 12/42 a 15/42 a 18/45 a
31/45 d 33/42 d 32/45 d 13/36 a 24/4c2 c 18/45 d 19/42 a 12/42 a 32/45 d
t~ z O
O t~
© X 0 Z "i"1
a'b'c'dsignificance o f differences: a, n o t significant ;b, c, and d, significant at P<.05, .01, and .001, respectively. =
e N u m b e r correct/total n u m b e r of judgments. fHolding time, 18 s. gTwo stage, with one-fourth of total on second stage.
ga
hcarrageenan fractions: lambda, Viscarin 402 ; kappa, Gelcarin HMR; and iota, Gelcarin SI. Marine Colloids, Inc., San Ramon, CA.
e~ < o
X o
Ox
1566
LANG ET AL.
TABLE 4. Effect of additions of emulsifiers to nonfat milk on detection of differences by triangle tests. (See footnotes for significance of differences. All samples were pasteurized at 73.8 C for 18 s and homogenized at 1400 N/cm 2 , with one-fourth of the total pressure on the second stage.) Triangle test, correct judgments e
Composition Trial
Emulsifier
Fat (%)
SNF (%)
22 23 24 25 26 27 28 29 30 31 32
Tf D M H D T T T H D M
.1 .1 .1 .1 .1 .1 .5 .5 .5 .5 .5
9 9 9 9 9 11 11 11 11 11 11
0 vs. 400 ppm 25/42 d 30/42 d 30/39 d 23/39 d 22/33 d 27/42 d 18/24 a 14/33 a 13/33 a 16/33 b 11/33 a
a'b'c'dsignificance of differences: a, not significant; b, c, and d, significant at P<.05, .01, and .001, respectively. eNumber correct/total number of judgments. fAbbreviations: T, Tally 100, a mixture of mono- and diglycerides, ethoxylated mono- and diglycerides, and hydrogenated vegetable oils, Glidden-Durkee, Berkeley, CA; D, Durfax 80, polysorbate 80, Glidden-Durkee, Berkeley, CA; M, Myvoplex, glyceryl monostearate, Distillation Products Industries, Rochester, NY; H, Hallmark GMS, glyceryl monostearate, Stein, Hall and Co., Inc., New York, NY.
could m o u t h f e e l . We suggest three possible explanations o f a relation b e t w e e n stabilizer addition and heated flavor. 1) Viscosity may have affected the d e t e c t i o n of flavor (2, 12), possibly by decreasing the intensity of flavor c o m p o n e n t s by the time t h e y reach the receptors. 2) Stabilizers may have stabilized the milk proteins by reacting with them, t h e r e b y reducing the release of sulfhydryl groups which contribute to h e a t e d flavors. 3) A b s o r p t i o n of water by the stabilizers m a y have influenced susceptibility o f the milk to h e a t e d flavor. Emulsifiers
Additions of f o u r emulsifiers at 400 p p m were d e t e c t e d readily in milks containing .1% fat (Table 4, trials 22 to 27) but n o t in milks with .5% fat (trials 28 to 32). Comparison o f trials 22 and 27 indicates that the difference in c o n c e n t r a t i o n of S N F did n o t influence detection o f added emulsifier. The higher fat in trials 28 to 32 prevented the d e t e c t i o n of added emulsifiers. Additions o f 400 p p m of emulsitiers did n o t increase viscosity o f the milks in any of the trials. The p r e d o m i n a n t characteristic used to difJournal of Dairy Science Vol. 59, No. 9
ferentiate the samples was watery with oxidized flavor n e x t in frequency. Heated flavor was n o t used for differentiation, probably because all samples were pasteurized at 73.8 C, the lowest t e m p e r a t u r e in the study, and stored 4 days. The c o m m e n t s o f o x i d i z e d m a y have resulted f r o m either flavor or m o u t h f e e l characteristics of the emulsifiers rather than f r o m o x i d a t i o n o f milk lipids. A C K N O W L EDGM ENT
The study was s u p p o r t e d in part by the Dairy Council of California. The authors gratefully acknowledge the suggestions and assistance of J. c. Bruhn, H. G. Schutz, and R. M. Pangborn, the c o o p e r a t i o n of the sensory panel, and technical assistance o f E. E. Moore, A. A. Franke, E. C. Jensen, and M. Cummings. REFERENCES
1 Amerine, M. A., R. M. Pangborn, and E. B. Roessler. 1965. Principles of sensory evaluation of food. Academic Press, New York. 2 Crocker, E. C. 1945. Flavor. McGraw-Hill Book Co., New York. 3 Deane, D. D., J. A. Chelesvig, and W. R. Thomas. 1967. Pasteurization treatment and consumer ac-
SENSORY PROPERTIES OF N O N F A T MILK ceptance of milk. J. Dairy Sci. 50:1216. 4 Devero, J. E. 1972. Effects of varying non-fat solids and fat on consumer acceptance. United Dairy Ind. Ass., m i m e o review. 5 Dunkley, W. L., and A. A. Franke. 1967. Evaluating susceptibility of milk to oxidized flavor. J.. Dairy Sci. 50:1. 6 Foust, W. L. 1948. Let's see more fat free milk. Milk Dealer 38:44. 7 Holland, B. K., and W. C. Winder. 1951. Preparation o f modified skim milk. Milk Dealer 40:43,
Aug.
8 Jenness, R., and S. Patton. 1959. Flavors and off-flavors in milk and its products. Page 360 in Principles of dairy chemistry. Wiley, NY.
1 567
9 Kelly, E. 1935. Promote the fresh milk business. Milk Plant Mon. 24:44. 10 Miller, D. D., and S. R. Skaggs. 1959. Controlling oxidized flavor with heat-treated milk. J. Dairy Sci. 42:1743. (Abstr.) 11 Pangborn, R. M., a n d W. L. Dunkley. 1964. Sensory discrimination of fat and solids-not-fat in milk. J. Dairy Sci. 47:719. 12 Pangborn, R. M., I. M. Trabue, and A. S. Szczesniak. 1972. Effect of hydrocolloids on oral viscosity and basic taste intensities. J. Texture Stud. 4:224. 13 Parks, O. W. 1974. The lipids o f milk: Deterioration II Autoxidation. Page 240 in Fundamentals o f dairy chemistry. B. H. Webb, A. H. J o h n s o n , a n d J. A. Alford, ed. Avi Publ. Co., Westport, CT.
Journal o f Dairy Science Vol. 59, No. 9
a n d Processing o n S e n s o r y
Milk MARIANNE LANG 1, R. FORMENT 2 , and W. L. DUNKLEY Department of Food Science and Technology University of California, Davis 95616
selection of conditions for subsequent use in studies of consumer acceptance.
ABSTRACT
Variations in pasteurization temperature and increases of 1 and 2% solids-notfat resulted in significant detection of differences by trained judges in triangle testing of nonfat milk. Pasteurization, particularly at 79.4 and 85 C, produced a heated flavor which decreased in intensity during storage (9 days). Changes in fat content within the range studied (.1 to .5%) did not produce detectable flavor or mouthfeel differences, nor did variations in homogenization pressure. Judges detected differences between samples with and without 200 and 300 ppm additions of stabilizers when the milk was pasteurized at 85 C, but not at 73.8 C. The ability of judges to detect 400 p p m additions of emulsifiers depended upon the composition of the nonfat milk, with .5% fat inhibiting detection of added emulsifiers. Addition of stabilizers increased viscosity, but addition of emulsifiers did not.
MATERIALS AND METHODS
INTRODUCTION
Added fat, solids-not-fat (SNF), or both influence the appearance, flavor, and mouthfeel of milk, but o p t i m u m percents have not been determined (4). Effects of pasteurization and homogenization on heated and oxidized flavors have been studied extensively in relation to whole milk (8, 13), but relatively little information is available regarding their effects on nonfat milk. We used triangle testing by trained judges to detect differences in flavor or mouthfeel associated with fat, SNF, pasteurizing temperature, homogenizing pressure, and additions of stabilizers and emulsifiers. The results were to guide
Received March 9, 1976. l Clorox Technical Center, Pleasanton, CA 94566. 2Carnation Research Laboratories, Van Nuys, CA 91412.
Samples were prepared from milk 1 to 2 days old produced by cows in the University herd. The milk was separated into skim milk and cream by a farm-type separator (DeLaval model 518). Condensed skim milk (approximately 24% SNF and .3% fat) was obtained from Crystal Cream and Butter Co., Sacramento, and was packaged in half-gallon plastic containers, frozen, and stored at - 2 6 C. When needed, it was thawed in water not exceeding 60 C. The ingredients were blended in proportions to give milks with desired compositions. Emulsifiers were dispersed in cold skim milk before addition to the mixtures. Stabilizers were added slowly with continuous agitation to skim milk at 50 C and were dissolved b y stirring 5 to 10 rain. Milks were pasteurized and homogenized with the desired conditions by pilot-scale equipment (APV Junior Paraflow heat exchanger and Crepaco homogenizer model 3 DDL fitted with a two-stage micro-shear homogenizing valve, and set to a capacity of 57 liters/h). The homogenizer served as the timing pump and provided a calculated holding time of 18 s. The cooled milks were packaged in 1.9-liter plastic bottles and stored at 1 C, protected from light, until time of tasting. Fat and total solids were determined in duplicate by the Mojonnier method, and SNF was calculated by difference. Viscosity determinations were in triplicate at 10 C with a Brookfield viscometer (Model LTV, fitted with a U.L. adapter). One series of experiments included comparis o n s of variables related to processing and composition o f the milks. The processing variables were pasteurization at 73.8, 79.4, and 85 C with 18 s holding time, and homogenization at 0, 1400, and 2800 N/cm 2. Composition variables were .1, .25, and .5% fat, and 9, 10,
1560
SENSORY PROPERTIES OF NONFAT MILK and 11% SNF. To reduce the numbers of combinations, reference treatments were selected. Processing variables were compared on two milk compositions, .1% fat, 9% SNF; and .5% fat, 11% SNF. To compare compositional differences, two processing conditions were pasteurization at 73.8 C without homogenization and pasteurization at 85 C with homogenization at 1400 N/cm 2. In all experiments, homogenization was two-stage with one-fourth of the total pressure on the second stage. All samples were evaluated after storage for 1, 3, and 9 days. In another series of experiments, effects of stabilizers and emulsifiers were studied. For experiments with stabilizers, three fractions of carrageenan (lambda, kappa, iota) were used at concentrations of 0, 200, and 300 ppm in milks with three compositions .1% fat, 9% SNF; .1% fat, 11% SNF; and .5% fat, 11% SNF. Processing treatments were pasteurization at 73.8 and 85 C, each without homogenization, and with homogenization at 1400 N/cm 2. For the emulsifier experiments, four emulsifiers were used at 400 ppm. Compositions of the milks were as for the stabilizer experiments, and all samples were pasteurized at 73.8 C and homogenized at 1400 N/cm 2 . The samples were stored 4 days at 1 C before sensory evaluation. For triangle tests, a panel of 15 judges was selected on prior experience and ability to distinguish by taste differences between milks pasteurized at 73.8 and 85 C. For a triangle test, the judges were given a set of three samples, two of which were the same, and they were asked to choose the different sample. Each day the judges were given six triangles which provided triplicate comparisons of one milk treatment or composition with two others. To prepare samples for triangle tests, 30-ml portions of milk were placed in 50-ml coded, brown, narrow-necked bottles. Six groups of three bottles each, for the six triangle tests, were placed in trays. The order of the six triangle tests was randomized as was the order within each triangle. The trays were covered with aluminum foil and were tempered 90 rain at 10 C. For the tests, the trays were served to judges in individual booths with red illumination to mask visual differences. Significance of differences between numbers of correct responses was determined from tables (1). The judges were asked to characterize their
1561
basis for differentiation (e.g., heated flavor, viscosity, etc.). For triangles in which the odd sample was identified correctly, the number of times each differentiating characteristic was mentioned was calculated as a percentage of the correct responses. Results were recorded only for characteristics used in 20% or more of the correct responses. RESULTS A N D DISCUSSION Processing
Table 1 summarizes results of the trials in which the principal variables were processing conditions. In trials 1 and 2 (which were duplicates to check reproducibility), the judges readily detected differences between samples pasteurized at 73.8 and 85 C at all storage times. For samples pasteurized at 73.8 and 79.4 C, differences were significant (P<~.01) on all 3 days in trial 1 but only on the 1st day in trial 2. In trial 3, the intermediate pasteurization temperature was compared with the two extreme temperatures. Results of this comparison between the 73.8 and 79.4 C samples were intermediate between those of trials 1 and 2. Differences between samples pasteurized at 79.4 and 85 C were detected readily after storage for 1 and 3 days (P~.001), but not so readily after 9 days (P~.05). In trial 4, the milks had increased percentages of fat and SNF, and the results were similar to those of trials 1 and 2. In trial 5, homogenization of the milks did not influence detection of differences between samples pasteurized at the different temperatures. In trials 6 and 7, effects of different homogenization treatments were compared for milks of two compositions. There were no significant differences related to homogenization treatments. In trials 1 to 5, heated flavor was the predominant characteristic for differentiation; oxidized flavor was next in frequency. Comments about heated flavor decreased in frequency with increase in storage time. In trials 6 and 7, although no differences were significant in triangle tests, watery was the dominant characteristic the judges used in selecting the odd sample when they were correct. Oxidized flavor was second in frequency in comparisons of samples homogenized at 0 and 2800 N/cm 2, Journal of Dairy Science Vol. 59, No. 9
Ox tJ
TABLE 1. Effect of pasteurization temperature and homogenization pressure of nonfat milks on detection of differences by triangle tests. (See footnotes for significance of differences.) O3
<
Q
Trial
Variable
Processing conditions Past temp f Homo pressg (C) (N/cm 2)
Composition Fat SNF (%) (%)
Day 1
Triangle test, correct judgments e Day 3 Day 9
Past temp (C) 1
73.8 vs. 79.4 h 73.8 vs. 85
0 0
.1 .1
9 9
23/42 c 32/42 d
26/45 d 31/45 d
25/45 c 24/45 c
2
73.8 vs. 79.4 73.8 vs. 85
0 0
.1 .1
9 9
27/42 d 33/42 d
19/42 a 34/42 d
11/42 a 28/42 d
3
79.4 vs. 73.8 79.4 vs. 85
0 0
.1 .1
9 9
32/42 d 38/42 d
21/42 b 34/42 d
21/42 b 20/42 b
4
73.8 vs. 79.4 73.8 vs. 85
0 0
.5 .5
11 11
20/39 b 37/39 d
23/39 d 27/39 d
15/45 a 22/45 b
5
73.8 vs. 79.4 73.8 vs. 85
1400 1400
.5 .5
11 11
26/39 d 23/39 d
14/36 a 24/36 d
17/42 a 21/42 b
6
0 vs. 1400 0 vs. 2800
73.8 73.8
.1 .1
9 9
13/42a 14/42 a
17/42 a 17/42 a
13/36 a 12/36a
7
0 vs. 1400 0 vs. 2800
73.8 73.8
.5 .5
11 11
20/45 a 14/45 a
1 5/42 a
19/45 a 12/45 a
Homo press (N/cm 2 )
a'b'c'dsignificance of differences: a, not significant; b, c, and d, significant at P<.O 5, .01, and .001, respectively. eNumber correct/total number of judgments. fHolding time, 18 s. gTwo stage, with one-fourth of total on second stage. hFirst number indicates the reference sample in each pair, compared in triplicate with the other two.
12/42 a
Z ~q
SENSORY PROPERTIES OF NONFAT MILK but there were no comments concerning oxidized flavor in comparisons of 0 and 1400 N/cm 2 . The results with different pasteurization temperatures (trials 1 to 5) were generally in accord with the expected increase in intensity of heated flavor with increase in pasteurizing temperature and decrease in intensity during storage (3, 7, 8). Differences between milks pasteurized at the low and high pasteurizing temperatures (73.8 and 85 C) were detectable up to 9 days of storage whereas with samples pasteurized at the lower and intermediate temperatures (73.8 and 79.4 C) differences were detected readily after 1 day but inconsistently after 3 and 9 days of storage. Because of the well known influence o f heat treatments (8, 10, 13) and homogenization (8, 13) on development of oxidized flavor in milk, special attention was given to identifying this characteristic. At the time the milks were in the triangle tests, they also were scored by three judges with 5 or more y r experience in scoring milk and were tested by TBA test (5). Generally the flavor scores indicated no or only slight oxidized flavor, and results of the TBA tests were low. Also, the results were inconsistent with oxidized flavor comments in the triangle tests. We concluded that the milks were so resistant to oxidized flavor that the results did not indicate whether pasteurizing and homogenizing treatments influenced development of the flavor. Composition
Differences between samples with the different fat percentages compared in trials 8 and 9 (.1 v s . . 2 5 , and .1 v s . . 5 , Table 2) were not detected in the triangle tests. However, varying SNF (trials 10 to 12) resulted in differences that were detected significantly. In samples containing 9 and 10% SNF, both with .1% fat (trials 10 and 11), differences were not detected after 3 and 9 days of storage when the milks were pasteurized at 73.8 C but were evident when the milks were pasteurized at 85 C and homogenized. The predominant characteristic for correct differentiation of samples that differed in fat (trials 8 and 9) was watery followed by heated and oxidized. These comments must be discounted, however, because the judges were not
1563
able to differentiate the samples significantly, but they were required to state the basis for their differentiation. For the samples that differed in SNF, watery was the dominant differentiating characteristic, and heated was the second most frequently mentioned term. In early studies of effects of milk composition on flavor, Kelly (9) and Foust (6) noted that differences in fat were not detected as readily as differences in SNF. Pangborn and Dunkley (11) found that the concentration of SNF influenced the minimum difference in fat that was detectable in nonfat milk. Minimum detectable differences in nonfat milks containing 8.5 and 10% SNF were, respectively, .3 and .8% fat. By interpolation of these results to those in trials 8 and 9 of our study, the minimum detectable difference in milk containing 9% SNF would be .4% fat. Our panel did not detect this difference. However, there was a difference in the percentage of fat in the reference milk in the two studies. In the study by Pangborn and Dunkley (11), the skim milk for the sample with the lower fat content was separated with an efficient commercial separator whereas the farm-type separator used in our study left about .1% fat in the skim milk. The detection of 1 and 2% differences in SNF in trials 10 to 12 is consistent with (4, 11). Stabilizers
Additions of stabilizers at both 200 and 300 ppm were detected readily in samples pasteurized at 85 C but not at 73.8 (Table 3, trials 13 to 21). Two results with carrageenan at 300 ppm appear inconsistent, which may have resulted from sample errors. In general, heat treatment was the only significant variable with no differences among results of the triangle tests attributable to stabilizer fraction or concentration, milk composition, or homogenization. Increases in viscosity in centipoises from additions o f the carrageenans at 200 and 300 ppm, respectively, were lambda, 1.2 and 1.8, kappa, 2.3 and 7.0, and iota, 1.0 and 3.3. The most frequent characteristics used to distinguish differences were watery and heated, with few designations of mouthfeel characteristics. Experience in the earlier trials may have attuned the judges to look principally for differences in flavor. However, additions of stabilizers could change flavor more than they Journal of Dairy Science Vol. 59, No. 9
Ox ~o
e~
TABLE 2. Effect o f fat and SNF concentration in nonfat milk on detection of differences by triangle tests. (See footnotes for significance of differences.)
< o
Trial
Variable
Processing conditions Past temp f Homo pressg
Composition Fat SNF
(C)
(N/cm ~)
(%)
Triangle test, correct judgments e
(%)
Day 1
Day 3
Day 9
0 0
9 9
14/45 a 16/45 a
16/45 a 20/45 a
18/45 a 21/45 b
1400 1400
9 9
20/42 b 18/42 a
15/39 a 10/39 a
15/45 a
Fat (%) 8
.1 vs..25 h .1 vs..5
73.8 73.8
9
.1 vs..25 .1 vs.. 5
85 85
SNF (%) 10
9 vs. 10 9 vs. 11
73.8 73.8
0 0
.1 .1
26/42 d 26/42 d
20/45 a 32/45 d
12/36 a 19/36 b
11
9 vs. 10 9 vs. 11
85 85
1400 1400
.1 .1
26/39 d 30/39 d
26/39 d 27/39 d
26/42 d 34/42 d
12
9 vs. 10 9 vs. 11
85 85
1400 1400
.5 .5
22/39 d 21/39 c
25/39 d 28/39 d
17/36 a 24/36 d
a'b'c'dsignificance of differences: a, not significant;b, c, and d, significant at P<.05, .01, and .001, respectively. eNumber correct/total number o f judgments. fHolding time, 18 s. gTwo stage, with one-fourth of total on second stage. hFirst number indicates the reference sample in each pair, compared in triplicate with the other two.
TABLE 3. Effect of additions of stabilizers to n o n f a t milk on detection of differences by triangle tests. (See f o o t n o t e s for significance of differences.)
Processing conditions Trial
Stabilizer
Past t e m p f (C)
13 14 15 16 17 18 19 20 21
lamb d a h kappa kappa iota iota lambda lambda lambda iota
85 85 85 85 85 73.8 73.8 73.8 73.8
Triangle test, correct j u d g m e n t s e
Composition
H o m o pressg ( N / c m 2)
Fat (%)
SNF (%)
0 vs. 200 p p m
0 vs. 300 p p m
1400 0 1400 0 1400 0 1400 0 0
.5 .1 .5 .1 .5 .1 .5 .1 .1
11 11 11 11 11 11 11 9 9
31/45 d 27/42 d 26/45 d 24/36 d 24/42 c 16/45 a 12/42 a 15/42 a 18/45 a
31/45 d 33/42 d 32/45 d 13/36 a 24/4c2 c 18/45 d 19/42 a 12/42 a 32/45 d
t~ z O
O t~
© X 0 Z "i"1
a'b'c'dsignificance o f differences: a, n o t significant ;b, c, and d, significant at P<.05, .01, and .001, respectively. =
e N u m b e r correct/total n u m b e r of judgments. fHolding time, 18 s. gTwo stage, with one-fourth of total on second stage.
ga
hcarrageenan fractions: lambda, Viscarin 402 ; kappa, Gelcarin HMR; and iota, Gelcarin SI. Marine Colloids, Inc., San Ramon, CA.
e~ < o
X o
Ox
1566
LANG ET AL.
TABLE 4. Effect of additions of emulsifiers to nonfat milk on detection of differences by triangle tests. (See footnotes for significance of differences. All samples were pasteurized at 73.8 C for 18 s and homogenized at 1400 N/cm 2 , with one-fourth of the total pressure on the second stage.) Triangle test, correct judgments e
Composition Trial
Emulsifier
Fat (%)
SNF (%)
22 23 24 25 26 27 28 29 30 31 32
Tf D M H D T T T H D M
.1 .1 .1 .1 .1 .1 .5 .5 .5 .5 .5
9 9 9 9 9 11 11 11 11 11 11
0 vs. 400 ppm 25/42 d 30/42 d 30/39 d 23/39 d 22/33 d 27/42 d 18/24 a 14/33 a 13/33 a 16/33 b 11/33 a
a'b'c'dsignificance of differences: a, not significant; b, c, and d, significant at P<.05, .01, and .001, respectively. eNumber correct/total number of judgments. fAbbreviations: T, Tally 100, a mixture of mono- and diglycerides, ethoxylated mono- and diglycerides, and hydrogenated vegetable oils, Glidden-Durkee, Berkeley, CA; D, Durfax 80, polysorbate 80, Glidden-Durkee, Berkeley, CA; M, Myvoplex, glyceryl monostearate, Distillation Products Industries, Rochester, NY; H, Hallmark GMS, glyceryl monostearate, Stein, Hall and Co., Inc., New York, NY.
could m o u t h f e e l . We suggest three possible explanations o f a relation b e t w e e n stabilizer addition and heated flavor. 1) Viscosity may have affected the d e t e c t i o n of flavor (2, 12), possibly by decreasing the intensity of flavor c o m p o n e n t s by the time t h e y reach the receptors. 2) Stabilizers may have stabilized the milk proteins by reacting with them, t h e r e b y reducing the release of sulfhydryl groups which contribute to h e a t e d flavors. 3) A b s o r p t i o n of water by the stabilizers m a y have influenced susceptibility o f the milk to h e a t e d flavor. Emulsifiers
Additions of f o u r emulsifiers at 400 p p m were d e t e c t e d readily in milks containing .1% fat (Table 4, trials 22 to 27) but n o t in milks with .5% fat (trials 28 to 32). Comparison o f trials 22 and 27 indicates that the difference in c o n c e n t r a t i o n of S N F did n o t influence detection o f added emulsifier. The higher fat in trials 28 to 32 prevented the d e t e c t i o n of added emulsifiers. Additions o f 400 p p m of emulsitiers did n o t increase viscosity o f the milks in any of the trials. The p r e d o m i n a n t characteristic used to difJournal of Dairy Science Vol. 59, No. 9
ferentiate the samples was watery with oxidized flavor n e x t in frequency. Heated flavor was n o t used for differentiation, probably because all samples were pasteurized at 73.8 C, the lowest t e m p e r a t u r e in the study, and stored 4 days. The c o m m e n t s o f o x i d i z e d m a y have resulted f r o m either flavor or m o u t h f e e l characteristics of the emulsifiers rather than f r o m o x i d a t i o n o f milk lipids. A C K N O W L EDGM ENT
The study was s u p p o r t e d in part by the Dairy Council of California. The authors gratefully acknowledge the suggestions and assistance of J. c. Bruhn, H. G. Schutz, and R. M. Pangborn, the c o o p e r a t i o n of the sensory panel, and technical assistance o f E. E. Moore, A. A. Franke, E. C. Jensen, and M. Cummings. REFERENCES
1 Amerine, M. A., R. M. Pangborn, and E. B. Roessler. 1965. Principles of sensory evaluation of food. Academic Press, New York. 2 Crocker, E. C. 1945. Flavor. McGraw-Hill Book Co., New York. 3 Deane, D. D., J. A. Chelesvig, and W. R. Thomas. 1967. Pasteurization treatment and consumer ac-
SENSORY PROPERTIES OF N O N F A T MILK ceptance of milk. J. Dairy Sci. 50:1216. 4 Devero, J. E. 1972. Effects of varying non-fat solids and fat on consumer acceptance. United Dairy Ind. Ass., m i m e o review. 5 Dunkley, W. L., and A. A. Franke. 1967. Evaluating susceptibility of milk to oxidized flavor. J.. Dairy Sci. 50:1. 6 Foust, W. L. 1948. Let's see more fat free milk. Milk Dealer 38:44. 7 Holland, B. K., and W. C. Winder. 1951. Preparation o f modified skim milk. Milk Dealer 40:43,
Aug.
8 Jenness, R., and S. Patton. 1959. Flavors and off-flavors in milk and its products. Page 360 in Principles of dairy chemistry. Wiley, NY.
1 567
9 Kelly, E. 1935. Promote the fresh milk business. Milk Plant Mon. 24:44. 10 Miller, D. D., and S. R. Skaggs. 1959. Controlling oxidized flavor with heat-treated milk. J. Dairy Sci. 42:1743. (Abstr.) 11 Pangborn, R. M., a n d W. L. Dunkley. 1964. Sensory discrimination of fat and solids-not-fat in milk. J. Dairy Sci. 47:719. 12 Pangborn, R. M., I. M. Trabue, and A. S. Szczesniak. 1972. Effect of hydrocolloids on oral viscosity and basic taste intensities. J. Texture Stud. 4:224. 13 Parks, O. W. 1974. The lipids o f milk: Deterioration II Autoxidation. Page 240 in Fundamentals o f dairy chemistry. B. H. Webb, A. H. J o h n s o n , a n d J. A. Alford, ed. Avi Publ. Co., Westport, CT.
Journal o f Dairy Science Vol. 59, No. 9