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Volatile Flavor Compounds and Sensory Evaluation of Commercially Available Apple Juices and Freshly Squeezed, Non-Blended Apple Juices
117
CHAPTER
Volatile Flavor Compounds and Sensory Evaluation of Commercially Available Apple Juices and Freshly Squeezed, Non-Blended Apple Juices Andreas Stangl and Herta Ziegler Erich Ziegler GmbH, Aufseβ, Germany
117.1 INTRODUCTION All over the world, fruit juices today are one of the staples of healthy and modern nutrition. In Germany, apple juice has traditionally been the most popular choice of consumers until 2009, when Germans joined the world-wide preference for orange juice. Within the scope of the present work, the focus was on the investigation of the composition of the volatile key aroma constituents of freshly squeezed, non-blended apple juices, as well as commercially available, naturally cloudy NFC-juices (not from concentrate) and clear apple juices from concentrate. Emphasis was on the quantitative analysis of alcohols, esters, and aldehydes as key aroma components. The patterns of apple juice aroma components were investigated using a specially designed gas chromatography (GC)-purge and trap method. Subsequently, all juices were evaluated and compared employing different model systems based on quantitative aroma values and sensory investigation. It was the aim of the present work to examine the correlation between the results of analytical methods and those of sensory evaluation, as it is the latter which determines consumer acceptance and preferences.
117.2 MATERIALS AND METHODS All apple juices were immediately investigated sensorially and analytically, either after opening the package or after pressing. Samples from V. Ferreira and R. Lopez (Eds): Flavour Science. DOI: http://dx.doi.org/10.1016/B978-0-12-398549-1.00117-3
© 2014 Elsevier Inc. All rights reserved.
635
636
Andreas Stangl and Herta Ziegler
N2 (20 mL/min)
Sampling tube containing ½ mL adsorbent (Tenax TA)
Juice matrix (10 mL) containing NaCl (2.0 g) and internal standard (linalool 1 mg/L)
Figure 117.1 Purge and trap device for the non-extractive accumulation of volatile aroma components of diluted aqueous samples.
fresh, non-blended NFC-juices were obtained in batches from five apples of each variety with a commercial juice extractor. The apples used in this study were grown in Germany (Lake Constance – Boskoop, Elstar, Golden Delicious, Jonagold), France (Pink Lady), and Italy (South Tyrol – Granny Smith, Red Delicious). The volatile aroma components were accumulated as shown in Figure 117.1. After addition of the internal standard (linalool, 1 mg/L) and sodium chloride (2.0 g), 10 mL of the respective juice were sampled at a temperature of 24°C to 25°C for 10 min. Subsequently, the loaded sample tubes were transferred to the thermal desorption unit (DANI Master TD). Conditions: desorption tube: 320°C/ 10 min (trap at 5°C); desorption trap: 320°C/20 min; aux. gas: N2 (1.1 bar); column: OV-1701; detection: flame ionization detector (FID).
117.2.1 Quantitative Analysis Assessment and comparison of the apple juices was carried out by employing different model systems, all based on the values of aroma volatiles: The Aroma Index (according to Wolters [1]): 10 relevant aroma constituents (esters, aldehydes, and alcohols) are measured and their standardized contributions (Table 117.1) to the overall aroma value are taken into account. The Total Ester Content [1] corresponds to the sum of all esters (with the exception of ethyl and butyl acetate) present in apple juices. The Simplified Ester Values, frequently used in industry and consumer tests, classifies juices solely on the basis of the analytical values of four predefined esters: ethyl butyrate, ethyl-2-methyl butyrate, 2-methylbutyl acetate, and hexyl acetate. ●
●
●
Volatile Flavor Compounds and Sensory Evaluation of Commercially Available Apple Juices
637
Table 117.1 Compounds N for the Calculation of the Aroma Index [A = Σ Ni [ppm] Fi] and their Normization Factors F Normization Normization No. Substance N Factor F No. Substance N Factor F
1 2 3 4 5
ethyl-2-methyl butyrate ethyl butyrate hexyl acetate 2-methylbutyl acetate hexyl aldehyde
2.000
6
butyl acetate
0.100
0.500 0.333 0.250
7 8 9
trans-2-hexenol 2-methyl-1-butanol trans-2-hexenal
0.050 0.033 0.025
0.100
10
hexanol
0.017
The Total C6-Content [1–3] corresponds to the sum of all C6aldehydes and C6-alcohols in apple juice: hexyl aldehyde, trans-2-hexenyl aldehyde, hexanol, and trans-2-hexenol. Each juice sample was quantitatively investigated thrice by the purge and trap/thermal desorption/GC cycle and the arithmetic average values were determined (see Table 117.2 and Figure 117.2A–D). ●
117.2.2 Qualitative Analysis The sensory assessment of the juice samples was performed by a panel of 10 trained persons. The German school mark system (ranging from 1 = very good to 6 = unsatisfactory) was used as a rating basis. The arithmetic average for each juice was determined and used for further evaluation (see Table 117.2 and Figure 117.2A–D) [4].
117.3 RESULTS A total of 21 apple juices (freshly pressed, non-blended, naturally cloudy juices; commercially available, naturally cloudy NFC-juices; clear juices from concentrate; seven samples each) were subjected to quantitative (Thermal Desorption/GC) and qualitative (sensory assessment) analysis. Figure 117.2 depicts the results of the quantitative analysis and demonstrates that fresh apple juices exhibit significant differences in their variety-specific aroma patterns [e.g. Total Ester Content (from ~200 ppb for Granny Smith to 1700 ppb for Red Delicious)] and in the concentration of the C6-bodies with the highest value for Golden Delicious (Figure 117.2A and B). In contrast, the industrially produced blends from concentrate exhibited aroma index values within a rather narrow range,
638
Andreas Stangl and Herta Ziegler
Table 117.2 Measured Values of the Quantitative Analysis and Results of the Hedonic Scoring of the Juice Samples used in this Study Aroma Total Ester Simplified Sum of C6Index Content Ester Value bodies Hedonic Juice Sample (ppb) (ppb) (ppb) (ppm) Scoring Fresh Juice Samples
Granny Smith Boskoop Elstar Jonagold Pink Lady Golden Delicious Red Delicious
316 317 316 455 424 605 532
217 397 526 853 850 1029 1714
68 155 202 538 363 553 983
3.8 5.2 4.9 4.7 4.9 6.6 3.8
1.9 2.1 1.9 2.6 3.0 3.0 3.4
432 732 763 798 1039 1049 1367
223 439 520 561 716 753 857
4.9 5.9 4.0 5.5 3.9 5.6 5.3
4.5 2.0 3.0 1.9 2.3 2.3 2.1
103 383 371 296 306 430 231
5.9 5.1 4.7 4.8 4.9 4.7 4.1
2.8 1.9 2.3 1.9 2.5 2.8 3.8
Commercial NFC-Juices
A B C D E F G
294 521 484 540 525 679 628
Commercial Juices from Concentrate
H J K L M N O
247 384 411 316 330 404 371
247 822 598 628 593 873 408
all below 400 ppb (Figure 117.2D), clearly indicating a significant loss of nature’s variety. The results of sensory investigation of the juices are summarized in Figure 117.3. In this context, the contrasting behavior of the two types of NFC-apple juices is remarkable to note. While the commercial juices (Figure 117.3C) follow the expectations of improved rating with increasing values of Aroma Index and Total Ester Content, the freshly squeezed juices (Figure 117.3A) behave to the contrary. Juices with higher aroma values received lower sensory assessments. The commercial juices from concentrate (Figure 117.3D) do not show an unambiguous correlation between aroma pattern and sensory investigation. While their Aroma
(B)
C6-Bodies in fresh apple juices of different varieties 7.0
1800
6.0
1400
5.0
1000 800 600 400 200 0
Granny smith
4.0
[ppm]
[ppb]
1200
simplified ester value Ester total Aroma index
1600
3.0 2.0 1.0
C6–Aldehydes
Fresh apple juices of different varieties 2000
C6–Alcohols C6 total
(A)
0.0 Boskoob
Elstar
Granny smith
Red Jonagold Pink Lady Golden delicious delicious
Boskoob
(D)
1000 800 600 400
[ppb]
[ppb]
1200
Simplified ester value Ester total Aroma index
1800 1400
200 0 A
B
C
D Juice sample
Pink Lady
Golden delicious
Red delicious
E
F
G
2000 1800 1600 1400 1200 1000 800 600 400 200 0
Aroma values in commercial apple juices from concentrate
Simplified ester value Ester total Aroma index
Commercial apple NFC-juices
2000 1600
Jonagold
Juice sample
Juice sample
(C)
Elstar
H
J
K
L
M
N
O
Juice sample
Figure 117.2 Quantification of key aroma volatiles of fresh non-blended juices 3A, commercial NFC juices 3C, and apple juice from concentrate 3D (average of three measurements/sample). Simplified Ester Value = ethyl butyrate + ethyl-2-methyl butyrate + 2-methyl butyl acetate + hexyl acetate. Ester Total = sum of all esters with exception of ethyl and butyl acetate.
[ppm]
Fresh apple juices of different varieties 1 = Elstar 2 = Granny smith 3 = Boskoop 4 = Jonagold 5 = Pink lady 6 = Golden Delicious 7 = Red delicious
Ester total and aroma index [ppb]
1600 1400 1200 1000 800 600
7
6 4
5
Ester Total :
1
Aroma index:
400 200 0 1.0
1.5
2.0
6
4
3 3
1,2 2
2.5
7
5
3.0
3.5
4.0
Hedonic scoring (German school marks)
(C)
4.0
2.0
0.0 1.0
6 3
1 2 2
1.5
6 5
4
3
2.0
5
4
1
7 7
2.5
3.0
3.5
4.0
Hedonic scoring (German school marks)
Commercial apple juice from concentrate
and Aroma index [ppb]
1600
1400
1400
G
1200
1200 E:F
1000 D
800 600
D
400
B B
E F
1000
C C
A A
200 1.5
2.0
2.5
3.0
Ester total
and aroma index [ppb] Ester total
1 = Elstar 2 = Granny smith 3 = Boskoop 4 = Jonagold 5 = Pink lady 6 = Golden delicious 7 = Red delicious
6.0
1800
1600
0 1.0
Fresh apple juices of different varieties; C6-bodies
8.0
(D)
Commercial apple NFC-Juices
1800
(B)
and C6-total
1800
C6-Aldehydes
(A)
3.5
4.0
Hedonic scoring (German school marks)
4.5
5.0
600
L
J
400
L
200 0 1.0
N
J
800
1.5
2.0
K M M K 2.5
O O
N II 3.0
3.5
4.0
Hedonic scoring (German school marks)
Figure 117.3 Calculations vs. sensory evaluation of fresh, non-blended apple juices, commercially available NFC juices, and juices from concentrate – a comparison: sensory scoring is based on the German school marks [1 (very good) to 6 (unsatisfactory)].
Volatile Flavor Compounds and Sensory Evaluation of Commercially Available Apple Juices
641
Index values are situated within a rather narrow range (200–400 ppb), sensory scores show broad variation (marks from 1.9 to 3.8). Analogously, a correlation between the content of the fresh, green-character C6-bodies (see Figure 117.3B for the fresh juices) and sensory investigation cannot be established. A summary of some analytical data is given in Table 117.2.
117.4 DISCUSSION AND CONCLUSIONS Quantification studies on volatile aroma compounds of fresh, non-blended apple juices show that aroma patterns differ significantly with apple variety. This diversity of nature is more or less lost in industrially produced juices from blended concentrates (see Figure 117.2A and Figure 117.2D). Although standardized analytical methods constitute reproducible and uncomplicated tools for the cost-effective handling of quality control in the juice processing industry, consumers’ acceptance of apple juices is clearly associated with hedonic scoring. All employed model evaluation systems are only based on measured aroma values and can unfortunately not sufficiently describe nor satisfactorily reproduce sensory perception of such complex natural matrices.
REFERENCES [1] C. Wolter, A. Gessler, P. Winterhalter, Aspects when evaluating apple juice aroma, Fruit Process. 2 (2008) 64–80. [2] M. Heil, V. Ara, Fruchtsaftaromen II; Über die Zusammensetzung und Bewertung von apfelsaftaroma, Flüssiges Obst. 74 (9) (2007) 62–67. [3] M. Hey, P. Kürbel, I. Hopf, H. Dietrich, Untersuchung sortenreiner apfelsaftaromen, Flüssiges Obst. 74 (9) (2007) 444–452. [4] S. Elβ, Dissertation Studies on technologically caused changes in aroma profiles of fruit juices. Universitüt Würzburg, 2007.
CHAPTER
Volatile Flavor Compounds and Sensory Evaluation of Commercially Available Apple Juices and Freshly Squeezed, Non-Blended Apple Juices Andreas Stangl and Herta Ziegler Erich Ziegler GmbH, Aufseβ, Germany
117.1 INTRODUCTION All over the world, fruit juices today are one of the staples of healthy and modern nutrition. In Germany, apple juice has traditionally been the most popular choice of consumers until 2009, when Germans joined the world-wide preference for orange juice. Within the scope of the present work, the focus was on the investigation of the composition of the volatile key aroma constituents of freshly squeezed, non-blended apple juices, as well as commercially available, naturally cloudy NFC-juices (not from concentrate) and clear apple juices from concentrate. Emphasis was on the quantitative analysis of alcohols, esters, and aldehydes as key aroma components. The patterns of apple juice aroma components were investigated using a specially designed gas chromatography (GC)-purge and trap method. Subsequently, all juices were evaluated and compared employing different model systems based on quantitative aroma values and sensory investigation. It was the aim of the present work to examine the correlation between the results of analytical methods and those of sensory evaluation, as it is the latter which determines consumer acceptance and preferences.
117.2 MATERIALS AND METHODS All apple juices were immediately investigated sensorially and analytically, either after opening the package or after pressing. Samples from V. Ferreira and R. Lopez (Eds): Flavour Science. DOI: http://dx.doi.org/10.1016/B978-0-12-398549-1.00117-3
© 2014 Elsevier Inc. All rights reserved.
635
636
Andreas Stangl and Herta Ziegler
N2 (20 mL/min)
Sampling tube containing ½ mL adsorbent (Tenax TA)
Juice matrix (10 mL) containing NaCl (2.0 g) and internal standard (linalool 1 mg/L)
Figure 117.1 Purge and trap device for the non-extractive accumulation of volatile aroma components of diluted aqueous samples.
fresh, non-blended NFC-juices were obtained in batches from five apples of each variety with a commercial juice extractor. The apples used in this study were grown in Germany (Lake Constance – Boskoop, Elstar, Golden Delicious, Jonagold), France (Pink Lady), and Italy (South Tyrol – Granny Smith, Red Delicious). The volatile aroma components were accumulated as shown in Figure 117.1. After addition of the internal standard (linalool, 1 mg/L) and sodium chloride (2.0 g), 10 mL of the respective juice were sampled at a temperature of 24°C to 25°C for 10 min. Subsequently, the loaded sample tubes were transferred to the thermal desorption unit (DANI Master TD). Conditions: desorption tube: 320°C/ 10 min (trap at 5°C); desorption trap: 320°C/20 min; aux. gas: N2 (1.1 bar); column: OV-1701; detection: flame ionization detector (FID).
117.2.1 Quantitative Analysis Assessment and comparison of the apple juices was carried out by employing different model systems, all based on the values of aroma volatiles: The Aroma Index (according to Wolters [1]): 10 relevant aroma constituents (esters, aldehydes, and alcohols) are measured and their standardized contributions (Table 117.1) to the overall aroma value are taken into account. The Total Ester Content [1] corresponds to the sum of all esters (with the exception of ethyl and butyl acetate) present in apple juices. The Simplified Ester Values, frequently used in industry and consumer tests, classifies juices solely on the basis of the analytical values of four predefined esters: ethyl butyrate, ethyl-2-methyl butyrate, 2-methylbutyl acetate, and hexyl acetate. ●
●
●
Volatile Flavor Compounds and Sensory Evaluation of Commercially Available Apple Juices
637
Table 117.1 Compounds N for the Calculation of the Aroma Index [A = Σ Ni [ppm] Fi] and their Normization Factors F Normization Normization No. Substance N Factor F No. Substance N Factor F
1 2 3 4 5
ethyl-2-methyl butyrate ethyl butyrate hexyl acetate 2-methylbutyl acetate hexyl aldehyde
2.000
6
butyl acetate
0.100
0.500 0.333 0.250
7 8 9
trans-2-hexenol 2-methyl-1-butanol trans-2-hexenal
0.050 0.033 0.025
0.100
10
hexanol
0.017
The Total C6-Content [1–3] corresponds to the sum of all C6aldehydes and C6-alcohols in apple juice: hexyl aldehyde, trans-2-hexenyl aldehyde, hexanol, and trans-2-hexenol. Each juice sample was quantitatively investigated thrice by the purge and trap/thermal desorption/GC cycle and the arithmetic average values were determined (see Table 117.2 and Figure 117.2A–D). ●
117.2.2 Qualitative Analysis The sensory assessment of the juice samples was performed by a panel of 10 trained persons. The German school mark system (ranging from 1 = very good to 6 = unsatisfactory) was used as a rating basis. The arithmetic average for each juice was determined and used for further evaluation (see Table 117.2 and Figure 117.2A–D) [4].
117.3 RESULTS A total of 21 apple juices (freshly pressed, non-blended, naturally cloudy juices; commercially available, naturally cloudy NFC-juices; clear juices from concentrate; seven samples each) were subjected to quantitative (Thermal Desorption/GC) and qualitative (sensory assessment) analysis. Figure 117.2 depicts the results of the quantitative analysis and demonstrates that fresh apple juices exhibit significant differences in their variety-specific aroma patterns [e.g. Total Ester Content (from ~200 ppb for Granny Smith to 1700 ppb for Red Delicious)] and in the concentration of the C6-bodies with the highest value for Golden Delicious (Figure 117.2A and B). In contrast, the industrially produced blends from concentrate exhibited aroma index values within a rather narrow range,
638
Andreas Stangl and Herta Ziegler
Table 117.2 Measured Values of the Quantitative Analysis and Results of the Hedonic Scoring of the Juice Samples used in this Study Aroma Total Ester Simplified Sum of C6Index Content Ester Value bodies Hedonic Juice Sample (ppb) (ppb) (ppb) (ppm) Scoring Fresh Juice Samples
Granny Smith Boskoop Elstar Jonagold Pink Lady Golden Delicious Red Delicious
316 317 316 455 424 605 532
217 397 526 853 850 1029 1714
68 155 202 538 363 553 983
3.8 5.2 4.9 4.7 4.9 6.6 3.8
1.9 2.1 1.9 2.6 3.0 3.0 3.4
432 732 763 798 1039 1049 1367
223 439 520 561 716 753 857
4.9 5.9 4.0 5.5 3.9 5.6 5.3
4.5 2.0 3.0 1.9 2.3 2.3 2.1
103 383 371 296 306 430 231
5.9 5.1 4.7 4.8 4.9 4.7 4.1
2.8 1.9 2.3 1.9 2.5 2.8 3.8
Commercial NFC-Juices
A B C D E F G
294 521 484 540 525 679 628
Commercial Juices from Concentrate
H J K L M N O
247 384 411 316 330 404 371
247 822 598 628 593 873 408
all below 400 ppb (Figure 117.2D), clearly indicating a significant loss of nature’s variety. The results of sensory investigation of the juices are summarized in Figure 117.3. In this context, the contrasting behavior of the two types of NFC-apple juices is remarkable to note. While the commercial juices (Figure 117.3C) follow the expectations of improved rating with increasing values of Aroma Index and Total Ester Content, the freshly squeezed juices (Figure 117.3A) behave to the contrary. Juices with higher aroma values received lower sensory assessments. The commercial juices from concentrate (Figure 117.3D) do not show an unambiguous correlation between aroma pattern and sensory investigation. While their Aroma
(B)
C6-Bodies in fresh apple juices of different varieties 7.0
1800
6.0
1400
5.0
1000 800 600 400 200 0
Granny smith
4.0
[ppm]
[ppb]
1200
simplified ester value Ester total Aroma index
1600
3.0 2.0 1.0
C6–Aldehydes
Fresh apple juices of different varieties 2000
C6–Alcohols C6 total
(A)
0.0 Boskoob
Elstar
Granny smith
Red Jonagold Pink Lady Golden delicious delicious
Boskoob
(D)
1000 800 600 400
[ppb]
[ppb]
1200
Simplified ester value Ester total Aroma index
1800 1400
200 0 A
B
C
D Juice sample
Pink Lady
Golden delicious
Red delicious
E
F
G
2000 1800 1600 1400 1200 1000 800 600 400 200 0
Aroma values in commercial apple juices from concentrate
Simplified ester value Ester total Aroma index
Commercial apple NFC-juices
2000 1600
Jonagold
Juice sample
Juice sample
(C)
Elstar
H
J
K
L
M
N
O
Juice sample
Figure 117.2 Quantification of key aroma volatiles of fresh non-blended juices 3A, commercial NFC juices 3C, and apple juice from concentrate 3D (average of three measurements/sample). Simplified Ester Value = ethyl butyrate + ethyl-2-methyl butyrate + 2-methyl butyl acetate + hexyl acetate. Ester Total = sum of all esters with exception of ethyl and butyl acetate.
[ppm]
Fresh apple juices of different varieties 1 = Elstar 2 = Granny smith 3 = Boskoop 4 = Jonagold 5 = Pink lady 6 = Golden Delicious 7 = Red delicious
Ester total and aroma index [ppb]
1600 1400 1200 1000 800 600
7
6 4
5
Ester Total :
1
Aroma index:
400 200 0 1.0
1.5
2.0
6
4
3 3
1,2 2
2.5
7
5
3.0
3.5
4.0
Hedonic scoring (German school marks)
(C)
4.0
2.0
0.0 1.0
6 3
1 2 2
1.5
6 5
4
3
2.0
5
4
1
7 7
2.5
3.0
3.5
4.0
Hedonic scoring (German school marks)
Commercial apple juice from concentrate
and Aroma index [ppb]
1600
1400
1400
G
1200
1200 E:F
1000 D
800 600
D
400
B B
E F
1000
C C
A A
200 1.5
2.0
2.5
3.0
Ester total
and aroma index [ppb] Ester total
1 = Elstar 2 = Granny smith 3 = Boskoop 4 = Jonagold 5 = Pink lady 6 = Golden delicious 7 = Red delicious
6.0
1800
1600
0 1.0
Fresh apple juices of different varieties; C6-bodies
8.0
(D)
Commercial apple NFC-Juices
1800
(B)
and C6-total
1800
C6-Aldehydes
(A)
3.5
4.0
Hedonic scoring (German school marks)
4.5
5.0
600
L
J
400
L
200 0 1.0
N
J
800
1.5
2.0
K M M K 2.5
O O
N II 3.0
3.5
4.0
Hedonic scoring (German school marks)
Figure 117.3 Calculations vs. sensory evaluation of fresh, non-blended apple juices, commercially available NFC juices, and juices from concentrate – a comparison: sensory scoring is based on the German school marks [1 (very good) to 6 (unsatisfactory)].
Volatile Flavor Compounds and Sensory Evaluation of Commercially Available Apple Juices
641
Index values are situated within a rather narrow range (200–400 ppb), sensory scores show broad variation (marks from 1.9 to 3.8). Analogously, a correlation between the content of the fresh, green-character C6-bodies (see Figure 117.3B for the fresh juices) and sensory investigation cannot be established. A summary of some analytical data is given in Table 117.2.
117.4 DISCUSSION AND CONCLUSIONS Quantification studies on volatile aroma compounds of fresh, non-blended apple juices show that aroma patterns differ significantly with apple variety. This diversity of nature is more or less lost in industrially produced juices from blended concentrates (see Figure 117.2A and Figure 117.2D). Although standardized analytical methods constitute reproducible and uncomplicated tools for the cost-effective handling of quality control in the juice processing industry, consumers’ acceptance of apple juices is clearly associated with hedonic scoring. All employed model evaluation systems are only based on measured aroma values and can unfortunately not sufficiently describe nor satisfactorily reproduce sensory perception of such complex natural matrices.
REFERENCES [1] C. Wolter, A. Gessler, P. Winterhalter, Aspects when evaluating apple juice aroma, Fruit Process. 2 (2008) 64–80. [2] M. Heil, V. Ara, Fruchtsaftaromen II; Über die Zusammensetzung und Bewertung von apfelsaftaroma, Flüssiges Obst. 74 (9) (2007) 62–67. [3] M. Hey, P. Kürbel, I. Hopf, H. Dietrich, Untersuchung sortenreiner apfelsaftaromen, Flüssiges Obst. 74 (9) (2007) 444–452. [4] S. Elβ, Dissertation Studies on technologically caused changes in aroma profiles of fruit juices. Universitüt Würzburg, 2007.