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Flavour release at the interfaces of stirred fruit yoghurt models
W.L.P. Bredie and M.A. Petersen (Editors) Flavour Science: Recent Advances and Trends 9 2006 Elsevier B.V. All rights reserved.
453
Flavour release at the interfaces of stirred fruit yoghurt models Alice Nongonierma a, Philippe Cayot a, Mark Springett b, Jean-Luc Le Qu~r~ ~ and Andr~e Voilley a
~Laboratoire IMSAPS, ENSBANA, UniversitO de Bourgogne, 1, Esplanade Erasme, 21000, Dijon, France," bDanone Vitapole, Centre de Recherche Daniel Carasso, R.D. 128, 91767, Palaiseau, France," ~UMR FLA VIC ENESAD-INRA, 17, rue Sully, 21065, Dijon, Cedex, France
ABSTRACT Model matrices consisting of a pectin and a dairy gel were investigated to study the transfer of flavour compounds between the different phases of stirred fruit yoghurt. Using a full factorial experimental design, different parameters (storage temperature, initial flavour concentration in the pectin gel and fat content of the dairy gel) were studied. The kinetics of the migration of flavour compounds between the two gels were investigated using a novel SPME method, where a Carboxen/Polydimethylsiloxane fibre was directly inserted into the pectin gel. Flavour compounds were predominantly retained in the pectin gel and thus, the presence of fat in the dairy gel did not affect their transfer. This retention depended on the hydrophobicity of the flavour compounds and the storage temperature, which modified the matrix structure and consequently the interactions between aroma compounds and matrix. 1. I N T R O D U C T I O N Stirred fruit yoghurt is a multiphase product made of fruit pieces (8% w/w) and a mix of stirred yoghurt (80% w/w) and syrup (12% w/w). In such a food, the concentration gradients are responsible for transfer of small ligands between the different phases [ 1, 2]. The aim of this research was to study the different parameters which might control these transfers and to better understand the mechanisms involved.
454 2. MATERIALS AND M E T H O D S
2.1. Flavour compounds A mix of 8 strawberry key flavour compounds (ethyl acetate, ethyl butanoate, ethyl isobutanoate, ethyl hexanoate, hexanal, 2-methylbutanoic acid, linalool and (Z)-3hexen-l-ol) was used. These compounds (purity > 98%) were obtained from SigmaAldrich (Steinheim, Germany) except for ethyl acetate, from Prolabo (Paris, France). Their logP (logarithm of the n-octanol/water partition coefficient) was estimated by the Hansch and Leo method [3]. 2.2. Fruit yoghurt model The dairy gels (0, 1.5 and 5% fat) consisted of stirred acidified (pH 4.4) milk gels [1]. They were made of 85.4%(w/w) water (Volvic, Danone, France), 14.5%(w/w) skimmed milk powder (Ingredia, Arras, France), 2.2%(w/w) glucono-~i-lactone (Prolabo, Paris, France) and 0.1%(w/w) potassium sorbate (Aldrich, Steinheim, Germany). The fat consisted of a mix of tributyrin (Prolabo, Paris, France) and triolein (Prolabo, Paris, France) in the ratio 2:5. The dairy gels were mixed with a syrup [1] in the proportion 1:9 syrup:dairy gel (w/w). The fruit model [2] was a pectin gel made of 57% (w/w) water (Volvic, Danone, France), 40% (w/w) sucrose (Sucre Union, Paris, France), 2% (w/w) low amidated pectin (Grindsted TM pectin LA 110, Danisco, France), 0.2% (w/w) citric acid (Prolabo, Paris, France), 0.1%(w/w) potassium sorbate (Aldrich, Steinheim, Germany) and 0.09% (w/w) calcium chloride (Prolabo, Paris, France). 2.3. Flavour transfer at the pectin/dairy gel interface Flavour transfers were studied with an experimental design (2 s) whose variables were the storage temperature (4 and 10 ~ the.[ht content of the dairy gel (0 and 5%) and the.flavour concentration in the pectin gel (10 and 20 ppm for each compound). The central point conditions were: 7 ~ 1.5% fat, and 15 ppm added flavour. A 50 g flavoured pectin gel and a 50 g dairy gel were placed in a cylindrical flask of 9.6 cm 2 x 10 cm, resulting in a bilayer sample. The flavour compounds were extracted by direct immersion of a 75 pm Carboxen/Polydimethylsiloxane fibre (Supelco, Bellefonte, PA, USA) in the pectin gel 5 mm below the interface for 30 min (at 0, 2, 5, 8, 24, 30, 48, 72, 96, 144, 192, 504 and 672 h storage). The details of the analysis are given in [1]. After sampling, the fibre was immersed in water, dried on a paper filter, then desorbed 5 rain at 250 ~ and subsequently cleaned (300 ~ 45 rain). Flavour compounds were analysed with a gas chromatograph CP 3800 (Varian, Walnut Creek, USA) equipped with an HP FFAP capillary column (30 mx 0,32 mmx 0,25 pm, Agilent Technologies, Karlsruhe, Deutschland). The oven temperature was: 50 ~ for 4 min, increase by 5 ~ to 180 ~ hold for 17 min. The temperature of the injector (splitless) and the FID were 250 and 200 ~ respectively. Helium was used as a carrier gas at a velocity of 42.8 cm/s at 40 ~
455 3. RESULTS AND DISCUSSION 3.1. Influence of t e m p e r a t u r e , concentration, fat content and logP on transfer
The initial rate of release (R0 and the concentration of flavour compounds in the pectin gel at equilibrium (Cpg ~:) were correlated to the experimental design variables and the logP of the flavour compounds. The significance of these variables was evaluated by means of ANOVA (Table 1). For Ri, the significant variables were the flavour concentration and the temperature. These results are in agreement with the fact that flavour compound retention in the pectin gel is higher at 10 than at 4 ~ Furthermore, this temperature decrease affects the pectin gel structure, which might result in an expulsion of water and flavour compounds [1,2]. An increase in the flavour concentration gradient increased Ri. The logP and the dairy gel fat content did not influence Ri. This is consistent with the results of Harisson et al. [4], who demonstrated that the rate of release was proportional to the flavour concentration, and the mass transfer coefficient at short times. Table 1. Effect of the storage temperature, flavour concentration, fat content and logP upon the initial rate of release (Ri) and the concentration of flavour compounds in the pectin gel at equilibrium (Cpg~). i i
ii
Storage temperature
Flavour concentration
Ri
***
***
Cpg ~
9
9 9
9
Dairy gel fat content
logP
n.s. n.s.
n.s. ***
n.s.: not significant (p>0.05), ***significant at p<0.001. The temperature, logP and flavour concentration affected Cpg~. At equilibrium, the release is governed by flavour partitioning, which is affected by the physicochemical properties of the compounds (e.g. logP) and extrinsic parameters (e.g. the temperature) [4,5]. The effect of logP and temperature suggests that hydrophobic interactions [6] together with entrapment within the pectin gel structure modify flavour transfer [7,8]. 3.2. M o d e l l i n g flavour transfer at the pectin/dairy gel interface
The Ri and Cpg~ were correlated with the significant variables (equations 1 and 2), except for ethyl butanoate which has an intermediate hydrophobicity (logP=l.75) and was therefore chosen to validate the models. R.1 = 0.055 - 0.008* 0 + 0.006* [C]
(1)
C ~ =-6.8 + 0.6* 0 + 0.6" [(2]+ 1.8*logP
(2)
Pg
Where e is the temperature (~ [C] the flavour compound concentration (ppm) and logP, the logarithm of the n-octanol/water partition coefficient.
456 The correlation between the predicted and experimental values is illustrated on Figure 1. The slopes of the curves, lower than 1, indicated that the models slightly underestimated the experimental values (by 2% for Ri and 8% for Cpg~). This is nevertheless below the coefficient of variation of the method (11.2%). The R 2 values show that the parameters studied are not sufficient to predict Ri and C~pg. Other parameters such as the gel structure and the retention of flavour compounds in the matrices might influence flavour transfers. (b) 20
(a) 0.20
A
13
E 15
0.15
e,J
13 j /
D. 0 . 1 0
e,J v e~
r~
x
0.05
re
0.00
.~_l
J
y = 0.98x R2 = 0 .7 4
~1o k j
5
j
{ ~ - y = 0.92x R2 = 0.78
0
0.00
0.05
0.10
0.15
Ri_ pred (ppm.h 1/2)
0.20
0
5
10
15
C=pg_pred (ppm)
Figure 1. Relationship (a) between the predicted (Ri_pred) and experimental (Ri_exp) initial rates of release and (b) between the predicted (C~pg_pred) and experimental (C~pg_exp) concentrations of ethyl butanoate remaining in the pectin gel at equilibrium. R is significant for p=0.005. 4. C O N C L U S I O N The flavour compound concentration, the storage temperature and the logP greatly affected flavour transfer between the pectin and dairy gels. Flavour compound migration was governed by the pectin gel, which retained flavour compounds owing to hydrophobic interactions and entrapment within the gel structure. Future studies should investigate the impact of flavour transfer upon the perception of stirred fruit yoghurts, together with the influence of the fruit preparation formulation (fruit variety, flavour compounds). References
1. A. Nongonierma, P. Cayot, T. Saint-Denis, M. Springett, J.-L. Le Qu6r6 and A. Voilley, J. Chromatogr. A, submitted. 2. A. Nongonierma, P. Cayot, R. Cachon, M. Springett, J.-L. Le Qu6r6 and A. Voilley, Food Hydrocolloid., submitted. 3. C. Hansch and A.J. Leo, Substituent constants for correlation analysis in chemistry and biology, New York, USA (1979). 4. M. Harrison, B.P. Hills, J. Bakker and T. Clothier, J. Food Sci., 62 (4) (1997) 664. 5. M. Marin, I. Back and A.J. Taylor, J. Agric. Food Chem., 47 (11) (1999) 4750. 6. A. Hansson, J. Andersson and A. Leufv6n, Food Chem., 72 (3) (2001) 363. 7. E. Bylaite, A.S. Meyer and J. Adler-Nissen, J. Agric. Food Chem., 51 (27) (2003) 8020. 8. B. Rega, E. Guichard and A. Voilley, Sci. Aliment., 22 (3) (2002) 235.
453
Flavour release at the interfaces of stirred fruit yoghurt models Alice Nongonierma a, Philippe Cayot a, Mark Springett b, Jean-Luc Le Qu~r~ ~ and Andr~e Voilley a
~Laboratoire IMSAPS, ENSBANA, UniversitO de Bourgogne, 1, Esplanade Erasme, 21000, Dijon, France," bDanone Vitapole, Centre de Recherche Daniel Carasso, R.D. 128, 91767, Palaiseau, France," ~UMR FLA VIC ENESAD-INRA, 17, rue Sully, 21065, Dijon, Cedex, France
ABSTRACT Model matrices consisting of a pectin and a dairy gel were investigated to study the transfer of flavour compounds between the different phases of stirred fruit yoghurt. Using a full factorial experimental design, different parameters (storage temperature, initial flavour concentration in the pectin gel and fat content of the dairy gel) were studied. The kinetics of the migration of flavour compounds between the two gels were investigated using a novel SPME method, where a Carboxen/Polydimethylsiloxane fibre was directly inserted into the pectin gel. Flavour compounds were predominantly retained in the pectin gel and thus, the presence of fat in the dairy gel did not affect their transfer. This retention depended on the hydrophobicity of the flavour compounds and the storage temperature, which modified the matrix structure and consequently the interactions between aroma compounds and matrix. 1. I N T R O D U C T I O N Stirred fruit yoghurt is a multiphase product made of fruit pieces (8% w/w) and a mix of stirred yoghurt (80% w/w) and syrup (12% w/w). In such a food, the concentration gradients are responsible for transfer of small ligands between the different phases [ 1, 2]. The aim of this research was to study the different parameters which might control these transfers and to better understand the mechanisms involved.
454 2. MATERIALS AND M E T H O D S
2.1. Flavour compounds A mix of 8 strawberry key flavour compounds (ethyl acetate, ethyl butanoate, ethyl isobutanoate, ethyl hexanoate, hexanal, 2-methylbutanoic acid, linalool and (Z)-3hexen-l-ol) was used. These compounds (purity > 98%) were obtained from SigmaAldrich (Steinheim, Germany) except for ethyl acetate, from Prolabo (Paris, France). Their logP (logarithm of the n-octanol/water partition coefficient) was estimated by the Hansch and Leo method [3]. 2.2. Fruit yoghurt model The dairy gels (0, 1.5 and 5% fat) consisted of stirred acidified (pH 4.4) milk gels [1]. They were made of 85.4%(w/w) water (Volvic, Danone, France), 14.5%(w/w) skimmed milk powder (Ingredia, Arras, France), 2.2%(w/w) glucono-~i-lactone (Prolabo, Paris, France) and 0.1%(w/w) potassium sorbate (Aldrich, Steinheim, Germany). The fat consisted of a mix of tributyrin (Prolabo, Paris, France) and triolein (Prolabo, Paris, France) in the ratio 2:5. The dairy gels were mixed with a syrup [1] in the proportion 1:9 syrup:dairy gel (w/w). The fruit model [2] was a pectin gel made of 57% (w/w) water (Volvic, Danone, France), 40% (w/w) sucrose (Sucre Union, Paris, France), 2% (w/w) low amidated pectin (Grindsted TM pectin LA 110, Danisco, France), 0.2% (w/w) citric acid (Prolabo, Paris, France), 0.1%(w/w) potassium sorbate (Aldrich, Steinheim, Germany) and 0.09% (w/w) calcium chloride (Prolabo, Paris, France). 2.3. Flavour transfer at the pectin/dairy gel interface Flavour transfers were studied with an experimental design (2 s) whose variables were the storage temperature (4 and 10 ~ the.[ht content of the dairy gel (0 and 5%) and the.flavour concentration in the pectin gel (10 and 20 ppm for each compound). The central point conditions were: 7 ~ 1.5% fat, and 15 ppm added flavour. A 50 g flavoured pectin gel and a 50 g dairy gel were placed in a cylindrical flask of 9.6 cm 2 x 10 cm, resulting in a bilayer sample. The flavour compounds were extracted by direct immersion of a 75 pm Carboxen/Polydimethylsiloxane fibre (Supelco, Bellefonte, PA, USA) in the pectin gel 5 mm below the interface for 30 min (at 0, 2, 5, 8, 24, 30, 48, 72, 96, 144, 192, 504 and 672 h storage). The details of the analysis are given in [1]. After sampling, the fibre was immersed in water, dried on a paper filter, then desorbed 5 rain at 250 ~ and subsequently cleaned (300 ~ 45 rain). Flavour compounds were analysed with a gas chromatograph CP 3800 (Varian, Walnut Creek, USA) equipped with an HP FFAP capillary column (30 mx 0,32 mmx 0,25 pm, Agilent Technologies, Karlsruhe, Deutschland). The oven temperature was: 50 ~ for 4 min, increase by 5 ~ to 180 ~ hold for 17 min. The temperature of the injector (splitless) and the FID were 250 and 200 ~ respectively. Helium was used as a carrier gas at a velocity of 42.8 cm/s at 40 ~
455 3. RESULTS AND DISCUSSION 3.1. Influence of t e m p e r a t u r e , concentration, fat content and logP on transfer
The initial rate of release (R0 and the concentration of flavour compounds in the pectin gel at equilibrium (Cpg ~:) were correlated to the experimental design variables and the logP of the flavour compounds. The significance of these variables was evaluated by means of ANOVA (Table 1). For Ri, the significant variables were the flavour concentration and the temperature. These results are in agreement with the fact that flavour compound retention in the pectin gel is higher at 10 than at 4 ~ Furthermore, this temperature decrease affects the pectin gel structure, which might result in an expulsion of water and flavour compounds [1,2]. An increase in the flavour concentration gradient increased Ri. The logP and the dairy gel fat content did not influence Ri. This is consistent with the results of Harisson et al. [4], who demonstrated that the rate of release was proportional to the flavour concentration, and the mass transfer coefficient at short times. Table 1. Effect of the storage temperature, flavour concentration, fat content and logP upon the initial rate of release (Ri) and the concentration of flavour compounds in the pectin gel at equilibrium (Cpg~). i i
ii
Storage temperature
Flavour concentration
Ri
***
***
Cpg ~
9
9 9
9
Dairy gel fat content
logP
n.s. n.s.
n.s. ***
n.s.: not significant (p>0.05), ***significant at p<0.001. The temperature, logP and flavour concentration affected Cpg~. At equilibrium, the release is governed by flavour partitioning, which is affected by the physicochemical properties of the compounds (e.g. logP) and extrinsic parameters (e.g. the temperature) [4,5]. The effect of logP and temperature suggests that hydrophobic interactions [6] together with entrapment within the pectin gel structure modify flavour transfer [7,8]. 3.2. M o d e l l i n g flavour transfer at the pectin/dairy gel interface
The Ri and Cpg~ were correlated with the significant variables (equations 1 and 2), except for ethyl butanoate which has an intermediate hydrophobicity (logP=l.75) and was therefore chosen to validate the models. R.1 = 0.055 - 0.008* 0 + 0.006* [C]
(1)
C ~ =-6.8 + 0.6* 0 + 0.6" [(2]+ 1.8*logP
(2)
Pg
Where e is the temperature (~ [C] the flavour compound concentration (ppm) and logP, the logarithm of the n-octanol/water partition coefficient.
456 The correlation between the predicted and experimental values is illustrated on Figure 1. The slopes of the curves, lower than 1, indicated that the models slightly underestimated the experimental values (by 2% for Ri and 8% for Cpg~). This is nevertheless below the coefficient of variation of the method (11.2%). The R 2 values show that the parameters studied are not sufficient to predict Ri and C~pg. Other parameters such as the gel structure and the retention of flavour compounds in the matrices might influence flavour transfers. (b) 20
(a) 0.20
A
13
E 15
0.15
e,J
13 j /
D. 0 . 1 0
e,J v e~
r~
x
0.05
re
0.00
.~_l
J
y = 0.98x R2 = 0 .7 4
~1o k j
5
j
{ ~ - y = 0.92x R2 = 0.78
0
0.00
0.05
0.10
0.15
Ri_ pred (ppm.h 1/2)
0.20
0
5
10
15
C=pg_pred (ppm)
Figure 1. Relationship (a) between the predicted (Ri_pred) and experimental (Ri_exp) initial rates of release and (b) between the predicted (C~pg_pred) and experimental (C~pg_exp) concentrations of ethyl butanoate remaining in the pectin gel at equilibrium. R is significant for p=0.005. 4. C O N C L U S I O N The flavour compound concentration, the storage temperature and the logP greatly affected flavour transfer between the pectin and dairy gels. Flavour compound migration was governed by the pectin gel, which retained flavour compounds owing to hydrophobic interactions and entrapment within the gel structure. Future studies should investigate the impact of flavour transfer upon the perception of stirred fruit yoghurts, together with the influence of the fruit preparation formulation (fruit variety, flavour compounds). References
1. A. Nongonierma, P. Cayot, T. Saint-Denis, M. Springett, J.-L. Le Qu6r6 and A. Voilley, J. Chromatogr. A, submitted. 2. A. Nongonierma, P. Cayot, R. Cachon, M. Springett, J.-L. Le Qu6r6 and A. Voilley, Food Hydrocolloid., submitted. 3. C. Hansch and A.J. Leo, Substituent constants for correlation analysis in chemistry and biology, New York, USA (1979). 4. M. Harrison, B.P. Hills, J. Bakker and T. Clothier, J. Food Sci., 62 (4) (1997) 664. 5. M. Marin, I. Back and A.J. Taylor, J. Agric. Food Chem., 47 (11) (1999) 4750. 6. A. Hansson, J. Andersson and A. Leufv6n, Food Chem., 72 (3) (2001) 363. 7. E. Bylaite, A.S. Meyer and J. Adler-Nissen, J. Agric. Food Chem., 51 (27) (2003) 8020. 8. B. Rega, E. Guichard and A. Voilley, Sci. Aliment., 22 (3) (2002) 235.