Oil Migration in Chocolate

Oil Migration in a Chocolate Confectionery System Evaluated by Magnetic Resonance ImagingYOUNG J. CHOI, KATHR YN L. MC C AR THY, AND MICHAEL J. MC C AR THY THRYN ARTHY ARTHY ABSTRA CT : O il migr ation is a common pr oblem in composite chocolate confectioner y pr oducts r esulting in ABSTRACT CT: Oil migration problem confectionery products resulting softening of chocolate and hardening of the filling. Spatial and temporal changes in the liquid oil content of a 2layer peanut butter and chocolate model system were evaluated using a magnetic resonance imaging (MRI) technique. The experimental factors were chocolate particle size, milk fat content, emulsifier concentration, , and stor age temper atur e. The r degr ee of temper esponses w er e migr ation r ate and o ver all change in signal temperatur ature responses degree temper, storage wer ere migration rate ov erall intensity (amount of migr ation). B ased on analysis of v ar iance (ANO VA), par ticle siz e, milk fat content, and migration). Based var ariance (ANOV particle size storage temperature were significant factors for oil migration rates. Milk fat content and temperature were significant factors for o all change in signal intensity . ov erall intensity. v er Keywor ds: chocolate , peanut butter , confectioner y, oil migr ation, magnetic r esonance imaging eywords: chocolate, butter, confectionery migration, resonance E: Food Engineering & Physical Properties Introduction O il migration occurs in chocolate confectionery products that contain 2 or more oil-containing components adjacent to one another (Wootton and others 1971; Wacquez 1975; Talbot 1990; Couzens and Wille 1997; Ziegleder 1997). Typical examples are composite chocolate products in which chocolate enrobes a fat-containing center (for example, nut pastes, peanut butter, truffles). Different oil species migrate at varying rates and to different extents during storage depending on physical and chemical properties. The migration of the liquid lipid into the chocolate layer results in unwanted changes such as softening of the chocolate coating, hardening of the filling, and recrystallization of oil, which eventually leads to fat bloom (Talbot 1995; Ziegleder 1997; Lonchampt and Hartel 2004). Oil migration also changes sensory properties, such as color and flavor (Ali and others 2001). A number of contributing factors have been reported in the literature. Temperature is a strong contributing factor; the rate of fat migration increases as temperature increases. Ali and others (2001) modeled the migration rate of oil from a desiccated coconut and palm mid-fraction blend through dark chocolate as a linear dependence, with the rate increasing as the temperature increased from 18 °C to 30 °C. These researchers used nuclear magnetic resonance (NMR) to evaluate the solid fat content in the system over time as a function of temperature, as did Couzens and Wille (1997) and Talbot (1990). Magnetic resonance imaging (MRI), in contrast, provides both spatial and temporal information and has been used in studies to differentiate between components (Duce and other 1990; McCarthy 1994; Couzens and Wille 1997) and to monitor crystallization as lipid samples cooled (Simoneau and others 1992). The same samples can be followed over time because the MRI technique is nondestructive. Guiheneuf and others (1997) documented migration profiles at 19 °C and 28 °C in a model system of hazel nut MS 20040759 Submitted 11/20/04, Revised 2/5/05, Accepted 3/2/05. The authors are with Dept. of Food Science and Technology, One Shields Ave, Univ. of California, Davis, Davis, CA 95616. Direct inquiries to author K.L. McCarthy (E-mail: [email protected]). oil and dark chocolate. The researchers suggested that the mechanism of migration involves both diffusion of the liquid triacylglycerols and capillary attraction of the oil into the chocolate matrix. Degree of temper was added as a contributing factor to oil migration in a follow-up study by Miquel and others (2001) using dark chocolate and hazelnut oil. Oil concentration from MRI data was plotted against the square root of time; rates were characterized by the slope of the line. This approach is consistent with diffusion of a component in a semi-infinite media (Crank 1975) and was also used by Ziegleder (1997). Although good temper provides the best resistance to fat migration (Bolliger and others 1998), the tempering regime was reported to have no effect on the speed of the migration (Miquel and others 2001). However, the degree of temper was not stated quantitatively for the low-temper and high-temper samples. The researchers did report a different saturation concentration in the under-tempered and well-tempered chocolate that was hypothesized to be due to structural differences. In the process of oil migration, 2 phenomena have been identified: migration due to diffusion and/or capillary action and phase behavior (Aguilera and others 2004; Ziegler and others 2004). The focus of the work by Ziegler and others (2004) was to discuss the changes in equilibrium between solid and liquid phases during oil migration that alter the fat phase structure. Implicit, however, is that anything that decreases the solid fat content will increase the migration rate, including formulation. Lower solid fat content (SFC) products are softer and more prone to migration. The interaction between cocoa butter and milk fat is particularly important in defining the characteristics of milk chocolate. Bigalli (1988) stated that high levels of milk fat (for example, 20%) promote softening. The dominant factor is due to the liquid fraction of milk fat, which behaves almost as a straight dilution effect, similar to liquid nut oils such as peanut oil. Cocoa butter is simply diluted by these liquid oils rather than forming eutectics (Lonchampt and Hartel 2004). As part of a larger study, Walter and Cornillon (2002) evaluated oil migration in a model confectionery system of a layer of peanut butter over a layer of dark chocolate in an NMR tube. After 1 d, the NMR signal from the chocolate region had higher signal intensity because above 0.57% cocoa liquor. and storage temperature. both in the 1dimensional profile (Figure 2a) and in the corresponding image (Fig- Figure 1—Schematic diagram of the model chocolate confectionery system E: Food Engineering & Physical Properties olate Temper Meter.S.08 0. and emulsifier level. Each layer was approximately 1 cm high.S. U. A spin echo imaging pulse sequence without phase encoding was used to acquire 1-dimensional MR images (that is. The resolution was 250-␮m /pixel. emulsifier concentration. signal intensity profiles). 3. and below –0.A. The degree of temper was controlled by adding seed chocolate crystals based on a standard curve developed for each milk chocolate formulation.96% moisture. 100% peanut butter paste. and 4). All chocolate formulations consisted of 26. Cooling curves were monitored using a chocolate temper unit (CTU) value and slope values from the temper meter (Model 205 Portable Choc- MRI measurements One-dimensional signal intensity profiles across the center of the sample container were obtained from 1H signal (liquid lipid) using a 7T superconducting magnet in conjunction with a Biospec console (Bruker Biospin MRI Inc.. U. AMF. and storage temperature. and over-tempered) to study the effect of tempering on oil migration of peanut oil into the milk chocolate.70% nonfat dry milk.57 3. .41% lactose. The experimental designs were performed with 2 levels each of particle size. as described by McCarthy (1994) and Callaghan (1991). this procedure compensated for day-today variations of the spectrometer signal. 0. Five different chocolate formulations and 1 peanut butter paste formulation were used. Table 1—Composition of the 5 chocolate formulations Particle size of chocolate AMF ( ␮ m) content (%) 45 60 45 45 45 3. The standard chocolate (Formulation 1) consisted of 3. For each formulation. Three types of standards were prepared in sample containers: 100% milk chocolate (Formulation 1). Formulation 5 had no emulsifier added.11 0. with a mean particle size of 45 ␮m.40 0 PGPR 0.5 °C and 30 ± 0. 2 other factors were incorporated: chocolate particle size and emulsifier concentration.20% fat. In addition to these factors previously reported in the literature as important to oil migration. and storage temperature. and a mixture of powdered cane sugar (30% w/w) in peanut oil. The mean particle size of Formulation 2 was 60 ␮m.57 Emulsifier concentration (%) a Lecithin 0. At that point.57 0 10 3. This research addressed oil migration in a composite confectionery product of milk chocolate and peanut butter paste. N. . The samples were removed from the controlled environment chambers and evaluated at room temperature.59-cm-dia × 3.Oil migration in chocolate .3 g. The experimental factors were milk fat content.2 g with a standard deviation of 0.4 cm with a slice thickness of 8 mm. obtained on the same day.A.35% total nonfat solids. The temperature of 20 °C represents normal storage conditions.6 is over-tempered (Bolliger and others 1998).9 ms. Proton density signal from oil was monitored during storage using MRI. Sample mass was 12. The powdered sugar/peanut oil standard was more time-invariant than the peanut butter paste standard and gave signal intensity values intermediate to the milk chocolate standard (low) and the peanut butter paste standard (high). 11. Formulations 3 and 4 contained 0% and 10% AMF. To change AMF content in formulations.40 0. and (3) emulsifier concentration (Formulations 1 and 5). part of the cocoa butter was replaced with AMF to maintain the total fat content. The data at the initial time (t = 0) were used to identify the chocolate region and the peanut butter region in each sample container (Figure 2a).6 is under-tempered.A. which corresponds to 300 MHz for 1H-resonance frequency. PGPR = polyglyceryl polyricinoleate.65% total fat and 76.3% lecithin. and emulsifier concentration. which the researchers suggested was a more complex mechanism of migration than diffusion alone. The samples were stored in controlled environment chambers at 20 ± 0. Materials and Methods Sample preparation and experimental design The model system was a 2-layer chocolate confectionery system. Replicates were performed to confirm the effect of chocolate particle size. The objective of this study was to identify and characterize important factors impacting oil migration in the model system. Billerica.78cm-high sample container. a low signal intensity layer appeared in the sample at the interface of the peanut butter and chocolate.. A layer of peanut butter paste was deposited on top of the solidified milk chocolate (Figure 1). of migration of liquid fat from peanut butter.). Poughkeepsie. Mass. U.11 0.. Therefore. respectively. The total nonfat solids included 4.. 61. the chocolate and peanut butter regions were clearly identifiable.6 and 0. . the milk chocolate paste was melted (T > 38 °C) in a temper machine (Revolation 1.S. Formulations vary in particle size. and 8. Tricor Systems Inc. AMF content. and echo time was 4.84% nonfat solids. degree of temper. 256 data points (pixels) were acquired for each echo and 8 echoes were averaged. A layer of milk chocolate was deposited into a 2. The peanut butter paste contained 36. the temperature of 30 °C represents accelerated shelf-life test. the mean particle size was 39 ␮m. The compositions of the chocolate formulations are given in Table 1. 3 levels were used for degree of temper and AMF content. The degree of temper was evaluated by an industrial standard in which the slope value between –0. (2) AMF content (Formulations 1. degree of temper.11 0 Formulation 1 2 3 4 5 a AMF = anhydrous milk fat. and storage temperature. and 1. degree of temper. degree of temper. and temperature..) and then cooled gradually to 30 °C. The experimental responses were the rate of migration of the oil from the peanut butter paste to the chocolate and the overall change in signal intensity in the chocolate region due to increased liquid fat.57% anhydrous milk fat (AMF). Three full factorial designs were used to evaluate the following combinations of factors: (1) chocolate particle size (Formulations 1 and 2).6 is considered well-tempered. ChocoVision Corp.40 0. Ill.Y. The chocolate samples were prepared to 3 different degrees of temper (under-. MRI signal intensities from the model confectionery system were normalized with the sugar/peanut oil standard. The field of view was 6.30 0.).08% polyglyceryl polyricinoleate (PGPR). The plastic container was sealed with an airand moisture-tight lid. Samples were at room temperature no longer than 20 min and then returned to storage conditions..5 ° C. Elgin. After the 2nd day. well-. and 0. and (b) 10% AMF at 20 °C and at 30 °C. Figure 4. Two distinct regions are visible in the 20 °C samples. very little oil migration was evident in the samples stored at 20 °C. the darker the gray. the signal intensity values have been summed. t = 0). designated as PO (for peanut oil).A. the signal intensity of the peanut butter paste decreased over time as the signal intensity of the chocolate increased. U. . Figure 6 corresponds to Experimental Design 3. Both the chocolate and peanut butter regions had virtually the same signal intensity that was evident on day 1 of imaging. and multiplied by 100%. The rate of oil migration at 30 °C was higher in the 10% AMF sample (Figure 3b) than with the 0% AMF sample (Figure 3a). which evaluated the effect of emulsifier level. As the oil moved from the peanut butter layer to the chocolate. as illustrated in Figure 3. normalized by the sugar/peanut oil standard acquired on the same imaging day. At day 11. the peanut butter paste is the top layer in the sample container with higher signal intensity. the signal was depleted in the peanut butter layer. which means low proton signal intensity is bright and high proton signal intensity is dark. is included to provide reference signal intensity values. Figure 4 corresponds to Experimental Design 1. Natick. the images of the samples stored at 30 °C illustrate the effect of oil migration on signal intensity (Figure 3). Results and Discussion T wo-dimensional cross-sectional images provided quantitative information on oil migration. and 6 illustrate the change in relative signal intensity over time for the well-tempered samples. . there are signal intensity variations in the peanut butter region.S. The data in these figures are viewed in terms of 2 regions: the upper region is the signal from the peanut butter paste and designated by dark markers. The change was more rapid and more distinct for the samples stored at 30 °C than for the samples stored at 20 °C. The color map for the MR image is inverted gray scale. and the lower region is the signal intensity from the chocolate region and designated by open markers. which evaluated the effect of chocolate particle size.. the heterogeneity was due in part to a small amount of air entrapped during sample preparation of the viscous paste. The chocolate region is at the bottom of the sample container with lower signal intensity. especially at the interface region between the peanut butter paste and the chocolate. Mass. In contrast. Data analysis was performed using MATLAB 6. The image of the sugar/peanut oil standard is designated PO. . As a general comment. E: Food Engineering & Physical Properties Figure 2—Representative magnetic resonance imaging (MRI) information for the chocolate confectionery system at the initial time (t = 0). (a) 1-dimensional signal intensity profile and (b) MR image. Although the phase separation also occurred in the 30 °C samples. In each experimental design. Representative images of different chocolate particle size samples after 11 d of storage are displayed in Figure 3. This phase separation had occurred by day 1 of imaging (day 0 was the initial time. the oil layer had reabsorbed into the bulk material by day 11. An image of the sugar/peanut oil standard. 5. which evaluated the effect of anhydrous milk fat content. The spatial regions were designated and used throughout the study to evaluate the average signal intensity due to chocolate and due to the peanut butter paste over the experimental timeframe of 15 wk. ure 2b). the higher the proton signal.). Figure 3—Two-dimensional images of samples after 11 d of storage for (a) 0% anhydrous milk fat (AMF) at 20 °C and at 30 °C. Both the 20 °C samples and sugar/peanut oil standard show phase separation of the liquid oil and the bulk material. For both the chocolate region and the peanut butter region. The normalization was performed in this way to ensure that possible phase changes by the lipid component would not be masked. Figure 5 corresponds to Experimental Design 2.5 software (Mathworks.Oil migration in chocolate . The chocolate region has increased in signal intensity due to the liquid lipid. 27 15.85 23.Oil migration in chocolate .70 1. which quantifies migration rate.85 31. Figure 7b illustrates the effect of AMF content (Experimental Design 2). the high level of these factors yielded higher overall content of liquid lipid. As stated in the Introduction.50 15. The greatest fractional change occurred for the 0% AMF sample.25 3 0% AMF 4 10% AMF 5 0% emulsifier a AMF = anhydrous milk fat.45 23. the signal intensity had not reached a constant value after 106 d of storage. Figure 5—Relative signal intensity as a function of anhydrous milk fat (AMF) concentration over storage time. At 30 °C.84 1. The rate of migration is clearly a strong function of temperature. final constant signal intensity values (Sf) in the chocolate region.96 28. the main effects and 2-way interactions were evaluated for each design at a level of significance of ␣ = 0.66 0.17 37. their difference. the relationship is consistent with capillary flow (Aguilera and others 2004). Analysis of variance (ANOVA) was performed to determine statistically significant differences in the values of the responses due to each of the 5 experimental factors.64 1.13 1.21 1.06 17. markers without a dot represent 30 °C storage temperature.63 31. The R2 values for the 20 °C storage samples were considerably lower than for the 30 °C storage samples. A linear regression was performed on the linear region of the signal intensity versus square root of time plots.31 15. Figure 7 illustrates the change in signal intensities for each experimental design: Figure 7a illustrates particle size effect (Experimental Design 1).75 0. E: Food Engineering & Physical Properties level particle size). .46 11.40 38.17 16. and Figure 7c illustrates the effect of emulsifier content (Experimental Design 3).63 28.65 17. Markers with a dot inside represent 20 °C storage temperature.74 15.76 0.96 1.15 15.47 22.77 23. the relative signal intensity (relative to the sugar/peanut oil standard) for the chocolate region was plotted against the square root of time.46 15.02 1.44 16.63 16. . Solid markers represent signal intensity from the peanut butter region.13 1.08 8.81 12. and the fractional change of the liquid fat signal relative to the signal intensity at day 1 for samples stored at 30 °Ca Formulation 1 0. circle markers represent 10% AMF. The 3 responses were rate of change of signal intensity from liquid fat in the chocolate phase (slope of the linear regression). The least change in signal intensity over time occurred for the 10% AMF sample (high-level AMF).87 24. Table 2—Signal intensity from the chocolate region on day 1 (S1). Table 2 gives signal intensity values at day 1 (S1). and the coefficient of determination (R2) are given in Table 3 for the well-tempered samples.17 1.72 20. Square markers represent 45 ␮m particle size.65 37.20 14.55 8. migration was much slower at 20 °C.65 Sf 31.46 16.90 22. well-.70 14.63 0. slope values at 30 °C storage differ by a factor of 10 from the slope values of samples stored at 20 °C.05 1. Markers with a dot inside represent 20 °C storage temperature.99 32.58 16.55 25. and oil concentration in the chocolate region reached a constant level by 3 wk.50 17. In contrast.39 14.26 1.89 16. markers without a dot represent 30 °C storage temperature. the oil migration progressed primarily within the 1st 2 wk. the rate of migration increased as particle size increased. Square markers represent 0% AMF.53 31. the constant level after storage (Sf). To evaluate migration rates.80 0. AMF content. and emulsifier content) is given by dark markers. and the fractional change of the liquid fat signal relative to the signal intensity at day 1 for the under-.63 27. open markers from the chocolate region. and overtempered chocolate samples stored at 30 °C.82 28.03 1.3% emulsifier 45-␮m particle size 3.63 37.04 31.91 16. this approach is consistent with diffusion of a component in a semi-infinite media. Solid markers represent signal intensity from the peanut butter region. To give a quantitative understanding of the extent (or amount) of oil migration.57% AMF 2 60-␮m particle size Te m p e r Under Well Over Mean Under Well Over Mean Under Well Over Mean Under Well Over Mean Under Well Over Mean S1 16.33 33. in addition.07 15.45 15. the time frame was 14 d.92 9.69 15.05. For each set of data. In addition. The value of the slope.26 8.67 32. For each experimental design.79 1. The high level of each of these factors (particle size. The greatest change in signal intensity over time occurred for the 60-␮m particle size (high- Statistical analysis—ANO VA analysis—ANOV Three-way ANOVA was performed for each experimental design. The lower values are due to a weaker linear relationship (slope near zero) rather than scatter in the experimental data.37 1.37 12. amount of change of signal Figure 4—Relative signal intensity as a function of chocolate particle size over storage time. open markers from the chocolate region. the intercept. . their difference (Sf – S1).09 1. circle markers represent 60 ␮m particle size.40 Sf – S1 (Sf – S1)/S1 15.94 15.69 13.54 14.16 16.06 14. For Experimental Design 2. the levels of the factors were as follows: 2 levels of particle size: 45 ␮ m. Based on the ANOVA results.06 rather than at ␣ = 0. The fractional change in signal was a more sensitive indicator of overall change in signal intensity than the difference between Sf and S1. triangle markers are well-tempered chocolate. temperature was a significant factor for all 3 responses. AMF content yielded statistically different rates and extents of oil migration in the range of 0% to 10%. The only difference between Table 5 and Table 4 is that the rates of oil migration are significantly different at P = 0. circle markers represent 0. of liquid fat over the storage time frame (Sf – S1). well-. Again. Solid markers represent signal intensity from the peanut butter region. Increasing the temperature from 20 °C to 30 °C increased the rate of migration and the extent of migration. 60 ␮m. the signal intensity at day 1 was also samples each). This value was viewed to be more indicative of changes at a constant temperature than the initial value at day 0 after sample preparation. The square markers are undertempered chocolate. Results of ANOVA are given in Table 4. The responses over 15 wk were evaluated. Increasing the particle size from 45 ␮ m to 60 ␮m increased the rate of migration. As with the 1st set of experimental designs.Oil migration in chocolate . Increasing the temperature from 20 °C to 30 °C increased the rate of migration and the extent of migration. Temperature was a significant factor for all 3 responses. Similar to Experimental Design 1. The degree of temper was not a significant factor. interaction terms were not significant. 3 levels of temper: under-. and fractional change of the liquid fat signal relative to the signal intensity at day 1. the levels of the factors were as follows: 3 levels of anhydrous milk fat: 0%. and circle markers are over-tempered chocolate. well-. 10%. 3 levels of temper: under-. Figure 7—Relative signal intensity changes in the chocolate region of different (a) particle size. The signal intensity at day 1 (S1) was the sum of the signal intensity after 24 h at storage temperature. Markers with a dot inside represent 20 °C storage temperature. markers without a dot represent 30 °C storage temperature. (b) anhydrous milk fat (AMF) content. The amount of migration was not statistically different. the degree of temper was not a significant factor.3% emulsifier. In this case.05. The statistical analysis indicates that the more porous structure due to the larger particle size facilitates more rapid oil migration but does not significantly affect the amount that migrates. . Open markers represent the low level of the factor. (Sf – S1)/S1. closed markers represent the high level of the factor. 3. and (c) emulsifier concentration samples with different degree of temper at 30 °C. the most significant factor was storage temperature. and 2 storage temperatures: 20 °C and 30 °C. over-tempered. Like Experimental Design 1. interaction terms between the factors were not significant except for temperature/AMF for the fractional change. over-tempered. and emulsifier levels (at 0% and 0. with particle size and milk fat content statistically signif- E: Food Engineering & Physical Properties Figure 6—Relative signal intensity as a function of emulsifier concentration over storage time. and 2 storage temperatures: 20 °C and 30 °C. and the ANOVA results are presented in Table 5. .3%) did not yield significantly different response values for either the rate or extent of migration. For Experimental Design 1. Conclusions T his study identified statistically significant factors impacting oil migration in a model chocolate confectionery system.57%. open markers from the chocolate region. particle sizes of 45 ␮m and 60 ␮m did not yield significantly different extents of migration. . Square markers represent 0% emulsifier. special thanks to W. Lebensm Wiss Technol 23:545–9. Sweigart.” non significance as “NS. 1992. New York: Chapman & Hall.63 6. icant as well. J. personnel for providing samples and lending instruments.69 5.3% Extent (Sf – S1)/S 1 NS S Emulsifier 0% 0. A “diluting” effect due to the liquid peanut oil (no eutectic) was expected. 42:66–71. Ali A.978 0.899 0. Food Res Int 35:761–7.Oil migration in chocolate . Spatial variations in liquid lipid signal were observed that were consistent with the observation of Walter and Cornillon (2002) for their sample of commercial peanut butter and dark chocolate. 1997. Hershey.93 5.15 0.899 0.51 9. A study of fat migration in chocolate enrobed biscuits. Int Food Ingred 1:40–5 Wacquez J. J. Shuleva.988 0. Mayor G. 2001. Carpenter TA.988 0. Proceedings of 42nd PMCA Production Conference on Practical aspects of the eutectic effect on confectionery fats and their mixtures. German JB.05 ( P Յ 0. 2004. 3.962 0. and D.: PMCA. Comparison of precrystallization of chocolate. Nuclear magnetic resonance imaging of chocolate confectionery and the spatial detection of polymorphic states of cocoa butter in chocolate. Zhao.63 7. McCarthy MJ.K. J Food Eng 35:281–97. Most notably. Food Chem 72:491–7.63 9.” bAMF = anhydrous milk fat. cDifferent than Table 4. 414 p.34 3.05) is designated as “S.30 0. Conf Prod 56:265–72 Talbot G.899 Samples at 30 °C Slope Intercept 5.3% 0. Manuf Conf 84(9):118–26. Walter P. 1988 April 26-8. Formulations: 1. Ziegler GR. Wootton M.22 7. Weeden D. U. 1994. Couzens PJ. aTwo samples at each formulation were tested.06 AMFb. Couzens PJ. Experimental Design 2.91 9. 2001. J Food Sci 69(7):R167–74. 2 Particle size S NS Degree of temper NS NS Temperature S S Particle size-temper NS NS Particle size-temperature NS NS Temper-temperature NS NS . 1997. 2nd ed. Fat bloom in chocolate and compound coatings. bloom formation and sensory attributes of filled dark chocolate.998 0. the proton density of liquid fat decreases dramatically at the interface between the peanut butter paste and the chocolate. Hershey. Oxford. J Sci Food Agric 73:265–73.990 Table 5—Analysis of variance (ANOVA) for the rate and extent of oil migration into the chocolate region of welltempered samples stored at 30 °Ca Rate Particle size.31 9. 3.733 0. Lonchampt P. Suria AM. These factors influenced oil migration rate and the amount of change in liquid oil content in the chocolate over time. Effect of storage temperature on texture. 1988. Selamat J.05) level is designated as “S. Fat migration and bloom.: Clarendon Press. Significance at ␣ = 0. 2 45 ␮m NSc 60 ␮m S at P = 0. Miquel ME. J. Teets for insightful discussions. polymorphic structure. Stranziner M. Hanselmann.05 (P Յ 0. Shetty A.80 8.40 AMF 0% 3. Wagner T. Simoneau C. 1995. Callaghan PT. 110 p.30 NS a AMF = anhydrous milk fat. 1975.958 0. Magnetic resonance imaging in foods. McCarthy MJ.57% 10% 0.. This work was supported by USDA grant 2002-35503-12276.91 15. Trends Food Sci Technol 3:208–11. Pa. Manuf Conf 77:45–7. Nut oil migration through chocolate. Rate References Aguilera JM. Munk N. Measurement of fat crystallization using NMR imaging and spectroscopy. E: Food Engineering & Physical Properties Experimental Design 1. Manuf Conf 77(2):43–4.57% S 10% Emulsifier.: Clarendon Press.96 9. 1990. Breitschuh B. 492 p.75 5.” b AMF = anhydrous milk fat.719 0. 5 Emulsifier NS NS Degree of temper NS NS Temperature S S Emulsifier-temper NS NS Emulsifier-temperature NS NS Temper-temperature NS NS a Significance at the ␣ = 0. Manuf Conf 55(3):19–26.19 R2 0. 5 0% NS 0. 1990. 2004. Che Man YB. 1997. Furjanic. Cornillon P.91 R2 0.28 0.684 0. Couzens PJ. 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Hall LD. Crank J.