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Bloom on chocolate chips baked in cookies
Food Research International 48 (2012) 380–386
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Bloom on chocolate chips baked in cookies A. Frazier a, R.W. Hartel b,⁎ a b
General Mills, 330 University Avenue SE, Minneapolis, MN 55414, United States University of Wisconsin, 1605 Linden Dr, Madison, WI 53706, United States
a r t i c l e
i n f o
Article history: Received 27 February 2012 Accepted 10 May 2012 Keywords: Chocolate Untempered bloom Baked cookies Fat migration
a b s t r a c t It is somewhat surprising that chocolate chips baked in cookies do not exhibit bloom despite what seems to be sufficient heat to melt and break temper of the chocolate. We hypothesize that fat migration from the cookie dough into the molten chocolate chip during baking disrupts cocoa butter crystallization upon cooling and is responsible for this bloom inhibition. To test this hypothesis, both chocolate chip cookies and a sand– fat model system were baked with different types and levels of fat in the matrix. Bloom was evaluated 10 days after baking by image analysis of stereomicroscope images to quantify white areas on the flat bottom surface of oriented chips in sample cookies. All fats used in the dough, except cocoa butter, were shown to inhibit bloom when fat levels were sufficiently high. For palm oil and olive oil, a minimum degree of fat migration of about 16% was required to inhibit bloom. Below this critical level, bloom was observed on chocolate chips. A sand model system was also studied with palm oil. Since a higher level of fat migration was required to inhibit bloom for the sand model system than for cookies, other ingredients in the cookie dough must also play a role in bloom inhibition. © 2012 Elsevier Ltd. All rights reserved.
1. Introduction A major quality issue for the shelf life of chocolate products is the formation of fat bloom. Bloomed chocolate has an unappealing, dulled, whitish appearance. Many factors can promote bloom formation on chocolate, such as fluctuating or improper storage temperatures, oil migration from a filling to a chocolate coating, or insufficient tempering. Consequently, bloom on chocolate can be difficult to control. The best method for prevention is to properly temper chocolate. Tempering is the process of pre-crystallizing cocoa butter to seed chocolate with the proper number, size and polymorphic form of cocoa butter crystals (Kleinert, 1970; Ziegler, 2001). Cocoa butter can crystallize into six different polymorphic forms (Chapman, Akehurst, & Wright, 1971; Loisel, Keller, Lecq, Bourgaux, & Ollivon, 1998; Lovegren, Gray, & Feuge, 1976; Wille & Lutton, 1966), with the βV form being the desired polymorph for tempered chocolate. A properly tempered chocolate is glossy and free of bloom, has a smooth mouthfeel, and delivers a hard snap when broken. Bloom on tempered chocolate is always associated with recrystallization of cocoa butter crystals from the βV form to the more stable βVI form, although this transformation can also occur without the formation of bloom (Adenier, Chaveron, & Ollivon, 1993; Bricknell & Hartel, 1998). The physical aspect of this type of bloom is large, needle-like cocoa butter crystals in the βVI form. Conditions such as
⁎ Corresponding author. Tel.: + 1 608 263 1965. E-mail address: [email protected] (R.W. Hartel). 0963-9969/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2012.05.011
improper storage temperatures and oil migration can promote the recrystallization of cocoa butter in tempered chocolate. Bloom on tempered chocolate due to oil migration often occurs when chocolate has direct contact with another fat containing component. Such is the case with filled or enrobed chocolate products, especially those with nut-based centers. Two-way oil migration will occur until fat compositional equilibrium is reached. As oil migrates into the chocolate, higher melting cocoa butter triacylglycerols (TAG) dissolve in the oil. These TAG eventually recrystallize on the surface of the chocolate in the βVI form, which can result in bloom. Oil migration is enhanced with high temperatures, long contact times between the chocolate and other fat containing component, and high levels of liquid oil in one or both of the components in the system (Talbot, Smith, & Cain, 2006; Talbot, Smith, & Zand, 2006; Timms, 1984; Ziegleder, 1997; Ziegler, Shetty, & Anantheswaran, 2004). The mechanism of bloom formation on untempered and undertempered chocolate is different from that of other types of bloom. When melted chocolate does not contain enough seed crystals, cocoa butter will crystallize in an unstable polymorph. The subsequent recrystallization to more stable polymorphs results in a contraction effect of the cocoa butter crystalline matrix, which pushes cocoa solids and sugar particles to the surface of the chocolate (Kinta & Hartel, 2010). Thus, the composition of bloom on untempered and undertempered chocolate is sugar particles and cocoa solids (Kinta & Hartel, 2010; Kinta & Hatta, 2005; Lonchampt & Hartel, 2006). Given the delicate balance of factors required to create a piece of bloom-free chocolate, it is noteworthy that bloom on chocolate chips baked in cookies is rarely a problem, even though the chocolate
A. Frazier, R.W. Hartel / Food Research International 48 (2012) 380–386
chips are subjected to conditions normally associated with bloom. For one, chocolate chips are exposed to very high temperatures during baking, where melting and resolidification should lead to bloom. Also, chocolate chips have direct contact with cookie dough, which normally contains a fat other than cocoa butter. These conditions are ideal for oil migration. There are two potential explanations for why chocolate chips do not bloom when baked in cookies. The first relates to the possibility of a crystal memory effect. When cocoa butter is heated just above its melting point for a short time, a small amount of high melting β crystals may remain in the liquid melt. As the cocoa butter is cooled, these β crystals can provide the structural information necessary for the cocoa butter to recrystallize directly to the β form (van Malssen, van Langevelde, Peschar, & Schenk, 1999). This in turn could result in bloom-free chocolate. If chocolate chips baked in cookie dough do not melt completely, perhaps as a result of evaporative cooling or an insulating effect from the cookie dough during baking, the chips could contain sufficient un-melted stable cocoa butter crystals to be seeded upon cooling. The second possible explanation involves the oil migration that occurs during baking between the cookie dough and chocolate chips. Migrating oil from cookie dough changes the fat composition of the chocolate chips, which may cause cocoa butter to crystallize in such a way that there is no visual bloom. The focus of this study was to demonstrate which conditions lead to bloom inhibition on chocolate chips baked in cookies, to determine if crystal memory effect and/or oil migration is responsible for the observed bloom inhibition, and to quantify the degree of migration occurring in chocolate chips baked in cookies.
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each cookie prior to baking. The chips were positioned upside down, so that the flat side of the chip was level with the cookie surface. The cookies were baked in a conventional oven (Frigidaire) for 12 min at 325 °F. After baking, cookies were cooled at room temperature (approximately 22 °C) on a cooling rack lined with parchment paper and stored on sheet trays at 20 °C for 10 days. A storage period of 10 days was chosen as it was adequate time for bloom to form on chocolate chips without sacrificing the overall quality of the cookie. Five individual batches of cookie dough were prepared for each fat level and type. Five cookies from each batch were reserved for analysis. One chip from each cookie was selected for analysis based on how well it remained embedded in cookie dough during and after baking. This resulted in 25 samples for each condition tested. 2.2. Temperature profile of chocolate chips during baking To determine if crystal memory effect was the cause of bloom inhibition on chocolate chips baked in cookies, it was necessary to verify that chips melted completely during baking. This was determined by observing the internal temperature of the chocolate chips during baking using a thermocouple. A small hole was carved into the side of the chocolate chip using a needle, and a wire temperature probe was inserted into the hole. The chocolate chip was pushed into the cookie dough with the point of the chip facing down, so that the flat side of the chip was even with the dough. Special care was taken not to dislodge the temperature probe. Samples were baked at 325 °F for 12 min. The chocolate chip temperature was recorded every minute for the duration of the baking process. 2.3. Monitoring bloom formation on chocolate chips
2. Material and methods 2.1. Preparation of cookies To determine the effects of different fats on chocolate chip bloom, chocolate chip cookies were formulated using a standard recipe (Table 1). The fat content of the cookie dough ranged from 7.8% to 22.9%. Fat content was calculated by dividing the amount of fat by the total sum of the ingredients in the cookie dough, excluding the weight of the chocolate chips. Fats used included fractionated palm oil shortening (Tropical Traditions, West Bend, WI), olive oil (Filippo Berio, Italy), peanut oil (Shurfine, Tigard, OR), and cocoa butter (ADM Cocoa, Milwaukee, WI). Cookie dough was prepared by mixing the fat and sugars in a stand mixer (KitchenAid, Custom 350 W, 5 qt.) with a paddle attachment. Next, the powdered egg–water solution and imitation vanilla were added and mixed. Flour, baking soda and salt were sifted together and added. The dough was mixed just until all the ingredients were incorporated. Finally, the chocolate chips were folded into the dough by hand. Cookie dough was divided into twelve portions on a sheet tray lined with parchment paper. In order to produce unobstructed images of bloomed chocolate chips, three additional chocolate chips were pushed into the top of
Table 1 Cookie formulation. Ingredient
Amount
Fat (palm oil shortening, cocoa butter, olive oil, or peanut oil) Granulated sugar Dark brown sugar Powdered whole egg Water Artificial vanilla extract All-purpose flour Baking soda Salt Nestle® semi-sweet chocolate chips
16–56 g 46 g 30 g 5g 21 g 2g 82 g 1.25 g 1.5 g 60 g
To quantify the amount of bloom formed on the chocolate chip surfaces after 10 days, images of chocolate chips were analyzed for bloom. Pictures of chocolate chips were taken using a stereomicroscope, magnification 1.5×, and a digital camera (Nikon SMZ-10 microscope; Nikon DS-5m camera head; Nikon DS-L1 control unit). Images were cropped to exclude portions of baked cookie surrounding the chip using Adobe Photoshop (CS2, version 9.0). Imaging software Image-Pro Plus 6.0 was used to highlight the white portions of the image, which corresponded to the bloomed areas of the chocolate surface. The number of pixels in the white areas was counted automatically and the percent bloom on the chocolate chip was calculated by comparing the number of pixels in the white areas to the total number of pixels in the image. Pixels were approximately 4 μm in width. A level of approximately 2% bloom on chocolate was the threshold where bloom was no longer visible with the naked eye. 2.4. Sand and fat mixtures Chocolate chips were baked in cups filled with mixtures of fat and washed sea sand to mimic the effect of fat in cookie dough on chocolate chips in the absence of other ingredients. The sand and fat were thoroughly mixed at room temperature in a stand mixer (KitchenAid, Custom 350 W, 5 qt.), similar to creaming sugar and fat in cookie dough preparation. Palm oil shortening was used in amounts ranging from 0% to 14%. Mixtures were scooped into cupcake holders and chocolate chips were pushed into the surface of the mixtures. As before, the chocolate chips were positioned upside down so that the flat side of the chip was even with the surface of the sand. The samples were baked, stored and analyzed using the method described above for the cookies. A minimum of one chip per cup was selected for analysis based on how well it remained embedded in the sand during and after baking. Three separate cups were prepared per batch of sand–fat mixture, and five batches of sand–fat mixtures were prepared for every level of fat tested, resulting in a minimum of 15 samples per fat level.
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2.5. Triacylglycerol (TAG) analysis Analysis of TAG profiles of chocolate chips baked in cookies and sand, unbaked chocolate chips, palm oil shortening and olive oil were obtained in order to verify and quantify oil migration during baking. Chocolate chips were carefully scraped out of cookies and sand–fat mixtures that had been stored for 10 days at 20 °C. The chocolate was dissolved in petroleum ether and filtered through syringe filters. TAG profiles were obtained using gas chromatography, courtesy of ADM Cocoa, Milwaukee, WI. Two samples from each chip were analyzed. 2.6. Degree of oil migration To quantify oil migration occurring in cookies and sand mixtures, degree of oil migration was calculated (Talbot, Smith, & Cain, 2006; Talbot, Smith, & Zand, 2006) using TAG levels from fat in cookie dough or sand/fat mixtures, and fat in chocolate chips before and after baking (Eq. (1)). The degree of oil migration (DM) was calculated for individual TAG. Average degree of migration was then calculated by averaging the degree of migration values for all TAG (Eq. (2)).
DMi ð% Þ ¼
ðX BC −X C Þ ðX FCD −X C Þ
least 4 min after baking. In total, the chips spent a minimum of eight minutes above 50 °C. It is common practice to melt chocolate to 60– 80 °C, well above the melting range of cocoa butter, in order to prevent crystal memory effect. However, van Malssen, Pschar, Brito, and Schenk (1996) studied the melting temperatures required to inhibit crystal memory effect and found that when cocoa butter was heated to 39 °C or higher, no direct β crystallization occurred after cooling for 45 min at 25 °C. They suggest that lower-melting cocoa butter TAGs are the most influential in the crystallization of cocoa butter. By raising the temperature just slightly higher than that of the melting temperature of cocoa butter, these lower melting TAG melt and no crystal memory effect is observed. Since the internal temperature of chocolate chips baked in cookie dough remained well above 39 °C for over 10 min, it can be expected that the chocolate broke temper during baking. Therefore, the absence of bloom on chocolate chips
a
ð1Þ
where: DMi XBC XC XFCD
degree of migration of particular TAG (%) % TAG in baked chip % TAG in unbaked chip % TAG in fat in cookie dough
b n ― X DMi DM ¼ n i
ð2Þ
where: ― DM i
average degree of migration individual TAG
Since each TAG migrates to a slightly different extent based on its individual difference in concentration between chocolate and cookie dough, this value provides an average extent of migration across all TAG. The primary TAG in both chocolate and cookie dough were taken into account in this calculation. 3. Results and discussion
c
3.1. Temperature profile for chocolate chips baked in cookies It has been suggested that chocolate chips baked in cookies do not bloom because the chips do not melt completely during baking. Even if trace amounts of cocoa butter crystals remain in the chocolate, a so-called crystal memory effect could influence how the chocolate re-solidifies after baking. If enough crystal structural information remains in the chocolate due to insufficient melting, the cocoa butter might crystallize directly into the β form, resulting in a bloom-free chocolate chip. To determine whether chocolate chips melt completely when baked in cookie dough, the internal temperature of chips was monitored during baking. It was observed that the temperature of the chips reached 60 °C at the end of the 12 min baking trial. In addition, the temperature of the chocolate chips remained above 60 °C for at
Fig. 1. Average bloom (% white pixels on chocolate chips baked in cookies made with a) palm oil shortening, b) olive oil, c) peanut oil. The dashed line at 2% average bloom indicates the threshold where bloom is not longer visible to the naked eye.
A. Frazier, R.W. Hartel / Food Research International 48 (2012) 380–386
a
b
Fig. 2. Bloom is visible on chocolate chips baked in cookies containing 14% palm oil shortening (a), but completely inhibited on chocolate chips baked in cookies containing 20% palm oil shortening (b).
baked in cookies cannot be a result of crystal memory effect, and another factor must be responsible. This is further supported by the observation of bloom on chocolate chips in cookies made with low fat content (see below). 3.2. Quantification of bloom on chocolate chips baked in cookies To study the effects of oil migration on bloom formation, chocolate chip cookies were formulated with a variety of fats including palm oil, olive oil, peanut oil and cocoa butter. Cookies were baked and stored for 10 days to observe bloom. For cookies made with fats other than cocoa butter, the amount of bloom visible on the chocolate chips decreased with increased fat content of the cookie dough (Fig. 1). When the fat level was above some critical amount, bloom was completely inhibited (Fig. 2). This demonstrates a connection between cookie dough fat content and bloom inhibition, possibly enabled by oil migration between the chocolate chip
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and cookie dough. Furthermore, the fact that some chocolate chips do bloom when baked in cookie dough further supports the notion that crystal memory effect is an unlikely cause of chocolate chip bloom inhibition. Cookies made with cocoa butter did not follow the trend of bloom inhibition with increased cookie dough fat content. Even with very high levels of cocoa butter added to cookie dough, the amount of bloom formed on chocolate chips did not change. The driving force for oil migration is the compositional difference between the two phases in contact with each other. If the fat in each phase is the same, no net migration will occur. Ziegler et al. (2004) demonstrated this by storing chocolate samples on filter paper saturated with cocoa butter. He found that no net migration occurred for a system containing only cocoa butter, whereas migration did occur when the filter paper was saturated with a fat other than cocoa butter. Furthermore, Kleinert (1970) found when cocoa butter centers were enrobed with chocolate and stored for 36 months under conditions designed to encourage bloom formation on enrobed chocolates, no bloom occurred, indicating that no net oil migration had occurred and the composition of the chocolate was not changed. Had significant net oil migration taken place, bloom likely would have formed. In the case of cookies made with cocoa butter, the same fat was present in both the dough and the chocolate chip. There was no driving force (or very little, depending on slight differences in cocoa butter composition) for oil migration to occur. Since no net oil migration occurred, the composition of the chocolate chip remained relatively unchanged after baking and bloom occurred as would be expected on untempered chocolate. In the case of cookies made with fats other than cocoa butter, the fat in the cookie dough was different enough from the cocoa butter in the chocolate chip, and as a result, migration readily occurred during baking. We conclude, therefore, that migration of fat from the cookie dough into the chocolate chip was, at least in part, responsible for the bloom inhibition observed here. Cookies made with palm oil shortening required greater amounts of fat in the dough for bloom inhibition to occur than cookies made with peanut oil and olive oil (Fig. 1). In general, liquid TAG are more mobile and migrate at a faster rate than crystalline TAG (Talbot, Smith, & Cain, 2006; Talbot, Smith, & Zand, 2006; Ziegleder, 1997; Ziegler et al., 2004). Since peanut oil and olive oil are liquid oils, with lower solid fat contents than palm oil shortening, it is likely that peanut oil and olive oil more readily migrated through the cookie dough. As a result, less of these oils were required in the dough to provide bloom protection. Of course, once a cookie is exposed to baking temperature, all the fat in the cookie will be in a liquid state. Perhaps since peanut and olive oil are liquid and do not require an initial melting period in the oven, cookies made with these fats experienced greater total migration, which leads to enhanced bloom inhibition with less fat needed to completely inhibit bloom. 3.3. TAG migration analysis for chocolate chips baked in cookies The degree of oil migration from cookie dough into a chocolate chip can be calculated by measuring the TAG profile of the fat phase of a chocolate chip before and after baking. TAG analysis was performed on chocolate chip samples taken from cookies made with
Table 2 Triacylglycerol (TAG) profiles for palm oil (PO), unbaked chocolate chips, and chocolate chips baked in cookies made with palm oil at different fat contents in the cookie dough. P — palmitic acid, L — linoleic acid, O — oleic acid, S — stearic acid. Courtesy Adam Lechter, ADM Cocoa, Milwaukee, WI. TAG
Palm oil
Unbaked chip
14.02% PO
16.48% PO
17.66% PO
20.02% PO
PLO POO PLP POP SOS POS
13.16 ± 0.05 23.31 ± 0.02 11.09 ± 0.10 27.43 ± 0.22 0.67 ± 0.02 5.15 ± 0.05
0.48 ± 0.02 3.31 ± 0.27 2.60 ± 0.05 14.73 ± 0.22 23.42 ± 0.01 35.34 ± 0.34
2.38 ± 0.15 6.05 ± 0.01 3.33 ± 0.24 15.72 ± 0.12 20.32 ± 0.03 31.69 ± 0.26
2.68 ± 0.07 5.73 ± 0.09 3.67 ± 0.11 15.78 ± 0.13 20.92 ± 0.19 31.98 ± 0.21
3.27 ± 0.04 6.93 ± 0.11 4.20 ± 0.18 15.86 ± 0.06 19.44 ± 0.12 30.45 ± 0.23
3.56 ± 0.08 7.57 ± 0.12 4.21 ± 0.23 16.72 ± 0.13 18.68 ± 0.16 30.10 ± 0.03
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Fig. 3. Degree of oil migration for chocolate chips baked in cookies made with palm oil shortening. Dashed lines indicate level at which bloom was inhibited.
Fig. 4. Degree of oil migration for chocolate chips baked in cookies made with olive oil. Dashed lines indicate level at which bloom was inhibited.
14.02%, 16.48%, 17.66% and 20.02% palm oil shortening (Table 2). The TAG profiles clearly show that fat migration occurred, and at greater levels in cookies made with higher amounts of fat. TAG found at higher levels in palm oil than in cocoa butter (PLO, POO, POP and PLP) increased in the chocolate chip after baking, indicating that palm oil migrated from the cookie dough into the chip. In addition, TAG found at higher levels in cocoa butter (SOS, POS) decreased in amount in the chip after baking. Supplementary TAG analysis, not presented here, showed increased SOS and POS levels in baked palm oil cookie, confirming that the observed decrease in SOS and POS levels in the chocolate chips was due to migration and not solely a result of dilution. This indicates that palm oil migrated from the cookie into the chip at the same time cocoa butter migrated out of the chip. The average degree of migration was calculated from Eqs. (1) and (2) based on PLO, POO, POP, PLP, SOS and POS levels. As expected, higher fat levels in cookie dough led to higher levels of fat migration, as seen in Fig. 3. From Fig. 1, about 18% palm oil in the cookie dough was required to inhibit bloom on chocolate chips baked in cookies. Thus, the degree of migration required to inhibit bloom was approximately 16%. TAG levels were also measured for chocolate chips baked in cookies made with olive oil. Levels of OOO, POO and PLO increased in the chocolate chip after baking and levels of POS, SOS and POP decreased (Table 3). In addition, levels of SOS and POS increased in the cookie dough after baking. Based on these TAG, the average degree of migration was calculated using Eqs. (1) and (2). From Fig. 1, 12% olive oil in the cookie dough was required to inhibit bloom on chocolate chips baked in cookies. Thus, the degree of migration required to inhibit bloom was approximately 16% (Fig. 4). Roughly equivalent degrees of migration were necessary to inhibit bloom in both palm oil and olive oil cookies (Fig. 5). In general, approximately 16% oil migration was required to prevent bloom formation on chocolate chips baked in cookies, regardless of the fat used in the cookie dough. Further work is needed to determine the degree of
migration necessary for cookies made with other fats and to verify these findings. 3.4. Sand–fat mixtures In order to observe the effect of cookie dough fat content on chocolate chip bloom without the influence of other components of cookie dough, chocolate chips were baked in cups filled with mixtures of fat and washed sea sand. If it is indeed fat migration in cookies that provided bloom protection, then the bloom inhibition on chocolate chips baked in sand should be equivalent to bloom inhibition on chips baked in cookies. 3.4.1. Temperature profile for chocolate chips during baking in sand To confirm that chocolate chips baked in sand–fat mixtures melted completely and broke temper during baking, the internal temperature of the chip was recorded. Chocolate chips baked in plain sand with no palm oil shortening reached 105.7 °C in 12 min and chocolate chips baked in sand mixed with 13% palm oil shortening reached 102 °C. The temperatures observed here were sufficiently high to completely melt the chocolate chips. As a result, no crystal memory effect could have occurred and any bloom inhibition on chocolate chips baked in sand–fat mixtures was due to some other factor. 3.4.2. Bloom on chocolate chips baked in sand–fat mixtures Chocolate chips baked in sand and palm oil shortening mixtures exhibited a similar bloom inhibition effect as observed for cookies. Higher amounts of palm oil shortening mixed into sand resulted in less chocolate chip bloom (Fig. 6). In fact, chocolate chips baked in sand and palm oil shortening mixtures above 8% remained unbloomed in excess of 24 months when stored at 20 °C. Since fat was the only component in the sand system, fat in cookie dough played a major role in bloom inhibition on chocolate chips.
Table 3 Triacylglycerol (TAG) profiles for olive oil (OO), unbaked chocolate chips, and chocolate chips baked in cookies made with olive oil at different fat contents in the cookie dough. P — palmitic acid, L — linoleic acid, O — oleic acid, S — stearic acid. Courtesy Adam Lechter, ADM Cocoa, Milwaukee, WI. TAG
Palm oil
Unbaked chip
14.02% OO
16.48% OO
17.66% OO
20.02% OO
PLO POO PLP POP SOS POS
13.16 ± 0.05 23.31 ± 0.02 11.09 ± 0.10 27.43 ± 0.22 0.67 ± 0.02 5.15 ± 0.05
0.48 ± 0.02 3.31 ± 0.27 2.60 ± 0.05 14.73 ± 0.22 23.42 ± 0.01 35.34 ± 0.34
2.38 ± 0.15 6.05 ± 0.01 3.33 ± 0.24 15.72 ± 0.12 20.32 ± 0.03 31.69 ± 0.26
2.68 ± 0.07 5.73 ± 0.09 3.67 ± 0.11 15.78 ± 0.13 20.92 ± 0.19 31.98 ± 0.21
3.27 ± 0.04 6.93 ± 0.11 4.20 ± 0.18 15.86 ± 0.06 19.44 ± 0.12 30.45 ± 0.23
3.56 ± 0.08 7.57 ± 0.12 4.21 ± 0.23 16.72 ± 0.13 18.68 ± 0.16 30.10 ± 0.03
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Fig. 5. Degree of oil migration and average bloom (% white pixels) for chocolate chips baked in cookies made with palm oil shortening and olive oil. The dashed line at 2% average bloom indicates the threshold where bloom was no longer visible to the naked eye.
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3.4.3. TAG migration analysis for chocolate chips baked in sand TAG profiles were obtained from chocolate chips baked in sand and palm oil mixtures (Table 4). As for chocolate chips baked in cookies, the levels of PLO, POO, POP and PLP increased and the levels of SOS and POS decreased in the chip after baking, indicating that fat migration occurred in both directions between the chocolate chip and the sand. The amount of migration was greatest for the chip baked in sand with the highest fat content. The degree of migration was calculated using Eqs. (1) and (2). About 10% fat in the sand mixture was needed to prevent bloom, so approximately 40% oil migration was required in order for bloom to be inhibited (Fig. 7). This was a noticeably higher degree of migration than the 16% migration required to inhibit bloom on chocolate chips baked in cookies. It is unclear why a higher degree of migration was required to inhibit bloom on chocolate chips baked in sand. It appears that when fat is the only ingredient in the system, much more fat is required to inhibit bloom. This suggests that other ingredients in the cookie dough may also contribute to bloom inhibition. Structural differences, such as particle size, shape and surface characteristics between in the cookie dough and the sand model system may explain the variation in migration levels observed. Also, the chocolate chips baked in sand reached higher temperatures and melted faster than chocolate chips baked in cookie dough, which may have resulted in more total oil migration. In addition, unlike cookie dough, the sand mixtures contained no water. The absence of polar interferences from water in the sand matrix may allow the fat to migrate more efficiently. Overall, the complex microstructure of cookie dough may impede fat migration compared to the simple sand-fat system. 4. Conclusion
Fig. 6. Average bloom (% white pixels) on chocolate chips baked in sand and palm oil mixtures. The dashed line at 2% bloom indicates the threshold where bloom is no longer visible to the naked eye.
In general, less fat was required to inhibit bloom on chocolate chips baked in sand–fat mixtures compared to chocolate chips baked in cookies. For example, while 18–19% palm oil shortening was necessary to inhibit bloom on chocolate chips baked in cookies, as little as 8% palm oil shortening inhibited bloom in the sand system. One reason for the disparity between the fat levels needed to inhibit bloom in cookies and sand-fat mixtures may be due to differences in the physical structure of the two systems. Cookie dough is a denser medium with a more complex microstructure than sand. Liquid fat may more readily migrate through sand due to the homogeneity of the system and larger particle size, resulting in more fat migration into the chocolate chip. As a result, less fat in the sand was required to inhibit bloom. In addition, the chocolate chips baked in sand reached higher temperatures and melted faster than chocolate chips baked in cookie dough, meaning chips baked in sand spent a longer time in the molten state during baking, which also resulted in more total oil migration.
To better understand why chocolate chips generally do not bloom in cookies, potential factors affecting chocolate chips were examined. It was demonstrated that chocolate chips in cookies melted completely during baking. Thus, crystal memory effect was not a factor in the observed bloom inhibition on chocolate chips. Fat migration was shown to be the primary factor that influenced bloom formation on chocolate chips baked in cookies. When the fat content of the cookie dough was sufficiently high, enough fat migrated into the chocolate chip such that, upon cooling and storage, bloom was inhibited. The degree of migration necessary to inhibit bloom on chocolate chips was similar for cookies made with palm oil shortening and olive oil, even though the amount of fat added to the cookie dough was not the same. Bloom inhibition also occurred on chocolate chips baked in a model system of sand and fat mixtures. A higher level of fat migration was required for palm oil to inhibit bloom on chocolate chips baked in the sand system compared to chocolate chips baked in cookies. This indicated that other ingredients in cookie dough may play a role in bloom inhibition on chocolate chips. Although fat migration clearly contributes to bloom inhibition in this case, the exact mechanism behind this inhibition is still unknown. Based on the soft texture of chocolate chips in cookies after baking, we speculate that the phase behavior and change in crystallization/ polymorphism of the mixed fat system is responsible for bloom
Table 4 Triacylglycerol (TAG) profiles for palm oil (PO), unbaked chocolate chips, and chocolate chips baked in sand and palm oil mixtures at different fat contents in the sand. P — palmitic acid, L — linoleic acid, O — oleic acid, S — stearic acid. Courtesy Adam Lechter, ADM Cocoa, Milwaukee, WI. TAG
Palm oil
Unbaked chip
3.85% PO
6.54% PO
8.26% PO
13.04% PO
PLO POO PLP POP SOS POS
13.16 ± 0.05 23.31 ± 0.02 11.09 ± 0.10 27.43 ± 0.22 0.67 ± 0.02 5.15 ± 0.05
0.48 ± 0.02 3.31 ± 0.27 2.60 ± 0.05 14.73 ± 0.22 23.42 ± 0.01 35.34 ± 0.34
2.05 ± 0.03 5.57 ± 0.12 3.57 ± 0.11 15.24 ± 0.28 21.19 ± 0.09 31.81 ± 0.13
5.03 ± 0.17 9.95 ± 0.25 4.80 ± 0.06 16.44 ± 0.08 17.06 ± 0.16 26.44 ± 0.04
6.83 ± 0.03 12.53 ± 0.05 5.99 ± 0.05 17.65 ± 0.03 14.93 ± 0.23 23.39 ± 0.12
7.18 ± 0.09 14.28 ± 0.12 6.52 ± 0.11 18.22 ± 0.42 13.25 ± 0.08 21.29 ± 0.05
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Fig. 7. Degree of oil migration for chocolate chips baked in sand and palm oil mixtures. Dashed lines indicate level at which bloom was inhibited.
inhibition. Perhaps the complex fat mixture in the chocolate chip after baking does not undergo polymorphic transformations thought to be responsible for bloom. Further work in the area is warranted. Acknowledgments Funding from the PMCA, an International Organization of Confectioners, is greatly appreciated. Thanks to Adam Lechter and ADM Cocoa, Milwaukee, WI for assistance with the analyses. References Adenier, H., Chaveron, H., & Ollivon, M. (1993). Mechanism of fat bloom development on chocolate. In G. Charalambous (Ed.), Shelf life studies on food and beverages: chemical, biological, physical and nutritional aspects (pp. 353–389). Amsterdam (Netherlands): Elsevier.
Bricknell, J., & Hartel, R. W. (1998). Relation of fat bloom in chocolate to polymorphic transition of cocoa butter. Journal of the American Oil Chemists' Society, 75, 1609–1615. Chapman, G. M., Akehurst, E. E., & Wright, W. B. (1971). Cocoa butter and confectionery fats. Studies using programmed temperature X-ray diffraction and differential scanning calorimetry. Journal of the American Oil Chemists' Society, 48, 824–830. Kinta, Y., & Hatta, T. (2005). Composition and structure of fat bloom in untempered chocolate. Journal of Food Science, 70, 450–452. Kinta, Y., & Hartel, R. W. (2010). Bloom formation on poorly-tempered chocolate and effects of seed addition. Journal of the American Oil Chemists' Society, 87, 19–27. Kleinert, J. (1970). Cocoa butter and chocolate: the correlation between tempering and structure. Revue Inter nationale Du Chocolat, 25, 386–399. Loisel, C., Keller, G., Lecq, G., Bourgaux, C., & Ollivon, M. (1998). Phase transitions and polymorphism of cocoa butter. Journal of the American Oil Chemists' Society, 75, 425–438. Lonchampt, P., & Hartel, R. W. (2006). Surface bloom on improperly tempered chocolate. European Journal of Lipid Science and Technology, 108, 159–168. Lovegren, N. V., Gray, M. S., & Feuge, R. O. (1976). Polymorphic changes in mixtures of confectionery fats. Journal of the American Oil Chemists' Society, 53, 83–88. Talbot, G., Smith, K., & Cain, F. (2006). Oil migration: Minimisation of extent and effects. Manufacturer Confectionery, 86, 63–66. Talbot, G., Smith, K., & Zand, I. (2006). Oil migration: The basics. Kennedy's Confection, 13, 48–51. Timms, R. E. (1984). Phase behaviour of fats and their mixtures. Progress in Lipid Research, 23, 1–38. van Malssen, K., Pschar, R., Brito, C., & Schenk, H. (1996). Real-time X-ray powder diffraction investigations on cocoa butter. III. Direct β-crystallization of cocoa butter: Occurrence of a memory effect. Journal of the American Oil Chemists' Society, 73, 1225–1230. van Malssen, K., van Langevelde, A., Peschar, R., & Schenk, H. (1999). Phase behavior and extended phase scheme of static cocoa butter investigated with real-time X-ray powder diffraction. Journal of the American Oil Chemists' Society, 76, 669–676. Wille, R., & Lutton, E. (1966). Polymorphism of cocoa butter. Journal of the American Oil Chemists' Society, 43, 491–496. Ziegleder, G. (1997). Fat migration and bloom. Manufacturer Confectionery, 77, 43–44. Ziegler, G. (2001). Solidification processes in chocolate confectionery manufacture. In N. Widlak, R. W. Hartel, & S. Narine (Eds.), Crystallization and solidification properties of lipids (pp. 215–224). AOCS Press. Ziegler, G., Shetty, A., & Anantheswaran, R. C. (2004). Nut oil migration through chocolate. Manufacturer Confectionery, 84, 118–126.
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Bloom on chocolate chips baked in cookies A. Frazier a, R.W. Hartel b,⁎ a b
General Mills, 330 University Avenue SE, Minneapolis, MN 55414, United States University of Wisconsin, 1605 Linden Dr, Madison, WI 53706, United States
a r t i c l e
i n f o
Article history: Received 27 February 2012 Accepted 10 May 2012 Keywords: Chocolate Untempered bloom Baked cookies Fat migration
a b s t r a c t It is somewhat surprising that chocolate chips baked in cookies do not exhibit bloom despite what seems to be sufficient heat to melt and break temper of the chocolate. We hypothesize that fat migration from the cookie dough into the molten chocolate chip during baking disrupts cocoa butter crystallization upon cooling and is responsible for this bloom inhibition. To test this hypothesis, both chocolate chip cookies and a sand– fat model system were baked with different types and levels of fat in the matrix. Bloom was evaluated 10 days after baking by image analysis of stereomicroscope images to quantify white areas on the flat bottom surface of oriented chips in sample cookies. All fats used in the dough, except cocoa butter, were shown to inhibit bloom when fat levels were sufficiently high. For palm oil and olive oil, a minimum degree of fat migration of about 16% was required to inhibit bloom. Below this critical level, bloom was observed on chocolate chips. A sand model system was also studied with palm oil. Since a higher level of fat migration was required to inhibit bloom for the sand model system than for cookies, other ingredients in the cookie dough must also play a role in bloom inhibition. © 2012 Elsevier Ltd. All rights reserved.
1. Introduction A major quality issue for the shelf life of chocolate products is the formation of fat bloom. Bloomed chocolate has an unappealing, dulled, whitish appearance. Many factors can promote bloom formation on chocolate, such as fluctuating or improper storage temperatures, oil migration from a filling to a chocolate coating, or insufficient tempering. Consequently, bloom on chocolate can be difficult to control. The best method for prevention is to properly temper chocolate. Tempering is the process of pre-crystallizing cocoa butter to seed chocolate with the proper number, size and polymorphic form of cocoa butter crystals (Kleinert, 1970; Ziegler, 2001). Cocoa butter can crystallize into six different polymorphic forms (Chapman, Akehurst, & Wright, 1971; Loisel, Keller, Lecq, Bourgaux, & Ollivon, 1998; Lovegren, Gray, & Feuge, 1976; Wille & Lutton, 1966), with the βV form being the desired polymorph for tempered chocolate. A properly tempered chocolate is glossy and free of bloom, has a smooth mouthfeel, and delivers a hard snap when broken. Bloom on tempered chocolate is always associated with recrystallization of cocoa butter crystals from the βV form to the more stable βVI form, although this transformation can also occur without the formation of bloom (Adenier, Chaveron, & Ollivon, 1993; Bricknell & Hartel, 1998). The physical aspect of this type of bloom is large, needle-like cocoa butter crystals in the βVI form. Conditions such as
⁎ Corresponding author. Tel.: + 1 608 263 1965. E-mail address: [email protected] (R.W. Hartel). 0963-9969/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2012.05.011
improper storage temperatures and oil migration can promote the recrystallization of cocoa butter in tempered chocolate. Bloom on tempered chocolate due to oil migration often occurs when chocolate has direct contact with another fat containing component. Such is the case with filled or enrobed chocolate products, especially those with nut-based centers. Two-way oil migration will occur until fat compositional equilibrium is reached. As oil migrates into the chocolate, higher melting cocoa butter triacylglycerols (TAG) dissolve in the oil. These TAG eventually recrystallize on the surface of the chocolate in the βVI form, which can result in bloom. Oil migration is enhanced with high temperatures, long contact times between the chocolate and other fat containing component, and high levels of liquid oil in one or both of the components in the system (Talbot, Smith, & Cain, 2006; Talbot, Smith, & Zand, 2006; Timms, 1984; Ziegleder, 1997; Ziegler, Shetty, & Anantheswaran, 2004). The mechanism of bloom formation on untempered and undertempered chocolate is different from that of other types of bloom. When melted chocolate does not contain enough seed crystals, cocoa butter will crystallize in an unstable polymorph. The subsequent recrystallization to more stable polymorphs results in a contraction effect of the cocoa butter crystalline matrix, which pushes cocoa solids and sugar particles to the surface of the chocolate (Kinta & Hartel, 2010). Thus, the composition of bloom on untempered and undertempered chocolate is sugar particles and cocoa solids (Kinta & Hartel, 2010; Kinta & Hatta, 2005; Lonchampt & Hartel, 2006). Given the delicate balance of factors required to create a piece of bloom-free chocolate, it is noteworthy that bloom on chocolate chips baked in cookies is rarely a problem, even though the chocolate
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chips are subjected to conditions normally associated with bloom. For one, chocolate chips are exposed to very high temperatures during baking, where melting and resolidification should lead to bloom. Also, chocolate chips have direct contact with cookie dough, which normally contains a fat other than cocoa butter. These conditions are ideal for oil migration. There are two potential explanations for why chocolate chips do not bloom when baked in cookies. The first relates to the possibility of a crystal memory effect. When cocoa butter is heated just above its melting point for a short time, a small amount of high melting β crystals may remain in the liquid melt. As the cocoa butter is cooled, these β crystals can provide the structural information necessary for the cocoa butter to recrystallize directly to the β form (van Malssen, van Langevelde, Peschar, & Schenk, 1999). This in turn could result in bloom-free chocolate. If chocolate chips baked in cookie dough do not melt completely, perhaps as a result of evaporative cooling or an insulating effect from the cookie dough during baking, the chips could contain sufficient un-melted stable cocoa butter crystals to be seeded upon cooling. The second possible explanation involves the oil migration that occurs during baking between the cookie dough and chocolate chips. Migrating oil from cookie dough changes the fat composition of the chocolate chips, which may cause cocoa butter to crystallize in such a way that there is no visual bloom. The focus of this study was to demonstrate which conditions lead to bloom inhibition on chocolate chips baked in cookies, to determine if crystal memory effect and/or oil migration is responsible for the observed bloom inhibition, and to quantify the degree of migration occurring in chocolate chips baked in cookies.
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each cookie prior to baking. The chips were positioned upside down, so that the flat side of the chip was level with the cookie surface. The cookies were baked in a conventional oven (Frigidaire) for 12 min at 325 °F. After baking, cookies were cooled at room temperature (approximately 22 °C) on a cooling rack lined with parchment paper and stored on sheet trays at 20 °C for 10 days. A storage period of 10 days was chosen as it was adequate time for bloom to form on chocolate chips without sacrificing the overall quality of the cookie. Five individual batches of cookie dough were prepared for each fat level and type. Five cookies from each batch were reserved for analysis. One chip from each cookie was selected for analysis based on how well it remained embedded in cookie dough during and after baking. This resulted in 25 samples for each condition tested. 2.2. Temperature profile of chocolate chips during baking To determine if crystal memory effect was the cause of bloom inhibition on chocolate chips baked in cookies, it was necessary to verify that chips melted completely during baking. This was determined by observing the internal temperature of the chocolate chips during baking using a thermocouple. A small hole was carved into the side of the chocolate chip using a needle, and a wire temperature probe was inserted into the hole. The chocolate chip was pushed into the cookie dough with the point of the chip facing down, so that the flat side of the chip was even with the dough. Special care was taken not to dislodge the temperature probe. Samples were baked at 325 °F for 12 min. The chocolate chip temperature was recorded every minute for the duration of the baking process. 2.3. Monitoring bloom formation on chocolate chips
2. Material and methods 2.1. Preparation of cookies To determine the effects of different fats on chocolate chip bloom, chocolate chip cookies were formulated using a standard recipe (Table 1). The fat content of the cookie dough ranged from 7.8% to 22.9%. Fat content was calculated by dividing the amount of fat by the total sum of the ingredients in the cookie dough, excluding the weight of the chocolate chips. Fats used included fractionated palm oil shortening (Tropical Traditions, West Bend, WI), olive oil (Filippo Berio, Italy), peanut oil (Shurfine, Tigard, OR), and cocoa butter (ADM Cocoa, Milwaukee, WI). Cookie dough was prepared by mixing the fat and sugars in a stand mixer (KitchenAid, Custom 350 W, 5 qt.) with a paddle attachment. Next, the powdered egg–water solution and imitation vanilla were added and mixed. Flour, baking soda and salt were sifted together and added. The dough was mixed just until all the ingredients were incorporated. Finally, the chocolate chips were folded into the dough by hand. Cookie dough was divided into twelve portions on a sheet tray lined with parchment paper. In order to produce unobstructed images of bloomed chocolate chips, three additional chocolate chips were pushed into the top of
Table 1 Cookie formulation. Ingredient
Amount
Fat (palm oil shortening, cocoa butter, olive oil, or peanut oil) Granulated sugar Dark brown sugar Powdered whole egg Water Artificial vanilla extract All-purpose flour Baking soda Salt Nestle® semi-sweet chocolate chips
16–56 g 46 g 30 g 5g 21 g 2g 82 g 1.25 g 1.5 g 60 g
To quantify the amount of bloom formed on the chocolate chip surfaces after 10 days, images of chocolate chips were analyzed for bloom. Pictures of chocolate chips were taken using a stereomicroscope, magnification 1.5×, and a digital camera (Nikon SMZ-10 microscope; Nikon DS-5m camera head; Nikon DS-L1 control unit). Images were cropped to exclude portions of baked cookie surrounding the chip using Adobe Photoshop (CS2, version 9.0). Imaging software Image-Pro Plus 6.0 was used to highlight the white portions of the image, which corresponded to the bloomed areas of the chocolate surface. The number of pixels in the white areas was counted automatically and the percent bloom on the chocolate chip was calculated by comparing the number of pixels in the white areas to the total number of pixels in the image. Pixels were approximately 4 μm in width. A level of approximately 2% bloom on chocolate was the threshold where bloom was no longer visible with the naked eye. 2.4. Sand and fat mixtures Chocolate chips were baked in cups filled with mixtures of fat and washed sea sand to mimic the effect of fat in cookie dough on chocolate chips in the absence of other ingredients. The sand and fat were thoroughly mixed at room temperature in a stand mixer (KitchenAid, Custom 350 W, 5 qt.), similar to creaming sugar and fat in cookie dough preparation. Palm oil shortening was used in amounts ranging from 0% to 14%. Mixtures were scooped into cupcake holders and chocolate chips were pushed into the surface of the mixtures. As before, the chocolate chips were positioned upside down so that the flat side of the chip was even with the surface of the sand. The samples were baked, stored and analyzed using the method described above for the cookies. A minimum of one chip per cup was selected for analysis based on how well it remained embedded in the sand during and after baking. Three separate cups were prepared per batch of sand–fat mixture, and five batches of sand–fat mixtures were prepared for every level of fat tested, resulting in a minimum of 15 samples per fat level.
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2.5. Triacylglycerol (TAG) analysis Analysis of TAG profiles of chocolate chips baked in cookies and sand, unbaked chocolate chips, palm oil shortening and olive oil were obtained in order to verify and quantify oil migration during baking. Chocolate chips were carefully scraped out of cookies and sand–fat mixtures that had been stored for 10 days at 20 °C. The chocolate was dissolved in petroleum ether and filtered through syringe filters. TAG profiles were obtained using gas chromatography, courtesy of ADM Cocoa, Milwaukee, WI. Two samples from each chip were analyzed. 2.6. Degree of oil migration To quantify oil migration occurring in cookies and sand mixtures, degree of oil migration was calculated (Talbot, Smith, & Cain, 2006; Talbot, Smith, & Zand, 2006) using TAG levels from fat in cookie dough or sand/fat mixtures, and fat in chocolate chips before and after baking (Eq. (1)). The degree of oil migration (DM) was calculated for individual TAG. Average degree of migration was then calculated by averaging the degree of migration values for all TAG (Eq. (2)).
DMi ð% Þ ¼
ðX BC −X C Þ ðX FCD −X C Þ
least 4 min after baking. In total, the chips spent a minimum of eight minutes above 50 °C. It is common practice to melt chocolate to 60– 80 °C, well above the melting range of cocoa butter, in order to prevent crystal memory effect. However, van Malssen, Pschar, Brito, and Schenk (1996) studied the melting temperatures required to inhibit crystal memory effect and found that when cocoa butter was heated to 39 °C or higher, no direct β crystallization occurred after cooling for 45 min at 25 °C. They suggest that lower-melting cocoa butter TAGs are the most influential in the crystallization of cocoa butter. By raising the temperature just slightly higher than that of the melting temperature of cocoa butter, these lower melting TAG melt and no crystal memory effect is observed. Since the internal temperature of chocolate chips baked in cookie dough remained well above 39 °C for over 10 min, it can be expected that the chocolate broke temper during baking. Therefore, the absence of bloom on chocolate chips
a
ð1Þ
where: DMi XBC XC XFCD
degree of migration of particular TAG (%) % TAG in baked chip % TAG in unbaked chip % TAG in fat in cookie dough
b n ― X DMi DM ¼ n i
ð2Þ
where: ― DM i
average degree of migration individual TAG
Since each TAG migrates to a slightly different extent based on its individual difference in concentration between chocolate and cookie dough, this value provides an average extent of migration across all TAG. The primary TAG in both chocolate and cookie dough were taken into account in this calculation. 3. Results and discussion
c
3.1. Temperature profile for chocolate chips baked in cookies It has been suggested that chocolate chips baked in cookies do not bloom because the chips do not melt completely during baking. Even if trace amounts of cocoa butter crystals remain in the chocolate, a so-called crystal memory effect could influence how the chocolate re-solidifies after baking. If enough crystal structural information remains in the chocolate due to insufficient melting, the cocoa butter might crystallize directly into the β form, resulting in a bloom-free chocolate chip. To determine whether chocolate chips melt completely when baked in cookie dough, the internal temperature of chips was monitored during baking. It was observed that the temperature of the chips reached 60 °C at the end of the 12 min baking trial. In addition, the temperature of the chocolate chips remained above 60 °C for at
Fig. 1. Average bloom (% white pixels on chocolate chips baked in cookies made with a) palm oil shortening, b) olive oil, c) peanut oil. The dashed line at 2% average bloom indicates the threshold where bloom is not longer visible to the naked eye.
A. Frazier, R.W. Hartel / Food Research International 48 (2012) 380–386
a
b
Fig. 2. Bloom is visible on chocolate chips baked in cookies containing 14% palm oil shortening (a), but completely inhibited on chocolate chips baked in cookies containing 20% palm oil shortening (b).
baked in cookies cannot be a result of crystal memory effect, and another factor must be responsible. This is further supported by the observation of bloom on chocolate chips in cookies made with low fat content (see below). 3.2. Quantification of bloom on chocolate chips baked in cookies To study the effects of oil migration on bloom formation, chocolate chip cookies were formulated with a variety of fats including palm oil, olive oil, peanut oil and cocoa butter. Cookies were baked and stored for 10 days to observe bloom. For cookies made with fats other than cocoa butter, the amount of bloom visible on the chocolate chips decreased with increased fat content of the cookie dough (Fig. 1). When the fat level was above some critical amount, bloom was completely inhibited (Fig. 2). This demonstrates a connection between cookie dough fat content and bloom inhibition, possibly enabled by oil migration between the chocolate chip
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and cookie dough. Furthermore, the fact that some chocolate chips do bloom when baked in cookie dough further supports the notion that crystal memory effect is an unlikely cause of chocolate chip bloom inhibition. Cookies made with cocoa butter did not follow the trend of bloom inhibition with increased cookie dough fat content. Even with very high levels of cocoa butter added to cookie dough, the amount of bloom formed on chocolate chips did not change. The driving force for oil migration is the compositional difference between the two phases in contact with each other. If the fat in each phase is the same, no net migration will occur. Ziegler et al. (2004) demonstrated this by storing chocolate samples on filter paper saturated with cocoa butter. He found that no net migration occurred for a system containing only cocoa butter, whereas migration did occur when the filter paper was saturated with a fat other than cocoa butter. Furthermore, Kleinert (1970) found when cocoa butter centers were enrobed with chocolate and stored for 36 months under conditions designed to encourage bloom formation on enrobed chocolates, no bloom occurred, indicating that no net oil migration had occurred and the composition of the chocolate was not changed. Had significant net oil migration taken place, bloom likely would have formed. In the case of cookies made with cocoa butter, the same fat was present in both the dough and the chocolate chip. There was no driving force (or very little, depending on slight differences in cocoa butter composition) for oil migration to occur. Since no net oil migration occurred, the composition of the chocolate chip remained relatively unchanged after baking and bloom occurred as would be expected on untempered chocolate. In the case of cookies made with fats other than cocoa butter, the fat in the cookie dough was different enough from the cocoa butter in the chocolate chip, and as a result, migration readily occurred during baking. We conclude, therefore, that migration of fat from the cookie dough into the chocolate chip was, at least in part, responsible for the bloom inhibition observed here. Cookies made with palm oil shortening required greater amounts of fat in the dough for bloom inhibition to occur than cookies made with peanut oil and olive oil (Fig. 1). In general, liquid TAG are more mobile and migrate at a faster rate than crystalline TAG (Talbot, Smith, & Cain, 2006; Talbot, Smith, & Zand, 2006; Ziegleder, 1997; Ziegler et al., 2004). Since peanut oil and olive oil are liquid oils, with lower solid fat contents than palm oil shortening, it is likely that peanut oil and olive oil more readily migrated through the cookie dough. As a result, less of these oils were required in the dough to provide bloom protection. Of course, once a cookie is exposed to baking temperature, all the fat in the cookie will be in a liquid state. Perhaps since peanut and olive oil are liquid and do not require an initial melting period in the oven, cookies made with these fats experienced greater total migration, which leads to enhanced bloom inhibition with less fat needed to completely inhibit bloom. 3.3. TAG migration analysis for chocolate chips baked in cookies The degree of oil migration from cookie dough into a chocolate chip can be calculated by measuring the TAG profile of the fat phase of a chocolate chip before and after baking. TAG analysis was performed on chocolate chip samples taken from cookies made with
Table 2 Triacylglycerol (TAG) profiles for palm oil (PO), unbaked chocolate chips, and chocolate chips baked in cookies made with palm oil at different fat contents in the cookie dough. P — palmitic acid, L — linoleic acid, O — oleic acid, S — stearic acid. Courtesy Adam Lechter, ADM Cocoa, Milwaukee, WI. TAG
Palm oil
Unbaked chip
14.02% PO
16.48% PO
17.66% PO
20.02% PO
PLO POO PLP POP SOS POS
13.16 ± 0.05 23.31 ± 0.02 11.09 ± 0.10 27.43 ± 0.22 0.67 ± 0.02 5.15 ± 0.05
0.48 ± 0.02 3.31 ± 0.27 2.60 ± 0.05 14.73 ± 0.22 23.42 ± 0.01 35.34 ± 0.34
2.38 ± 0.15 6.05 ± 0.01 3.33 ± 0.24 15.72 ± 0.12 20.32 ± 0.03 31.69 ± 0.26
2.68 ± 0.07 5.73 ± 0.09 3.67 ± 0.11 15.78 ± 0.13 20.92 ± 0.19 31.98 ± 0.21
3.27 ± 0.04 6.93 ± 0.11 4.20 ± 0.18 15.86 ± 0.06 19.44 ± 0.12 30.45 ± 0.23
3.56 ± 0.08 7.57 ± 0.12 4.21 ± 0.23 16.72 ± 0.13 18.68 ± 0.16 30.10 ± 0.03
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Fig. 3. Degree of oil migration for chocolate chips baked in cookies made with palm oil shortening. Dashed lines indicate level at which bloom was inhibited.
Fig. 4. Degree of oil migration for chocolate chips baked in cookies made with olive oil. Dashed lines indicate level at which bloom was inhibited.
14.02%, 16.48%, 17.66% and 20.02% palm oil shortening (Table 2). The TAG profiles clearly show that fat migration occurred, and at greater levels in cookies made with higher amounts of fat. TAG found at higher levels in palm oil than in cocoa butter (PLO, POO, POP and PLP) increased in the chocolate chip after baking, indicating that palm oil migrated from the cookie dough into the chip. In addition, TAG found at higher levels in cocoa butter (SOS, POS) decreased in amount in the chip after baking. Supplementary TAG analysis, not presented here, showed increased SOS and POS levels in baked palm oil cookie, confirming that the observed decrease in SOS and POS levels in the chocolate chips was due to migration and not solely a result of dilution. This indicates that palm oil migrated from the cookie into the chip at the same time cocoa butter migrated out of the chip. The average degree of migration was calculated from Eqs. (1) and (2) based on PLO, POO, POP, PLP, SOS and POS levels. As expected, higher fat levels in cookie dough led to higher levels of fat migration, as seen in Fig. 3. From Fig. 1, about 18% palm oil in the cookie dough was required to inhibit bloom on chocolate chips baked in cookies. Thus, the degree of migration required to inhibit bloom was approximately 16%. TAG levels were also measured for chocolate chips baked in cookies made with olive oil. Levels of OOO, POO and PLO increased in the chocolate chip after baking and levels of POS, SOS and POP decreased (Table 3). In addition, levels of SOS and POS increased in the cookie dough after baking. Based on these TAG, the average degree of migration was calculated using Eqs. (1) and (2). From Fig. 1, 12% olive oil in the cookie dough was required to inhibit bloom on chocolate chips baked in cookies. Thus, the degree of migration required to inhibit bloom was approximately 16% (Fig. 4). Roughly equivalent degrees of migration were necessary to inhibit bloom in both palm oil and olive oil cookies (Fig. 5). In general, approximately 16% oil migration was required to prevent bloom formation on chocolate chips baked in cookies, regardless of the fat used in the cookie dough. Further work is needed to determine the degree of
migration necessary for cookies made with other fats and to verify these findings. 3.4. Sand–fat mixtures In order to observe the effect of cookie dough fat content on chocolate chip bloom without the influence of other components of cookie dough, chocolate chips were baked in cups filled with mixtures of fat and washed sea sand. If it is indeed fat migration in cookies that provided bloom protection, then the bloom inhibition on chocolate chips baked in sand should be equivalent to bloom inhibition on chips baked in cookies. 3.4.1. Temperature profile for chocolate chips during baking in sand To confirm that chocolate chips baked in sand–fat mixtures melted completely and broke temper during baking, the internal temperature of the chip was recorded. Chocolate chips baked in plain sand with no palm oil shortening reached 105.7 °C in 12 min and chocolate chips baked in sand mixed with 13% palm oil shortening reached 102 °C. The temperatures observed here were sufficiently high to completely melt the chocolate chips. As a result, no crystal memory effect could have occurred and any bloom inhibition on chocolate chips baked in sand–fat mixtures was due to some other factor. 3.4.2. Bloom on chocolate chips baked in sand–fat mixtures Chocolate chips baked in sand and palm oil shortening mixtures exhibited a similar bloom inhibition effect as observed for cookies. Higher amounts of palm oil shortening mixed into sand resulted in less chocolate chip bloom (Fig. 6). In fact, chocolate chips baked in sand and palm oil shortening mixtures above 8% remained unbloomed in excess of 24 months when stored at 20 °C. Since fat was the only component in the sand system, fat in cookie dough played a major role in bloom inhibition on chocolate chips.
Table 3 Triacylglycerol (TAG) profiles for olive oil (OO), unbaked chocolate chips, and chocolate chips baked in cookies made with olive oil at different fat contents in the cookie dough. P — palmitic acid, L — linoleic acid, O — oleic acid, S — stearic acid. Courtesy Adam Lechter, ADM Cocoa, Milwaukee, WI. TAG
Palm oil
Unbaked chip
14.02% OO
16.48% OO
17.66% OO
20.02% OO
PLO POO PLP POP SOS POS
13.16 ± 0.05 23.31 ± 0.02 11.09 ± 0.10 27.43 ± 0.22 0.67 ± 0.02 5.15 ± 0.05
0.48 ± 0.02 3.31 ± 0.27 2.60 ± 0.05 14.73 ± 0.22 23.42 ± 0.01 35.34 ± 0.34
2.38 ± 0.15 6.05 ± 0.01 3.33 ± 0.24 15.72 ± 0.12 20.32 ± 0.03 31.69 ± 0.26
2.68 ± 0.07 5.73 ± 0.09 3.67 ± 0.11 15.78 ± 0.13 20.92 ± 0.19 31.98 ± 0.21
3.27 ± 0.04 6.93 ± 0.11 4.20 ± 0.18 15.86 ± 0.06 19.44 ± 0.12 30.45 ± 0.23
3.56 ± 0.08 7.57 ± 0.12 4.21 ± 0.23 16.72 ± 0.13 18.68 ± 0.16 30.10 ± 0.03
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Fig. 5. Degree of oil migration and average bloom (% white pixels) for chocolate chips baked in cookies made with palm oil shortening and olive oil. The dashed line at 2% average bloom indicates the threshold where bloom was no longer visible to the naked eye.
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3.4.3. TAG migration analysis for chocolate chips baked in sand TAG profiles were obtained from chocolate chips baked in sand and palm oil mixtures (Table 4). As for chocolate chips baked in cookies, the levels of PLO, POO, POP and PLP increased and the levels of SOS and POS decreased in the chip after baking, indicating that fat migration occurred in both directions between the chocolate chip and the sand. The amount of migration was greatest for the chip baked in sand with the highest fat content. The degree of migration was calculated using Eqs. (1) and (2). About 10% fat in the sand mixture was needed to prevent bloom, so approximately 40% oil migration was required in order for bloom to be inhibited (Fig. 7). This was a noticeably higher degree of migration than the 16% migration required to inhibit bloom on chocolate chips baked in cookies. It is unclear why a higher degree of migration was required to inhibit bloom on chocolate chips baked in sand. It appears that when fat is the only ingredient in the system, much more fat is required to inhibit bloom. This suggests that other ingredients in the cookie dough may also contribute to bloom inhibition. Structural differences, such as particle size, shape and surface characteristics between in the cookie dough and the sand model system may explain the variation in migration levels observed. Also, the chocolate chips baked in sand reached higher temperatures and melted faster than chocolate chips baked in cookie dough, which may have resulted in more total oil migration. In addition, unlike cookie dough, the sand mixtures contained no water. The absence of polar interferences from water in the sand matrix may allow the fat to migrate more efficiently. Overall, the complex microstructure of cookie dough may impede fat migration compared to the simple sand-fat system. 4. Conclusion
Fig. 6. Average bloom (% white pixels) on chocolate chips baked in sand and palm oil mixtures. The dashed line at 2% bloom indicates the threshold where bloom is no longer visible to the naked eye.
In general, less fat was required to inhibit bloom on chocolate chips baked in sand–fat mixtures compared to chocolate chips baked in cookies. For example, while 18–19% palm oil shortening was necessary to inhibit bloom on chocolate chips baked in cookies, as little as 8% palm oil shortening inhibited bloom in the sand system. One reason for the disparity between the fat levels needed to inhibit bloom in cookies and sand-fat mixtures may be due to differences in the physical structure of the two systems. Cookie dough is a denser medium with a more complex microstructure than sand. Liquid fat may more readily migrate through sand due to the homogeneity of the system and larger particle size, resulting in more fat migration into the chocolate chip. As a result, less fat in the sand was required to inhibit bloom. In addition, the chocolate chips baked in sand reached higher temperatures and melted faster than chocolate chips baked in cookie dough, meaning chips baked in sand spent a longer time in the molten state during baking, which also resulted in more total oil migration.
To better understand why chocolate chips generally do not bloom in cookies, potential factors affecting chocolate chips were examined. It was demonstrated that chocolate chips in cookies melted completely during baking. Thus, crystal memory effect was not a factor in the observed bloom inhibition on chocolate chips. Fat migration was shown to be the primary factor that influenced bloom formation on chocolate chips baked in cookies. When the fat content of the cookie dough was sufficiently high, enough fat migrated into the chocolate chip such that, upon cooling and storage, bloom was inhibited. The degree of migration necessary to inhibit bloom on chocolate chips was similar for cookies made with palm oil shortening and olive oil, even though the amount of fat added to the cookie dough was not the same. Bloom inhibition also occurred on chocolate chips baked in a model system of sand and fat mixtures. A higher level of fat migration was required for palm oil to inhibit bloom on chocolate chips baked in the sand system compared to chocolate chips baked in cookies. This indicated that other ingredients in cookie dough may play a role in bloom inhibition on chocolate chips. Although fat migration clearly contributes to bloom inhibition in this case, the exact mechanism behind this inhibition is still unknown. Based on the soft texture of chocolate chips in cookies after baking, we speculate that the phase behavior and change in crystallization/ polymorphism of the mixed fat system is responsible for bloom
Table 4 Triacylglycerol (TAG) profiles for palm oil (PO), unbaked chocolate chips, and chocolate chips baked in sand and palm oil mixtures at different fat contents in the sand. P — palmitic acid, L — linoleic acid, O — oleic acid, S — stearic acid. Courtesy Adam Lechter, ADM Cocoa, Milwaukee, WI. TAG
Palm oil
Unbaked chip
3.85% PO
6.54% PO
8.26% PO
13.04% PO
PLO POO PLP POP SOS POS
13.16 ± 0.05 23.31 ± 0.02 11.09 ± 0.10 27.43 ± 0.22 0.67 ± 0.02 5.15 ± 0.05
0.48 ± 0.02 3.31 ± 0.27 2.60 ± 0.05 14.73 ± 0.22 23.42 ± 0.01 35.34 ± 0.34
2.05 ± 0.03 5.57 ± 0.12 3.57 ± 0.11 15.24 ± 0.28 21.19 ± 0.09 31.81 ± 0.13
5.03 ± 0.17 9.95 ± 0.25 4.80 ± 0.06 16.44 ± 0.08 17.06 ± 0.16 26.44 ± 0.04
6.83 ± 0.03 12.53 ± 0.05 5.99 ± 0.05 17.65 ± 0.03 14.93 ± 0.23 23.39 ± 0.12
7.18 ± 0.09 14.28 ± 0.12 6.52 ± 0.11 18.22 ± 0.42 13.25 ± 0.08 21.29 ± 0.05
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Fig. 7. Degree of oil migration for chocolate chips baked in sand and palm oil mixtures. Dashed lines indicate level at which bloom was inhibited.
inhibition. Perhaps the complex fat mixture in the chocolate chip after baking does not undergo polymorphic transformations thought to be responsible for bloom. Further work in the area is warranted. Acknowledgments Funding from the PMCA, an International Organization of Confectioners, is greatly appreciated. Thanks to Adam Lechter and ADM Cocoa, Milwaukee, WI for assistance with the analyses. References Adenier, H., Chaveron, H., & Ollivon, M. (1993). Mechanism of fat bloom development on chocolate. In G. Charalambous (Ed.), Shelf life studies on food and beverages: chemical, biological, physical and nutritional aspects (pp. 353–389). Amsterdam (Netherlands): Elsevier.
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