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Hazelnut quality influences shelf life of chocolate with whole nuts


Abstract and Figures

Nuts in chocolate are a very popular combination. Most popular in the European market is the use of hazelnuts. Similar to filled products nut oil may migrate into the chocolate matrix with the effect of fat bloom formation. This can be seen as a matt halo around the nut. Fat bloom often is not accepted by the consumer and leads to discard of the finished products. Therefore the knowledge on the influence of the quality of nuts on fat bloom formation and possible ways to delay it, is of big interest for the chocolate industry. Hazelnuts may come from different growing areas with different climates and from different breeds. Therefore they may differ in size, taste, fat content and fatty acid composition. Usually for chocolate application nuts are roasted. This can be performed in different ways, for example with higher temperatures in shorter time or vice versa. All these parameters might influence the potential for fat migration and fat bloom formation in the finished chocolates. Knowing the influence of nut quality on fat bloom formation may be used to optimize technological nut processing. In this study different hazelnuts from Turkey from the same size where roasted differently and water contents of roasted nuts was adjusted. Color, fat and water content, oxidative stability, surface oil and mobile fat were measured. The nuts were used for the production of dark chocolate bars. The chocolates were stored at 18°C, 20°C and 23°C and fat bloom formation was investigated. The study showed that roasting parameters have a great influence on the oxidative stability of nuts, even though, roasting color might be the same. A test for mobile oil from whole and chopped hazelnuts could be established. The results from mobile oil and fat content often gave good correlation to fat bloom formation. Roasting parameters had little to no influence on fat bloom formation.
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4 6 8 10 12 14
relative oil migration / slope
start of fat bloom / weeks
roast 1 - a
roast 1 - b
roast 2 - a
roast 2 - b
roast 3 - a
roast 3 - b
A(30-142) A(7-200) O(30-142) O(7-200)
storage time [weeks]
start of fat bloom 1st roast
start of fat bloom 2nd roast
start of fat bloom 3rd roast
Hazelnut quality influences shelf life of chocolate with whole nuts
Contact person:
Wolfgang Danzl
Phone: +49 (0) 81 61 / 491-607
Wolfgang Danzl, Isabell Rothkopf
Fraunhofer Institute for Process Engineering and Packaging IVV, Giggenhauser Straße 35, 85354 Freising, Germany
Chocolates with whole nuts or coarse nuts are popular chocolate products.
Like filled products nut oil migrates into the chocolate matrix and can
produce a special type of fat bloom around the nuts, which is a known
problem. The causes for fat bloom do not only lie on the chocolate part
(solid fat content, tempering) put can also be found on the nuts part. Type
of nut, quality and processing of the nuts may have a major influence. In
addition the chocolates used for such products often contain already
grinded nuts or nut oils. The complex interaction of these factors make the
question for the correlation off fat migration and fat bloom a thrilling and
challenging task.
Qualities of A and O nuts were different. A nuts had a higher fat content which resulted in
higher amounts of measured oil migrating into cocoa butter in the model setup.
In dark chocolate system, nuts with higher fat content and higher oil migration rate also
showed earlier fat bloom results (figure 2 and figure 3).
Roasting temperatures and time had only a little effect on the mobility of oil and therefore
on fat bloom results. However all nuts roasted wit higher temperature but shorter time
showed substantial higher susceptibility against oxidation and rancidity (results not shown)
Nuts in chocolates are a system which can result in undesirable fat bloom development.
The system is highly complex (figure 1). In our first studies, we could show, that fat
migration from the nuts are one substantial cause for fat bloom growth. The potential
migration rates can be estimated using a cocoa butter model. The fat content of the nuts
had a greater influence on migration and bloom than roasting conditions. However these
results have to be confirmed with other nuts.
Still other strategies to minimize fat bloom development can be done on the technology of
chocolate processes such as optimizing the fat compositions and the fat crystal networks.
1 Briones V, Aguilera JM (2005) Image analysis of changes in surface color of
chocolate. Food Research International 38 (1) p.8794. doi:
14th Euro Fed Lipid Congress
Experimental Procedure
Our studies focused on the nut quality side. Therefore two different types of hazelnuts one from Ordu (O) and the other from Akcakoca (A) region in Turkey were
investigated. Both were from harvest 2014 and had a calibrated size of 11-13 mm. The nuts were roasted in a Buehler-Barth (Freiberg am Neckar / Germany) nut roaster
Barth NR in batches of 30 kg. Two different roasting conditions were used: Low temperature long time (LT: 142°C-30min) and high temperature, short time (HT: 200°C-
7min) were performed with each hazelnut batch. The roasting degrees regarding color of the roasted nuts for LT and HT were the same. An oil migration test of the
roasted nuts was performed by storing whole nuts in cocoa butter at 40°C and measuring the solid fat content (SFC) at 20°C via pNMR in the separated cocoa butter
after complete crystallization. Roasted hazelnuts were used in dark chocolate bars for fat bloom examination. Therefore the nuts were stirred into tempered (TI 5-6) dark
chocolate for 3min. Then poured into molds with one nut for each cavity. After crystallization of the chocolate, the bars were demolded and stabilized at 18°C for 24h.
Storage tests were then performed at 18°C, 20°C and 23°C. The samples were analyzed using a DigiEye System by VeriVide was used to take pictures of the samples and
determine L*a*b*-values of each chocolate bar around the hazelnut. From these values the whiteness index (WI) was calculated [1].
Figure 2: Fat bloom development (beginning) on dark chocolates with hole
hazelnuts with different roasting conditions and of different origins.
Figure 1: Basic influences on fat migration an fat bloom development in chocolates with whole nuts.
Figure 3: Possible relation between fat migration from nuts into cocoa butter and
starting time of fat bloom on dark chocolates with whole roasted hazelnuts.
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Blooming or the migration of fat to the surface of chocolate results in color changes and development of non-uniform color patterns. These phenomena were assessed during storage of milk chocolate tablets (cycling temp. between 16 and 28 °C for 52 days) by a computer vision system and image analysis. Eight features were extracted from images (L*, a* and b* values, whiteness index, chroma, hue, % bloom and energy of Fourier). Major changes occurred after day 36 of storage, coincidental with visual perception. Initially, white specks emerged on the brown background but were superseded by the development of a whitish color extending over most of the surface. L*, whiteness index, a* and chroma correlated well with values taken with a commercial colorimeter (R2>0.70). Changes in image texture (energy of Fourier) followed a similar trend as color changes. The sequential forward selection strategy allowed correct classification of 97.8% of samples into four classes with only five features. The computer vision system has the capability to quantify overall changes as well as particular features over the whole chocolate surface thus enabling customization and standardization for quality assessment.