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Fat bloom on chocolate confectionery systems - From core to surface

Dahlenborg, Hanna LU (2014)
Abstract (Swedish)
Popular Abstract in Swedish

Populärvetenskaplig sammanfattning



Utvecklingen av nya innovativa chokladprodukter har tagit fart under de senaste åren i takt med att konsumenterna ställer allt högre krav på chokladkvaliteten. Eftersom produktionsprocessen är komplicerad och hållbarhetstiden begränsad uppskattas att man slänger drygt 100 000 ton chokladprodukter varje år i Europa till ett värde av 1.2 miljarder Euro. Att optimera produkternas egenskaper är därför en viktig parameter för chokladindustrin.



Choklad har en mycket unik egenskap. I rumstemperatur är en chokladbit hård men så fort man stoppar den i munnen smälter den. Orsaken till detta är att kakaosmörets fettkristaller smälter... (More)
Popular Abstract in Swedish

Populärvetenskaplig sammanfattning



Utvecklingen av nya innovativa chokladprodukter har tagit fart under de senaste åren i takt med att konsumenterna ställer allt högre krav på chokladkvaliteten. Eftersom produktionsprocessen är komplicerad och hållbarhetstiden begränsad uppskattas att man slänger drygt 100 000 ton chokladprodukter varje år i Europa till ett värde av 1.2 miljarder Euro. Att optimera produkternas egenskaper är därför en viktig parameter för chokladindustrin.



Choklad har en mycket unik egenskap. I rumstemperatur är en chokladbit hård men så fort man stoppar den i munnen smälter den. Orsaken till detta är att kakaosmörets fettkristaller smälter vid 32-34°C, strax under kroppstemperatur. Detta är dock endast fallet om chokladen tillverkats under speciella, kontrollerade förhållanden. Kakaosmör är ett polymorft fett, vilket betyder att det kan anta flera olika kristallformer, alla med olika stabilitet och smältpunkt. Vid chokladproduktion tempererar man chokladen, vilket betyder att man med hjälp av en temperaturcykel styr in kakaosmöret till den kristallform som smälter vid just 32-34°C. Genom naturlagarna kommer denna kristallform med tiden att omvandlas till den mest stabila formen som har en högre smältpunkt och större, nålformade kristaller. Chokladen förlorar då sin initiala glans och får en matt, grå-vit yta. Framför allt leder detta till estetiska förändringar men det påverkar även de sensoriska egenskaperna vilket gör chokladen mindre aptitlig. Fenomenet kallas fettblom och har kommit att utgöra grunden till min avhandling.



Fettblom utvecklas snabbare om något gått fel i produktionen eller om man förvarat chokladen under felaktiga temperaturförhållanden. Produkter som består av en fet fyllning med ett omgivande chokladskal, exv. chokladpraliner tenderar att utveckla fettblom mycket tidigare än en vanlig chokladkaka. Detta beror på att fettmolekylerna från fyllningen förflyttar sig eller migrerar in i chokladskalet och påskyndar processen. Fettmigrering ger också upphov till att chokladskalet blir mjukt medan fyllningen blir hård vilket inte är önskvärt hos konsumenterna. Genom att fördröja fettmigreringshastigheten i chokladpraliner kan man alltså få produkter med längre hållbarhet. Men för att kunna göra detta måste man veta vilka mekanismer som ligger bakom migreringen samt vilka egenskaper hos produkten som påverkar den. Under den senaste 10-årsperioden har en hel del forskning inom området bedrivits och man diskuterar framförallt tre olika fettmigreringsmekanismer; diffusion, kapillära flöden och konvektiva flöden.



Syftet med avhandlingen har varit att bidra till denna pågående forskning genom att utveckla nya metoder för att studera fettmigrering och fettblomutveckling, samt att undersöka chokladskalets mikrostrukturella inverkan. Genom att använda en nyutvecklad metod (EDS) kan man se hur snabbt märkta fettmolekyler från fyllningen rör sig in i chokladskalet under olika förhållanden. Detta kan vidare kopplas till resultat från elektronmikroskopibilder och ytråhetsdata vilket ger en verktygslåda där man kan relatera fettmigreringshastighet till utveckling av fettblomkristaller på chokladytan. Ytterligare en ny teknik som använts för analys av choklad är konfokalt Raman mikroskopi. Med hjälp av detta har vi identifierat bubblor på chokladytan som fortsätter in i chokladskalet i form av kanaler. Dessa kanaler och bubblor kan vara en möjlig väg för fyllningsfettet att vandra genom chokladen och bidra till fettblomutveckling.



Chokladskalets mikrostruktur har visats ha en betydlig påverkan på fettmigreringshastigheten. En kristallstruktur bestående av fler små fettkristaller som packats tätt ledde till långsammare fettmigrering och därigenom långsammare utveckling av fettblom. Även partikelstorleken visade sig påverka hastigheten av fettmigrationen, då mindre partikelstorlek i chokladen ledde till en snabbare migrering och snabbare utveckling av fettblom. Förvaringstemperaturen visade sig ha en mycket stor påverkan på fettmigreringshastigheten och fettblomsutvecklingen. En förvaringstemperatur på 23°C gjorde att det gick betydligt snabbare än en förvaringstemperatur på 20°C. Med stöd av ovannämnda resultat diskuteras tänkbara fettmigreringsmekanismer avslutningsvis i avhandlingen. Förhoppningen är att genererade resultat kan leda till en djupare förståelse för mekanismer bakom fettmigrering och fettblomutveckling i chokladpraliner, och därigenom skapa förutsättningar för vidare produktutveckling inom industrin. (Less)
Abstract
Abstract



Fat bloom on chocolate is a major problem for the confectionery industry since the unappetising appearance and negative sensory effects lead to rejection by customers. The presence of fat bloom on chocolate confectionery systems is usually connected to migration of liquid fat due to the difference in composition between filling triacylglycerols (TAGs) and cocoa butter TAGs. The filling TAGs migrate into the chocolate shell where they can dissolve cocoa butter crystals. Consequently, cocoa butter TAGs migrate to the surface followed by a re-crystallisation into the most stable polymorph β1VI. Cocoa butter is the main fat in chocolate which can be considered as a composite material consisting of solid particles... (More)
Abstract



Fat bloom on chocolate is a major problem for the confectionery industry since the unappetising appearance and negative sensory effects lead to rejection by customers. The presence of fat bloom on chocolate confectionery systems is usually connected to migration of liquid fat due to the difference in composition between filling triacylglycerols (TAGs) and cocoa butter TAGs. The filling TAGs migrate into the chocolate shell where they can dissolve cocoa butter crystals. Consequently, cocoa butter TAGs migrate to the surface followed by a re-crystallisation into the most stable polymorph β1VI. Cocoa butter is the main fat in chocolate which can be considered as a composite material consisting of solid particles (i.e. cocoa particles, sugar crystals and in some cases milk solids) in a lipid continuous matrix of cocoa butter. The final quality of the product is highly dependent on the polymorphic forms of the cocoa butter TAGs in the fat phase and the distribution and size of the solid particles.



In this thesis the migration of filling oil into model shells of cocoa butter and of chocolate has been investigated as well as the fat bloom development. This was implemented through the development of novel analytical methods, where optical profilometry and confocal Raman microscopy give information regarding the shell microstructure at and below the surface, and energy dispersive X-ray spectroscopy (EDS) provides the opportunity to follow the movement of brominated TAGs from the filling into the shell. By combining these techniques with established methods such as low vacuum scanning electron microscopy (LV SEM) and differential scanning calorimetry (DSC) a toolkit for the investigation of oil migration connected to surface microstructure development has been established.



Imperfections, in form of pores and protrusions, at chocolate surfaces have been identified, confirming previous studies reporting these features. These imperfections were characterised using confocal Raman microscopy indicating that some protrusions are filled with fat and some are air-filled in conjunction with a fat shell, while the pores consist of air. These imperfections continued further into the chocolate shell, thus, it is suggested that they could be connected to oil migration and further to fat bloom development.



The microstructure of model shells was shown to have a substantial impact on the TAG migration rate which was connected to fat bloom development. By applying seeding as pre-crystallisation technique to the shells the migration rates were decreased as well as the development of fat bloom crystals at the surface. In contrast, model pralines with poorly tempered shells indicated a higher oil migration rate and accelerated development of fat bloom. Furthermore, the presence of non-fat particles was shown to increase the migration rate and the fat bloom development. Additionally, the particle size of the non-fat particles proved to have an impact, where a smaller particle size gave rise to higher migration rates and thus, accelerated fat bloom development. The importance of controlled storage temperature was further demonstrated, where a minor increase in temperature from 20 to 23°C lead to substantially higher migration rates and accelerated fat bloom development.



The mechanisms of oil migration in chocolate confectionery systems have mainly been referred to as molecular diffusion or capillary flow in literature. However, through results from the work of this thesis, convective flow is suggested to be an important contribution to the migration of filling oil in addition to molecular diffusion and capillary flow. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Prof. Marangoni, Alejandro G., Department of Food Science, University of Guelph, Canada.
organization
publishing date
type
Thesis
publication status
published
subject
keywords
surface structure, particles, migration, fat bloom, cocoa butter, chocolate
pages
154 pages
defense location
Lecture hall B, at the Centre of Chemistry and Chemical Engineering, Getingevägen 60, Lund University Faculty of Engineering, Lund
defense date
2014-02-11 13:15
ISBN
978-91-978122-8-3
language
English
LU publication?
yes
id
5dbc4c31-918f-46a2-aa09-571614afd9f3 (old id 4248907)
date added to LUP
2014-01-15 12:09:59
date last changed
2016-09-19 08:45:19
@phdthesis{5dbc4c31-918f-46a2-aa09-571614afd9f3,
  abstract     = {Abstract<br/><br>
<br/><br>
Fat bloom on chocolate is a major problem for the confectionery industry since the unappetising appearance and negative sensory effects lead to rejection by customers. The presence of fat bloom on chocolate confectionery systems is usually connected to migration of liquid fat due to the difference in composition between filling triacylglycerols (TAGs) and cocoa butter TAGs. The filling TAGs migrate into the chocolate shell where they can dissolve cocoa butter crystals. Consequently, cocoa butter TAGs migrate to the surface followed by a re-crystallisation into the most stable polymorph β1VI. Cocoa butter is the main fat in chocolate which can be considered as a composite material consisting of solid particles (i.e. cocoa particles, sugar crystals and in some cases milk solids) in a lipid continuous matrix of cocoa butter. The final quality of the product is highly dependent on the polymorphic forms of the cocoa butter TAGs in the fat phase and the distribution and size of the solid particles.<br/><br>
<br/><br>
In this thesis the migration of filling oil into model shells of cocoa butter and of chocolate has been investigated as well as the fat bloom development. This was implemented through the development of novel analytical methods, where optical profilometry and confocal Raman microscopy give information regarding the shell microstructure at and below the surface, and energy dispersive X-ray spectroscopy (EDS) provides the opportunity to follow the movement of brominated TAGs from the filling into the shell. By combining these techniques with established methods such as low vacuum scanning electron microscopy (LV SEM) and differential scanning calorimetry (DSC) a toolkit for the investigation of oil migration connected to surface microstructure development has been established. <br/><br>
<br/><br>
Imperfections, in form of pores and protrusions, at chocolate surfaces have been identified, confirming previous studies reporting these features. These imperfections were characterised using confocal Raman microscopy indicating that some protrusions are filled with fat and some are air-filled in conjunction with a fat shell, while the pores consist of air. These imperfections continued further into the chocolate shell, thus, it is suggested that they could be connected to oil migration and further to fat bloom development. <br/><br>
<br/><br>
The microstructure of model shells was shown to have a substantial impact on the TAG migration rate which was connected to fat bloom development. By applying seeding as pre-crystallisation technique to the shells the migration rates were decreased as well as the development of fat bloom crystals at the surface. In contrast, model pralines with poorly tempered shells indicated a higher oil migration rate and accelerated development of fat bloom. Furthermore, the presence of non-fat particles was shown to increase the migration rate and the fat bloom development. Additionally, the particle size of the non-fat particles proved to have an impact, where a smaller particle size gave rise to higher migration rates and thus, accelerated fat bloom development. The importance of controlled storage temperature was further demonstrated, where a minor increase in temperature from 20 to 23°C lead to substantially higher migration rates and accelerated fat bloom development.<br/><br>
<br/><br>
The mechanisms of oil migration in chocolate confectionery systems have mainly been referred to as molecular diffusion or capillary flow in literature. However, through results from the work of this thesis, convective flow is suggested to be an important contribution to the migration of filling oil in addition to molecular diffusion and capillary flow.},
  author       = {Dahlenborg, Hanna},
  isbn         = {978-91-978122-8-3},
  keyword      = {surface structure,particles,migration,fat bloom,cocoa butter,chocolate},
  language     = {eng},
  pages        = {154},
  school       = {Lund University},
  title        = {Fat bloom on chocolate confectionery systems - From core to surface},
  year         = {2014},
}