magistrsko delo
Barbara Derganc (Author), Nataša Čelan Korošin (Mentor), Krištof Kranjc (Thesis defence commission member), Romana Cerc Korošec (Thesis defence commission member)

Abstract

Čokolada je opredeljena kot homogen izdelek iz kakavove tekočine (kakavove mase ali paste) in kakavovega masla, z ali brez dodatkov sladkorja, sladil, suhega mleka (razen sirotke), rastlinskih maščob do 5 % in dovoljenih aditivov za živila. Je kompleksna zmes približno 70 % finih trdnih delcev (iz sladkorja in kakava) v neprekinjeni maščobni fazi. Pripravljena je iz kakavovih zrn, ki rastejo na kakavovcu (Theobroma cacao) in se morajo pred izdelavo čokolade tehnološko obdelati. Najprej jih fermentirajo, da se odstrani grenkoba, zatem sušijo, pražijo, na koncu zmeljejo in zmešajo z različnimi sestavinami. Pri sobni temperaturi (okoli 25 °C) je čokolada trdna, tali se pri telesni temperaturi (37 °C), pri čemer nastane gladka mešanica trdnih delcev v kakavovem maslu. Glede na njeno sestavo razlikujemo temno, mlečno in belo čokolado. Ker povpraševanje po tekoči in trdni čokoladi na svetovnih trgih narašča, je razumevanje dejavnikov, ki vplivajo na njeno kvaliteto, koristno tako za njene proizvajalce kot potrošnike. Ena večjih težav, povezanih s proizvodnimi parametri, distribucijo in pogoji skladiščenja čokoladnih izdelkov, je razvoj maščobnega cveta, ki je povezan s kristalizacijo maščobe. Poznavanje kristalizacijskega vedenja kakavovega masla je pomembno pri razvoju čokoladnih izdelkov. Pri eksperimentalnem delu smo razvili različne metode za diferenčno dinamično kalorimetrijo (DSC) in enostavne kemijske eksperimente, ki so primerni za študente ter dijake gimnazije. Z različnimi pogoji meritev smo optimizirali metodo cikličnega DSC za merjenje kakavovega masla in različnih vzorcev čokolad, jim določili polimorfne modifikacije ter vzorce med seboj tudi primerjali. Primerjali smo tudi oksidativno stabilnost kakavovega masla in temne čokolade, ki vsebuje veliko antioksidantov, z določanjem časa induciranja oksidacije (OIT); izračunali smo tudi aktivacijsko energijo oksidativnega razpada za ta dva vzorca. Z DSC-meritvami do 600 °C v atmosferi dušika in zraka pa smo podrobneje pogledali sestavo čokolade in razpad njenih posameznih sestavin. Z enostavnim utemeljevalnim šolskim eksperimentu smo preučili vpliv lecitina in nekaterih drugih dejavnikov na viskoznost različnih mešanic, ki jih lahko povežemo s čokolado, pogledali, zakaj je pravilno temperiranje čokolade tako pomembno s pomočjo problemskega eksperimenta in z digitalnim optičnim mikroskopom posneli vzorca kakavovega masla in temne čokolade med ciklično DSC-meritvijo, da bi si dijaki tudi vizualno lažje predstavljali, kaj se med samo meritvijo dogaja z vzorcem. Za vse šolske eksperimente smo pripravili delovne liste z rešitvami za dijake in navodila za učitelje.

Keywords

kakavova zrna;kakav;kakavovo maslo;polimorfizem;diferenčna dinamična kalorimetrija;DSC-termooptometrija;šolski eksperimenti;delovni listi;magistrska dela;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FKKT - Faculty of Chemistry and Chemical Technology
Publisher: [B. Derganc]
UDC: 543.57:663.91(043.2)
COBISS: 195807235 Link will open in a new window
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Downloads: 3
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Other data

Secondary language: English
Secondary title: Thermal analysis of chocolate and preparation of school experiments
Secondary abstract: Chocolate is defined as a homogeneous product made from cocoa liquor (cocoa mass or paste) and cocoa butter, with or without additions of sugar, sweeteners, dry milk (except whey), vegetable fats up to 5%, and permitted food additives. It is a complex mixture of approximately 70% fine solid particles (from sugar and cocoa) in a continuous fat phase. It is prepared from cocoa beans grown on the cocoa tree (Theobroma cacao) that need to be technologically processed before consumption. First, they are fermented to remove bitterness, then dried, roasted and finally ground and mixed with various ingredients. At room temperature (around 25°C), chocolate is solid and melts at body temperature (37°C), forming a smooth mixture of solid particles in cocoa butter. Depending on its composition we distinguish between dark, milk, and white chocolate. As the demand for liquid and solid chocolate increases in global markets, understanding the factors affecting its quality is beneficial for both producers and consumers. A serious problem related to production parameters, distribution, and storage conditions of chocolate products is the development of fat bloom, which is associated with fat crystallization. Understanding the crystallization behaviour of cocoa butter is important in the development of chocolate products. In experimental work, we developed various methods for differential scanning calorimetry (DSC) and simple chemical experiments suitable for students. With various measurement conditions, the cyclic DSC method for measuring cocoa butter and various chocolate samples were optimized, samples were compared with each other and their polymorphic modifications were determined. We also compared the oxidative stability of cocoa butter and dark chocolate, which contains a lot of antioxidants, by determining the oxidation induction time (OIT); for these samples we also calculated the activation energy of oxidative degradation. With DSC measurements up to 600°C in nitrogen and air atmospheres, we took a closer look at the composition of chocolate and the decomposition of its individual components. The effect of lecithin and some other factors affecting the viscosity of different mixtures that can be associated with chocolate were studied with a simple educational experiment. We showed why proper tempering of chocolate is so important using a problem-based experiment. Samples of cocoa butter and dark chocolate were recorded with a digital optical microscope during cyclic DSC measurement to help students visually understand what happens to the sample during the measurement itself. For all school experiments, we prepared worksheets for students with solutions and instructions for teachers.
Secondary keywords: cocoa butter;chocolate;thermal analysis;polymorphism;DSC thermooptometry;Termična analiza;Čokolada;Univerzitetna in visokošolska dela;
Type (COBISS): Master's thesis/paper
Study programme: 1000379
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Fak. za kemijo in kemijsko tehnologijo, smer Kemijsko izobraževanje
Pages: 1 spletni vir (1 datoteka PDF (87 str.))
ID: 23643060