A study of the phase transitions of sugars found in chocolate

The overall aim of the PhD project was to investigate the phase transitions of f chocolate sugars. To achieve this, the chemical purity and the re-crystallisation of both iamorphous lactose and amorphous sucrose in a number of model systems were imonitored. Both amorphous lactose and sucrose were prepared by spray- and freeze- drying |of aqueous solutions of lactose and sucrose respectively. The amorphicity of the dried I fsamples was successfully confirmed by differential scanning calorimetry (DSC) and Idynamic mechanical analysis (DMA). NMR analysis was performed and peak areas of tially resolved doublets at 6.3 and 6.6 ppm were used to calculate the percentage (%) :&lt;x- and (3- lactose present. The [3/a anomer contents of amorphous lactose measured by 1H-NMR had standard deviations as low as 0.1% w/w (n = 6). Drying a lactose ilution 4 h after its preparation led to almost 35% w/w difference in anomer Icomposition within solid amorphous material compared to samples dried after only 30 lin e.g. in freeze-dried samples, the (3- content was 60 ± 0.1% w/w (4 h) and 25 ± 1.0% p/w (30 min). Polarimetery was used not only to investigate the kinetics of mutarotation for close solutions at different temperatures but also to confirm the purity of amorphous ucrose by measuring the content of invert sugars, if any. A design of experiments (DoE) pproach was applied to investigate the impact of minerals, water vapour and sugar icomposition on the crystallisation of both sugars. Hot stage microscopy was utilised to jtnomtor the phase changes during crystallisation upon heating. DoE work showed that a shortage of water during crystallisation of sucrose led a higher crystallisation temperature T t. This finding supports the empirical observation from pilot scale chocolate crumb making which states that increasing tpressure, which will increase H2O in the head space, encourages more crystallisation as crystallisation temperature is predicted to be lower.<br/>Minerals also had an impact on recipe by reducing the rate of crystallisation at a concentration of 3% w/w NaCl. actose present in the recipe interacted with sucrose inhibiting the crystallisation of both s. DoE has also proven to be a very efficient methodology, by saving time and Durces, to investigate the correlations that may exist among different variables.

Name dc:type.qualificationname

Doctor of Philosophy

Level dc:type.qualificationlevel

Doctoral Thesis

Grantor dc:publisher.institution

King's College London

Year dc:date.issued

2013

Author dc:creator

• Jawad, Rim

Advisor dc:contributor.advisor

• Royall, Paul Garry

Language dc:language

eng

Identifier

oai:kclpure.kcl.ac.uk:studenttheses/fcdf5172-fd42-4912-bbba-0a49afb13872

OAI identifier oai:identifier

oai:kclpure.kcl.ac.uk:studenttheses/fcdf5172-fd42-4912-bbba-0a49afb13872