Hogan, Sarah Eve; (2002) Investigation of the amorphous and crystalline properties of lactose and raffinose. Doctoral thesis (Ph.D.), University College London.

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Abstract

Amorphous material is often induced accidentally during the processing of crystals and can have a detrimental effect on product performance. This thesis aimed to develop techniques for the quantification of such amorphous material occurring at less than 10% w/w in the bulk, using lactose as a model. An investigation of the amorphous and crystalline behaviour of raffinose at various relative humidities was also undertaken. It has previously been shown that changes in physical form are reflected in enthalpy of solution. Solution Calorimetry was found capable of quantifying amorphous content to ± 1% w/w. Similarly, enthalpy of crystallisation values from Isothermal Microcalorimetry, calculated via both a sealed ampoule and RH perfusion technique, were also used to successfully quantify amorphous content. Dynamic Vapour Sorption and Near Infrared Spectroscopy (DVS/NIRS) were employed in a technique combining two independent quantification methods simultaneously. With the gravimetric approach it was found possible to correlate water sorption and expulsion during crystallisation with amorphous content. NIRS correlated amorphous content with absorbance at several wavelengths, achieving quantification to ± 1% w/w. The above-mentioned techniques were used to characterise the hydration and dehydration behaviour of amorphous and crystalline raffinose. Through a combination of DVS/NIRS and calorimetric data it was found that, unlike other common carbohydrates, raffinose does not expel plasticising water upon crystallisation. Data from these techniques also showed that crystallisation of amorphous raffinose leads to the formation of different hydrates or hydrate mixes, depending on the amount of water available to the sample. These were characterised by their enthalpies of crystallisation, fusion and solution. The applicability of the above techniques to study the physical properties of carbohydrates has been demonstrated. In addition to the quantification of disorder in crystalline lactose, they have been used to improve our understanding of the complex amorphous and crystalline behaviour of raffinose.

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