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Title: Microstructural development of high solid food systems during freeze-drying
Author: Malik, Nur Hafizah
ISNI:       0000 0004 7432 5123
Awarding Body: University of Birmingham
Current Institution: University of Birmingham
Date of Award: 2018
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Freeze-drying is an energy demanding operation involving dehydration through sublimation of ice crystals. It has important application in the production of high quality dried food such as instant coffee. Correlating the operating conditions with product attributes is essential to design processes that are energy efficient whilst producing product of desired characteristics. In this study, microstructure development and evaluation for gum arabic and coffee solutions during freeze-drying have been considered. Freeze-drying processes were carried by varying the material’s concentration (20-60% w/w) and properties as well as freezing and primary drying conditions. Microstructural evaluation and reconstitution behaviour of freeze-dried solids were assessed using scanning electron microscopy, X-ray computed tomography and high resolution camera. Initially, water crystallization was studied under temperature oscillation, slow, fast and unidirectional freezing where large crystal dendrites developed on fluctuating temperature and different freezing rates produced comparable crystal network. At reduced water content, smaller crystals developed and distinct orientation of crystal growth was visible. Meanwhile, at increasing primary drying temperature and concentration, the freeze- dried systems showed extensive structure expansion. The potential of aeration to assist freeze-drying of high solid solutions is demonstrated by improved structure uniformity and porosity. Reconstitution of the freeze-dried solids was influenced by the microstructure generated and physical mechanisms involved during dissolution. High porosity and presence of large pores enable rapid dissolution of the dried solids. Different dissolution mechanisms between gum arabic and coffee had strong impact on the kinetics of dissolution. The concept of process-microstructure-property relationship is thus very clear in this study.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General) ; TP Chemical technology