Abstract:
Mozzarella cheese is primarily consumed in its melted form due to its desirable melt and stretch characteristics that emerge when heated. Existing researches commonly have been conducted with unmelted mozzarella using obsolete techniques which proved insufficient in demonstrating the relationship between the anisotropic structure and melt-stretch properties. In order to further explore the microstructure of mozzarella, this thesis generated a set of ex situ and in situ structure analytics to reveal transient changes during deformation of mozzarella under dynamic heat-shear conditions. Ex situ protocols involved the implementation of a sample extraction device to fabricate melted and stretched mozzarella samples for microstructure analysis. Transformations in anisotropy were examined by probing into the extracted mozzarella samples using a combination of environmental scanning electron microscopy (ESEM), confocal laser scanning microscopy (CLSM) and cryo-scanning electron microscopy techniques coupled with image analysis. In situ compression and tensile tests were developed to allow real time observation of mozzarella undergoing deformations in the ESEM under dynamic heat-shear conditions. The links between mozzarella‟s anisotropic structure and melt-stretch properties were established through the use of microscopy and structural transformations. Unmelted mozzarella possessed an anisotropic arrangement of elongated columns of milk fat. Ex situ tests showed coalescence of milk fat into large droplets upon heating (70°C) with concomitant loss of anisotropy. However, when stretched (50mm), large fat droplets agglomerated into smaller droplets and protein strands realigned. As a result, anisotropy was regained. When stretched further (150mm), adhesion between the agglomerated fat droplets was broken by the forces exerted from the contracted protein fibres. This suggests that large fat droplets are necessary as they act as shock absorbents that enable protein fibres to become pliable; allowing greater length of stretch. In addition, in situ tests in ESEM revealed that straining enhanced fat coalescence and increased free oil discharge at melt temperature. Microscopy and image analysis techniques were developed to expand present understanding of the structure-property of melted mozzarella. The techniques covered in this research can be employed as a tool to tailor the microstructure to achieve desired characteristics in mozzarella as well as other cheese types.