Assessment of process variables on the structural, material, and physical properties of acid milk gels : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand. EMBARGOED until 9 June 2026.

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The aim of this study was to investigate the effect of process and formulation variables on cream cheese microstructure, properties, and their interactions. A systematic approach toward assessing these effects was conducted with a model cream cheese that was developed as part of the study design. Preliminary analysis compared the structural and material properties of commercial cream cheeses against the model composition to determine the extent of formulation variations on the performance of the cream cheese. In terms of compositional variables, both the ratios of fat to moisture and protein to moisture were found to positively correlate with large deformation material properties cream cheeses. These ratios were accordingly fixed in the model cream cheese formulation used within the study. The impact of coagulation kinetics on the structural and material properties of the model cream cheese was then investigated. Milk coagulation was conducted using either glucono delta-lactone (GDL) or lactic acid starter. Acid milk gels formed using GDL showed faster pH decrease during the early stage of acidification, causing earlier gelation at higher gelation pH when compared to gels using culture as acidulant. Amongst other observations, it was seen that the application of GDL as acidulant produced greater acid gel firmness (i.e., storage modulus (G′)) and higher rigidity in the corresponding cream cheeses when compared to acid gels and cream cheeses prepared using starter cultures as the acidulant. The role of additional processing and formulation variables (homogenisation pressure, coagulation pH, coagulation temperature, and stabiliser level) on cream cheese physical, material, and microstructural properties was also determined. Protein-protein and protein-fat interactions were hypothesised as the primary structural contributors to the physical properties of cream cheese, and thus variables that impacted on these interactions were considered as most actively influencing cream cheese properties. Findings were able to show that cream cheese microstructure and its associated properties demonstrated well-defined correlations to specific and controllable processing elements within the manufacturing process, showing significance in interactions between parameters in multivariable linear regression analysis (P < 0.05). Finally, the role of mineral balance of the properties of creams cheese was investigated. Here, different concentrations of the calcium chelating agent, ethylenediaminetetraacetic acid (EDTA), were added to the milk prior to coagulation. Progressive addition of EDTA was seen to reduce levels of insoluble calcium, which in turn led to weakened structural and material properties of both acid milk gels and corresponding cream cheeses. Findings here indicated the particular contribution of ionic content and equilibrium on cream cheese properties during manufacture.
Embargoed to 9 June 2026
Cream cheese, Analysis, Milk, Curdling, Organic acids