Physicochemical changes during the creaming reaction in acid curd fresh cheese: Water mobility and forced synaeresis

Abstract:

Water mobility changes during a structure building reaction of full-fat cream cheese were studied by applying low-resolution nuclear magnetic resonance. A significant decrease in mobility (T2 relaxation times from 148 to 116 ms) was found in the mobile water phase during texture building. Furthermore, the results were compared to forced synaeresis of the same cheese, which was deter- mined by applying a multistep centrifugation method. The plotted forced synaeresis results dis- played the inverse shape of the structure building reaction: ~14.6% at the beginning (0 min), ~7.4% at peak (47 min) of the reaction and ended with ~9.9% (126 min).

Conclusion:

The relatively weak gel network formed during milk acidification in acid soft cheesemaking is broken down during the mechanical steps in the downstream processing and the loss in structure could be rebuilt during a thermo-mechanical step in a reactor tank or blender, which mimicked the creaming reaction in process cheese. During this last manufacturing step before filling, the particle growth and breakage that takes place affected the viscosity and forced synaeresis results. We suggest that forced synaeresis was promoted by the temperature and shear induced and increased intermolecular attractions between the acid caseins in the matrix as well as by any further denaturation of whey proteins and their cross-linking within the network but also to breakage of protein links. The T2 relaxation time results clearly showed how mobile water interactions varied during the course of the reaction which might have arisen from the changes in the viscosity of the cheese. The two methods, used to describe synaeresis, appear to analyse two different aspects of the cheese. The free water, or expressible serum, which is released through centrifugal forces, is most likely the water in the open capillaries and bigger pores that escapes through the channels of the gel network when the cheese is being highly compressed. The gel network of a cheese in the exponential phase of creaming or shortly after is in its most stable state and likely consists of bigger aggregates, holding water effectively. When the cheese passes the optimal creaming stage, these aggregates start to disassemble, allowing small spaces to be formed from which water can be released when centrifuged. This water could be considered as the mobile water of the cheese macrostructure. The information obtained from NMR measurements is based on the interactions with the nonwater molecules and describes the location inside the cheese microstructure. Nonetheless, the first three samples (123) illustrate the relationship between the two methods, showing a definite decrease in water mobility until the end 3 of the exponential phase. It seems that a correlation exists while the cheese is highly reactive and stops at the point when the methods begin to describe different aspects of water immobilisation. The forced synaeresis method by centrifugation measures the ability of the cheese to hold water, while NMR measures water mobility and thereby the level of freedom that the water of a certain phase has in the cheese. Certainly, due to the processing temperature of almost 80 °C, protein covalent and noncovalent interactions may play a role as well. Agreeing with Mediwaththe et al. (2018), we postulate that the shear and heat regime applied to the protein system in the cream cheese created both favourable and unfavourable conditions for the post-processing structure building and that this step could be used to monitor and control qualitative aspects of the cheese production.

References:

Mediwaththe A, Chandrapala J and Vasiljevic T (2018) Shear-induced behavior of native milk proteins heated at temperatures above 80°C.International Dairy Journal 77 29–37.

[142] Dang, B.; Wolfschoon-Pombo, A. F.; Kulozik, U. Physicochemical changes during the creaming reaction in acid curd fresh cheese: Water mobility and forced synaeresis. International Journal of Dairy Technology, Vol 72, No 2 May 2019.