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 determined by applying a multistep centrifugation method. The plotted forced synaeresis results displayed 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).  

Introduction

The major components (protein and fat) of the microstructure of acid, soft cheeses, which are responsible for their rheological properties underego thermal and shear stresses during manufacturing. According to Nöbel et al. (2014) and Senge and Blochwitz (2009), the network formation during fermentation and the destruction of the created gel via concentration and further mechanical treatments in the downstream process determine the structure of fermented dairy products. The formed microgel particles then remain suspended in the serum phase forming thus the next potential structural level. The literature in relation to the effect of post-processing steps on fresh soft cheese is, contrary to, for example acid gels like strred yoghurt, relatively sparse (Sanchez et al., 1996; Schulz-Collins; Sengue, 2004; Mokoonlall et al., 2016; Ningtyas et al., 2018) although the impact of downstream processing on the product quality is extremely high. Defects such as structural graininess (Hahn et al., 2012a) undesirable synaeresis in the final product as well as overly firm products can occur. The temperature and time treatment post-processing have been shown to be crucial to adjust the particle size (Hahn et al., 2012b). The shear effect on the mechanical spectra has been investigated by Sengue and Blochwitz (2009), who reported the structural destruction resulted in a viscosity reduction, hence consistency decrease in the product.

According to Sengue and Blochwitz (2009), certain restructuring of the product takes places after filling, attributed to the thixotropic behaviour, to ‘memory effects’ of the microgel suspended particles and to the temperature. In analogy to the so-called creaming reaction in process cheese (Heertje, 1993; Kapoor and Metzger, 2008; Guinee, 2016), a restructuring of the ‘destructed’ acid microgel mass dispersion can be achieved if shear, time and temperature are applied in a strictly controlled batch or continuous process, followed by the development of viscosity. The latter reaction leading to a viscosity increase is not a formal approach in acid soft cheesemaking, whereas the compositional and processing factors influencing this reaction in process cheese have been investigated in detail by Röck (2010). Hinrichs et al. (2004) studied the effect of shearing at 50 rpm and holding at 80 ºC for 0, 10 and 30 min on the water mobility, viscosity, firmness and synaeresis of restructured cream cheese with added microparticulated and fermente dor acidified whey protein concentrates. The cheeses made with fermented WPC showed a higher firmness and lower synaeresis after 30-min processing at 80 ºC compared to the cheese made with acidified WPC. The sum of the moderate and mobile water fractions, determined by nuclear magnetic resonance (NMR), was around 80%, and the immobilised phase fraction kept at a 15%–18% level for both cheeses. Hinrichs et al. (2004) also found a correlation between the water holding capacity in the cream cheese at the end of the thermomechanical restructuring process just before filling. Hahn et al. (2012b) showed how important temperature and holding time during post-processing are to controle the graininess and structure of yoghurt or fresh cheese.

In a recente evaluation of the forced synaeresis in comercial cream cheese samples, Wolfschoon Pombo et al. (2018) reported that in cheeses with added hydrocolloids physicochemical parameters such as pH, Zeta potential and Ca2+ activity played a negligible role. The effect of down-stream thermo-mechanical treatment in blenders prior to filling on the forced synaeresis should be evaluated as it is a common practice by cheese producers. It is hypothesised that the structuring reactions induced and initiated in the upstream processing steps continue during the more or less undefined and uncontrolled conditions (temperature, residence time, shear rate) in a blender or filler hopper. We assume that a part of product texture variability observed in comercial products can be explained by this situation and could potentially be avoided if more focus was to be put on processing control in the final manufacturing steps. We are not aware of any publication specifically related to this topic. For this purpose, in the present study, a processing tank and not a traditional blender was used for the restructuring (creaming) step. The water mobility and the forced synaeresis during the creaming process of a full-fat soft cheese were investigated using NMR and a stepwise increment in g-force, respectively. 

Conclusions 

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 tht forced synaeresis was promoted by the temperature and shear induced and increased intermolecular attractions bteween 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, wich 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 agregates 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 (1 2 3) ilustrate 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 cheese is highly reactive and stop sat he 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 freedon that the water of a certain phase has in the cheese. Certainly, due to the processing temperature of amost 80 ºC, 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 condictions for the post-processing structure building and that this step could be used to monitor and control qualitative aspects of the cheese production. 

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[122] DANG, B. P.; POMBO, A. F. W; KULOZIK, U. Physicochemical changes during the creaming reaction in acid curd fresh cheese: water mobility and forced synaeresis. International Journal of Dairy Technology, v. 70, p. 1-8, 2019.