Effect of the compositional factors and processing conditions on the creaming reaction during process cheese manufacturing

Abstract:

Select influence factors in processed cheese making (protein and fat content, fat globule size, and rework addition) affecting the physical changes known as “creaming” were investigated for their effect on this multistage structure formation reaction. The creaming curve (viscosity vs. time) shows four typical stages: an initiation phase, a first exponential stage, a plateu, and a second exponential phase. Increasing the protein content from 10 to 17% (w/w) accelerated the reaction. Light microscopy showed that the fat contente (0–20%) affected the shape of the creaming curve as well and it was shown that a fat level of 15–20% is rewquired for the characteristic creaming curve to occur. Moreover, modifications in the initial milkfat globule size (3.7 μm down to 1.1 μm) by means of upstream homogeneization (0–250/50 bar) accelerated the exponential phase and modified the shape of the creaming curve, shortening the initiation and plateau phases. The reaction started earlier with decreasing incoming fat globule size, and the slope was steeper. When fat was present in the system, it was not only the content, but the milkfat globule size which dictates the viscosity change and shape of the curve. The addition of rework dramatically affects the structure formation process, rework probably acting as a catalyst accelerating the reaction. However, protein polymerization was found to be constant during the entire course of the reaction suggesting that physical bonds are responsible for the structuring of the matrix.

Keywords: Multistage structure formation. Creaming reaction. Processed cheese. Emulsion. Protein network.

Introduction:

In dairy products, quite often protein gels prevail as the basic structure. Processed cheese, in particular, represents an extremely complex system. The underlying principles of processed cheese manufacture have been already extensively reviewed (Fox et al., 2000; Ennis et al., 1998; Fox et al., 1996; Caric; Kalab, 1993). During processing, the presence of “emulsifying” (calcium chelating) salts and the application of temperature and shear at certain pH result in a number of physical-chemical changes. The casein in the cheese disaggregates, disperses, hydrates, swell, and solubilizes, whereby its emulsifying ability is enhanced. This, in turn, is responsible for a structural transformation Leading to a stable finer oil-in-water (o/w) emulsion, physicallyencased within a concentrated para-caseinate matrix. The reduction in the concentration of casein-bound calcium results in hydration of the para-caseinate and its partial conversion to a sodium phosphate para-caseinate dispersion sol (Guinee; O’Kennedy, 2009; Barth et al., 2017). The disintegration and dispersion of the proteins are referred to as “peptidization” (Chambre; Daurelles, 2000; Lee et al., 1979). The latter implies an increase in the water-soluble protein. The degrees of calcium sequestration and casein hydration are dependent on processing conditions, the type and the level of emulsifying salts, and the calcium content in the natural cheese used as well (Mizuno; Lucey, 2005; Guinee; O’Kennedy, 2009; Guinee, 2009; Ennis et al., 1998). McIntyre et al. (2017) report on calcium and protein solubilization during small-scale manufacture of semi-solid casein-based food matrices. Calcium concentration in the dispersed during the manufacture of the matrices containing calcium chelating salts with ~23% of total calcium solubilized by the end of manufacture. Depending on the emulsifier type and on the shear conditions, the fat globule size decrease as the processing time at high temperature proceeds. This results in an increase of ther mumber and in the reduction of the mean diameter of the emulsified fat globules (Kalab et al., 1987; Rayan et al., 1980). Marchesseau et al. (1997) have shown the importance of pH in the structural stabilizationof process cheese. Ramel and Marangoni (2018) describe processed cheese as a particle filled gel network. The report that the addition of rigid particle fillers generally results in increased hardness of the matrix, which could allowfor the replacement of fat by non-fat particles for nutritional reasons. Cunha et al. (2013) reporto n the sensory acceptance of the finally obtained spreadable cheese analogue; the course of structural development was not described.

The reactions described above (calcium exchange, protein dispersion, hydration, swelling, aggregation, network formation, and breakdown) can be followed up using a rheometer (Fu et al., 2018b; Lee et al., 2003; Ennis et al., 1998), and they are better known under the term “creaming reaction” in the process cheese community. The strenght of the composition of the cheese used, and of the shear stress and time. It is also postulated that creaming reconstructs the casein sub-structures to an insoluble matrix, which increases the viscosity of the molten cheese. During cooling, the restructuring continues and most of the characteristic body is formed, which probably includes fat crystallization, protein-protein interactions, and interactions between the dispersed emulsified fat globules and the para-caseinate in the bulk phase (Kapoor; Metzger, 2008; Kawasaki, 2008; Guinee, 2003).

One particularity in process cheese making practice is the optional use of rework (already processed cheese from previous manufacturing) to improve the texture and stability of the processed cheese. Furthermore, the addition of rework leads to an aceleration of the abovementioned reactions. Viscosity of the hot cheese melt and firmness of the final products increase When rework is added even only at a 3% (Kawasaki, 2008).

Similar results were reported in more recentes studies by Černiková et al. (2018), Lee et al. (2015), and Weiserová et al. (2011). The effect of rework addition or other factors like fat and protein concentration was primarily or exclusively looked at with Regard to finished product properties, while in Fu et al. (2018a), the influence on structure development was assessed as a function of time, but limited to a reaction time of below 30 min; the course of viscosity increase was not reported up to the final stage, but limited to 15 min. Guinee et al. (2004) provide possibile explanations for the mechanism on how rework exerts its effects. A further heating of precooked cheese may cause a higher degree of thermally induced dehydration and aggregation of the para-caseinate. Due to a more effective dissolution of the melting salts in the rework, the influence of the melting salts increases and thus the viscosisty, which, according to the authors, results in a more efficient fat dispersion and emulsification of the fresh blend.

Lee et al. (2003) indicated that the creaming reaction is a protein-based interaction, because a similar viscosity increase was observed in a fat-free model process cheese. Berger et al. (1995) postulated the creaming reaction as a process during which a rapid viscosity change of the melting mass takes place and, in contrast to Lee et al. (2003), only fat-containing cheeses were described as able to cream. Guinee et al. (2004) think that creaming may be attributed to the ongoing interaction of the emulsifying salts with te casein and to resulting increases in para-caseinate hydration and the degree of fat emulsification, while Kawasaki (2008) suggested that the creaming reaction reconstructs the soluble para-caseinate submicelles into an insoluble form, thus increasing the viscosity of the hor melt and the final cheese.

Dimitreli and Thomareis (2004) found that fat seems to have no significant influence on the creaming reaction, whereas moisture and protein contents do. Černiková et al. (2018) found that with increasing fat in the dry matter content, the rigidity of the processed cheeses decreased and the size of the fat globules increased. Other work like Panouillé et al. (2004) and (2005) have shown that the aggregation rate and gelation were faster with increasing temperature and casein concentration.

Only few studies have investigated structure formation reactions under stirring and under elevated temperature conditions in an online mode so far (Kapoor; Metzger, 2005; Dimitreli; Thomareis, 2004; Heertje, 1993). Insights on the kinetics of the reaction are scarce. This complex and partially contradictive or incomplete state of knowledge shows that various physical-chemical changes are taking place during the structure formation in processed cheese. However, important practical aspects are still not fully understood according to Kapoor and Metzger (2008) and the interaction of influencing factors have not been investigated sufficiently to firmly state, which reaction mechanisms could be responsible for the creaming reactions.  

The objective of the presente study was to provide further scientific and practical evidence for the influence of compositional parameters and of operational condictions, on the viscosity changes induced by the so-called creamig reaction, both in a benchtop process cheese making and in a model system, and in a continuous online mode. Specifically, we investigated the effects of fat level, protein content, and an upstream homogenization step of the fat component, as well as the effect of rework addition, on the course of the viscosity development during the creaming reaction over longer periods of time. In addition to rheology, light, and electron microscopy, we also analyzed structuralchanges on the micro-level by assessing the degree of polymerization between proteins using gel permeation chromatography.    

Conclusion: 

The viscosity change and shape of the curve versus time is influenced by both the protein and the fat content, as well as by the incoming fat particle size and the addition of rework. A more rapid increase of the viscosity in the first exponential phase is also obtained with an increased protein content. The plateau phase seems to be related to slow diffusional processes, Where proteins at the fat globule interface can be thought to migrate into the continuous phase to form new structures in the form of protein aggregates or a network-like structures. Overall, our conclusion from the accelerating effect of rework is that the course of reaction follows the typical scheme of an autocatalytic reaction, with the rework containing the starting catalyst in the form of pre-structured protein facilitating self-assembly of protein based on van der Wals attractive forces, hydrophobic interactions, and lower electrostatic repulsion. Further research is necessary to assess the influence of additional compositional factors, like pH value, addition of emulsifiers, and the effect of other processing variables, in order to develop a more elaborated mechanistic model for the structure formation mechanism by targeted analytical characterization and to validate the findings at a larger, i.e., pilot plant level. 

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[123] LENZE, S.; WOLFSCHOON-POMBO, A.; SCHRADER, K.; KULOZIK, U. Effect of the compositional factors and processing conditions on the creaming reaction during process cheese manufacturing. Food and Bioprocess Tchnology, [online] 11 january 2019.

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