Abstract
Milk protein concentrate (MPC) and micellar casein (MC) powders are commonly used to increase the protein concentration of cheese milk. However, highly-concentrated milk protein powders are challenging in terms of solubility. The research question was whether and how incompletely dissolved agglomerates affect the protein functionality in terms of rennet gelation behavior. For the experiments, skim milk was enriched with either MC88 or MPC85 to a casein concentration of 4.5% (w/w) and sheared on a laboratory and pilot scale in rotor/stator systems (colloid mill and shear pump, respectively) and high-pressure homogenizers. The assessment criteria were on the one hand particle sizes as a function of shear rate, and on the other hand, the rennet gelation properties meaning gelling time, gel strength, structure loss upon deformation, and serum loss. Furthermore, the casein, whey protein, and casein macropeptide (CMP) recovery in the sweet whey was determined to evaluate the shear-, and hence, the particle size-dependent protein accessibility. We showed that insufficient powder rehydration prolongs the rennet gelation time, leading to softer, weaker gels, and to lower amounts of CMP and whey protein in the sweet whey.
Highlights
In cheese manufacture, it is common to increase the casein or the total protein concentration of the vat milk to increase the cheese yield [1,2]
We hypothesized that remaining powder particles of poorly soluble MC88 and MPC85 impair the rennet gelation behavior due to inaccessible proteins in the powder aggregates as well as the gel properties, which could be disturbed by large powder particles
The particle sizes in MC88- as well as in MPC85enriched skim milk decreased with increasing shear rate. 3.3 × and 3.6 × min−1 showed the worst dissolution results as their mean particle sizes were around 30 μm and their d50,3 varied between 0.4 and 0.2 μm (Figure 2b,d)
Summary
It is common to increase the casein or the total protein concentration of the vat milk to increase the cheese yield [1,2]. With powders the protein content can be standardized flexibly, and seasonal fluctuations of the milk composition can be compensated [3]. These are known to have a major impact on the curd forming properties and, on the composition and the yield of the final cheese [4,5,6,7]. We found out that remaining powder particles increase the shear stress of reconstituted milk protein concentrates. It was not investigated so far whether and how incompletely dissolved powder agglomerates affect the protein functionality in terms of rennet gelation behavior
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