Reconstituted milk

Four reconstituted milks were prepared by blending hydrated skim milk powder (35g/L) with four different emulsions (35g/L) differing by composition of the fat-water interface. Whole reconstituted milks were coded MP (milk proteins), BCAS ( 6-casein), and BLG5 (j6-lactoglobulin 5 g/L). 

Skimming fresh whole milk allowed us to obtain milk fat globules with natural membranes that were blended at a concentration of 35 g/L with hydrated skim milk powder (35g/L). This reconstituted milk was coded CREAM. 

The pH of the reconstituted milks was adjusted to 6.4 with 1 N HCL. First, the acidification phase was carried out with glucono(5)lactone (2 g/L) at 30°C in order to exponentially decrease the pH and obtain a stabilized value corresponding to pH = 6.0 after 2 h incubation. Then, rennet was added to the acidified reconstituted milks at a final concentration of 19.5 mg/L and the coagulation phase was performed at 30°C for 3h. 

To reduce scattering effects and to allow a comparison between the different reconstituted milks, the data were normalized by reducing the area under each spectrum to a... 

TABLE 1 Average Diameter of the Natural Milk Fat Globules and Emulsified Milk Fat Droplets Stabilized by Different Fat-Water Interfaces in Reconstituted Milks... 

FIG. 5 Laurdan fluorescence excitation spectra recorded between 250 and 420 nm (emission wavelength, 439 nm) at different times during the acidification and the rennet-induced coagulation kinetics of BLG5 reconstituted milk 35, 70, 125, 175, and 300 min. A.U. = arbitrary units. 

FIG. 6 Evolution of the maximal fluorescence intensity of Laurdan at 363 nm (expressed in arbitrary units) recorded vs. time during BLG5 reconstituted milk acidification and coagulation phases (excitation 250-420 nm emission 439 nm). 

The principal component 1 (PCI) separated the acidification phases of BLG5, CREAM, BCAS, and MP clustered with negative values, from their rennet-induced coagulation phases that spread in a specific order associated with time from the left to the right of the map. These results showed that acidification and gelation of reconstituted milks induced different modifications in the fluorescence properties of Laurdan. 

Dynamic Rheological Properties of the Reconstituted Milks During the Coagulation Kinetics... 

The starting time for rheological measurements correspond to t = 120 min. Indeed, the rheological parameters were only recorded during the rennet-induced coagulation phase to avoid structural modifications during the acidification phase which may consequently influence the gelation process. Elastic and viscous properties of reconstituted milks... 

FIG. 10 Evolution of the elastic modulus (G ) recorded during the 3h of the rennet-induced coagulation phase of the reconstituted milks. 

TABLE 2 Rheological Parameters Measured for the Reconstituted Milks and Skim Milk During Coagulation Kinetics... 

Reconstituted milks with natural milk fat globules (CREAM) or emulsified milk fat droplets stabilized by jS-casein (BCAS), /i-lactoglobulin 5g/L (BLG5), skim milk proteins (MP). 

While liquid milk is little used in biscuit manufacture for practical reasons to do with lack of stability, skimmed milk solids are used. The preferred ingredient is skimmed milk powder. This is normally dispersed in twice its own weight of water to ensure that it is evenly dispersed in the finished product. The reconstituted milk powder has the same keeping properties as liquid milk so it must be refrigerated. Merely dry blending the milk powder is likely to produce a finished product with small brown specks of caramelised milk powder in it. 

Principal micelle characteristics. The structure of the casein micelles has attracted the attention of scientists for a considerable time. Knowledge of micelle structure is important because the stability and behaviour of the micelles are central to many dairy processing operations, e.g. cheese manufacture, stability of sterilized, sweetened-condensed and reconstituted milks and frozen products. Without knowledge of the structure and properties of the casein micelle, attempts to solve many technological problems faced by the dairy industry will be empirical and not generally applicable. From the academic viewpoint, the casein micelle presents an interesting and complex problem in protein quaternary structure. 

Lingnert et al. (1983) reported that addition of 0.3% of the Maillard products of histidine and glucose to milk powder and storage under nitrogen gave the reconstituted milk both a low initial intensity of cardboard flavor and almost total inhibition of its further development after reconstitution. 

Some recommendations could be drawn from the technical discussions, which are summarised in the certification report [34]. In particular, it was stressed that some common extraction procedures may not be suitable for complete extraction of fat and of the analytes from the material. Soxhlet extraction with pure toluene was not found to be adequate quantitative extraction can be achieve by Soxhlet extraction with ethanol/ toluene, or by slurring the milk powder with water, mixing and drying with sodium sulphate and silica, followed by Soxhlet extraction with hexane/acetone. Procedures based on the AOAC protocols applied on reconstituted milk can also be recommended all these procedures are based on liquid/liquid extraction and therefore emulsion is possible. 

The units are given in number of colony forming particles per ml reconstituted milk... 

Figure 6. Effect of MTG treatment on water-holding capacity of the acid milk gel (set-type yogurt). MTG was added to reconstituted milk solution and incubated at 25 C for 2 hr. After enzyme reaction, the lactic starter was added, and the acid milk gel, set-type yogurt, was prepared after 4-6 hr fermentation.

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