Processing Considerations in the Manufacture of Milk Protein Concentrate

Previous | Home | Next

Turbulent flow

Due to wide variations in linear velocity associated with basic design differences, membrane formats and configurations and liquid rheology, very different flow dynamics can be observed.

Turbulent flow

This simplified model depicts transport of various solutes in a cross-flow membrane filtration system. The flow dynamics suggests lower viscosity and/or higher velocity systems resulting in a turbulent flow regime.

Laminar flow

By contrast, the flow dynamics in this model suggests lower velocity and/or higher viscosity systems resulting in a laminar flow regime.

Laminar flow

Mixed flow

Additionally, intermediate models exist where elements of both turbulent and laminar flow regimes coexist due to collision with turbulence promoting devices.

Mixed flow

Thermal

As already discussed, thermal energy input is an important process variable that should be minimized to the extent possible during process. Thermal energy input with regard to temperature and time relationship is generally well understood and respected. Often, however, the relationship with regard to rate of heat transfer is far less appreciated resulting in some thermal abuse of products. Within certain product-specific temperature ranges, it becomes equally important to monitor and control product and media temperature differences in order to avoid localized over-heating of the product.

Evaporation

• Falling film
• Product distribution
• low T_E
• low t_E

Another potential source of thermal input that can be minimized occurs around the Evaporation step, both in the pre-heating step and during the actual evaporation. Rapid and efficient heating with low exposure time and low residence volume is preferred to retard microbiological activity.

Excellent product distribution, film-layer integrity, low boiling point and limited time exposure are all important considerations for operating efficiency and product quality.

Concentration

The graphic depicts the expanding, accelerating vapors thinning the liquid film layer along the heat transfer surface. The design strikes a balance between efficient heat transfer and minimal thermal input to the product.

Short tube

A photograph of a Compact, short-tube Evaporation Plant.

Long tube

A photograph of a long-tube Evaporation Plant.

Spray drying

A final opportunity exists for excessive temperature treatment of the product during the Spray Drying step.

Product is atomized into a chamber of hot air for the express purpose of removing most of the remaining water phase and transitioning the product to a shelf-stable, dehydrated powder.

Previously explored issues surrounding time and temperature exposure apply with equal importance here.

Dehydration

The graphic depicts a single droplet of liquid falling through a zone of hot, dry air. As heat and mass are transferred, the hot, dry air becomes progressively cooler and moister. As the droplet releases moisture to the air, the effect of evaporation keeps the particle cool. It is important that as the cooling effect of evaporation diminishes with dehydration, the particle is quickly removed from the hot zone and final drying is accomplished with lower temperature air. Again, a gentle balance is struck in the temperature and time relationship. With too high of an air temperature, an outer skin layer can form around the droplet inhibiting outward migration of the remaining water within the droplet. With too long of a residence time, the temperature of the dehydrated particle will quickly rise to that of the surrounding environment resulting in thermal degradation.

Two-stage drying

A photograph of the bottom of a Spray Drying chamber with integrated fluid bed dryer.

Summary

• As a prerequisite:
  • High quality raw material
• Then:
  • Limit energy inputs
  • Limit process cycle times
  • Minimize reactive environment

In conclusion, it bears noting that none of the considerations to process variables is particularly important unless we begin with a high quality feed material.

With this as our foundation, we must then minimize to the extent possible the thermal and mechanical energy inputs so as to limit the extent to which we physically change the product and its corresponding characteristics. Further to this, if we limit exposure times in relationship to temperature events, we can also minimize environmental conditions conducive to both chemical and enzymatic reaction.