Processing Considerations in the Manufacture of Milk Protein Concentrate

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Overview

• The process
• Process considerations
  • Chemical
  • Enzymatic
  • Thermal
  • Mechanical
• Summary recommendations

We will start with a basic review of the various process steps involved in the manufacture of milk protein concentrates (MPC).

This will be followed by exploring several processing considerations in the manufacture of MPC that can influence end product quality and/or functionality. While not representing a collectively exhaustive list of process variables due to time constraints, more importantly we attempt to demonstrate that none of these variables are mutually exclusive and a high tendency for cumulative interactivity exists. Particular focus will be given to thermal treatment considerations since many of the unit operations involved in the manufacturing process include a substantial thermal effect.

Finally we will summarize recommendations for minimizing the impact of these process variables on end-product characteristics.

Milk Protein Concentrate MPC 70 - 85

Fresh, refrigerated raw milk is received and stored at the process plant.

The raw milk is regeneratively heated to separation temperature and sent to a centrifugal separated where the cream fraction is removed, cooled and stored for shipping or for further processing. The skim milk fraction is heated to pasteurization temperature and held the requisite time to satisfy the pasteurization requirement. The skim milk is then cooled to the Ultrafiltration (UF) operating temperature and directed to the feed section of the UF Plant. The skim milk is pumped into the filtration section of the UF Plant where the relatively larger molecules, mainly proteins, are progressively concentrated to the desired end point while the relatively smaller molecules, particularly lactose, freely pass through (permeate) the UF membrane. The permeate stream is directed away from the UF Plant for disposal or further processing. The milk protein concentrate fraction, referred to as retentate, is cooled and stored or directed to down-stream processing.

MPC 42-85 % Powder Production

The retentate can be further concentrated in a falling-film evaporator prior to spray drying and packaging.

Chemical

Milk represents a complex organic mix of macro- and micronutrients and as such creates a rich environment for chemical reaction. One such example is the Maillard reaction whereby an amino acid chemically reacts with a reducing sugar, in this case lactose, producing a host of reaction intermediates and end products that contribute to color, odor and flavor and a degradation of nutritive value.

Amino acid + reducing sugar + heat = Maillard reaction

• Color
• Flavor
• Nutritive

Heat tends to promote this reaction so, when considering processing conditions, it is important to minimize thermal treatments.

With good milk handling and storage practices we can also limit proteolysis and therefore limit the concentration of free amino acids.

Enzymatic

With good milk collection, handling and storage practices we can also limit proteolysis, and therefore limit the concentration of free amino acids, or other enzyme-induced product deterioration.

• Initial
  • Milk quality
• Developed
  • Milk handling/processing

Ultrafiltration

This photo depicts a typical UF Plant arrangement in spiral-wound membrane format arranged for stage-in-series, continuous operation.

Polarization layer

• Kinetics of reaction
  • Concentration
  • Time
  • Temperature

The graphic depicts a static view of a dynamic boundary layer that forms at the membrane interface during UF processing. The mass transfer of solution through the semi-permeable membrane drives larger solutes to the membrane surface where they are size-excluded and accumulate into a polarized layer. This dynamic layer continuously rebuilds itself as solutes back-diffuse into the bulk stream and new solutes deposit by convective transport.

This polarized layer creates a rich environment for protein interactions including enzyme adsorption, reaction and desorption.

Mechanical

Consideration to mechanical design and fluid mechanical effects is also important in these complex, mixed organic streams.

	Butterfly valve and flow path	The graphics compare and contrast an open and a partially closed flow path for a butterfly-style of valve and a piston-style of valve. Turbulence and shear stress associated with velocity and directional changes within these two flow models is of course substantially different.
Effect of Impingement Shear Cavitation	Piston valve and flow path