The hurdle for the processor is that until recently, low fraction volumes and the extremely high cost to separate and individualize fractions from within the whey stream created a solid roadblock to discovering which market niche might offer the best revenue potential for their individual situation. This is changing with the advent of a multi-filtration method known generically as closed loop ultrafiltration technology. Laboratory and working trials have shown that using by this type of ultrafiltration technology it is not only feasible to separate commercially valuable components from basic dairy fluids, but it is easy and cost effective. This area of new application opportunities for dairy processors will open up profit centers that complement their current production processes.
The Technology of Closed Loop FiltrationThe most simplistic description of closed loop ultrafiltration technology is a unit comprised of multiple levels of filter membranes. The process feeds the fluid, in this case skim milk or whey fluids, through a series of 5 levels of filtration, each recycling through the next, therefore recovering sequentially smaller particles until nothing is left but water. The design of the filtration module provides flexibility to modify each of the controlling physical parameters such as concentration-polarization, transmembrane pressure, closed loops, fluid distribution, flow channel length and channel height. The membrane, support plates, and spacer plates are tightly stacked and have a uniform flow in the retentate flow channels. The permeate outlet is positioned in such a way that air is never entrapped in the plate (Figure 1).
Using cross flow technology rather than the perpendicular flow of conventional depth filtration, the process fluid flow is directed parallel to each filter membrane surface at high velocities (Figure 2). The resulting turbulent flow continuously cleans the membrane surface allowing it to consistently permeate (i.e.: selectively remove/concentrate) to the highest possible output for any given feed concentration level. Uniform flow across the entire membrane surface allows for precise and accurate control of the parameters affecting filtration. These parameters include velocity, pressure, angle of attack (channel height), and gel layer formation.
The patented filter module design creates uniform retentate flow channels. The distance and the resulting pressure drop is equal for each channel because the inlet and outlet ports are positioned diagonally opposite in both the horizontal and vertical planes with parallel ribs positioned on the surface of the membrane. Successful passage or retention of the various whey fractions as potentially valuable commercially viable products, depends on a wide variety of parameters, all of which are balanced and controlled with precision. These include: size exclusion of the membrane, membrane type, membrane material type, transmembrane pressure, pressure differential, velocity of the fluid, shear rate, temperature, concentration of solutes in the fluid and the liquid volume to membrane surface area ratio.
Membranes used in whey fraction applications are made from Regenerated Cellulose, Polysulfone, Polyethersulfone, Polyvinylidinedifluoride and Sulphonated Polysulfone, depending upon where they are used in the filtration flow process. These filter membranes used in the closed loop system are selected for their individual characteristics, defined by the size, charge and shape of the pore. The basic types are:
-- "Microfilter" membranes have a pore size from 0.1 Km to 5 Km
-- "Ultrafilter" membranes have a pore size from 5,000 to 250,000 MWCO (0.0063 Km)
-- "Nanofilter" membranes have a pore size from 90 to 120 MWCO (0.0005 Km)
-- "Reverse Osmosis" membranes have a pore size of 58 MWCO (00004 Km)
Used in closed loop filtration for improved molecular separations, sequential filter modules are able to fractionate milk or whey into numerous individual components as well as produce interesting milk and whey byproducts in high concentration.
The concept of "total utilization" of skim milk by filtration was tested over time under both controlled laboratory and field trial processing conditions. The results yielded excellent results in separation and mass transfer.
Each of the five filtering process steps were done in tandem, in the closed loop ultrafiltration design described earlier. (Figure 3)
1. Using skim milk as the starting fluid, it was passed through a microporous membrane at a velocity of 80cm - 200cm/sec, a pressure drop of 0.4 to 0.6 bar, a transmembrane pressure of 0.2 to 0.3bar, and a temperature of approximately 10C. Casein was effectively held back in the "retentate" (upstream side of the filter). The whey "permeate" stream was obviously still high in a multiple of various other proteins.
2. Instead of simply concentrating those proteins for animal feed which would be the common practice, the next step passed the whey through a 100,000 Dalton regenerated cellulose membrane with the operating parameters the same as the previous step. In doing this, it held back fractions including IgG (molecular weight of approximately 160K).
3. The remaining permeate stream was passed the fluid through a 30,000mw regenerated cellulose membrane. This separation step held back fractions including betalactoglobulin (b-lactoglobulin).
4. Next, the permeate was passed through a 5000mw membrane which held back fractions such as alphalactalbumin (a-lactalbumin).
5. Finally, the permeate stream now containing only small molecular weight components such as siallylactose and other complex carbohydrates, was separated using nanofiltration membranes; leaving only lactose, lactic acid, and various smaller micromolecules and minerals and water.
These tests proved that increases in concentration of several different protein fractions of whey were substantial even after the very first pass separation. In that first processing step, the IgG was increased almost 10X, while the betalactoglobulin increased by a factor of more than 10X. Passage through each sequential membrane with smaller size exclusions increased the concentration of each prior fraction and gathered many other fractions such as alphalactalbumin and the sugars.
Market PotentialWhey concentrates are sold for a variety of commercial purposes including body building complexes, bakery and frozen food additives and have become a valuable source of revenue for the dairy industry. They are typically sold at prices ranging from $2.00 to $3.5/kg depending on purity. Taking this to the next level, the micro-fractions that can now be economically filtered beyond the realm of current processes add a new range of potential revenue. The neutraceutical and biopharmaceutical industries are only two examples of virtually untapped, but important, new markets.
Whey fractions, such as alphalactalbumin which markets at approximately $23-27/kg, needs no further production other than filtration to separate and concentrate the protein in profitable quantities. There are many additional proteins and components within the whey permeate stream that could prove to be highly valuable commercial products, but have not yet been harvested in sufficient quantities to make the various markets commit to research and recognize their commercial value. Application of closed-loop ultrafiltration technology will stimulate this.
The value of these whey fractions lies in the fact that unlike most plant proteins, dairy proteins are complete and also in usable supply from a single source-milk byproducts. Because much of this is in part, still unexplored territory, the markets are highly application dependent. One industry section has been known to offer as much as $800/kg for a specific type of concentrated pure protein fraction. There are no absolutes regarding the dollar value of the individual proteins and other fractions derived from dairy byproducts. The only commercial fact that can be stated currently, is that they hold much higher value harvested, separated and sold individually for special markets than any unfiltered whey concentrate can ever bring. The table below lists just a few examples of potential markets for some of the major items that abound in the whey stream.
Markets are continually evolving, so the true potential of all the sub-markets for extractions from dairy products is not fully known. It's much like a handshake-one hand needs the other to perform the task. The more medical and biopharmaceutical laboratories, food product and health/sport supplement formula developers and other industries have access to useable volumes of pure dairy derivatives, the more uses will be found for them. New products will be developed. These in turn, will create a growing need for each particular molecular substance required. The dairy producer is currently able to explore these new market opportunities cost effectively by using the dairy byproduct that he/she produces every day and currently can only be sold as much less profitable animal feed or to other low dollar bulk byproduct secondary markets.