Whey to add value

12-Jun-2005 - Last updated on 13-Mar-2017 at 11:11 GMT

Techniques are being developed to make money from the waste produced during milk processing. John Dunn reports on the science behind it

World milk production is slowing down. But while the output of liquid milk and traditional milk products such as butter may be declining, the production of cheese and milk-based food and animal feed ingredients is on the increase. And now, thanks to recent developments in milk microfiltration technology, it is the whey -- once the waste product of cheese-making that was fed to the pigs -- that is destined to become the most valuable part of our pinta. Whey is where it's at for milk processors today -- if they can afford the technology.

According to figures from the Dutch Dairy Board, a decline in cow's milk production in North America and Europe means that total world milk production is slowing down. Output grew by just 3mt last year to 612mt; this compares with an increase of 80mt since 1994.

But today the most valuable part of dairy milk is not the part that's used to make butter and cheese, it's the stuff that's left over. When cheese is made, only 10-15% of the milk is turned into cheese. The remaining 85-90% is whey, and it still contains 50% of the nutrients from the original milk.

And it is these nutrients, known variously as whey protein fractions (WPFs) or whey protein isolates (WPIs), which, if efficiently and precisely separated and concentrated, can become high value-added ingredients in other foods and in animal feeds. But until recently it has been a big, and expensive, if.

The first whey protein fractions were produced in the 1980s as a replacement for egg albumen using expensive ion exchange technology. Now reverse osmosis, ultrafiltration, and more recently microfiltration technology using ceramic membranes with pores just a few tenths of a micron in size, have helped lower the cost and increase the efficiency of producing and concentrating whey proteins.

As a result, whey protein fractions are now being increasingly used by the food industry as gelling and whipping agents, emulsifiers, foaming agents, and stabilisers. They are used in performance-enhancing foods such as sports nutrition bars. And they are used in animal feeds, albeit on a much more scientific basis than mere 'pig swill'.

To the public the best-known whey protein fraction is probably lactoferrin which is variously promoted as an antimicrobial, antibacterial, antifungal, anticancer, and anti-inflammatory supplement in functional foods. Another antibacterial WPF, lactoperoxidase, is used in human (and animal) toothpastes, as well as in mouthwashes and a medical disinfectant. Alpha lactalbumin is used in infant formula milk and nutritional supplements because it is made up of easily digested amino acids. And immunoglobulins have immunity-enhancing, disease prevention characteristics.

Microfiltration

Whey is quickly becoming the value-added food of the 21st century as new microfiltration technology promises to allow processors to take milk to pieces and sell its components -- the proteins, the fats, the casein, and the lactose. About a year ago, for instance, it was estimated that the US market price for 'ordinary' concentrated whey protein, as used as a food ingredient, was $1.50 per pound; the price for WPFs was $3.40 a pound; and for lactoferrin it was anywhere from $150 to over $200 a pound.

But these prices also reflect the high cost of separating milk efficiently and precisely into its valuable component parts. However, a new development from microfiltration specialist GEA Filtration in Denmark promises to make the production of WPFs and other filtered milk products simpler and cheaper. GEA has launched what it describes as the third generation of ceramic microfilters. The new Isoflux membrane, developed in France, overcomes the problems of varying pressure flow in conventional tubular ceramic microfilters by varying the thickness of the membrane along the length of the filter.

As whey is pumped down the filter, there is a pressure drop along the filter as the liquid permeates through to the outside. The Isoflux filter evens up pressure flow across the membrane and helps reduce clogging. It promises to make microfiltration more efficient, more economical, and simpler to control, says GEA.

Ceramic membranes have been used for many years in whey fractionation (separation) and concentration. Unlike polymer membranes, ceramic membranes are tough and heat resistant and stand up well to cleaning. They consist of a thin active layer of ceramic filter mounted on a much thicker ceramic support layer to give a filter element typically up to 25mm diameter and about 1.2m long. Whey is pumped in one end and out the other with the bulk of the liquid permeating through the filter, leaving the required whey protein concentrate or fraction behind inside the filter tube.

But in conventional microfilter elements, as the whey flows down the tubular element, the pressure drops. As a result, flow through the filter is much higher at the inlet than the outlet. Large particles collect near the inlet, clogging up the filter, so decreasing efficiency and reducing running time.

A second generation of microfilters, the UTP or Uniform Trans-membrane Pressure filter, attempts to cure this by packing plastic beads around the outside of filter to provide some resistance to the liquid permeating through. First developed commercially by Tetra Pak in the mid 1980s, UTP filters are expensive, requiring the constant recirculation of the liquid permeating through the filter, so increasing complexity, cost, and the risk of contamination. Also, the process has to be run at a fixed capacity. If you want to change flow rates, it requires a lot of complex adjustment.

Now Tami Industries of France has developed the Isoflux membrane which controls flow across the filter by having a membrane that is thicker at the inlet end than at the outlet. It is a simpler and more flexible process, says John Jensen, division manager at GEA in Denmark. It makes control easier, and it is more efficient. Isoflux filter elements have nearly 50% more active membrane area, giving greater capacity per element and flow rates across the filter up to a third higher.

Bacterial spore removal

The technology is being used by a number of Scandinavian cheese processors, says Jensen, to remove the spores of micro-organisms which can cause problems with the formation of gas and unwanted holes in some cheese types as the cheeses age.

Previously the cheese producers would have added nitrate salts to kill off the spores, says Jensen. However, this is becoming more and more undesirable and may even be prohibited in some countries. Up to 99.99% of bacteria and spores can be removed by microfiltration.

Other applications for the new Isoflux technology include casein and whey protein fractionation for use in protein supplements. Separating them out from the milk prior to cheesemaking produces better quality and consistency, and it avoids the added colour, enzymes, cultures, or heat treatment that occur during cheesemaking.

Microfiltration is also used to remove bacterial spores from milk prior to spray drying; and to remove bacterial spores in whey and whey protein concentrates to eliminate spoilage in canned milk, infant formula, and beverages that are supplemented with whey proteins.

The new Isoflux microfilters are also being used to remove fat in whey protein isolates (WPI) to increase clarity, says Jensen. "If you put in a microfilter you can reduce the fat to 0.005% or so -- very, very low. Then when you concentrate the whey protein up to 90% (WPI 90), you will end up with a fat content below 0.5% in the powder. This is used in low fat health drinks to give a completely clear colour," he says.

Outside the dairy industry, Isoflux technology is being used to clarify raw fruit and vegetable juices; to clarify and concentrate dextrose and maltodextrins; and to concentrate vegetable and plant proteins.

"Whey protein fractionation is a rapidly growing market," says Jensen. Previously price was the stumbling block to all but the biggest dairies, he says. But now the price of ceramic filter elements is dropping. "With Isoflux, it makes microfiltration of milk very simple to control and much, much cheaper to operate." And it means, he says, that the dairy industry can now revisit a lot of the ideas it had in the past for using milk but had to abandon because the technology wasn't there. "We can take them up again and put them into practice."FM