Membrane-based techniques also promise rapid isolation of fine components.
“We are examining substitute membranes that will extract particles not just according to molecular size but on the basis of charge or hydrophobicity,” says Smithers. Different molecules, he explains, tend to partition into different types of oils – some toward fats, others toward more water-soluble oils.
Together these techniques may open cost-effective means of extracting plasma and its immunoglobulins and non-carrying transferrins.
On the plant side of the food world, the techniques may be used to isolate polyphenols and take advantage of their antioxidant properties.
Conventional heating (conduction, convection, radiant) transfers heat from an external source to the surface of a food, which conducts the heat through to the center of the food.
Radio frequency is a different heating concept altogether, heating product at the molecular level from the surface and the center of the product at the same time. The industrial microwave has long played a role in processing plants.
That role, however, has been limited by the rate of penetration of microwaves and the uniformity of heat that microwave units provide. As consumers well know from their kitchen microwaves, part of the product can remain frozen while another part is overly hot.
Make way for radio-frequency heating.
“It’s still in the development stage, but with particulates, radio-frequency heating might better penetrate product,” says FPA’s Allah.
Work in RF sterilization is roughly at the same stage as high-pressure sterilization research, says Allah, and he sees its commercialization on roughly the same timetable.
Carbon dioxide extrusion
Extrusion is common practice in the manufacture of breakfast cereals, pet products, pasta and snacks. “But the extrusion process is a high-temperature, high-shear process. At up to 160°C, that is devastating to lots of nutrients,” says Sy Rizvi, professor at Cornell University’s Institute of Food Science.
Water, an essential ingredient in extruded food products, serves two functions, Rizvi explains: acting as a blowing agent, blowing material into a porous structure; and as a platicizer, converting a powder into dough. These roles are coupled. “You can’t change one without affecting the other,” he explains. “Too much moisture and the temperature won’t go up enough because you have too much liquid in the mix.”
To take on the challenge of balancing moisture and temperature, Rizvi and his colleagues aimed at decoupling the roles, using water as a plasticizer but not as a blowing agent.
His answer was using supercritical carbon dioxide and keeping the temperature during extrusion below 100°C. The process controls the number and size of cells by controlling the rate at which pressure is dropped.
“If there are a lot of small cells, the mechanical properties of the extruded material and its texture will be different – more crumbly and harder,” says Rizvi. “If you have a few big cells, the product will break easily.”
With CO2 extrusion, the process can be performed at temperatures of 40-90° C, well below water’s boiling point.
“At these lower temperatures, it is a good process for porous structure,” Rizvi goes on. “A lot of heat-sensitive ingredients can be added – proteins, flavorings, colorings and functional ingredients.” Rizvi and his Cornell associates develop the supercritical fluid extrusion (SCFX) process on a Wenger TX52 co-rotating, self-wiping, twin-screw extruder.
Two major advantages of the system are:
- Secondary flavor deposition – With conventionally extruded products, flavoring is added after the rigorous process. The SCFX process enables the manufacturer to deposit flavoring materials into the material prior to extrusion, resulting in higher flavor impact.
- Leavening without yeast – While water level must be carefully controlled in extrusion, CO2 can be used liberally. “You can get a leavened dough in two minutes,” says Rizvi. Normal yeast leavening may take up to four hours.
Rizvi is working with bakeries and dough makers to develop this leavening option.
“My dream is to see someone put this to work,” he says.