New technique characterizes the pore structure of food.

The pore structure of a food product controls many of its important attributes. Processing variables can be manipulated to control pore structure. Unfortunately, the appropriate techniques for determining a product's pore structure are not widely harnessed.

One technique--mercury intrusion porosimetry--has been used to test the porosity of food. In this process, mercury, which is normally nonwetting, is forced into the pores of the sample under pressure. The intrusion pressure indicates pore diameter, and the intrusion volume yields information on pore volume.

But many pore properties and flow characteristics are not measurable. Moreover, the high pressures used in the test tend to distort pore structure. And, using toxic mercury contaminates the sample, pollutes the environment and prevents reuse of the sample.

Scientists at Porous Materials have developed an innovative alternative. In this technique, no toxic material or high pressure is used. Flow properties and through-pore characteristics are measurable. The samples are reusable.

In the new process, the sample is supported by a membrane's largest pore that is smaller than the smallest pore of interest in the sample. A wetting liquid is allowed to spontaneously fill the pores of the sample, the pores of the membrane and the sample chamber below the membrane. The pressure of an inert gas is increased on the sample to displace the wetting liquid from the pores.

Then the scientists measure the differential pressure and the weight of the displaced liquid flowing out through the liquid-filled pores of the membrane. The through-pore volume, diameter, distribution and liquid permeability are computed from the measured values. The technique is environmentally friendly and safe to use. The equipment involved costs between $20,000 and $30,000. The company also offers to test products in its testing services division.

Food and beverage technology is becoming more sophisticated as researchers address issues involving healthier cooking, ease of digestion and the more efficient storage of product. Some important pore structure characteristics on this front involve the liquid and vapor permeability of vegetables, the pore structure of products like cornflakes and the relative flow rates of fat from meat when it is cooked. Suitable pore size distribution in filter media is required to efficiently remove bacteria, pollens and fungi from beverages. Low oxygen permeability of packaging materials is desirable to prevent the degradation of stored food.

Patent. 6,684,685--Liquid extrusion porosimeter and method. Issued: Feb. 3, 2004. Inventors: Krishna Gupta and Akshaya Jena. Assigned to Porous Materials Inc. A porosimeter evaluates the porosity characteristics, specifically, pore volume, pore distribution and liquid permeability, of a porous sample of material.

Further information. Akshaya Jena or Krishna Gupta, Porous Materials Inc., 20 Dutch Mill Rd., Ithaca, NY 14850; phone: 607-257-5544; fax: 607-257-5639; email: jena@pmiapp.com.