Measuring Quality in Cultured Dairy Products

Both the flow-ability (viscosity) and spoon-ability (yield point) of cultured dairy products may also be compared by using a single test. A texture analyzer can be used to drive a cylindrical probe slowly into the product while measuring the force required during probe travel. A typical test with a texture analyzer consists of driving a probe of specific dimensions at a constant speed into a product at specified distances, then withdrawing it. The increase in positive force (or load) recorded just after the probe contacts the sample surface is an indicator of stiffness, or modulus, in the gel structure of the yogurt. In Figure 4 this slope is indicated by the dotted lines labeled “modulus”.

As the probe descends and displaces the sample, the combination of stiffness and flow-ability contributes to the force profile. The shallower slope and lower, flatter force plateau of the full fat yogurt are caused by its softer gel set and smoother flow. Its appearance is glossy compared to the graininess noticed in the low and non-fat variety. This characteristic is represented by the absence of peaks along the plateau of the full fat yogurt. Then, as the probe withdraws, a negative load is encountered because the yogurt adheres to the probe. These force profiles become the primary test result.

Samples can be compared, and quality control can be assured, by repeating the same test in successive products and comparing results. A manufacturer might use this information to adjust the formulation until the force profiles compare favorably to that of the full fat product. This result would correlate to a more similar “mouth feel” to the consumer.

Sample and test considerations which will affect results of a texture analysis test are:

• Sample temperature;
• Dimension of sample containers;
• Flat and level surface of the sample;
• Homogeneity (fruit bits will add variability for example);
• Dimensions of test probe;
• Probe travel speed and penetration distance.

Each of the test techniques described in this article can provide information about one or more of the physical properties of cultured dairy products. When used in combination these techniques will complement and reinforce each other.

Len Thibodeau is a senior sales engineer for Brookfield Engineering Laboratories (Middleboro, Mass.). He can be reached 508-946-6200, ext. 199 or [email protected].

Norovirus Grown in Lab

The norovirus, a highly contagious source of food poisoning, has been successfully grown in a laboratory for the first time by researchers at Washington University in St. Louis, Mo., a feat that could speed the development of a vaccine.

Noroviruses are highly contagious and cause diarrhea, vomiting and other problems. Two years ago, these viruses caused repeated outbreaks of illness on cruise ships that were widely reported in the media.

Scientists showed that the mouse norovirus MNV-1 could be grown inside cells from mice with defective immune systems. The university said those findings could ease the way for further research about the mouse virus and may help researchers seeking to duplicate the accomplishment with human forms.

“By looking at the mouse virus we’d grown in the lab, we were able to identify a part of the capsid, the virus’s protein shell, that is essential to its ability to cause disease,” senior author Dr. Skip Virgin, a professor of pathology and immunology and molecular biology, said in a prepared statement.

“If this part of the capsid has an equivalent in human noroviruses, altering or disabling it may give us a way to produce forms of the viruses that are weak enough to serve as vaccines,” he added.

According to the U.S. Centers for Disease Control and Prevention, noroviruses are involved in about half of all food poisoning cases and annually cause about 23 million cases of acute gastroenteritis in the United States.