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INSIGHTS on Material Characterization

INSIGHTS on Material Characterization

Many factors in materials impact foods and beverages. These range from safety issues, such as microbiological contamination, to texture issues, such as the smoothness of peanut butter.

Mike May, PhD

Mike May is a freelance writer and editor living in Texas.

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Keeping foods and beverages yummy and safe

If a health agency or customer raises an issue, a food or beverage manufacturer needs to find the source of the trouble and resolve the problem. In many cases, that requires characterizing the material, be it food, beverage, or packaging. The range of raw materials, final products, and containers that can be involved requires the application of various technologies and techniques.

Furthermore, this industry has more concerns than just contamination. For example, a food manufacturer might suspect that a competitor is using its patented recipes, and material characterization might prove this. On the other hand, a manufacturer might just want a product analyzed to find a better way to make it.

All of these applications raise challenges. “Probably the key challenge is measuring structures without breaking down their three-dimensional nature,” says Rich Hartel, professor of food engineering at the University of Wisconsin, Madison. “For example, how do you analyze and quantify the structure of whipped toppings or frozen desserts without destroying that structure?” He points out that clusters of fat globules help whipped toppings stand up to gravity, but he adds, “How those structures actually come together to provide that yield stress is difficult to characterize.”

Microscopic Methods

McCrone Associates—the analysis arm of the Illinois- based McCrone Group—uses primarily microscopy to investigate contamination in food. This includes the use of light and electron microscopy. Kate Martin, a senior research chemist for McCrone Associates, says, “In the food and beverage industry, contaminants are among the many challenges, and they include microbiological organisms, heavy metals, chemicals, and pesticides.” She adds, “We focus on particulate analysis, as well as other problems that can be addressed using microscopic methods, but are also beginning to explore food adulterants.”

Problems can be found in the food or its container. As Martin points out, “We have done lots of work on packaging, looking at flaws, and that fits nicely with our microscopy skills.”

The problem and material determine the best approach. For instance, a scientist can use a stereomicroscope and a tungsten needle to isolate specific parts of a sample. Or a sample can be sliced—like sectioning a biological sample— and then observed under a light microscope or electron microscope at higher resolution to examine structure and morphology that may affect, say, textural characteristics. If a gritty texture is a problem, identifying the cause can be simpler than expected. As Martin mentions, “It’s common for grit to come from an overbaked product. So maybe something is just off in an oven.”

Nature's Twists

Kate Martin uses Fourier Transform Infrared Spectroscopy (FTIR), a nondestructive characterization method, to analyze a material suspected to be a contaminant in a food sample.Image courtesy of McCrone Associates.Although many of today’s consumers seek out foods composed of natural products, these create challenges for characterizing the material. “There has been an increased use of natural products over the years,” says Martin, “and they are extremely complex.” Moreover, natural products vary depending on the country or region of origin. “The same natural product can even vary between central and northern California,” Martin says. “Consequently, manufacturers face problems in setting specifications in a meaningful way.”

To decide if a natural product is defective or even dangerous, an analytical lab must first determine its variability. That range must be assessed to provide a standard against which samples can be tested. Still, Martin says, “It’s a challenge to understand what is out of specification.”

Other experts agree. Shri Thanedar is CEO at the Michigan-based analytical laboratory Avomeen, which specializes in the chemical analysis of foods, beverages, and other samples. He says, “A lot of natural ingredients are not well-defined chemically. They can be mixtures of 50, 100, 500 chemicals.” He adds, “Analyzing a material with a single organic molecule is a lot easier than analyzing a natural product that is a blended mixture.”

We All Scream

Yes, we do all—or most of us, anyway—scream for ice cream, and we’d sure scream about it if something went wrong with the product. That happens more often than you might think, because “ice cream is a really complex and delicate product,” says Kirsten Schimoler, who is technically a principal food scientist at Vermont-based Ben & Jerry’s, but also is known as one of its “Flavor Gurus.” She adds, “Ice cream is a four-phase solution, an emulsion.” The phases are air, ice, fat, and matrix, which is sucrose, lactose, stabilizers, and so on. “The control of these four phases creates a microstructure, and it is that microstructure that gives you the final texture of the ice cream you eat,” Schimoler explains.

Ice cream depends on the right balance of those phases, as well as a variety of manufacturing variables, including homogenization pressure, freezing time, temperatures, and more. “The levels of fat and air and the ice content will all impact how the product ‘eats,’” Schimoler tells us. “Is it smooth and creamy? Is it cool and icy? Is it dense or light and fluffy?” Adjusting the formulation and processing controls these qualities. For example, Schimoler points out that “the pressure which is used to homogenize the ice cream mix, and the size of the fat droplets in the product, will impact the final texture.” She adds, “The way you freeze a product will also impact the texture. The faster you can freeze the product, the smaller the ice crystals and the smoother the eat.”

As with many foods, an ice cream maker must worry about many things after manufacturing, especially how the product travels from a factory to a consumer. In particular, the quality of ice cream varies with the storage temperature. “If stored at too high of a temperature, the stability of the emulsion is compromised and the microstructure will degrade,” Schimoler explains. “This is when you see ice crystals grow, giving an icy texture.”

To keep ice cream lovers happy around the world, Schimoler and others rely on a variety of tools, and they love an old favorite among scientists. As Schimoler goes on, she says, “Microscopy is an awesome tool when applied to ice cream.” She continues, “You can get down to the micron level and look at the microstructure of a product, seeing how the fat and air interface, and the size of ice crystals and any lactose crystals.” That information helps Schimoler learn about a product’s stability over time, and adjust the formulation to improve it.

And Schimoler and her colleagues work and work to make the best ice cream they can. With so much at stake—it’s the favorite dessert in many polls—lots of details in the ice cream business must stay secret. Still, Schimoler will say, “I am working on some really cool, top-secret formulas, but on one of them I created about 45 different recipes for a mix before I finally got the perfect balance of ingredients and processing.” She won’t say more, for now.

Seeking Sensitivity

To get the most from material characterization, companies continually seek new tools for analysis. “More and more,” says Kate Martin of McCrone Associates, “this means using mass spectrometry (MS).” Part of this technology’s value comes from its various forms, such as triple-quadrupole MS. In some cases, though, MS can be almost too sensitive. “It picks up everything,” Martin explains, “including additives to the plastic bag that the sample was in.”

Shri Thanedar and his colleagues at Avomeen chemically analyze foods, beverages, and other samples.The techniques must be sensitive, because it doesn’t take much to upset the balance in a food product. “A small amount of material, like parts per billion or trillion, can cause an odor,” Shri Thanedar of Avomeen explains. Recently, his company faced such a challenge when a client brought in its frozen hash browns that suddenly acquired a bleach-like odor. Thanedar says, “We did a comparative analysis of good hash browns and ones with the odor, and we found very small differences.” Like detectives, Thanedar and his colleagues explored the manufacturing process for these hash browns, and they found that the food company had recently changed the supplier of a chemical that is used to minimize foam in the manufacturing process, and this caused the problem. As Thanedar explains, “This material had stayed with the product.”

The issue at hand usually determines the best analytical approach. If the suspected problem comes from heavy metals, inductively coupled plasma mass spectrometry could be used. For an odor, gas chromatography could be the best tool. Other issues might require high-performance liquid chromatography or near-infrared spectroscopy.

In analyzing the product, most techniques damage or even destroy it. As Rich Hartel of the University of Wisconsin, Madison says, “Normal microscope methods—polarized light, fluorescence, scanning electron microscopy, transmission electron microscopy, et cetera—require extensive sample preparation, which generally destroys the structures and introduces artifacts.” He points out that “confocal scanning laser microscopy is an alternative but is also somewhat limited by the density of many food structures.”

Hartel uses these tools to study ice cream, toppings, and confections. He says that his team’s primary tools are “optical microscope techniques and light scattering methods for particle size quantification.” They use confocal scanning laser microscopy where they can to examine a product’s three-dimensional structure.

To sidestep the problems of destroying the sample, food scientists might use magnetic resonance imaging, but Hartel mentions challenges with getting enough resolution. In the future, he expects to see more use of tomography in this area. As he mentions, “We have begun to collaborate with other researchers to use tomography to image complex three-dimensional structures of foods like ice cream.”

Even with all these technologies, it’s simple, effective communication that matters most when solving a food and beverage problem. The manufacturer understands the product and how it was made, and the analytical company knows the most about the potential tools for testing. As Martin says, “We depend on communication— back and forth—to build an answer.”

In fact, the communication that goes on behind material characterization in the food and beverage industry extends even farther. It often starts when a customer points out a problem with a product. That information gets back to the company, and the detective work starts with company scientists and probably outside analytical experts. These teams work together to find and fix the problem, and everyone—from the consumer and creator to the food scientists and process engineers—makes a crucial contribution to the process.

It’s a complicated food world out there. Most of us tearing open a package marked “all natural” would never guess that this makes a food detective’s life more complicated rather than less. We’d never imagine all of the work going on at Ben & Jerry’s to ensure the very best ice cream. But without these efforts, just think how our lives would change. The ongoing, high-tech work in this field aims to feed people safely around the world. Few things matter as much as that.