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Volume 86 Issue 25 | p. 14
Issue Date: June 23, 2008

Cover Stories: Devising Healthier Foods

Understanding Healthier Foods With Analytical Chemistry

Department: Science & Technology
Analysis
Researchers frequently use high-performance liquid chromatography to analyze nonvolatile food samples.
Credit: Michael Kellett Photography (both)
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Analysis
Researchers frequently use high-performance liquid chromatography to analyze nonvolatile food samples.
Credit: Michael Kellett Photography (both)

Figuring out exactly what's in the food you eat calls for chemists and their analytical instrumentation. Advances in analytical instrumentation have allowed food scientists to answer increasingly intricate questions about food and health.

In developing healthier foods, researchers use the techniques to find bioactive compounds and standardize how much of those compounds are fed to the test subjects in clinical trials. The researchers also rely on these tools to analyze what happens to compounds in the frying pan or after the body digests them. All of this means that food scientists have a huge number of samples to analyze.

Credit: Michael Kellett Photography
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Credit: Michael Kellett Photography

The analytical workhorses among modern food science labs are mass spectrometers and gas or liquid chromatographs. Whatever the instrument is, the method has to be fast because hundreds of samples are run on a regular basis, says Linda M. Pollak, a corn breeder at the Department of Agriculture's Agricultural Research Service at Iowa State University who uses several analytical techniques for a project on modifying the fatty acid content in corn oils. For many food research labs, attaching autosamplers to the instrumentation is a must, she adds.

Gas chromatographs analyze volatile samples, so they are the best instrument for analyzing fatty acid content in corn that has been processed into oil, says Pamela White, a food chemist at Iowa State who collaborates with Pollak. Freshly processed oils are tested for composition. Researchers also examine oils for stability after they have been stored in a sealed container on a shelf or have been used, for example, to fry a basket of coconut shrimp.

Preparing samples for food studies is time-intensive. To procure corn oil for her studies, White explains, a corn kernel is first soaked. Then the germ is removed and crushed. Hexane is used to extract oil from the germ. The fatty acids in the oil are then converted to methyl esters for two reasons: to pluck them from a glycerol backbone and to make them volatile enough for the gas chromatograph.

Extracting limonoids—triterpenoid compounds that are unique to citrus fruit and that may help prevent cancer—from grapefruits originally took 10 steps. So when food scientists in Bhimanagouda S. Patil's group at Texas A&M University figured out how to cut out six steps, they patented the process. Now only four steps are needed to obtain crystallized limonoids for analysis or for dosing in clinical trials.

In the process, the researchers first use wet chemistry to extract limonoids from the fruit's pulp. The compounds are further purified with flash chromatography techniques. Patil and colleagues use liquid chromatography to profile limonoids because, like the β-carotene and anthocyanins found in maroon carrots studied at the same university, they are not volatile enough for gas chromatography. The researchers determine the structure and purity with a nuclear magnetic resonance spectrometer.

Animal studies and human clinical trials create numerous biological samples that must be prepared for analytical instrumentation. Techniques and methods vary depending on the analytes and sample matrix; Wallace H. Yokoyama can attest to that. Yokoyama is a research chemist at USDA's Western Regional Research Center in Albany, Calif., collaborating with Dow Wolff Cellulosics, which developed Fortefiber, a cellulose material functionalized to reduce blood glucose and cholesterol levels in those who eat it. He studies the effects of Fortefiber and other kinds of fiber intake on metabolic disease in hamsters. He created analytical methods suitable for blood and fecal samples from the dosed hamsters. To understand how the animals digest fat, for example, he uses a liquid chromatograph and mass spectrometer to quantify triglycerides and sterols, components of cholesterol, that have been centrifuged from blood samples or extracted from feces (J. Ag. Food Chem. 2007, 55, 9750).

Although the types of instrumentation may be fairly consistent in labs examining food, the methodologies can vary considerably. These disparities can draw into question what the results really mean for the eating public, write food scientists Edwin N. Frankel of the University of California, Davis, and John W. Finley of Louisiana State University in the Journal of Agricultural & Food Chemistry (DOI: 10.1021/jf800336p). They are particularly concerned about antioxidants because different labs have used multiple protocols to evaluate the activity of natural antioxidants. These techniques employ a wide range of free-radical-generating systems, as well as different methods of inducing oxidation and measuring the endpoint of oxidation. To help make these studies more comparable, the authors recommend that each antioxidant evaluation be carried out under various conditions of oxidation, using several methods to measure different products of oxidation related to real food quality.

Advances in analytical chemistry have allowed food scientists to answer many questions, but other questions, including the debate on how best to analyze antioxidants, may have to wait for more sensitive detection techniques to emerge.

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