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Spectroscopy Probes Gum Content

Photonics Spectra
Jun 2005
Hank Hogan

Gums, or galactomannans and cellulose-backbone polysaccharides, improve the taste and appeal of food. For example, the addition of a dash of gum can make a texture more gelatinous. However, monitoring what types of gums are added during manufacturing has been difficult. By applying photonics technology, researchers have developed a means to check that a gum recipe is correct -- making food a bit easier to swallow and, possibly, less expensive.

Lisa J. Mauer, an assistant professor of food science at Purdue University in West Lafayette, Ind., and colleagues use Fourier transform infrared (FTIR) spectroscopy to differentiate gum mixtures. The technique promises to address two basic problems in the food industry: the quality control of gum mixtures and the identification of locust bean gum that has been adulterated with guar gum.

The two types of gum are structurally similar, but locust bean gum may be key to a recipe because of its different characteristics, such as its tendency to form a rigid gel during food processing. Producers trying to ensure the proper ratio of the gums must contend with quality control issues in which an honest mistake is made and with situations in which guar gum is deliberately and illegally substituted for the more expensive locust bean gum.

How often the latter happens is anyone's guess, Mauer said, but it's not unheard of. "Every food company seems to have at least one story of this happening, but nothing is published." She noted that this adulteration often does not show up until the gums are added to a product during processing. By that point, food manufacturers must discard the product.

Current analysis methods that measure gum mixtures involve chromatography, electrophoresis or hydrolysis, all of which lack sensitivity and are time-consuming. Mauer and her group turned to FTIR because every molecule has a unique spectral fingerprint in the mid-infrared region. The technique can be used on powders, liquids, gases and polymers with little sample preparation, and it is relatively fast and simple.

The researchers collected an assortment of gums, blending locust bean and guar in concentrations from 0.5 to 15 percent by weight. They also produced mixtures of other gums, such as xanthan and guar, that are commonly used in the food industry. They used two FTIR methods to look for distinctive spectral features in the pure gum samples, settling on the diffuse reflectance of powered gum samples.

With a correlation between values derived from FTIR to the actual ratio of the samples of better than 95 percent, the investigators concluded that the technique is suitable for use in quality control of a gum mix. There is some sample preparation required, but much less than for other techniques.

Mauer acknowledged that its application would require the development of a spectral library. Such a database of molecular fingerprints, however, would be valuable both for research and for commercial purposes.


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