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  • Getting Juiced

Photonics Spectra
Jul 2007
Hank Hogan

Sugar is sweet, but sometimes its use can lead to bitter results. Such is the case with fruit juice when unscrupulous suppliers use sugar solutions as a replacement for high-cost ingredients in juice drinks to cut costs. Similarly, substituting fruit that is not authentic in Concord grape juice can boost the bottom line. The prospect of money and the inability to detect adulterations easily are factors that tempt manufacturers to alter juice.

Now a group from Ohio State University in Columbus has used infrared spectroscopy to sample juice rapidly, achieving 100 percent correct classification in test cases after obtaining spectral signatures from samples. “This instrumental method is capable of simultaneous monitoring of multiple components and allows monitoring for differences due to plant material and processing or differences due to adulteration,” said M. Mónica Giusti, an assistant professor of food science and technology.

She noted that periods of industry problems with adulteration come and go, with reliable statistics hard to come by. Typically, the industry depends upon sensory panels, people with highly trained noses or tongues who can distinguish one fruit variety from another. That information is supplemented by detection of marker compounds. The first technique is expensive, time-consuming and dependent on individuals. The second provides only limited information.

Increasing signal

The Ohio State group used mid-infrared spectroscopy with a spectrometer made by Digilab Inc. of Canton, Mass. (the technology has since been acquired by Varian Inc. of Palo Alto, Calif.), and an attenuated total reflectance accessory from Pike Technologies Inc. of Madison, Wis. Luis E. Rodriguez-Saona, the group’s infrared spectroscopy expert, said that the researchers were helped by the multiple bounce accessory and by the development of different crystals — both of which increased the signal and sensitivity.

Team members scanned a variety of juices from 750 to 1800 cm–1, looking at both the sugar- and phenol-rich fractions of prepared samples. They found that the phenol-rich samples provided signaturelike spectral information after the raw data was processed. Armed with these spectral fingerprints, they classified various juices without error and identified differences among manufacturers.

The group continues to explore the sources for sample variability. Giusti noted that the technique eventually could address concerns about geographic varietal authentication.

Journal of Agricultural and Food Chemistry, May 30, 2007, pp. 4443-4452.

infrared spectroscopy
The measurement of the ability of matter to absorb, transmit or reflect infrared radiation and the relating of the resultant data to chemical structure.
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