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In real time, study chemical modifications of tomato carotenoids.

Tomatoes are the second most produced and consumed vegetable in the United States, providing a rich source of dietary carotenoids. More than 120 million tons of tomatoes were produced worldwide in 2008. China was the largest producer, accounting for about 25% of global output. For one variety, known as plum or processing tomatoes, California accounts for about 90% of U.S. production and 35% of world production.

There is conflicting evidence on the impact of thermal treatments on carotenoids in tomatoes. We need to improve the information we have on the chemical changes that occur during the processing and storage of tomatoes, with a goal of optimizing their potential health benefits.

Attenuated total reflectance (ATR) infrared spectroscopy makes it possible to rapidly monitor subtle compositional changes in tomatoes and helps determine, non-invasively and in real time, the effects that different processing methods might have on these compounds. So, scientists at The Ohio State University developed an infrared technique that could be used to monitor in real time the structural and chemical transformations of carotenoids when they undergo thermal treatment. Essentially, understanding the thermal behavior of carotenoids will help processors develop carotenoid-rich products.

Using hexane, acetone, ethanol and water, the scientists extracted oleoresins from carotenoid-rich tomato pastes, including trans-lycopene, cis-lycopene, various carotenes and a low carotenoid control. The hexane layer of the samples was removed, dried under a nitrogen stream environment, re-dissolved in chloroform and deposited onto a temperature-controlled zinc selenide crystal coupled to an infrared spectrometer. Spectra in the range from 600 [cm.sup.-1] to 4000 [cm.sup.-1] were collected in real time from samples exposed at 60, 80, 100 and 120 C for 95 minutes.

Infrared spectra yielded absorption profiles that showed in real time carotenoids undergoing changes during thermal treatment. The spectra collected at 60 C did not show any noticeable variations, indicating how stable the carotenoids were. Above 80 C, several spectral changes were observed with marked shifts at the 956 [cm.sup.-1] trans lycopene band with time toward a higher frequency (966 [cm.sup.-1]). The changes were consistent with heat-induced isomerization reactions. Increased temperatures created complex spectral trends associated with the oxidation and breakdown of the carotenoids.

Further information. Luis Rodriguez-Saona, Department of Food Science, The Ohio State University, 325 Parker Food Science and Technology Building, 2015 Fyffe Rd., Columbus, OH 43210; phone: 614-292-3337; fax: 614-292-0218; email:
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Publication:Emerging Food R&D Report
Date:Nov 1, 2009
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