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Studies Show Benefit of UV Light on Fresh Produce

Preliminary studies by Tara H. McHugh, a food technologist and research leader at the Agricultural Research Service (ARS) Processed Foods Research Unit at the Western Regional Research Center in Albany, California, along with her research team, have recently revealed the benefits of exposing vegetables to certain kinds of ultraviolet light.

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The suns rays are a natural source of the three bands of ultraviolet radiation, namely UV-A, UV-B, and UV-C. Although invisible to the human eye, ultraviolet light in all of its forms can be damaging to human health. Specifically, it can cause sunburn or discoloration, premature aging of the skin, and even some forms of skin cancer through indirect DNA damage.

However, at the opposite end of the spectrum, ultraviolet light can also produce many beneficial effects, most significantly, the healthy production of vitamin D in the skin.

Under the direction of McHugh, the research team at ARS, USDA’s chief intramural scientific research agency, was able to harness those beneficial aspects of ultraviolet light to quickly, safely, and easily increase the antioxidant activity of carrots. This comes as an important finding since antioxidants are recognized as lowering the risk of cancer and heart disease.

In their investigation, McHugh and others exposed fresh, sliced carrots to a 14-second dose of UV-B. The results of the trial indicated that this short exposure of UV-B can actually enhance the antioxidant capacity of the carrots by about threefold without significantly heating or drying the carrots.

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According to the report in the January 2011 issue of Agricultural Research magazine, “Scientists have known for at least a decade that exposing plants to UV-B may cause what’s known as ‘abiotic stress.'” McHugh believes that this is most likely what happened when the sliced carrots underwent UV-B exposure.

Abiotic stress is defined as the, typically negative, impact of non-living stress factors on a living organism that must affect the organism in a significant way. One such stress factor is ultraviolet light.

In plants, the natural reaction to abiotic stress is to intensify their production of two natural enzymes, polyphenylalanine ammonia-lyase and chalcone synthase, as a mechanism to adapt to the stress conditions. As this happens, levels of phenolics, chemical compounds synthesized by the enzymes, will also grow. McHugh explained that some phenolics are classified as antioxidants. Accordingly, ultraviolet exposure will induce this chemical process, ultimately producing antioxidants as a byproduct.

Although previous studies have identified these antioxidant-producing reactions in various plant species, there has been little data collected on how fresh produce respond to UV-B. McHugh hopes that her research, which she recently presented at the annual meetings of the American Chemical Society and the Institute of Food Technologists, will help to expand that knowledge and prove that fresh produce undergo chemical reactions similar to other plants resulting in greater antioxidant power.

Working with ultraviolet light and studying its effects on fresh produce is not a new endeavor for McHugh. In her earlier research, McHugh experimented with the potential for UV-B to boost the vitamin D content of mushrooms.

In partnership with the Mushroom Council, based in San Jose, California, and Monterey Mushrooms, Inc., of Watsonville, California, McHugh found that the ergosterol in mushrooms, a component of fungal cell membranes which serves the same function as cholesterol in animal cells, could be converted into vitamin D by exposure to controlled UV-B. Since mushrooms usually grow in dark, damp areas, there is little opportunity for them to absorb the sun’s natural ultraviolet rays necessary to undergo this process.

Eventually, McHugh and Monterey Mushrooms together developed a technique to introduce UV-B to mushrooms during packing, allowing the company to market a line of mushrooms rich in vitamin D. The product effectuated the first-ever commercial use of UV-B to increase mushrooms’ vitamin D content.

The research conducted by McHugh and her fellow scientists on the beneficial use of ultraviolet light is just one segment of the many National Programs at ARS. In particular, the study falls under the Quality and Utilization of Agricultural Products program whose mission is to “[e]nhance the economic viability and competitiveness of U.S. agriculture by maintaining the quality of harvested agricultural commodities or otherwise enhancing their marketability, meeting consumer needs, developing environmentally friendly and efficient processing concepts, and expanding domestic and global market opportunities through the development of value-added food and nonfood technologies and products, except energy and fuels.”

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Photo below of pilot-scale UV-B treatment of carrot slices courtesy ARS’s Western Regional Research Center

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