New approach for nutritional analysis.

The way we preserve and test a particular food sample to analyze its nutritional content can influence the quantity of bioactive chemicals reported to be found in that food. This fact is especially important to private and public research laboratories striving to precisely measure compounds in products that have been found to provide health benefits beyond basic nutrition.

New steps for optimizing sample preservation, analytical preparation and extraction methods for testing the quantity of bioactive phytochemicals in foods have been developed by USDA-ARS scientists. The approach was detailed recently by ARS scientists during the national meeting of the American Chemical Society.

The new approach involves validating sampling and preservation procedures and the application of current extraction techniques, such as pressurized liquid and ultrasonic irradiation. These steps support the optimal extraction of bioactive phytochemicals from different plant sources. Describing such methods is an important step toward consistency in reporting.

Scientists emphasize the importance of optimized and uniform sample preparation because of the wide variations in the quantities of bioactive phenolic phytochemicals reported in foods by different research groups. Accurately quantifying such plant chemicals allows other investigators to determine more precisely the amounts of these compounds people consume in their diets, and to study associations between those intakes and health outcomes.

There will continue to be large variations in the quantity of reported bioactive plant chemicals due to differences in cultivars grown, environmental or postharvest conditions, and the maturity of crops at the time of harvest. But analysts strive to minimize any uncertainty introduced by preparation and analytical methods.

A growing area of interest is the effect upon human health of trace chemicals, collectively called phytochemicals--nutrients typically found in edible plants, especially colorful fruits and vegetables. Unlike the anecdotal and sometimes specious nutritional claims about medicinal herbs and compounds, the effects of phytochemicals increasingly survive rigorous testing by prominent health organizations. Perhaps the most rigorously tested phytochemical is zeaxanthin, a yellow-pigmented carotenoid present in many yellow and orange fruits and vegetables. Repeated studies have shown a strong correlation between the consumption of zeaxanthin and the prevention and treatment of age-related macular degeneration.

Further information. Dave Luthria, USDA-ARS Food Composition Laboratory, Room 202B, 10300 Baltimore Ave., Building 161, BARC-EAST, Beltsville, MD 20705; phone: 301-504-7247; fax: 301-504-8314; email: d.luthria@ars.usda.gov.