A Food's Composition, By Any Preparation Method, Is Not
By Rosalie Marion
March 29, 2007
The method of preserving and testing a
particular food sample for nutrient analysis can influence the quantity of
bioactive chemicals reported to be found in that food. This is especially
important to private and public research laboratories striving to precisely
measure compounds in food 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 Agricultural Research Service (ARS) scientists.
The approach was outlined today by ARS scientist
Luthria during the national meeting of the
Society in Chicago, Ill. Luthria is a chemist with the
Food Composition Laboratory, which is part of the
(Md.) Human Nutrition Research Center. ARS is the
U.S. Department of Agriculture's chief
scientific research agency.
The steps described included validating sampling, preservation and
application of modern extraction procedures, such as use of pressurized liquid
and ultrasonic irradiation. These steps support optimal extraction of bioactive
phytochemicals from different plant sources. Describing such methods is an
important step toward consistency in reporting.
Luthria emphasized the importance of renewed interest in optimized and
uniform sample preparation because of the wide variations in quantities of
bioactive phenolic phytochemicals reported in foods by different research
groups. Accurately quantifying such plant chemicals allows other researchers to
determine more precisely the amounts of these compounds people consume in their
diets, and to study associations between those intakes and health outcomes.
ARS food composition scientists develop procedures and test methods for
accurately analyzing bioactive chemicals in foods. They also provide key data
for use in nutrient databases and establishing recommended intakes for
nutrients in foods.
Large variations in the quantity of reported bioactive plant chemicals will
persist due to differences in cultivars grown, environmental and/or postharvest
conditions, and maturity at the time of harvest. But analysts strive to ensure
that uncertainty introduced by preparation and analytical methods is small
compared to other uncertainties.