Nutrient Retention of Safer Salads Explored
By Rosalie Marion
May 27, 2010
Irradiating salad leaves after washing
reduces harmful and non-harmful microorganisms. Now,
Agricultural Research Service (ARS)
scientists and colleagues have looked into the effect of various levels of
irradiation on concentrations of four vitamins and four carotenoids in two
popular baby-leaf spinach cultivars.
The study was conducted by post-harvest plant physiologist
Lester and entomologist
Hallman at the ARS
Quality and Fruit Insects Research Unit in Weslaco, Texas. Lester is now
with the ARS
Quality Laboratory in Beltsville, Md.
For the study, two spinach cultivars were grown, harvested, sanitized and
packaged according to industry practices. Each cultivar was packaged in both
air or nitrogen gas as used by industry to extend shelf life. The cultivars
then were exposed to up to 2.0 kiloGrays (kGy) of radiation in 0.5 kGy
increments. The U.S. Food and Drug Administration has approved up to 4 kGy of
irradiation for fresh iceberg lettuce and spinach.
Following irradiation, leaf tissues were tested for concentrations of
vitamins C, E, K and folate (sometimes called vitamin B9) and the four
carotenoids lutein/zeaxanthin, neoxanthin, violoxanthin and beta-carotene.
Lester and colleagues found generally that four nutrientsfolate, E, K and
neoxanthinexhibited little or no change in concentration with increasing
levels of irradiation.
Levels of lutein/zeaxanthin, and B-carotenewhich make up 80 percent of
all carotenoids in spinachwere reduced on average by 12 percent at the
2.0 kGy level, which is within the range of natural variation.
In addition, irradiation decreased ascorbic acid levels by 42 percent,
mainly due to irradiation converting vitamin C to an oxidized form called
dehydroascorbic acid. While the increased dehydroacsorbic acid with irradiation
is an indicator of stress, the converted ascorbic acid provides the same
benefits as vitamin C inside the leaf, according to the authors.
The researchers wanted to build on literature-based food safety evidence by
controlling growth and other environmental variables that could affect nutrient
depletion. More details on this study can be found in the Journal of Agricultural
and Food Chemistry.
ARS is the principal intramural scientific research agency of the
U.S. Department of Agriculture (USDA). The
research supports the USDA priority of ensuring food safety.