Retaining Nutrients In Irradiated Salads

Irradiation is known to reduce microorganisms in food, both harmful and nonharmful. For leafy greens, in particular, Agricultural Research Service (ARS) scientists are looking into the effect of various levels of irradiation on concentrations of four vitamins and four carotenoids in two baby leaf spinach cultivars.


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 to extend shelflife. The cultivars then were exposed to up to 2.0 kiloGrays (kGy) of radiation in 0.5 kGy increments. FDA 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 and the four carotenoids lutein/zeaxanthin, neoxanthin, violoxanthin, and beta carotene. Researchers found generally that the nutrients folate, E, K, and neoxanthin showed little or no change in concentration with increasing levels of irradiation.

Levels of lutein/zeaxanthin, and B-carotene, which are said to make up 80% of all carotenoids in spinach, were reduced on average by 12% at the 2.0 kGy level, which is within the range of natural variation.

In addition, irradiation decreased ascorbic acid levels by 42%, largely 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 is said to provide the same benefits as vitamin C inside the leaf.

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.

Source: USDA ARS

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