Nutritional Quality of Marigolds Dependent on Drying Method

Marigold flower has widespread use in both human and animal nutrition (for medicinal and functional purposes), but drying is an important process in the manufacture of market-ready marigold powder. Thanks to a recent Thai study, it's now clear that the nutritional and functional quality of marigold depends on the commercial drying method.

Researchers from Mahasarakham University in Thailand measured the response of marigold (Tagetes erecta L.) petals to three different commercial drying methods: freeze drying, hot air drying, and far-infrared radiation with hot air convection. Hot air drying is industry's most popular drying method. Each method was used to dry 500 g of fresh petals, and results were compared to those from an unprocessed control batch.

One of marigold's biggest commercial markets is in chicken feed, as its yellow-orange pigment can enhance the color of a chicken's egg yolk. Using a Minolta CR-300 Chroma Meter, the team of researchers observed less color change when petals were dried under the far-infrared radiation and hot air convection method compared to the other two methods. They believe this drying method better preserved original marigold color at least in part because it created more favorable temperature and humidity conditions.

The human nutrition market for marigold (at least in Western countries) is mainly centered around lutein, a marigold-sourced compound found in eye health and beauty products. Other bioactives found in marigolds include lycopene and beta-carotene. The researchers measured for changes to all three of these compounds and found some variation.

With lycopene, a combination of far-infrared radiation and hot air convection was, again, superior to other methods, yielding 58.7 mg/mg of dry weight compared to 51.2 mg and 48.7 mg of lycopene with hot air and freeze drying respectively. Each drying process actually increased lycopene content over the amount found in fresh petals-a result also reported in published research on lycopene from tomatoes.

Hot air drying and far-infrared radiation with hot convection both increased available betacarotene-in this order-compared to fresh petals. Freeze drying evidently decreased beta-carotene concentration 8.6% from fresh levels.

When it came down to lutein, freeze drying and the far-infrared radiation method were comparably beneficial, yielding lutein levels about five times as high as fresh petals, according to the researchers.

The far-infrared procedure also proved superior in preserving numerous phenolic acids and preserving the antioxidant potential of marigold.

“These results demonstrate that (far-infrared radiation and hot air convection) should be considered as a suitable drying method for marigold with respect to preserving its color, antioxidant properties, and bioactive compounds, and provided useful information for industrial production of marigold powder,” wrote the researchers. In light of the varied results, however, the researchers did add that "different drying methods could be suitable for different products with respect to targeted compounds such as phenolics, flavonoids, or carotenoids."

Thailand's Office of Higher Education Commission funded this study.