Changes in colour, antioxidant activities and carotenoids (lycopene, β-carotene, lutein) of marigold flower (Tagetes erecta L.) resulting from different drying processes

Marigold (Tagetes erecta L.) flower has long been used as a food colourant and ingredient in human food and animal feed. Drying is one of the most important processes for producing marigold powder. Therefore the effects of different drying processes, namely freeze drying (FD), hot air drying (HA) and combined far-infrared radiation with hot air convection (FIR-HA), on the colour, carotenoids (lycopene, β-carotene and lutein) and phenolic compounds of marigold flowers were evaluated. The results indicate that colour changes were less for FIR-HA dried marigold than after FD and HA drying. Different drying methods resulted in changes in the content of individual bioactive compounds. HA gave the highest content of β-carotene (15.5 mg/100 g dry weight (DW)), while FIR-HA and FD provided the highest levels of lutein and lycopene. The predominant phenolic acids in all samples of marigold are p-coumaric acid, ferulic acid and sinapic acid. Gallic, protocatechuic, caffeic, syringic, p-coumaric and ferulic acid showed the highest content in marigold after FIR-HA drying. These results demonstrate that FIR-HA should be considered as a suitable drying method for marigold with respect to preserving its colour, antioxidant properties and bioactive compounds and provided useful information for industrial production of marigold powder.

► Marigold dried with FIR-HA was observed smallest decreases in L and b value.
► Major carotenoids found in marigold were lutein, lycopene and β-carotene.
► HA gave highest content of β-carotene.
► FIR-HA and FD provided highest amount of lutein and lycopene.
► Phenolic compounds showed the highest content in marigold with FIR-HA.