# A Comparative Study of Cast‐Tape, Freeze, and Oven Drying on the Physicochemical and Bioactive Properties of Red Cabbage Microgreen (Brassica oleracea var. capitata f. rubra) Foam Powders

## TL;DR

This study compares different drying methods for red cabbage microgreen powders, finding freeze-drying preserves more nutrients but takes longer.

## Contribution

The study introduces a foam-based approach to drying red cabbage microgreens and evaluates the impact of three drying methods on bioactive compound retention.

## Key findings

- Freeze-dried powders retained higher levels of phenolics, flavonoids, anthocyanins, and antioxidant activity compared to other methods.
- Cast-tape drying was faster but led to greater degradation of bioactive compounds due to heat and light exposure.
- Oven drying provided a balance between processing efficiency and preservation of compounds.

## Abstract

The aim was to produce red cabbage microgreen foams and dry them by cast‐tape drying (CTD), freeze‐drying (FD), and oven drying (OD) to obtain powder and characterize them. The foam composition was water (74.7%), microgreens (14.2%), emulsifier (6.5%), pre‐gelatinized starch (2.8%), and maltodextrin (1.8%). Drying conditions were CTD (98°C, 2–3 mm thick), FD (0.14 mbar, −58°C, for 48 h), and OD (70°C, 2–3 mm thick). Drying times were 32 min for CTD, 2880 min for FD, and 150 min for OD (moisture <0.1 g/g). The foam spreads easily in the CTD, enabling quick drying, whereas OD and FD processes take longer. The FD powder exhibited higher levels of phenolics, flavonoids, anthocyanins, and antioxidant activity despite high water activity and a greener coloration. The Fourier transform infrared spectroscopy (FTIR) spectrum of the powders, especially FD and CTD, indicated the presence of bioactive compounds (flavonoid compounds), carbohydrates (starch, maltodextrin, cellulose, and hemicellulose), and fatty acids (esterified carboxyl groups). CTD enabled rapid and scalable processing but led to greater bioactive degradation due to temperature and light exposure, whereas OD provided an intermediate balance between process efficiency and compound preservation. Foam formulation resulted in low moisture and water activity in CTD and OD powders. Overall, the findings highlight trade‐offs between drying efficiency and nutritional quality, supporting the use of microgreen powders in value‐added food formulations.

Powdered microgreens are versatile and easy to incorporate into most meals and beverages as a neutral nutritional booster or even a flavor enhancer. The foam red cabbage microgreens dehydrated by freeze‐drying, cast‐tape drying, and hot‐air drying produce purple cabbage powders with interesting physicochemical properties and significant amounts of bioactive compounds, such as phenolics and anthocyanins, particularly in those obtained by freeze‐drying. These characteristics highlight the great potential for utilization and possible applications of these products in various fields of food, nutrition, and pharmaceuticals.