A Protocol for Preparing Preserved Flowers with Natural Color and Texture (2024)

Plant materials.

Flowers of ‘Moondust Velvet Blue’, a genetically engineered carnation variety with delphinidin-type anthocyanins (f*ckui et al., 2003), were used to establish a protocol of three combined processes because its pigments have already been identified and it shows the highest pigment content among the three “Moondust” varieties. Cut ‘Moondust Velvet Blue’ flowers imported from Columbia were obtained from Suntory Flowers (Tokyo). The stem bases were inserted in a vase with 20 mL·L⁻¹ of a preservative containing sugars, inorganic ions, and antibacterial agents (Misaki; Otsuka Chemical, Osaka, Japan). Flowers after full bloom were used within 1 week.

Thirty kinds of flowers with different pigments such as flavonoids, carotenoids, chlorophylls, betalains, and anthocyanins were used for the applicability test of the established protocol. Flowers were obtained from florists or experimental fields and were used immediately.

A protocol for flower processing.

Unless otherwise mentioned, ethyl alcohol was used to prevent petal shrinkage in the primary soaking process, followed by polypropylene glycol (diol type, average molecular weight: 400) to prevent petal discoloration in the secondary soaking process.

The protocol consisted of 1) soaking flowers in the primary solvent (ethyl alcohol) overnight; 2) soaking in the secondary solvent (100% polypropylene glycol) overnight or 2 d; 3) rinsing the flowers for 1 min with ethyl alcohol. The ‘Moondust Velvet Blue’ flowers with their stems trimmed to 10 cm were held upside down and the whole flower was soaked in 500 mL plastic containers containing 300 mL of primary or secondary soaking solvent. Thirty other kinds of flowers were soaked in the same way using 100 to 1000 mL of solvents, depending on the flower volume. The temperature of the solvents was 25 °C. The containers were covered with plastic wrap during steps 1 and 2. After the three treatment steps, the processed flowers were allowed to stand in a room at 25 °C and 45% ± 25% relative humidity (RH) for 1 d or more. Three replicate flowers were processed.

‘Moondust Velvet Blue’ carnation and the 30 other kinds of flowers were evaluated and classified into one of three groups: 1) petals that retained their color, 2) petals that retained their color only somewhat, and 3) petals that almost or completely lost their color.

Other preservation solvents such as 1-hexanol or methyl alcohol as the primary soaking solvents or polyethylene glycol (average molecular weight: 400); 2-methyl-2,4-pentanediol; or 1,3-butanediol as the secondary soaking solvents also were tested.

Flower processing.

A protocol for preparing preserved ‘Moondust Velvet Blue’ carnations so that they retain their natural color and texture is detailed with bold frames in Fig. 1. Five serious quality defects were observed during and after the flower preservation process when solvents such as 1-hexanol or methyl alcohol were used instead of ethyl alcohol as the primary soaking solvent or polyethylene glycol; 2-methyl-2,4-pentanediol; or 1,3-butanediol was used instead of polypropylene glycol as the secondary soaking solvent (Figs. 1 and 2).

The quality defects observed were as follows: 1) Petal shrinkage occurred by soaking flowers in high-viscosity solvents (e.g., 1-hexanol) as the primary soaking solvent (Fig. 2C). The use of polypropylene glycol, polyethylene glycol, and glycerin also caused the same defects (data not shown). 2) Petal discoloration occurred by soaking flowers in high-hydrophilic solvents (e.g., methyl alcohol) as the primary soaking solvent or polyethylene glycol as the secondary soaking solvent (Fig. 2, D and E). The use of ethylene glycol, propylene glycol, and glycerin caused the same defects (data not shown). 3) Petal shrinkage occurred due to the volatilization of the primary soaking solvent when the flowers were kept in air before being transferred to the secondary soaking solvent (Fig. 2F). Flowers must be soaked in the secondary soaking solvent immediately after being soaked in ethyl alcohol as the primary soaking solvent (Fig. 2B). Severe petal shrinkage also occurred even when a low-volatile solvent (e.g., 2-methyl-2,4-pentanediol) was used as the secondary soaking solvent (Fig. 2J). The use of 2-(2-ethylhexyloxy)ethanol; 2,3-butanediol; and 4-hydroxy-2-butanone caused the same defects (data not shown). 4) The natural texture was not obtained just after soaking treatment with a nonvolatile sticky solvent (e.g., polypropylene glycol) because it remained on the petal surface (Fig. 2I). The flower needed to be rinsed with low-viscosity solvents (e.g., ethyl alcohol) to remove the secondary soaking solvent (Fig. 2G). The use of propylene glycol, glycerin, and 2-[2-(2-ethylhexyloxy)ethoxy]ethanol caused the same defects (data not shown). 5) Petals gradually lost their color after being processed using 1,3-butanediol as the secondary soaking solvent (Fig. 2K). The use of 1,3-propanediol; 1,4-butanediol; and 1,5-pentanediol caused the same defects (data not shown). Petal color was retained for at least 6 months by using polypropylene glycol as the secondary soaking solvent (Fig. 2L).

Application to various flowers.

Similar to ‘Moondust Velvet Blue’ carnation, the flower shapes of most species tested were retained when the standard preserving protocol was used (Fig. 3). Flower species with thin petals that are particularly easy to deform were exceptions (Fig. 3, C2, D2, K2, L2, and S2). Compared with the color of unprocessed flowers (Fig. 3, A1–DD1), processed petals were grouped into those that retained their color well (Fig. 3, A2–L2), those that somewhat retained their color (Fig. 3, M1–O2), or those that nearly or completely lost their color (Fig. 3, P2–DD2). Some multicolor flowers retained their color patterns (Fig. 3, B2, E2, F2, G2, and N2).