Beta vulgaris L.-A Source with a Great Potential in the Extraction of Natural Dyes Intended for the Sustainable Dyeing of Wool

Abstract

Beta vulgaris L. is a biennial plant easily accessible all over the world, rich in various biologically active compounds, especially a class of extremely bioactive pigments known as betalains. These dyes predominate in the pulp and peels of beetroot, which is why they can be valorized in food, medicine or in the textile industry. In this work, betalains extractions were carried out applying 3 sustainable options: (1) dissolving/solubilizing betalains in water; (2) extraction under pressure; (3) extraction assisted by an enzyme/pectinase. The obtained extracts were analyzed in the UV-Vis domain, which allowed their characterization by determining the total monomeric anthocyanins, color density (control), polymeric density and browning index. The HPLC-MS analysis highlighted the extracts composition. The colors characteristics were determined through CIELab measurements. The performances of these 3 extracts, during green dyeing (without mordants), were evaluated according to the color characteristics (L*, a*, b* and K/S) of the dyed wool samples under different conditions: pH, temperature, duration of dyeing and volume of extract and stabilizers (Vitamin E and EDTA). Betalains can be considered acid dyes, with a low affinity for wool, which in a pronounced acidic environment dye the wool in an intense, uniform way and with good resistance to washing and rubbing.

Keywords: betalains; decarboxylation; deprotonation; dyeing; pectinase; pressure; stabilizer.

Figure 1

The influence of pH on the absorption of extracts: REx1 (a); PecEx1 (b).

Figure 2

The luminosity of the extracts depending on the duration of the extraction process; (Conditions for obtaining: 100 mL protonated extract with acetic acid, 30 min, pH = 3.5). The figure was obtained at a level of significance α = 0.05.

Figure 3

The a* and b* values for REx, PresEx and PecEx extracts, obtained from extractive processes with different durations (1–24 h). The figure was obtained at a level of significance α = 0.05.

Figure 4

Influence of pH on CIElab values of wool samples dyed at 30 °C, for 24 h (Legend: 2* represents a pH = 2 made with H₂SO₄, the other acidic environments being made with acetic acid). The figure was obtained at a level of significance α = 0.05.

Figure 5

Influence of pH on color intensity (K/S) values of wool samples dyed at 30 °C, for 24 h; (Legend: 2* represents a pH = 2 made with H₂SO₄, the other acidic environments being made with acetic acid). The figure was obtained at a level of significance α = 0.05.

Figure 6

Appearances and the color intensities for wool samples before dyeing (a), dyed for 4 h with colored extracts, without acid addition (b); dyed 4 h with colored extracts acidified with H₂SO₄ up to pH = 2 (c); dyed with REx24/PresEx24/PecEx24 at pH 2 (d), pH 3 (e), pH 4 (f); (Dyeing conditions: 100 mL extract, for 4–24 h at 30 °C (room temperature, summer)).

Figure 7

The influence of stabilizers on the color of wool dyed 24 h at 30 °C, pH = 3.5 with 100 mL extract. The figure was obtained at a level of significance α = 0.05.

Figure 8

The influence of stabilizers (Vitamin E and EDTA) on color intensity when dyeing wool with 100 mL extract + 5–10 mL stabilizer, at pH = 3.5, T = 30 °C for 24 h. The figure was obtained at a level of significance α = 0.05.

Figure 9

Appearances and a* values of wool samples dyed with 100 mL extract at pH = 3.5, T = 30 °C for 24 h, without stabilizer (a) and with stabilizer: 5 mL Vitamin E (b), 10 mL Vitamin E (c), 5 mL EDTA (d) and 10 mL EDTA (e).

Figure 10

The influence of the extract volume (25–100 mL Rex24, PresEx24 or PecEx24) on the color characteristics (L*, a* and b*) of wool dyed 24 h at pH = 3.5 and T = 30 °C. The figure was obtained at a level of significance α = 0.05.

Figure 11

Appearances and the color intensities of wool samples before dyeing (a), after dyeing with a certain volume of extract: 25 mL (b), 50 mL (c), 75 mL (d) and 100 mL (e); (dyeing conditions: 24 h at pH = 3.5 and T = 30 °C).

Figure 12

Dependence of the color intensity of wool dyed with 25–100 mL Rex24, PresEx24, and PecEx24 extracts, at T = 30 °C and pH = 3.5. The figure was obtained at a level of significance α = 0.05.

Figure 13

The influence of the dyeing temperature (40–70 °C) on the color characteristics of wool dyed with 100 mL extract, at pH = 3.5, t = 1 h. The figure was obtained at a level of significance α = 0.05.

Figure 14

Dependence of the color intensity of wool dyed at 40–70 °C, with 100 mL extracts, at pH = 3.5 (CH₃COOH), t = 1 h. The figure was obtained at a level of significance α = 0.05.

Figure 15

Appearances and the color intensities of dyed wool samples at 40–70 °C, with 100 mL extracts, at pH = 3.5 (CH₃COOH), t = 1 h.

Figure 16

Dependence of L*, a* and b* on the duration of dyeing (24–26 h) if the dyeing is done at pH = 3.5, T = 30 °C with volumes of 100 mL extracts. The figure was obtained at a level of significance α = 0.05.

Figure 17

Dependence of K/S on the duration of dyeing with 100 mL extract, at 30 °C, pH = 3.5. The figure was obtained at a level of significance α = 0.05.