Orientadora: Profª Drª Grasiele Scaramal Madrona

Data da Defesa: 23/02/2022


In natural products, one of the main responsible for coloring is part of the flavonoid class, with emphasis on the anthocyanidins group. These pigments are intended for providing food coloring. Hibiscus calyxes are endowed with bioactive compounds, such as anthocyanins and phenolic compounds, which are responsible for their antioxidant properties. In this context, the replacement of synthetic dyes by natural ones has been gaining notoriety. Ultrasound is an extraction technique known as ecologically correct, cheap, fast and efficient for the extraction of phenolic compounds. Along with this fact, the encapsulation technique has also stood out in the case of natural dyes.
This work aims to develop a natural dye of hibiscus (Hibiscus Sabdariffa L.) through its aqueous extract (using ultrasound and conventional extraction) and subsequent lyophilization and encapsulation by ionic gelation. The kinetics of degradation of this dye and application in food matrix were also evaluated.
After being dried and crushed, the hibiscus calyxes were subjected to
and phenolics were also calculated. A yogurt formulation with the addition of 1% natural hibiscus dye was subjected to analysis of rheology, color, pH, moisture, anthocyanins, phenolic compounds, flavonoids and antioxidant activity (DDPH, FRAP, ABTS). All analyses were performed in triplicate and submitted to analysis of variance and Tukey's test (p<0.05) for the least significant difference between means using the statistical program STATISTICA version 7.0.
Thermosonification worked effectively in extracting anthocyanins and phenolic compounds from hibiscus extracts, the antioxidant activity of the thermosified extract was higher (p<0.05) than that of the conventional extract, in all evaluated methods (FRAP, DPPH and ABTS), being increased by 1.16, 1.27 and 1.12 times. Regarding the color, it was observed that the samples tended towards the red color. After the lyophilization process, the same behavior is observed, the antioxidant activity was higher (1.42-fold for flavonoids, 1.07-fold for phenolic compounds, 1.48-fold for FRAP and 1.14-fold for ABTS) for the sample that has been thermosonified and lyophilized. There is even greater extraction of compounds such as quercetin and rutin, being respectively 2.67 and 1.22 times higher for thermosonified samples. In the extraction process followed by encapsulation, the powders obtained after thermosinification (TE) had a higher content of phenolic compounds (1.05 times) and gallic acid (1.23 times) when compared to the conventional process (CE). Capsules in general have a lower value probably due to the fact that the extract is dispersed within the wall material, protecting it from its direct and complete dispersion. The encapsulation efficiency was 75.94% in the thermosonified extraction and 77.44% in the conventional one. Regarding the stability test, it is noted that light negatively affected phenolic compounds and anthocyanins during storage, with greater stability being observed in samples stored without light. The half-life was shorter for all samples submitted to light, as there was a greater degradation of phenolic compounds and anthocyanins. The lyophilized powders showed a variation of ΔE between 1.78 and 8.43. When comparing the extraction techniques, the thermosonified samples showed greater stability of ΔE, (1.78 for the powder and 2.0 for the capsule) and better half-life. In summary, the encapsulated samples showed longer half-life and lower color variations (ΔE) and, therefore, were chosen for application in food matrix. When applied to yogurt, the EC sample (freeze-dried encapsulated conventional hibiscus extract) showed an antioxidant content (ABTS) 1.09 times higher than the conventional sample. There was no significant difference for moisture, pH and rheology, which shows that the extraction techniques followed by lyophilization did not influence these characteristics evaluated. Regarding color, the encapsulated thermosonified sample (TE) was darker (lower luminosity) and with a tendency to red, while CE showed higher luminosity (L*), greater chromaticity (C), with values tending to yellow.
The thermosonified extract showed better results for bioactive compounds, antioxidant activity and half-life values between 38.23 and 376.23 days. The presence of light negatively affected the samples. And when added to yogurt, the encapsulated thermosonified (TE) sample was darker (lower brightness value) and with a greater tendency to red, being potentially recommended for use as a natural food coloring. It was concluded that the extraction method using the solvent as water is ecologically correct and viable to use followed by encapsulation by ionic gelation to obtain natural hibiscus dye.
Key words: Hibiscus sabidariffa, natural dye, stability, thermosonification, encapsulation.