Orientadora: Profa. Dra. Grasiele Scaramal Madrona

Data da Defesa:19/11/2021



Hibiscus sabdariffa L., also known as hibiscus or roselle, is a plant species of
the Malvaceae family grown worldwide. The commercial interest of hibiscus is
mainly in dry calyces that have in their composition high content of antioxidant molecules (anthocyanins, flavonoids, and phenolic acids) capable of reduce disease risks. Membrane filtration is a technique based on the permeation of
solute molecules through a semipermeable membrane, being an efficient alternative for clarification and concentration of plant extracts, due to the preservation of product characteristics. This process offers several advantages, including low temperature operation, no phase transition, high separation efficiency, low power consumption, simple equipment and easy scale-up. The greatest limitation for membrane separation processes is membrane fouling, since during operation particles are deposited in the membrane (surface and/or pores). Therefore, it is essential to understand the mechanisms of membrane fouling and provide solutions for this problem.
The general objective of this work was to apply membrane filtration processes to
hibiscus (Hibiscus Sabdariffa L.) extracts. The specific objectives were: (1) To
evaluate the application of centrifugation followed by membrane filtration to produce ready-to-drink tea with high antioxidant content and (2) To use turbulence promotor and ultrasound in filtration to reduce membrane fouling.
This study is divided into two parts, in the first the focus was filtration through
asymmetric hollow fiber membranes with composition of 25% dolomite and 75%
alumina (pore sizes ranging from 0.16 to 5.29 μm) for the clarification of hibiscus
extract with and without centrifugation (8000 rpm for 20 min). In the second part of the study, the use of 3D turbulence promoters (108 pins, spacing of 6 mm between pins, 2.5 mm in diameter and 1.8 mm in height), ultrasound (Ultracleaner 1650 Unique, frequency of 40 KHz) and the association of turbulence promoter plus ultrasound to mitigate fouling in flat membranes of polyethersulfone (5 kDa) during cross-flow ultrafiltration of hibiscus extract. In the two stages of the study, hibiscus extracts and permeated extracts were analyzed for pH, total soluble solids, total solids, total phenolic compounds, total anthocyanins, antioxidant (DPPH and FRAP), instrumental color and chromatographic analysis (UPLC-MS/MS). Mathematical modeling and the resistance series model were performed to describe the scale during extract filtration. In the first part, tea cream was evaluated and membranes were characterized before and after filtration with scanning electron microscopy (MEV), and Fourier transform infrared spectroscopy (FTIR-ATR). In the second part, membranes were evaluated by atomic force microscopy (AFM) and Fourier
transform infrared spectroscopy (FTIR-ATR). The data were statistically evaluated using variance analysis (ANOVA), and Tukey test with a significance level of 5% (p≤ 0.05) using the statistical program Sisvar 5.6.
In the first part of the study it was observed that centrifugation provided a significant improvement in permeate flux in the asymmetric hollow fiber membrane. For extracts without centrifugation the initial flux was 460.23 kg m-2 h-1, whereas for centrifuged extracts the initial flux was 694.79 kg m-2 h-1 representing a flux increase of 51%. Complete pore blockage (n=2) was the main fouling mechanism and according to SEM and FTIR-ATR data, polysaccharides, proteins and phenolic compounds were probably responsible for fouling. After sequential membrane filtration total soluble solids and total solids were reduced from 5.53 to 4.03 °Brix, and 47120 to 37780 mg L-1, respectively. Clarification of the product also occurred after sequential membrane filtration, in which the L* color coordinate increased from 15.69 to 22.03. Seven compounds were identified by UPLC-MS/MS in the extracts and permeate: Cyanidine (m/z 287.1), delphinidin (m/z 303.1), 4-cafeoglycenquine acid (m/z 353 0), hexoside quercetin (m/z 463.0), quercetin (m/z 595.0), myricetin (m/z 611.0) and kaempferol (m/z 285.0). Centrifuged extracts with membrane filtration showed greater stability after 20 days of storage at 5°C, with 43.1% reduction in tea cream formation. In the second part of the study, it was observed that the use of ultrasound, turbulence promoter, and ultrasound plus turbulence promoter, increased the flux by 21, 44 and 88%, respectively. Pore blockage was the main fouling mechanism and polysaccharides, proteins and bioactive compounds probably caused membrane fouling as shown by FTIR-ATR results. AFM analysis exposed membrane roughness after filtration, and compared with the roughness of the virgin membrane, the control membrane was 12 times larger, while the membrane from ultrasound plus turbulence promoter was only 2 times larger. Retention greater than 60% was observed for total phenolic compounds, total anthocyanins, cyanidine-3-glycoside, delphinidin, quercetin, myricetin, and rutin
after ultrafiltration.
Through this study, it was possible to conclude that: - The application of centrifugation as pretreatment resulted in higher permeate  fluxs in filtration by asymmetric hollow fiber membrane. Furthermore, it is important to highlight that the centrifuged and filtered extract was clarified and presented greater stability after 20 days of storage at 5°C, reducing the formation of tea cream. Thus, the sequential process of pretreatment (centrifugation) and membrane filtration can be potentially applied to produce ready-to-drink hibiscus tea, with high antioxidant content. - The use of ultrasound, turbulence promoter, and ultrasound plus turbulence promoter, for membrane filtration resulted in higher fluxes of hibiscus extract permeate. Polysaccharides, proteins and bioactive compounds were most likely responsible for membrane fouling. Furthermore, it is important to highlight that the use of turbulence promoter in association with ultrasound did not alter the quality of hibiscus extract. Thus, the combined use of turbulence promoter and ultrasound in the ultrafiltration module shows great potential to significantly mitigate membrane fouling and improve cross-flow filtration.
Keywords: membrane, fouling, phenolic compounds, antioxidant.

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