Asymmetric Al2O3 and PES/Al2O3 hollow fiber membranes for green tea extract clarification

• Published in: Journal of food engineering 2020-07, Vol.277, p.109889, Article 109889
• Main Authors: Bindes, Marlon Menezes Maciel, Terra, Natália Mazzarioli, Patience, Gregory Scott, Boffito, Daria Camilla, Cardoso, Vicelma Luiz, Reis, Miria Hespanhol Miranda
• Format: Article
• Language: English
• Subjects: Alumina; Green tea; Hollow fiber; Stabilization; Tea clarification
• ISSN: 0260-8774; 1873-5770
• DOI: 10.1016/j.jfoodeng.2019.109889

Green tea (Camellia sinensis) leaves are particularly rich in polyphenols. Here we propose the clarification of green tea extract by an innovative process consisting of a two-stage filtration through asymmetric alumina (Al2O3) hollow fibers, which we specially designed for this application by the phase inversion technique. The fibers presented outer sponge like-layers, mainly responsible for the membrane selectivity (turbidity of green tea extract was reduced by 90%) and mechanical strength (135 MPa), and an inner finger-like layer that reduced the resistance to flux permeation (water permeability of 2.56 × 10−9 m3 s−1 m−2 Pa−1). In order to increase the membrane retention coefficient, we deposited a polyethersulfone (PES) coating layer on the fiber outer surface. This polymeric layer further reduced the green tea extract turbidity by 97.8% in the permeate. As a consequence, no team cream formed even after 30 days of refrigerated storage. Thus, the membranes that we conceived enabled to obtain a product with superior clarity and stability. Additionally, a mathematical description of flux decay during the filtration processes showed that cake formation and internal pore blockage models better described flux decay through Al2O3 and PES/Al2O3 hollow fibers, respectively. [Display omitted] •Green tea extract clarification by a sequential filtration through Al2O3 and PES/Al2O3 hollow fibers.•Asymmetric Al2O3 hollow fibers reduce turbidity by 89.8% with a polyphenol rejection of just of 2.3%.•PES/Al2O3 hollow fibers reduce turbidity by 97.8% while polyphenol rejection is less than 10%.•PES/Al2O3 hollow fibers produce a stable permeate under refrigeration.