Antioxidant and flexible bioplastics based on microwave-assisted extracted coffee fruit cascara pectic polysaccharides
Gonçalo Oliveira, Sílvia Petronilho, Kamila Kapuśniak, Janusz Kapuśniak, M. Dolores del Castillo, Manuel A. Coimbra, Paula Ferreira, Cláudia P. Passos, Idalina Gonçalves
Abstract
Pectic polysaccharides with film-forming ability are often recovered from renewable agrifood by-products through solid-liquid extraction (SLE). Targeting an organic solvent-free approach, in this work, it is hypothesized that pectic polysaccharides of interest for bioplastics development can be recovered by microwave-assisted extraction (MAE) and purified by ultrafiltration. Coffee fruit cascara (CFC) was used as raw material. MAE of CFC-derived pectic polysaccharides was carried out at 120 °C at different times (2, 5, and 10 min). A 3-times (1 h each) sequential SLE with 2% acetic acid under reflux at atmospheric pressure was also performed. High molecular weight (HMW) extracts obtained by MAE for 2 min (HMW_MAE 2’) and by SLE for 1 h (HMW_SLE1), composed of 60 mol% and 54 mol% uronic acids with 8% and 12% methyl-esterification, and 3% and 5% acetylation, respectively, were selected for bioplastics development. HMW_MAE 2’ originated slightly transparent, dark brown, hydrophilic (ca. 32° water contact angle), and antioxidant (90% ABTS•+ inhibition after 5 min) bioplastics, similar to HMW_SLE1-derived materials, but 10-fold more stretchable (20% and 2% elongation at break, respectively). Therefore, MAE followed by ultrafiltration showed to be a fast and clean strategy to recover low methyl-esterified CFC pectic polysaccharides with the ability to develop antioxidant and flexible bioplastics.