Antioxidant and flexible bioplastics based on microwave-assisted extracted coffee fruit cascara pectic polysaccharides

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.