Upcycling of carrot waste into pectin-arabinogalactan and lignin-cellulose films via hydrothermal treatment, ultrafiltration/diafiltration, and casting

Abstract

Discarded carrots were repurposed to produced bio-based films through a pilot-scale hydrothermal treatment of the pulp. The process, conducted at 140 °C and 180 °C using single and multiple flow-through reactors, successfully extracted high molecular weight pectin-containing arabinogalactan (P-AG). Separation and purification through ultrafiltration and diafiltration yielded fractions with molecular weights ranging from 3.48 to 102.75 kDa. The solid residue from the hydrothermal process was subjected to mechanical treatments to obtain lignin-containing cellulose nanofibers (L-CNFs). Comparative analysis showed the P-AG film possessed superior oxygen barrier properties (67.73 vs. 239.83 cm3·µm/m2/kPa/day), while the L-CNFs film displayed higher tensile strength (7.74 vs. 3.14 MPa). Combining both fractions revealed that L-CNFs could be incorporated at percentages exceeding 15% (w/w) without compromising the P-AG-based film’s integrity, resulting in a 57.5% increase in water contact angle (125.8°). In examining P-AG samples, a higher molecular weight reduced oxygen permeability by 14.6% (41.14 cm3·µm/m2/kPa/day) but increased the water vapor permeability by 11.4% (2.78·10−10 g·m/m2/s/Pa). Tensile strength showed a 150.9% increase at lower molecular weights and higher pectin content (2.84 MPa), attributed to arabinogalactan’s pronounced branching. Elongation increased by 157.9% at higher arabinogalactan content (15.28%). This study achieved a groundbreaking milestone by obtaining purified fractions of P-AG and L-CNFs from carrot waste, demonstrating promising film properties suitable for food packaging applications.