From waste to eco-friendly biofilms: Harnessing cottonseed hull proanthocyanidins for sustainable solutions

A circular sustainable bioeconomy model, utilizing renewable resources like agricultural waste biomass, can address environmental issues caused by the massive utilization of fossil resources. The study aims at exploring the potential utilization of underutilized cottonseed hulls (CSHs) as a source of bioactive proanthocyanidins (PAs), and investigate their applicability in the production of biodegradable films. FT-IR, HPLC-QTOF/MS, MALDI-TOF/MS analyses served for characterizing the structure of PAs extracted from CSHs, and thiolysis reaction revealed that they primarily consisted of (epi)catechins with a few (epi)gallocatechins and (epi)afzelechin units, forming oligomeric proanthocyanidins of which the mean degree of polymerization (mDP) was 2.99. Three monomers, ten dimers, one tetramer, one pentamer, and one hexamer were theoretically identified in CSHs for the first time. The unique structure of CSHs sets them apart from most plants. The extracts displayed high in vitro antioxidant activity with IC50 value of 0.074 in DPPH assay and 0.018 mg/mL in ABTS assay. Additionally, the CSH extracts were incorporated as antioxidants into chitosan (CS)-based biodegradable films. The addition of 0.25% CSH extracts significantly improved film thickness and water vapor resistance, and also reduced the water solubility and visible light transmission. Furthermore, the films enhanced the blueberry quality and extended the shelf-life. This comprehensive study not only addresses waste management issues but also offers avenues for innovative applications in sustainable agriculture and packaging.