Optimised Extraction of Bioactives from Strawberry Lignocellulosic Byproducts for Edible Active Coatings in Fresh Fruits Preservation

This study proposes a sustainable strategy to valorise strawberry lignocellulosic agro-industrial byproducts through the recovery of antioxidant and antimicrobial compounds (AOM) for use in active edible coatings. Subcritical water extraction (SWE), optimised using response surface methodology, was applied to maximise phenolic content and antioxidant capacity while minimising sugars’ co-extraction. Optimal SWE conditions (120 °C, 5 min, and S/L ratio 40) yielded a total phenolic content (TPC) of 146.9 mg GAE/g DM and an antioxidant activity of 24.8 mg TE/g DM, comparable to ethanolic reflux extraction (138.4 mg GAE/g DM and 23.4 mg TE/g DM). Scale-up in a Parr pressurised reactor achieved 91.2% polyphenol recovery relative to accelerated solvent extraction (ASE). Purification using Amberlite® XAD 7 resin enhanced TPC purity and antioxidant activity more than 2.5-fold, producing a desorbed fraction with a polyphenol purity of 93.9% (w/w, dry basis) and no detectable sugars. The purified AOM was incorporated (1% w/v) into a 1.5% (w) chitosan solution obtained from Hermetia illucens pupal exuviae to produce a biopolymeric active coating. Application to strawberries was associated with a reduction in fungal infection severity (−72%) and incidence (−66.7%) under natural infection conditions. Although fruit firmness declined during storage, coated samples showed significantly better firmness retention. These results demonstrate the effectiveness of combining chitosan with phenolic extracts obtained by SWE to enhance microbial stability and maintain fruit quality.