Valorization of hops by-product for development of active poly(butylene succinate) film

Abstract

Hop by-product powder (HBP), obtained from milling branches, leaves, and discarded cones, was valorized as a functional additive in polybutylene succinate (PBS) films to develop biodegradable antioxidant packaging. The HBP was first characterized for water absorption/desorption capacity and particle size distribution, then separated into three fractions based on fiber size (HBP-S: 63–160 μm; HBP-M: 160–220 μm; HBP-L: 220–710 μm). Total HBP (HBP-T) and each fraction were analysed for chemical composition and antioxidant properties. Four PBS composite films containing 10 wt.% of HBP-T, -S, -M, and -L were produced via melt blending, pelletizing, and compression molding. Their optical, thermal, mechanical, barrier, and water sorption properties were evaluated, together with antioxidant activity assessed by ethanolic extraction and in contact with food simulants. Smaller HBP particles exhibited higher cellulose content (≈79%), greater polyphenol concentration (≈10 mg GAE/g_dw), and stronger antioxidant activity (≈14 mg TEAC/g_dw). Incorporating HBP enhanced the films' elastic modulus and water absorption, shifting color toward red-yellow hues, particularly with smaller fibers. Fiber size had minimal impact on mechanical and thermal properties or antioxidant retention, suggesting that fractionation may be unnecessary. HBP maintained its antioxidant properties in PBS and demonstrated different release profiles in food simulants. The antioxidant activity of films increased over time, reaching values of 1.7 mg TEAC/g_film (DPPH, 7 days) and 23 mg TEAC/g_film (ABTS, 10 days). Simulants C and D1 had a higher capacity to solubilize antioxidant compounds from the film. These findings confirm HBP’s potential to enhance PBS films functionality, making them promising for biodegradable antioxidant food packaging.