Barrièrelagen op basis van aardappelschillen voor verpakkingsmaterialen geschikt voor proteïnerijke levensmiddelen

In response to growing environmental challenges the use and development of more sustainable packaging solutions is becoming increasingly important. A key strategy in this transition is the shift from petrochemical-based to bio-based resources, with a particular emphasis on the valorization of side streams. Especially in multilayer packaging applications, viable bio-based alternatives to conventional oxygen barrier materials, such as ethylene vinyl alcohol (EVOH) and polyamide (PA), have yet to be developed. The focus of this PhD thesis was to investigate the potential of the agro-industrial side stream potato peel (PPeel) as an oxygen barrier for food packaging, particularly targeting applications for protein-rich foods. Therefore, freshly obtained PPeel was processed into a powder and different processing methods were investigated to select the most promising approach for film and coating development, prior to the fabrication of multilayer structures suitable for food packaging applications. Two distinct methods for converting the PPeel powder into polymer films were explored: a thermal approach and a solvent-based approach. Thermal processing of PPeel was explored through integration of PPeel powder as a filler into a poly(lactic acid) (PLA) matrix. The study examined how, and to what extent, the particle size of the PPeel powder influenced the physical properties of the resulting PPeel-PLA composites. In particular, different fractions of PPeel powder (0-53 μm, 125-250 μm, and 315-500 μm) were incorporated into a PLA matrix via compounding and injection-molding and the influence of particle size on the structure, thermal, mechanical and barrier properties of the injection molded composites was investigated. The study showed that the shape of the PPeel particles remained independent of the particle size and that PPeel powder can be incorporated as a filler into PLA composited that may provide sufficient protection of packed goods. Cold crystallization temperature and water vapor transmission rate of the composites were independent of particle size but increased upon the incorporation of PPeel particles. For the solvent-based processing of PPeel powder, the primary objective was to develop a standardized formulation for casting PPeel-based films, using 30% (w/w PPeel) glycerol as a plasticizer. The influence of varying PPeel concentrations (2-7% w/w) on the film-forming behavior, as well as on the structural and physicochemical properties of the resulting cast films, was subsequently examined. Microscopic and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) measurements revealed remarkable structural differences between 2-3% (w/w) and 4-7% (w/w) PPeel-based films, resulting in significant (p ≤ 0.05) differences in oxygen permeability (3.0 - 9.1 cm3 m-2 d-1 bar-1), water vapor transmission rate (66.8 - 111.9 g m-2 d-1) and tensile properties. Tensile strength of films containing 2-7% (w/w) PPeel varied between 2.1 MPa and 6.0 MPa and elongation at break between 13.7% and 28.1%, respectively. Accordingly, distinct mechanisms for PPeel-based film formation were proposed for formulations containing either 2-3% (w/w) or 4-7% (w/w) PPeel, indicating a dependence of film-forming behavior on PPeel concentration. Given the superior processability and oxygen barrier performance of films produced via solvent-based processing, and in alignment with the overall objective of developing multilayer structures incorporating a PPeel-based oxygen barrier, formulations containing 7% (w/w PPeel powder) were selected for further application in this PhD project. As the physicochemical properties of the developed PPeel-based films were still inferior to those of petrochemical polymers, such as EVOH, a variety of physical, chemical, and biochemical modification methods for potato constituents were extensively reviewed and the modification of PPeel-based films using citric acid (CA) was chosen to be further explored. The CA-modified formulation was then applied as a coating on various substrates (polyethylene (PE), polypropylene (PP), PLA) to create bi-layer structures. The influence of CA concentration, formulation pH, and drying/curing temperature on the structural and physicochemical properties of the PPeel-based coatings were systematically studied. First, the impact of CA concentration (10-50% w/w PPeel) on the esterification/cross-linking of PPeel-based films and coatings was investigated, taking the influence of pH into account. Therefore, the structure and physicochemical properties of the cast films and coatings were evaluated using ATR-FTIR spectroscopy, moisture sorption isotherms, tensile properties, light transmittance, oxygen permeability, carbon dioxide transmission rate and water vapor transmission rate measurements. This study demonstrated the concentration-dependent function of CA as both a cross-linking agent and a plasticizer. In particular, the results indicated that increasing the CA concentration from 10% to 30% (w/w PPeel) enhanced esterification/crosslinking resulting in minimal values for the oxygen permeability (0.08 cm3 m–2 d–1 bar–1 at 50% RH) and the water vapor transmission rate (1.6 g m–2 d–1 at 50% &rarr; 0% RH). However, increasing CA concentration from 30% to 50% (w/w PPeel) led to a higher proportion of free CA, resulting in an enhanced flexibility of PPeel-based cast films. This suggests that at higher concentrations, excess CA primarily functions as a plasticizer. As CA-promoted esterification/cross-linking is also known to be temperature dependent, the influence of drying and curing temperature (ranging from 50 to 150 °C) on the physicochemical properties of PPeel-based films and coatings containing 30% (w/w PPeel) CA was investigated. As no significant differences in physicochemical properties were observed across the examined temperature range, it was concluded that these properties are largely temperature-independent, indicating a broad processing window for potential industrial upscaling. To assess the suitability for food packaging applications, the PP-PPeel and PLA-PPeel bi-layers were laminated to multilayers using an epoxy-based laminating adhesive. Vacuum bags were then produced from the developed multilayers and compared to a commercial PP/EVOH/PP multilayer packaging and assessed for their potential to be used for the storage of fresh pork meat under vacuum conditions for 28 days. The PP-based multilayers containing either PPeel or EVOH as the oxygen barrier showed comparable oxygen and water vapor transmission rates (< 1.5 cm3 m-2 d-1 and < 1 g m-2 d-1, respectively). As a result, both multilayers effectively preserved the color and microbial quality of vacuum-packed raw pork meat in a similar manner. Overall, this PhD thesis demonstrated the great potential of PPeel, an unpurified agro-industrial side stream, as a sustainable alternative to EVOH in multilayer food packaging applications.