Nowadays, sustainable development goals indicated by FAO are crucial for ensuring a resilient future to our planet. Reuse and recycling of waste products through upcycling approaches are increasingly exploited. Upcycling transforms discarded materials into higher-value new products, reducing the consumption of natural resources, and increasing environmental sustainability. Up to 11 million tons of dairy waste are discarded annually, posing a serious environmental threat due to its high organic matter content. In particular, fresh dairy products have a short shelf life, typically lasting only 1 to 2 weeks, making their management challenging. A novel upcycling approach could valorize expired fresh dairy products, recovered from retailers, by producing a biopolymer with potential packaging applications. Owing to the abundance of polar functional groups of milk protein, casein films have demonstrated their effectiveness as oxygen barrier to protect food products against oxidation [1]. This research focuses on the recovery of casein from dairy waste and its further processing through green approaches, to produce a biofilm with suitable thermal and mechanical properties [2]. To obtain the raw material, casein was separated through acid precipitation, neutralized, and powdered by freeze-drying. Powders with different contents of fat (30%, 20%, 1%) were produced. The film forming solutions were prepared by dispersing the powders in water with a plasticizer. Each solution, produced in duplicate, underwent degassing by two different treatments. Finally, films were prepared through solution-casting, left to dry under controlled conditions, and peeled out from the mold. A film produced using commercial caseinate was used as reference. Thereby films were analyzed to investigate the influence of composition and processing on relevant properties. Among other techniques, thermal characterization was carried out by performing differential scanning calorimetry and dynamic-mechanical analysis.

DSC analysis revealed how the partial crystallinity of the obtained polymer films are strongly correlated with the thermal history of the specimens and how the various fabrication methods have an impact on their thermal and structural properties. DMA analysis was performed in tension mode in the temperature range from - 150°C to 250°C in order to obtain a full spectrum of the viscoelastic properties of the solution-casted films. All the analyzed samples showed a low temperature transition (below -20°C) and a high- temperature transition ascribable to the glass transition temperature (Tg) of the film. In view of the potential application as packaging material, the storage modulus at room temperature of the various specimens has been taken as a descriptor of the film’s quality. Interestingly, the elastic properties of the casein-based films were perfectly in line with the Young modules of oil-based plastic films such as low density polyethylene (i.e., 10 8 Pa).

References

1. S. Gerna, P. D’Incecco, S. Limbo, M. Sindaco, L. Pellegrino. Foods 2023, 12, 1271.
2. B.M. Plumier, S. Akkurt, L.M. Bonnaillie, W. Yee, R.D. Ashby, M. McAnulty, R.A. Garcia, J.A. Reyne Jr, P.M. Tomasula Int. Dairy J. 2024, 151,