Synergistically stabilized wet foams from heat treated β-lactoglobulin and cellulose nanofibrils and their application for green foam production

•Heat-treated β-lactoglobulin is a natural foaming agent with pH-dependent properties, mainly governed by peptides.•Integrating cellulose nanofibrils (CNFs) and a controlled pH reduction enhances the long-term stability of the foams.•The wet foam's stability is attributed to CNFs and amyloid nanofibrils forming a robust gel network around air bubbles.•Stability of wet foams enables solid foam production via oven drying, without the need for solvent exchange or freeze drying.•The dry foams exhibit a low density of 10 kg.m-3 and a specific compression modulus surpassing conventional cellulose foams. Achieving a sustainable foam production requires a complete substitution of synthetic components with natural and renewable alternatives, as well as development of an environment–friendly production process. This work demonstrates a synergetic combination of heat-treated β-lactoglobulin proteins and cellulose nanofibrils (CNFs) to create fully bio-based and highly-stable wet foams. Furthermore, a gradual reduction in the pH, enabled oven-drying of the wet foams without any major structural collapse of the foam, resulting in the preparation of lightweight solid foams with the density of 10.2 kg.m−3. First, the foaming behavior of heat-treated β-lactoglobulin systems (HBSs) containing amyloid nanofibrils (ANFs) and non-converted peptides was investigated at different pHs. Subsequently, the HBS foams were stabilized using CNFs, followed by a gradual acidification of the system to a final pH of 4.5. To gain a deeper understanding of the stabilization mechanism of the foam, the interactions between the foam's components, their positioning in the foam structure, and the viscoelasticity of the fibrillar network were investigated using quartz crystal microgravimetry, confocal microscopy and rheology. The analysis of the obtained data suggests that the stability of the foams was associated with the accumulation of CNFs and ANFs at the air–water interface, and that the concomitant formation of an intertwined network surrounding the air bubbles. This together resulted in a significant decrease in drainage rate of the liquid in the foam lamellae, bubble coarsening and bubble coalescence within the foams. The results also show that the major surface–active component participating in the creation of the foam is the free peptide left in solution after the formation of the ANFs. A slow reduction in pH to 4.5 lead to further gelation of the fibrillar network and an improved stora