Spectroscopic studies on the stability and nucleation-independent fibrillation of partially-unfolded proteins in crowded environment

•Stability and fibrillation of partially-unfolded proteins in PEG is studied.•PEG stabilizes lysozyme, decreases rate of fibrillation at higher concentrations.•Stability of α-lactalbumin varies with size and concentration of PEG.•Change in initial partially-unfolded conformation affects fibrillation propensity.•Rate of fibrillation is altered by crowding effect and soft-interactions.