Upgrading the functional properties of apricot kernel proteins through fibrillization

Apricot kernel meal is an understudied and underutilized by-product of the apricot industry. In this study, apricot kernel protein (AKP) was obtained from apricot kernel meal by a simple one-step salting-in method, exhibiting high yield (38.4 g AKP/100 g defatted meal), high protein content (91.4%), and high solubility (92.5% at neutral pHs). The possibility and kinetics of AKP fibrillization were further investigated. It was found that apricot kernel protein amyloid fibrils (AKPFs) with twisted nanofibrillar structures were readily formed by heating at pH 2.0 and 90 °C. SDS-PAGE analysis indicated that these AKPFs contained peptide fragments with the molecular weight of around 6.5 kDa. Atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), circular dichroism spectroscopy (CD) and intrinsic fluorescence spectroscopy revealed that the structure, morphology and properties of AKPFs were analogous to other food protein-derived amyloid fibrils. Importantly, AKPF has upgraded foaming characteristics, e.g., AKPF-18h (AKPF formed at 18 h) has 31.7% higher foaming capacity and 30.2% higher foam stability relative to AKP. This is attributed to the formation of a homogeneous interfacial film at the air/water interface of the foam. The DPPH radical scavenging activity of AKPF-18h was also improved, reaching 53.0%, about twice that of AKP (28.4%). In addition, the developed AKP and AKPFs were not cytotoxic in vitro. All these findings suggest that AKPFs have great potential for future food applications.