Effect of pulsed ultrasound, a green food processing technique, on the secondary structure and in-vitro digestibility of almond milk protein

Abstract In recent years, almond has been considered as one of the most common alternative plant-based protein sources due to its nutritional attributes and health benefits. However, almond protein has a lower digestibility compared with the animal protein. The objective of this study is to investigate the impact of pulsed high-intensity ultrasound on the secondary structure of the almond protein. The changes in the in-vitro protein digestibility (IVPD %) are also evaluated to investigate the relationship between the structure and digestibility of the almond protein. The secondary structures were analyzed using Fourier-transform infrared spectroscopy (FT-IR) and circular dichroism (CD) spectroscopy. FT-IR analysis showed a slight relocation in the ordered and unordered structures in the ultrasonicated almond protein compared to the control. CD spectroscopy revealed that ultrasound resulted in the restructuring of α-helices into β-sheets. However, upon treating the almond protein for 16 minutes, a slight recovery in α-helices was observed. Moisture content was found to affect the secondary structure orientations of almond protein significantly. Although the IVPD% change was not statistically significant, it was found to be increasing slightly with processing duration and was dependent on protein secondary structure.