Mechanism of improving the digestibility of coconut globulin by atmospheric cold plasma treatment: The perspective of protein structure

Abstract

As a natural emulsifier in coconut milk, coconut globulin (CG) is a potential plant-based protein source to replace animal protein. However, due to its poor solubility and poor digestive properties, CG is not sufficiently utilized. The aim of this study was to improve the digestibility of CG by employing atmospheric cold plasma (ACP) technology. The influence of ACP treatment on the digestive properties of coconut globulin was evaluated by measurements of digestibility, degree of hydrolysis, free amino acids (FAAs), and polypeptide distribution after gastrointestinal digestion. These results implied that application of ACP treatment facilitated the digestion of CG, resulting in the hydrolysis of the compound into numerous smaller peptides (<1000 Da) and FAAs. The quartz crystal microbalance with dissipation technique was utilized to monitor the dynamic digestion process of CG. The results observed that ACP-treated CG had increased affinity for pepsin and trypsin, especially at 60 kV (the adsorbed mass was 7.60 μg/cm2). Various analytical techniques, including circular dichroism spectroscopy, Fourier transform infrared spectroscopy, fluorescence spectroscopy, and particle size distribution, demonstrated that ACP treatment facilitated the structural unfold of CG, resulting in increased exposure of enzyme binding sites and hydrolysis into smaller fragments. In addition, in vitro and cell-based antioxidant experiments provided evidence of the significant antioxidant activity of the hydrolysate derived from ACP-treated CG. Hence, the utilization of ACP treatment at 60 kV emerged as the optimal approach for enhancing the digestibility of CG (from 71.65% to 78.65%). This finding provides a theoretical basis for the use of ACP treatment in protein-rich foods, thereby providing insights for expanding the application of ACP treatment in the field of food processing.