Determination of the critical pH for unfolding water-soluble cod protein and its effect on encapsulation capacities

Hydrophobic polyphenols, with a variety of physiological activities, are often practically limited due to their low water solubility and chemical instability, among which curcumin (Cur) is a representative hydrophobic polyphenol. To improve Cur, the cod protein (CP)-Cur composite particles (CP-Cur) were successfully prepared using the pH-shift method, but this pH-shift method (7-12-7) required a higher pH, which limited application and increased cost. The critical pH of CP structure unfolding during pH-shift and its encapsulation effect on Cur were investigated in this paper. During the pH-shift process, the critical pH of the structural unfolding of CP was pH 10, and the degree of protein structure unfolding was higher, which was attributed to the increasing electrostatic repulsion, and the weakened hydrogen bond and hydrophobic interaction. The encapsulation efficiency of CP-Cur formed after pH 10-shift was higher than that formed after pH 9.8-shift, which increased by 22.17 %. At pH 9.8, the binding sites in CP reached saturation at the molar ratio of 10, while at pH 10 and 10.2, the binding sites in CP both reached saturation at the molar ratio of 14, also indicating that the protein treated with critical pH could bind more Cur. The binding between Cur and CP was mostly hydrophobic interaction, accompanied by hydrogen bonding and electrostatic interactions. The above results verified the necessity of critical pH in the experiment, indicating that critical pH could indeed improve the encapsulation effect and obtain a higher encapsulation efficiency. This work will help improve the large-scale application of hydrophobic functional substances in production.

Reducing disulfide bonds as a robust strategy to facilitate the self-assembly of cod protein fabricating potential active ingredients-nanocarrier

In this study, a novel method was developed to encapsulate hydrophobic compounds by self-assembly of cod protein (CP) triggered by breaking disulfide bonds. Curcumin (Cur), a representative lipid-soluble polyphenol, was selected as a model to evaluate the potential of CP nanoparticles as novel and accessible nanocarriers. Results showed that the protein structure gradually unfolded with increasing dithiothreitol (DTT) concentration, indicating that S-S cleavage was conducive to forming a looser structure. The resultant unfolded CP exposed more hydrophobic sites, facilitating its interaction with hydrophobic compounds. The encapsulation efficiency (EE) of formed CP-Cur nanoparticles was relatively high, reaching 99.09%, 98.8%, and 89.77% when the mass ratios of CP to Cur were 20:1, 10:1, and 5:1 (w/v), respectively. The hydrophobic interaction, weak van der Waals, and hydrogen bond were the forces contributing to the formation of CP-Cur nanoparticles, whereas the hydrophobic interaction played a crucial role. The CP-Cur complex exhibited increased stability and a homogeneous-stable structural phase. Thus, this research not only proposed a novel and simple encapsulation method of hydrophobic bioactive compounds but also provided a theoretical reference for the application of reductants in food or pharmacy system.

Supplementation with cod protein hydrolysate in older adults: a dose range cross-over study

A large proportion of older adults are affected by impaired glucose metabolism. Previous studies with fish protein have reported improved glucose regulation in healthy adults, but the evidence in older adults is limited. Therefore, we wanted to assess the effect of increasing doses of a cod protein hydrolysate (CPH) on postprandial glucose metabolism in older adults. The study was a double-blind cross-over trial. Participants received four different doses (10, 20, 30 or 40 mg/kg body weight (BW)) of CPH daily for 1 week with 1-week washout periods in between. The primary outcome was postprandial response in glucose metabolism, measured by samples of serum glucose and insulin in 20 min intervals for 120 min. The secondary outcome was postprandial response in plasma glucagon-like peptide 1 (GLP-1). Thirty-one subjects aged 60–78 years were included in the study. In a mixed-model statistical analysis, no differences in estimated maximum value of glucose, insulin or GLP-1 were observed when comparing the lowest dose of CPH (10 mg/kg BW) with the higher doses (20, 30 or 40 mg/kg BW). The estimated maximum value of glucose was on average 0·28 mmol/l lower when the participants were given 40 mg/kg BW CPH compared with 10 mg/kg BW (P = 0·13). The estimated maximum value of insulin was on average 5·14 mIU/l lower with 40 mg/kg BW of CPH compared with 10 mg/kg BW (P = 0·20). Our findings suggest that serum glucose and insulin levels tend to decrease with increasing amounts of CPH. Due to preliminary findings, the results require further investigation.