Evaluation of the properties of whey protein films with modifications.

Whey protein concentrate (WPC) has been widely studied as a biodegradable bio-based packaging material in the food industry. In this study, different whey protein films were obtained through physical, chemical, enzymatic, and composite modifications. The molecular structure, micro-morphology, mechanical properties, barrier properties, and other characteristics of the films were evaluated. The results illustrated that the thickness of WPC with composite modification increased and the transmittance decreased, but the mechanical properties and barrier properties were more prominent. The WPC film prepared by physical modification combined with transglutaminase has the best film-forming effect, the tensile strength (TS) was 5.45 MPa, the elongation at break (EAB) was 25.19%, the WVP was 5.53 g·mm/m2 ·hr·kPa, and the Oxygen permeability (OP) was 1.83 meq/K, and its microstructure was and uniform. In addition, based on the the results of SDS-PAGE and Fourier transform infrared spectroscopy (FTIR), the intermolecular and intramolecular interactions of various modification methods on WPC were studied, thus contributing to analyze the properties of the film. This study provides theoretical basis and technical support for the industrial production of protein-based films.

Plastein reaction enhanced bile-acid binding capacity of soybean protein hydrolysates and whey protein hydrolysates.

Plastein reaction is a modification reaction that can improve the functional properties of protein hydrolysate. The product of the reaction is a thixotropic aggregation of peptides. This study investigated the formation condition of soybean-whey plastein and bile acid binding capacity of plastein. Soy protein and whey protein were hydrolyzed by pepsin. The mixture (1:1, w/w) of two hydrolysates was modified by pepsin again. After the reaction, the decrease in free amino groups and the turbidity of the modified hydrolysate were measured to obtain appropriate reaction condition. Results showed that the concentration of hydrolysates 40% (w/v), enzyme ratio of 2.0 KU/g protein, pH 5.0, 37 °C, reaction time of 3.0 h respectively, were showed maximum changes in protein hydrolysates. Tricine SDS-PAGE analysis under denaturing conditions revealed that whey protein was more sensitive to pepsin and yielded different polypeptides (PPs) of molecular weight ranged from 3.5-17 kDa. However, a high molecular weight PP was completely hydrolyzed while PPs of 14.2-26 kDa were partially digested after pepsin treatment. Native page analysis further revealed the presence of a high-molecular weight PP in crude and purified plastein product. The bile acid binding capacity was improved by the plastein reaction. The amount of binding sodium deoxycholate, sodium taurocholate, and sodium cholate were 0.75, 2.0 and 1.87 µmol/100 mg respectively.

Screening for cholesterol-lowering probiotic based on deoxycholic acid removal pathway and studying its functional mechanisms in vitro.

Elevated serum cholesterol in humans is generally a risk factor correlated with the development of coronary heart disease (CHD). Reducing deoxycholic acid (DCA) content in the intestine can reduce serum cholesterol levels, which reduce the incidence of CHD. A total of 150 strains of lactic acid bacteria and bifidobacteria were isolated from human fecal samples. The DCA removal ability of these strains was evaluated. Results showed that 9 strains displayed above 10% DCA removal rate. The probiotic potentials of the 9 strains were evaluated. The strain Lactobacillus casei F0822 was screened out due to the stronger adhesion to HT-29 cells and tolerance to bile and acid. DCA removal for this strain resulted from that the S-layer protein locating the cell surface bound DCA. The FTIR spectra showed that the carboxyl group in DCA was the principal group by which DCA was bound to the S-layer protein of L. casei F0822. These findings suggested that L. casei F0822 is a better candidate probiotic strain, which has the potential to reduce human serum cholesterol levels.

Inhibition of Shigella sonnei adherence to HT-29 cells by lactobacilli from Chinese fermented food and preliminary characterization of S-layer protein involvement.

In this study, seven lactobacilli with a high degree of antagonistic activity against three pathogens and good adherence to HT-29 cells were selected. The ability of these seven lactobacilli to inhibit adhesion of Shigella sonnei to intestinal mucosa was studied on cultured HT-29 cells. Lactobacilli were added simultaneously with, before or after S. sonnei to test for their effectiveness in exclusion, competition and displacement assays, respectively. Lactobacillus paracasei subp. paracasei M5-L, Lactobacillus rhamnosus J10-L and Lactobacillus casei Q8-L all exhibited significant inhibitory activity. In order to elucidate the inhibitory functions of S-layer proteins, the S-layer proteins were removed with 5 M LiCl from the M5-L, J10-L and Q8-L strains. Under such conditions, inhibition activity was decreased in all three strains, as revealed in exclusion, competition and displacement assays. SDS-PAGE analysis confirmed the presence of S-layer proteins with dominant bands of approximately 45 kDa. Further analysis of S-layer proteins revealed that the hydrophobic amino acids accounted for 40.5%, 41.5% and 43.8% of the total amino acid for the M5-L, J10-L and Q8-L strains, respectively. These findings suggest that the M5-L, J10-L and Q8-L strains possess the ability to inhibit S. sonnei adherence to HT-29 cells, and S-layer proteins are involved in this adhesion inhibition.