Associative properties of rapeseed napin and pectin: Competition between liquid-liquid and liquid-solid phase separation

Ultrafiltration of Rapeseed Protein Concentrate: Effect of Pectinase Treatment on Membrane Fouling

Membrane filtration technologies have shown great potential as a gentle and effective method for concentrating and fractionating proteins for food applications. However, the application of this technology to plant-derived protein streams is in its infancy. In this study, an aqueous rapeseed protein concentrate was obtained with wet milling, and its performance during ultrafiltration with two distinct molecular weight cut-offs (10 and 100 kDa) was tested. All rapeseed proteins were retained during filtration. The addition of pectinase during extraction prior to filtration caused important structural modifications to the extract, resulting in increased permeate fluxes, increased carbohydrate permeation and a reduction in irreversible fouling. Lager pore sizes led to more pronounced fouling. FTIR analysis of the spent membranes showed that proteins and lipids are causing irreversible fouling.

Recovery of soy whey protein from soy whey wastewater at various cavitation jet pretreatment time and their structural and emulsifying properties

Protein-polysaccharide composite is of great significance for the development of soluble protein recovery process. This study investigated the effects of cavitation jet (CJ) pretreatment at different time (0, 60, 120, 180, 240, 300 s) intervals on the recovery of soy whey protein (SWP) from soy whey wastewater using chitosan (CH). In addition, the structure and properties of the SWP/CH complexes were examined. The results showed that the recovery yield of SWP reached 84.44 % when the CJ pretreatment time was 180 s, and the EAI and ESI values of the SWP/CH complex increased from 32.39 m2/g and 21 min to 48.47 m2/g and 32 min, respectively. In the CJ pretreatment process, SWP promotes the recombination with chitosan through electrostatic interaction and hydrogen bond, while hydrophobic interaction is also involved. This study has guiding significance for CJ technology in the recovery and utilization of protein in industrial wastewater.

Encapsulation of Vitamin B12 by Complex Coacervation of Whey Protein Concentrate-Pectin; Optimization and Characterization

Vitamin B12 (VB12) is one of the essential vitamins for the body, which is sensitive to light, heat, oxidizing agents, and acidic and alkaline substances. Therefore, the encapsulation of VB12 can be one of the ways to protect it against processing and environmental conditions in food. In this work, the influence of pectin concentration (0.5−1% w/v), whey protein concentrate (WPC) level (4−8% w/v) and pH (3−9) on some properties of VB12-loaded pectin−WPC complex carriers was investigated by response surface methodology (RSM). The findings showed that under optimum conditions (1:6.47, pectin:WPC and pH = 6.6), the encapsulation efficiency (EE), stability, viscosity, particle size and solubility of complex carriers were 80.71%, 85.38%, 39.58 mPa·s, 7.07 µm and 65.86%, respectively. Additionally, the formation of complex coacervate was confirmed by Fourier-transform infrared (FTIR) spectroscopy and atomic force microscopy (AFM). In addition, it was revealed that the most important factor in VB12 encapsulation was pH; at a pH < isoelectric point of WPC (pH = 3), in comparison with higher pH values (6 and 9), a stronger complex was formed between pectin and WPC, which led to an increase in EE, lightness parameter, particle size and water activity, as well as a decrease in the zeta-potential and porosity of complex carriers.

In Silico, Molecular Docking and In Vitro Antimicrobial Activity of the Major Rapeseed Seed Storage Proteins

BACKGROUND

In addition to their use as an edible oil and condiment crop, mustard and rapeseed (Brassica napus L., B. juncea (L.) Czern., B. nigra (L.) W.D.J.Koch, B. rapa L. and Sinapis alba L.) have been commonly used in traditional medicine for relieving pain, coughs and treating infections. The seeds contain high amounts of oil, while the remaining by-product meal after oil extraction, about 40% of seed dry weight, has a low value despite its high protein-content (~85%). The seed storage proteins (SSP) 2S albumin-type napin and 12S globulin-type cruciferin are the two predominant proteins in the seeds and show potential for value adding to the waste stream; however, information on their biological activities is scarce. In this study, purified napin and cruciferin were tested using in silico, molecular docking, and in vitro approaches for their bioactivity as antimicrobial peptides.

MATERIALS AND METHODS

The 3D-structure of 2S albumin and 12S globulin storage proteins from B. napus were investigated to predict antimicrobial activity employing an antimicrobial peptide database survey. To gain deeper insights into the potential antimicrobial activity of these SSP, in silico molecular docking was performed. The purified B. napus cruciferin and napin were then tested against both Gram-positive and Gram-negative bacteria for in vitro antimicrobial activity by disc diffusion and microdilution antimicrobial susceptibility testing.

RESULTS

In silico analysis demonstrated both SSP share similar 3D-structure with other well studied antimicrobial proteins. Molecular docking revealed that the proteins exhibited high binding energy to bacterial enzymes. Cruciferin and napin proteins appeared as a double triplet and a single doublet, respectively, following SDS-PAGE. SDS-PAGE and Western blotting also confirmed the purity of the protein samples used for assessment of antimicrobial activity. Antimicrobial susceptibility testing provided strong evidence for antimicrobial activity for the purified napin protein; however, cruciferin showed no antimicrobial activity, even at the highest dose applied.

DISCUSSION

In silico and molecular docking results presented evidence for the potential antimicrobial activity of rapeseed cruciferin and napin SSP. However, only the in vitro antimicrobial activity of napin was confirmed. These findings warrant further investigation of this SSP protein as a potential new agent against infectious disease.

Use of molecular interactions and mesoscopic scale transitions to modulate protein-polysaccharide structures

Mixed protein-polysaccharide structures have found widespread applications in various fields, such as in foods, pharmaceuticals or personal care products. A better understanding and a more precise control over the molecular interactions between the two types of macromolecules leading to an engineering of nanoscale and colloidal building blocks have fueled the design of novel structures with improved functional properties. However, these building blocks often do not constitute the final matrix. Rather, further process operations are used to transform the initially formed structural entities into bulk matrices. Systematic knowledge on the relation between molecular structure design and subsequent mesoscopic scale transitions induced by processing is scarce. This article aims at establishing a connection between these two approaches. Therefore, it reviews not only studies on the underlying molecular interaction phenomena leading to either a segregative or associative phase behavior and nanoscale or colloidal structures, but also looks at the less systematically studied approach of using macroscopic processing operations such as shearing, heating, crosslinking, and concentrating/drying to transform the initially generated structures into bulk matrices. Thereby, a more comprehensive look is taken at the relationship between different influencing factors, namely solvent conditions (i.e. pH, ionic strength), biopolymer characteristics (i.e. type, charge density, mixing ratio, biopolymer concentration), and processing parameters (i.e. temperature, mechanical stresses, pressure) to generate bulk protein-polysaccharide matrices with different morphological features. The need for a combinatorial approach is then demonstrated by reviewing in detail current mixed protein-polysaccharide applications that increasingly make use of this. In the process, open scientific questions that will need to be addressed in the future are highlighted.

Contrasting Assemblies of Oppositely Charged Proteins

Oppositely charged proteins can form soluble assemblies that under specific physical chemical conditions lead to liquid-liquid phase separation, also called heteroprotein coacervation. Increasing evidence suggests that surface charge anisotropy plays a key role in heteroprotein complexation, and coacervation. Here, we investigated complexation of an acidic protein, β-lactoglobulin (BLG), with two basic proteins, rapeseed napin (NAP) and lysozyme (LYS), of similar net charge and size but differing in surface charge distribution. Using turbidity measurements and isothermal titration calorimetry, we confirmed that LYS binds BLG as expected from previous studies. This interaction leads to two types of phase separation phenomena, depending on pH: liquid-solid phase separation in the case of strong electrostatic attraction and liquid-liquid phase separation for weaker attraction. More interestingly, we showed using dynamic light scattering that NAP interacts with BLG, resulting in formation of assemblies in the nanometer size range. The formation of assemblies was also evident when modeling the interactions using Brownian dynamics for both BLG + NAP and BLG + LYS. Similarly, to DLS, BLG and NAP formed smaller assemblies than BLG with LYS. The molecular details rather than the net charge of BLG and NAP may therefore play a role in their assembly. Furthermore, simulated BLG + NAP assemblies were larger than those experimentally detected by DLS. We discuss the discrepancy between experiments and simulations in relation to the limitations of modelling precisely the molecular characteristics of proteins.