pH and ionic strength responsive core-shell protein microgels fabricated via simple coacervation of soy globulins

Oral Astringency in Plant Proteins: An Underestimated Issue in Formulating Next-Generation Plant-Based Foods

Ensuring the supply of affordable, palatable, healthy, and sustainable nutrients to feed the growing population without transgressing the planetary boundaries remains a key challenge in the food science community. A dietary transition toward low-emission, plant-based foods, with less reliance on animal agriculture, is advocated for sustainability, health, and ethical reasons. A major hurdle for mainstream adoption of plant-based foods is their poor sensorial performance, such as nonjuicy and astringent textures as well as various off-flavors. This review presents the current understanding of astringency and oral friction of plant-based foods. It focuses on plant proteins and their application in plant-based meat and dairy analogs. In addition, the latest advances in the quantitative characterization of astringency using tribology, electrochemistry, and cellular tools are covered. Finally, we examine factors influencing astringency and propose easy-to-implement colloidal strategies that may mitigate astringency issues, thereby underpinning the design of the next generation of sustainable and pleasurable plant-based foods.

Simple and complex coacervation in systems involving plant proteins

Plant-based foods are gaining popularity as alternatives to meat and dairy products due to sustainability and health concerns. As a consequence, there is a renewed interest in the phase behaviour of plant proteins and of mixtures of plant proteins and polysaccharides, in particular in the cases where coacervation is found to occur, i.e., liquid-liquid phase separation (LLPS) into two phases, one of which is rich in biopolymers and one of which is poor in biopolymer. Here we review recent research into both simple and complex coacervation in systems involving plant proteins, and their applications in food- as well as other technologies, such as microencapsulation, microgel production, adhesives, biopolymer films, and more.

Protein-Based Fat Replacers: A Focus on Fabrication Methods and Fat-Mimic Mechanisms

The increasing occurrence of obesity and other non-communicable diseases has shifted the human diet towards reduced calorie intake. This drives the market to develop low-fat/non-fat food products with limited deterioration of textural properties. Thus, developing high-quality fat replacers which can replicate the role of fat in the food matrix is essential. Among all the established types of fat replacers, protein-based ones have shown a higher compatibility with a wide range of foods with limited contribution to the total calories, including protein isolate/concentrate, microparticles, and microgels. The approach to fabricating fat replacers varies with their types, such as thermal-mechanical treatment, anti-solvent precipitation, enzymatic hydrolysis, complexation, and emulsification. Their detailed process is summarized in the present review with a focus on the latest findings. The fat-mimic mechanisms of fat replacers have received little attention compared to the fabricating methods; attempts are also made to explain the underlying principles of fat replacers from the physicochemical prospect. Finally, a future direction on the development of desirable fat replacers in a more sustainable way was also pointed out.

Self-coacervation of carboxymethyl chitosan as a pH-responsive encapsulation and delivery strategy

Carboxymethyl chitosan (CMCS)-based complex coacervate has attracted much attention in drug oral delivery due to its pH-responsive property. As a unique ampholyte polymer, the self-coacervation of CMCS has great research potential. In this work, CMCS self-coacervates were prepared by adjusting the pH of the CMCS aqueous solution close to its isoelectric point. The Fourier-transformed infrared spectroscopy (FTIR) results revealed that electrostatic interactions, hydrogen bonding, and hydrophobic interactions were involved in the self-coacervation of CMCS. The obtained self-coacervates presented a dense surface structure, and were stable at a wide pH range of 3.0-6.0, and gradually dissolved under basic conditions. Although self-coacervation decreased the crystallinity and thermal stability of CMCS, the obtained coacervates showed excellent pH-responsive properties and ionic strength stability. We also investigated its potential in lactoferrin (LF) encapsulation and oral delivery. The CMCS self-coacervates exhibited a high encapsulation efficiency (EE) of 94.79 ± 0.49% and loading capacity (LC) of 26.29 ± 0.52% when the addition amount of LF was 2 mg. The simulated gastric digestion results demonstrated that CMCS self-coacervates could protect more than 80% of LF from hydrolysis and maintain the bioactivities of LF. Accordingly, the self-coacervation of CMCS could be used as a pH-responsive encapsulation and delivery strategy.

Effect of cellobiose on the myofibrillar protein denaturation induced by pH changes during freeze-thaw cycles

The aim of this study was to investigate myofibrillar protein (MFP) denaturation induced by pH changes during freeze-thaw (FT) cycles, and to propose an effective mitigation strategy. Owing to the selective crystallization of Na₂HPO₄·12H₂O and the consequent pH change, a pH change of 3.32 units was observed when the MFP solution were frozen. The surface hydrophobicity, particle size and confocal laser scanning microscopy showed that the protein molecules gradually unfolded and formed larger protein aggregation as the number of FT cycles increases. Additionally, protein degradation, secondary and tertiary structure alterations suggested that the FT cycle could disrupt structural integrity. The addition of cellobiose could maximize the inhibition of pH changes (decrease of ∼0.62 unit), no Na₂HPO₄·12H₂O crystallization was observed by X-ray diffraction. Cellobiose could minimize FT damage to myofibrillar protein, which was closest to the control. Thus, cellobiose can be used as a new and effective cryoprotectant.

Resolving the Mechanisms of Soy Glycinin Self-Coacervation and Hollow-Condensate Formation

Self-coacervation of animal-derived proteins has been extensively investigated while that of plant proteins remains largely unexplored. Here, we study the process of soy glycinin self-coacervation and transformation into hollow condensates. The protein hexameric structure composed of hydrophilic and hydrophobic polypeptides is crucial for coacervation. The process is driven by charge screening of the intrinsically disordered region of acidic polypeptides, allowing for weak hydrophobic interactions between exposed hydrophobic polypeptides. We find that the coacervate surface exhibits order, which stabilizes the coacervate shape during hollow-condensate formation. The latter process occurs via nucleation and growth of protein-poor phase in the coacervate interior, during which another ordered layer at the inner surface is formed. Aging enhances the stability of both coacervates and hollow condensates. Understanding plant protein coacervation holds promises for fabricating novel functional materials.

Emulsion-filled hydrogels for food applications: influence of pH on emulsion stability and a coating on microgel protection

Encapsulation structures for oral administration have been widely employed by the food, personal care, and pharmaceutical industries. Emulsion-filled microgels can be used to encapsulate bioactive compounds, allowing the entrapment of lipid droplets in biopolymer networks and promoting bioactive protection. The influence of pH and biopolymer concentration on the formation and structure of emulsions was evaluated, allowing the production of emulsion-filled hydrogels with potato starch as the main compound, a low alginate concentration, and gelatin in the continuous phase. Potato starch was used because it is generally recognized as safe (GRAS) and has phosphate groups, which allow electrostatic interactions with biopolymers and provide resistance to the network. Emulsion stability was achieved at pH 6, while complexation was verified under acidic conditions, which made the ionic gelation process unfeasible for the production of microgels. After defining the pH for emulsion production, microgels were formed by ionic gelation and coated microgels by electrostatic interactions, as evidenced by quartz crystal microbalance. The alginate and gelatin coating did not affect the morphology of the microparticles. An in vitro digestion assay showed that microgels composed mainly of potato starch were not degraded in the simulated mouth step. The coating layer provided extra microgel protection during digestion, demonstrating the ability of encapsulation systems to promote targeted delivery of bioactive compounds.