Cysteine inducing formation and reshuffling of disulfide bonds in cold-extruded whey protein molecules: From structural and functional characteristics to cytotoxicity

Pecan (Carya illinoinensis (Wangenh.) K. Koch) nuts as an emerging source of protein: extraction, physicochemical and functional properties

BACKGROUND

The increasing demand for sustainable alternatives to traditional protein sources, driven by population growth, underscores the importance of protein in a healthy diet. Pecan (Carya illinoinensis (Wangenh.) K. Koch) nuts are currently underutilized as plant-based proteins but hold great potential in the food industry. However, there is insufficient information available on pecan protein, particularly its protein fractions. This study aimed to explore the physicochemical and functional properties of protein isolate and the main protein fraction glutelin extracted from pecan nuts.

RESULTS

The results revealed that glutelin (820.67 ± 69.42 g kg-1) had a higher crude protein content compared to the protein isolate (618.43 ± 27.35 g kg-1), while both proteins exhibited amino acid profiles sufficient for adult requirements. The isoelectric points of protein isolate and glutelin were determined to be pH 4.0 and pH 5.0, respectively. The denaturation temperature of the protein isolate (90.23 °C) was higher than that of glutelin (87.43 °C), indicating a more organized and stable conformation. This is further supported by the fact that the protein isolate had a more stable main secondary structure than glutelin. Both proteins demonstrated improved solubility, emulsifying, and foaming properties at pH levels deviating from their isoelectric points in U-shaped curves. Compared to the protein isolate, glutelin displayed superior water and oil absorption capacity along with enhanced gelling ability.

CONCLUSION

The protein isolate and glutelin from pecan nuts exhibited improved stability and competitive functional properties, respectively. The appropriate utilization of these two proteins will support their potential as natural ingredients in various food systems. © 2024 Society of Chemical Industry.

Mechanism of l-cysteine-induced fibrous structural changes of soybean protein at different high-moisture extrusion zones

In this study, the fibrous structure formation mechanism of soybean protein during high moisture extrusion processing was investigated using a dead-stop operation, and based on the interaction between soybean protein concentrate (SPC) and L-cysteine (CYS). The thermal properties, SDS-PAGE and particle size distribution of the samples from different extrusion zones were investigated. It was revealed that the addition of a moderate amount of CYS (0.1 %) promoted the fibrous structure formation in the SPC extrudates and optimised the textural properties of the SPC extrudates. In the extruder barrel, addition of CYS (0.1 %) promoted protein depolymerisation and unfolding in the mixing and cooking zones, and facilitated protein aggregation in the die and cooling zones. Protein solubility and raman spectroscopy revealed that disulfide bonds were principally responsible for fibrous structure formation; favoured when the intermolecular disulfide bonds (t-g-t mode) was increased. Finally, the transformation of protein conformation was revealed by secondary structure and surface hydrophobicity, which confirmed that the effect of CYS on protein conformation mainly occurred in the cooling zone. This study provides a theoretical basis for the application of CYS to regulate the fibrous structure of meat analogues.

Effects of unfolding treatment assisted glycation on the IgE/IgG binding capacity and antioxidant activity of ovomucoid

Ovomucoid is the immune-dominant allergen in the egg white of hens. Due to its structure based on nine disulfide bonds as well as its resistance to heat and enzymatic hydrolysis, the allergenicity of this food protein is difficult to decrease by technological processes. We sought to reduce its allergenicity through the Maillard reaction. The unfolding of ovomucoid with L-cysteine-mediated reduction was used to increase accessibility to conformational and linear epitopes by modifying the secondary and tertiary structures of the allergen. Glycation with different saccharides revealed the beneficial effect of maltose glycation on the IgG-binding capacity reduction. By determining the better glycation conditions of unfolded ovomucoid, we produced ovomucoid with reduced IgE binding capacity due to the glycation sites (K17, K112, K129, and K164) on epitopes. Moreover, after simulated infant and adult gastrointestinal digestion, the unfolded plus glycated ovomucoid showed higher ABTS˙+ scavenging activity, O2˙- scavenging activity, ˙OH scavenging activity, Fe2+ chelating activity, and a FRAP value; in particular, for ˙OH scavenging activity, there was a sharp increase of more than 100%.

Recent advances in mass spectrometry-based methods to investigate reversible cysteine oxidation

The post-translational modification of cysteine to diverse oxidative states is understood as a critical cellular mechanism to combat oxidative stress. To study the role of cysteine oxidation, cysteine enrichments and subsequent analysis via mass spectrometry are necessary. As such, technologies and methods are rapidly developing for sensitive and efficient enrichments of cysteines to further explore its role in signaling pathways. In this review, we analyze recent developments in methods to miniaturize cysteine enrichments, analyze the underexplored disulfide bound redoxome, and quantify site-specific cysteine oxidation. We predict that further development of these methods will improve cysteine coverage across more diverse organisms than those previously studied and elicit novel roles cysteines play in stress response.

Effect of milk and whey on proliferation and differentiation of placental stromal cells

Fetal bovine serum (FBS), which is widely used in cell culture media, has the potential to cause medical and ethical problems. Here, an experimental study using milk or whey proteins containing essential nutrients and growth factors is presented to limit the use of FBS in cell culture media produced for cell and tissue regeneration. Study groups were formed by culturing human placenta mesenchymal stem cells, known to have high proliferation and differentiation capacity, with milk or whey solution at increasing concentrations, alone or in combination with FBS. Osteogenic and adipogenic differentiation capacities of proliferating cells were observed in FBS, milk or whey groups. Milk, whey or FBS groups obtained in P3 and after differentiation were separately analyzed for protein mRNA expression by reverse transcriptase-polymerase chain reaction (RT-qPCR). Fibroblast Growth Factor 2 (FGF2), Octamer-binding Transcription Factor 4 (OCT4), Bone Morphogenetic Protein 6 (BMP6), and adipogenic differentiation marker Peroxisome Proliferator-Activated Receptor Gamma (PPARG) were analysed by RT-qPCR. Proliferation was more pronounced in FBS alone and in its combinations with milk-whey compared to the groups in which only milk and whey were used. OCT4 mRNA and FGF2 mRNA expression decreased in differentiated cells. BMP6 mRNA expression increased with osteogenic and adipogenic stimuli. As expected, PPRG expression also increased with adipogenic stimulation. With this experimental study, evidence has been obtained that milk or whey can provide nutritional support to the culture media of repair cells and preserve the functional capacity of the cells, with a slightly more limited capacity than FBS.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s10616-023-00585-z.

BODIPY-based fluorescent probe for cysteine detection and its applications in food analysis, test strips and biological imaging

Cysteine, as one of semi-essential amino acids, which is absorbed from protein-rich foods and acts considerable role in various physiological processes. Here, we designed and synthesized a BODIPY-based turn-on fluorescent probe BDP-S for detecting Cys. The probe displayed short reaction time (10 min), distinct color response (from blue to pink), large signal noise ratio (3150-fold), high selectivity and sensitivity (LOD = 11.2 nM) toward Cys. Moreover, BDP-S could not only be used for quantitative determination of Cys in food samples, but also be conveniently deposited on the test strips for qualitative detection of Cys. Notably, BDP-S was successfully used for imaging Cys in living cells and in vivo. Consequently, this work provided a hopefully powerful tool for detecting Cys in food samples and complex biological systems.

Preparation and characterization of soy protein isolate films by pretreatment with cysteine

The effect of cysteine concentration on the viscosity of soy protein isolate (SPI)-based film-forming solution (FFS) and physicochemical properties of SPI films was investigated. The apparent viscosity of FFS decreased after adding 1 mmol/L cysteine but did not change after adding 2-8 mmol/L cysteine. After treatment with 1 mmol/L cysteine, the film solubility decreased from 70.40% to 57.60%, but the other physical properties did not change. The water vapor permeability and contact angle of SPI films increased as cysteine concentration increased from 4 mmol/L to 8 mmol/L, whereas the film elongation at break decreased. Based on scanning electron microscopy and X-ray diffraction results, cysteine crystallization could be aggregated on the surface of SPI films treated with 4 or 8 mmol/L cysteine. In conclusion, pretreatment with approximately 2 mmol/L cysteine could reduce the viscosity of SPI-based FFS, but did not change the physicochemical properties of SPI films.

Effect of lactylation on functional and structural properties of gluten

Gluten is widely used as a high-quality protein material in the food industry, however, low solubility restricts its development and applications. In this study, gluten was treated with lactate and sodium lactate for lactylation. Lactylation of gluten altered surface charges of the protein, leading to a significant improvement in the solubility. An improvement in oil absorption capacity (OAC) could be attributed to a decrease in protein folding degree after lactylation. In addition, the emulsifying properties of gluten were significantly enhanced. The introduction of lactate group also significantly increased the viscoelasticity of gluten. Fourier transform infrared spectroscopy (FTIR) showed there was a significant decrease in β-turns content and a significant increase in β-sheets content. The folded conformation of gluten was gradually extended after lactation by fluorescence spectroscopy measurement. Both in lactate and sodium lactate treatment, the maximum emission wavelength indicated a blue shift, and the UV intensity showed an increase. These results could demonstrate that lactylation could extend the structure and improve the functional property.

Limited hydrolysis of glycosylated whey protein isolate ameliorates the oxidative and physical stabilities of conjugated linoleic acid oil-in-water emulsions

Conjugated linoleic acid contains unsaturated fatty acids with multiple bioactivities, but it has poor oxidative and physical stabilities. Its emulsion was fabricated with glycosylated whey protein isolate and hydrolysates of glycosylated whey protein isolate to enhance its stability. An obvious decrease in peroxide value, thiobarbituric acid-reactive substances, particle size and creaming index of emulsion loaded by hydrolysates of glycosylated protein isolate with the increase of hydrolysis time. However, the absolute value of zeta-potential and interfacial adsorption rate of emulsion stabilized by hydrolysates of glycosylated whey protein isolate, were increased by 10.99 and 16.94% at hydrolysis time of 120 min, compared with emulsion loaded by glycosylated whey protein isolate. Thus, limited hydrolysis of glycosylated whey protein isolate as an effective method, remarkably improved the oxidative and physical stability of emulsion.