The impact of konjac glucomannan on the physical and chemical stability of walnut oil-in-water emulsions coated by whey proteins.

BACKGROUND: Walnut oil, which is rich in polyunsaturated fatty acids (PUFAs), can be incorporated into food emulsions to increase their nutritional value. However, these emulsions are highly susceptible to deterioration during storage due to lipid oxidation. Konjac glucomannan (KGM) is a neutral plant polysaccharide used as a stabilizer, thickener or gelling agent in foods. The goal of this study was to incorporate KGM into oil-in-water emulsions containing walnut oil droplets coated by whey protein isolate (WPI) and then determine its effects on their physical and oxidative stability. RESULTS: At pH 3, inclusion of KGM (0.1-1 g kg-1 ) reduced the positive surface potential on the droplets in the emulsions and modified the secondary structure of the adsorbed whey proteins, suggesting an interaction between KGM and WPI at the droplet surfaces. The physical stability of the emulsions was enhanced when 0.1-0.6 g kg-1 KGM was added but reduced at higher levels. Lipid oxidation was inhibited in the emulsions in a dose-dependent manner when 0.2-0.6 g kg-1 KGM was added but protein oxidation was promoted at higher KGM levels. The steric hindrance provided by the thick WPI-KGM interfaces, as well as the ability of the polysaccharides to modify the antioxidant properties of the adsorbed proteins, may account for these effects. CONCLUSION: These results suggest that KGM can be used to inhibit lipid oxidation in emulsified foods containing protein-coated oil droplets. However, its level must be optimized because higher doses can result in droplet aggregation and protein oxidation. © 2022 Society of Chemical Industry.

Properties and Stability of Perilla Seed Protein-Stabilized Oil-in-Water Emulsions: Influence of Protein Concentration, pH, NaCl Concentration and Thermal Treatment.

Perilla seed protein (PSP) was extracted from defatted perilla seed meal and applied in oil-in-water (O/W) emulsions as an emulsifier. We investigated the influences of protein concentration (0.25⁻1.5 wt %), pH (3.0⁻9.0), NaCl concentration (0⁻350 mmol/L) and thermal treatment (70⁻90 °C, 30 min) on the physical characteristics of O/W emulsions, including volume-average diameter, ζ-potential, interfacial protein concentration, microstructure and so on. Results showed that increasing PSP concentration would decrease the d4,3 and a 1.0 wt % PSP concentration was sufficient to ensure the stability of emulsion. Under pH 3.0⁻9.0, emulsions were stable except at pH 3.0⁻5.0 which was proximal to the isoelectric point (pH 4.5) of PSP. At high NaCl concentrations (250⁻350 mmol/L), the emulsions exhibited relatively lower absolute ζ-potential values and a large number of aggregated droplets. A moderate thermal treatment temperature (e.g., 70 °C) was favorable for the emulsion against aggregation and creaming. However, when 90 °C thermal treatment was performed, a clear layer separation was observed after 2 weeks storage and the emulsion showed a poor stability. The findings of this work are of great importance for the utilization and development of PSP as an emulsifier for food emulsions.

Ultrasound improving the physical stability of oil-in-water emulsions stabilized by almond proteins.

BACKGROUND: Vegetable proteins are increasingly used to stabilize oil-in-water (O/W) emulsions. However, emulsions are thermodynamically unstable. Recently, high-intensity ultrasound (US) has been used to enhance the stability of emulsions. For these reasons, and considering almond (Prunus dulcis L.) as a good source of high-quality proteins, the aim of this work was to investigate the effect of US treatment on the stability of pre-emulsification O/W emulsions coated with almond protein isolate (API). RESULTS: The influence of API concentration (0.25-2.0 g L-1 ), ion strength (0-500 mmol L-1 NaCl), and pH (3.0-7.0) on the stability of US-treated emulsions was evaluated. US treatment (200-600 W, 25 kHz, 15 min) led to a significant reduction in the particles size of droplets in emulsions, increased critical osmotic pressure and additional protein interfacial adsorption, and thus the formation of more stable emulsions. The more unfolded and random coil structures of the proteins were detected at higher US power, facilitating protein interfacial adsorption. Increasing API concentrations resulted in higher stability of US-treated emulsions against untreated counterparts. The US-treated emulsions were more resistant to salt than untreated samples. In the range from pH 3.0 to7.0, US treatment also enhanced the physical stability of emulsions compared with untreated emulsions. CONCLUSION: US technology could be applied to produce more stable O/W food emulsions stabilized by proteins. © 2018 Society of Chemical Industry.

The effects of resonance acoustic mixing modulation on the structural and emulsifying properties of pea protein isolate.

The effects of resonant acoustic mixing (RAM) with different treatment times (0, 5, 10, 15, 20 and 30 min) on the structural and emulsifying properties of pea protein isolate (PPI) were investigated for the first time. Increasing the RAM treatment time from 0 to 20 min decreased the α-helix/ß-sheet ratio and particle size of the PPI samples by 37.84 % and 46.44 %, respectively, accompanied by an increase in solubility from 54.79 % to 71.80 % (P < 0.05). Consequently, the emulsifying activity index of PPI (from 10.45 m2/g to 14.2 m2/g) and the physical stability of RAM-PPI emulsions were effectively enhanced, which was confirmed by the small and uniformly distributed oil droplets in the micrographs of the emulsions. However, excessive RAM treatment (30 min) diminished the effectiveness of the aforementioned improvements. Therefore, obviously enhanced solubility and emulsifying properties of PPI can be attained through proper RAM treatment (15-20 min).

Molecular mechanism associated with the use of magnetic fermentation in modulating the dietary lipid composition and nutritional quality of goat milk.

Standard fermentation (SF) mainly affected the metabolism of glycerophospholipid and sphingolipid, and increased the total lipid content of goat milk. Content of total lipid was decreased by magnetic fermentation compared with SF, mainly due to triacylglycerol and diacylglycerol. Comprehensive characteristic of lipids dynamic changes during standard and magnetic fermentation was performed using high-throughput quantitative lipidomics. Totally, 488 lipid molecular species covering 12 subclasses were detected, and triacylglycerol was the highest levels, followed by diacylglycerol and phosphoethanolamine in the whole fermentation stage. Specifically, except for ceramide and simple Glc series, the content of all polar lipids in SF was dropped and neutral lipids subjoined. Compared with SF, the decrease of triacylglycerol (1752.47 to 784.78 µg/mL), diacylglycerol (60.36 to 24.89 µg/mL) and simple Glc series (4.36 to 2.40 µg/mL) were observed, while ceramide (6.54 to 25.87 µg/mL) increased, suggesting magnetic fermentation as effective approach to potentially improve the nutritional of goat milk.

Antioxidant and prooxidant activities of tea polyphenols in oil-in-water emulsions depend on the level used and the location of proteins.

We studied the impacts of protein location (interface or aqueous phase) on the antioxidant and prooxidant activities of tea polyphenols (TP) in model oil-in-water emulsions (pH 7) at a low (0.01% w/v) or high (0.04 % w/v) concentration. TP at 0.01% reduced the levels of both lipid and protein oxidation markers in emulsions, independent of the protein location. However, TP were more potent when proteins were located at the interface. At 0.04%, TP were only weakly antioxidant towards lipids but were prooxidant towards proteins in emulsions with proteins at the interface, whereas they were still somewhat antioxidant for aqueous phase proteins. These results indicate that TP may act as either antioxidants or prooxidants depending on their concentration and also on the location of the proteins in emulsions. The level of TP should be optimized for emulsion-based foods or beverages to achieve optimum antioxidant activity.

Structural characteristics of pea protein isolate (PPI) modified by high-pressure homogenization and its relation to the packaging properties of PPI edible film.

This study modified pea protein isolate (PPI) structure by high-pressure homogenization (HPH) and investigated PPI structural relation to the packaging properties of PPI film. HPH decreased PPI particle size, reduced surface charge, increased surface hydrophobicity, and increased free sulfhydryl, providing greater potential for covalent bonding during film formation. HPH decreased opacity of PPI films from 7.39 to 4.82 at pressure of 240 MPa with more homogeneous surface. The tensile strength and elongation at break were increased from 0.76 MPa to 1.33 MPa and from 96% to 197%, respectively, after treatment at 240 MPa. This improvement was due to the enhanced protein-protein and protein-glycerol hydrogen bonding as evidenced by FTIR. Increased ß-sheet and decreased α-helix by HPH was also observed, and ß-sheet was highly correlated to film tensile strength (Pearson coefficient of 0.973, P < 0.01). Principle component analysis visualized the influence of HPH treatment, and confirmed the association between structural characteristics and film properties.

Proteomics analysis to investigate the impact of diversified thermal processing on meat tenderness in Hengshan goat meat.

During the thermal processing, proteins of Hengshan goat meat undergo structural modifications such as degradation, oxidation and denaturation, ultimately affect the palatability and acceptability. The results of several objective metrics demonstrated that thermal processing exhibited significant impacts on the tenderness of goat meat. The 551, 84, 72, and 121 proteins were identified in the control and thermal processed groups (boiled, steamed, and roasted), respectively. Compared with the control group, the 101, 98, and 109 differentially-expressed proteins were explored in the treatment groups. Furthermore, the functions of metabolic and skeletal muscle proteome were investigated and discussed. Sensory evaluation and proteomics analysis showed that steaming and boiling treatment had no significant effect on the tenderness of goat meat, while roasting significantly reduced the tenderness, indicating that the available thermal processing methods to ensure the tenderness of goat meat were steaming and boiling treatments. Thus, the established proteomics database of goat meat provided the valuable reference for rational selection of thermal processing methods.

A High-Throughput Comparative Proteomics of Milk Fat Globule Membrane Reveals Breed and Lactation Stages Specific Variation in Protein Abundance and Functional Differences Between Milk of Saanen Dairy Goat and Holstein Bovine.

Large variations in the bioactivities and composition of milk fat globule membrane (MFGM) proteins were observed between Saanen dairy goat and Holstein bovine at various lactation periods. In the present study, 331, 250, 182, and 248 MFGM proteins were characterized in colostrum and mature milk for the two species by Q-Orbitrap HRMS-based proteomics techniques. KEGG pathway analyses displayed that differentially expressed proteins in colostrum involved in galactose metabolism and an adipogenesis pathway, and the differentially expressed proteins in mature milk associated with lipid metabolism and a PPAR signaling pathway. These results indicated that the types and functions of MFGM proteins in goat and bovine milk were different, and goat milk had a better function of fatty acid metabolism and glucose homeostasis, which can enhance our understanding of MFGM proteins in these two species across different lactation periods, and they provide significant information for the study of lipid metabolism and glycometabolism of goat milk.

Time-Series Lipidomics Insights into the Progressive Characteristics of Lipid Constituents of Fresh Walnut during Postharvest Storage.

A high-throughput lipid profiling platform adopting an accurate quantification strategy was built based on Q-Orbitrap mass spectrometry. Lipid components of fresh walnut during postharvest storage were determined, and the fatty acid distributions in triacylglycerol and polar lipids were also characterized. A total of 554 individual lipids in fresh walnut were mainly glycerolipids (56.7%), glycerophospholipids (32.4%), and sphingolipids (11%). With the progress of postharvest storage, 16 lipid subclasses in the stored walnut sample were significantly degraded, in which 34 lipids changed significantly between the fresh and stored groups. The sphingolipid metabolism, glycerolipid metabolism, and linoleic acid metabolism pathways were significantly enriched. The oxidation and degradation mechanism of linoleic acid in walnut kernel during postharvest storage was proposed. The established lipidomics platform can supply reliable and traceable lipid profiling data, help to improve the understanding of lipid degradation in fresh walnut, and offer a framework for analyzing lipid metabolisms in other tree nuts.

Synergistic recovery and enhancement of gelling properties of oxidatively damaged myofibrillar protein by l-lysine and transglutaminase.

The influence of combined Lysine (Lys) and transglutaminase (TG) on the conformation and gelling properties of oxidatively damaged myofibrillar protein (MP) was investigated. The addition of Lys (5 mM) significantly increased the α-helix content (by 47.8%) and decreased the particle size of oxidatively damaged MP, and improved the cooking yield (by 16.8%) and the breaking strength of MP gels (by 65.5%). The treatment with TG (E:S = 1:500) led to a slightly reduced α-helix content but improved breaking strength (by 41.8%) and cooking loss (by 13.3%) of the gels. Their combination (Lys + TG) showed the greatest and synergistic overall improvement, with the set gel displaying a fine, smooth and compact network structure. Notably, the gelling ability of oxidatively damaged MP upon Lys + TG treatment was significantly stronger than that of non-oxidized MP far exceeding its recovery. Therefore, significantly enhanced gelling properties of oxidatively damaged MP can be attained through the combination Lys and TG.

Molecular mechanism of protein dynamic change for Hengshan goat meat during freezing storage based on high-throughput proteomics.

As traditional frozen storage leads to the degradation of meat quality, elucidation of dynamic change mechanism is urgently needed. Proteomic differences in postmortem frozen storage time (0, 30 and 60 days) of Hengshan goat meat at -18 °C were studied by label-free proteomics based on high resolution quadrupole-Orbitrap mass spectrometry. A total of 492 proteins were identified, of which 485 proteins were quantified, and the difference of 199 proteins was observed. The analysis of the differentially expressed proteins related to quality observed that triosephosphate isomerase and peroxiredoxin-6 were potential biomarkers for goat meat discoloration. Troponin and myosin can represent the tenderness of goat meat. Heat shock protein 70 can be used as water-retaining proteins in goat meat. Bioinformatics analysis suggested that the distinguishingly expressed proteins were involved in glycolysis and the ubiquitin-proteasome pathway revealing that the strong degradation of proteins, which cause of the degradation of long-term frozen meat quality. These results could enrich and beyond the existing knowledge of frozen meat, expecting to have a further understanding of the changes of meat quality at the molecular level.

Robust and recyclable magnetic nanobiocatalysts for extraction of anthocyanin from black rice.

Anthocyanins, which are natural pigments and nutraceuticals, can be extracted from plant materials using enzyme-assisted methods. However, the enzymes used are often expensive, fragile, and hard to recover/reuse. In this study, cellulase and α-amylase were immobilized on amino-functionalized magnetic nanoparticles to prepare a magnetic nanobiocatalyst. The enzymes in this nanobiocatalyst exhibited higher stability and greater catalytic activity than free enzymes, including good thermal stability (50 to 70℃) and pH stability (pH 4.5-7.5). Nanobiocatalyst efficacy was demonstrated by extracting anthocyanins from black rice, with a maximum yield of 266 mg anthocyanin/100 g black rice obtained. After six reuse cycles, cellulase and α-amylase retained around 70% and 64% of their activity, respectively. Immobilization also increased their reusability. In summary, a novel magnetic nanobiocatalyst was developed for extracting anthocyanins from black rice, which may also have other applications within the food industry.

One-step extraction of oat protein by choline chloride-alcohol deep eutectic solvents: Role of chain length of dihydric alcohol.

The aim of this study is to investigate the effect of dihydric alcohol chain length (1,2-ethanediol, 1,3-propanediol, and 1,4-butanediol) on the structure of deep eutectic solvents (DESs) and the properties of the extracted oat proteins. Herein, five anhydrous and nine hydrated DESs were successfully prepared by mixing choline chloride, dihydric alcohol, and/or water in a heating method. The structures of DESs were confirmed by FTIR and 1H NMR. Among them, only four anhydrous and six hydrated DESs were able to extract oat proteins from flours by one-step extraction. SDS-PAGE and FTIR analyses indicated that the structural properties of the oat proteins were highly reliant on the composition of the DESs; while physicochemical properties were primarily ruled by the environmental pH. Overall, the hydrated DES composing of all food-grade compounds, including choline chloride, 1,3-propanediol, and water at a molar ratio of 1:3:1, demonstrated its great potential for one-step biorefinery of oat proteins.

Formation of Antioxidant Multilayered Coatings for the Prevention of Lipid and Protein Oxidation in Oil-in-Water Emulsions: Lycium barbarum Polysaccharides and Whey Proteins.

The impact of Lycium barbarum polysaccharides (LBPs) on the physical and chemical stability of oil-in-water emulsions coated by a whey protein isolate (WPI) was investigated. At pH 3.0, the anionic LBP (0.2-0.6 wt %) molecules were electrostatically deposited onto the cationic surfaces of the WPI-coated oil droplets, leading to the formation of stable multilayered emulsions containing WPI-/LBP-coated oil droplets. However, increasing the LBP concentration to 0.8 wt % led to oil droplet aggregation, which was attributed to charge neutralization, bridging flocculation, and/or depletion flocculation. For subsequent experiments, a low (0.2%) and an intermediate (0.6%) LBP dose was used to prepare the secondary emulsions, and then their physical and oxidative stability was studied during 8 days of storage at 37 °C. The presence of the multilayer WPI/LBP coatings around the oil droplets inhibited lipid oxidation (reduced levels of lipid hydroperoxides and 2-thiobarbituric acid-reactive substances), as well as protein oxidation (reduced levels of carbonyl formation, sulfhydryl consumption, molecular weight modifications, intrinsic fluorescence loss, and Schiff-base fluorescence gain). The antioxidant effects of the multilayer coatings were greater at the higher LBP concentration. These results suggest that LBP, a natural plant-based polysaccharide isolated from a traditional Chinese medicine, can be used to improve the quality of emulsion-based foods. However, the level used should be optimized to ensure good physical and oxidative stability of the emulsions.

Impact of tea polyphenols on the stability of oil-in-water emulsions coated by whey proteins.

The ability of tea polyphenols (0, 0.01, 0.02 or 0.04 w/v %) to inhibit lipid and protein oxidation in walnut oil-in-water (O/W) emulsions was examined, as well as to alter their stability to aggregation and creaming. The lipid droplets in these emulsions were coated by whey proteins. The physical stability of the emulsions during storage (50 °C, 96 h) was improved by addition of 0.01% tea polyphenols, but reduced when higher levels were added. Low levels (0.01%) of tea polyphenols inhibited lipid oxidation (lipid hydroperoxide and 2-thiobarbituric acid-reactive substance formation) and protein oxidation (carbonyl and Schiff base formation, sulfhydryl and intrinsic fluorescence loss, and molecular weight changes). However, high levels (0.04%) of tea polyphenols were less effective at inhibiting lipid oxidation, and actually promoted protein oxidation. Tea polyphenols are natural antioxidants that can enhance the quality and shelf life of emulsified polyunsaturated lipids when used at an appropriate concentration.

Adsorption capacity and cold-water solubility of honeycomb-like potato starch granule.

Honeycomb-like granules, with 2-4 µm pores on the surface, were prepared by heating potato starch suspensions in water at the pasting temperature. These granules with a yield of 84% were most amorphous (relative crystallinity 1.9%). Their total pore area was 0.668 m2/g, porosity was 73.4%, and mean particle size (D50) was 154.3 µm. The molecular weights (MW) of honeycomb-like granules were: amylopectin, 8.7 × 107 g/mol; amylose, 3.1 × 105 g/mol, close to those of native starch. The chain length distribution profiles of honeycomb-like granules were similar to those of native starch, while the proportions of B2 and B3 chains were higher. The water and oil adsorption of honeycomb-like granules were about 1.5 and 2.4 times those of native starch, respectively; and the cold water solubility of honeycomb-like granules was 88.5%, while native starch showed no solubility in cold water. Thus honeycomb-like starch granules have the potential to be applied as adsorbents, thickeners and adhesives for their dispersibility, adsorption capacity and cold water solubility.

Comparison of natural and synthetic surfactants at forming and stabilizing nanoemulsions: Tea saponin, Quillaja saponin, and Tween 80.

HYPOTHESIS: This study compared the interfacial and emulsification properties of tea saponins, quillaja saponins, and Tween 80. We hypothesized that tea saponins are an effective and sustainable source of plant-based emulsifiers that could replace synthetic or animal-based emulsifiers in many commercial applications. EXPERIMENTS: Interfacial tension measurements were used to characterize the behavior of the three surfactants at an oil-water interface. The emulsifying properties of the surfactants were determined by preparing oil-in-water emulsions containing 10 wt% medium chain triglycerides (MCT) and varying surfactant levels (0.1-2 wt%) using high-pressure homogenization (pH 7). The impact of surfactant type on emulsion formation and stability was determined by measuring particle size, zeta-potential, microstructure, and creaming stability. FINDINGS: The tea saponins were capable of producing nano-scale droplets (d32 < 200 nm) at low surfactant-to-oil ratios (SOR < 0.1). Emulsions containing tea saponins remained stable to droplet aggregation when exposed to various temperatures (30-90 °C), salt levels (0-200 mM NaCl), and pH values (3-9). However, droplet flocculation and/or coalescence occurred under highly acidic (pH 2) and high ionic strength (300-500 mM NaCl) conditions. Tea saponin-coated oil droplets appeared to be mainly stabilized by a combination of electrostatic and steric repulsion. The tea saponins behaved similarly or better than the other two emulsifiers under most conditions. These results suggest that tea saponins are effective plant-based surfactants that may have applications in commercial products.

The prooxidant activity of salts on the lipid oxidation of lecithin-stabilized oil-in-water emulsions.

Salts reduction/substitution have gained a lot interest from food industry since the US Food and Drug Administration (FDA) has issued a draft guidance for salt reduction. However how changes of salts in food formulation could influence lipid oxidation is still not fully understood. Using oil-in-water emulsions stabilized by a natural emulsifier - lecithin at pH 7.0 as a model system, this study evaluated how salts affect the physical parameters of the emulsion, the chelating activity of lecithin and thus the lipid oxidation of these emulsions. Results showed that salts increased the particle size, the negative charge of the oil droplets, and the amount of iron chelated by lecithin. Lipid oxidation lag phases were shortened by addition of salts, by 1 day and 2 days for lipid hydroperoxides and thiobarbituric acid reactive substances measurements respectively. These results provide some new insights on the mechanisms of how salts could affect the lipid oxidation of food emulsions.

Impact of Interfacial Composition on Lipid and Protein Co-Oxidation in Oil-in-Water Emulsions Containing Mixed Emulisifers.

The impact of interfacial composition on lipid and protein co-oxidation in oil-in-water emulsions containing a mixture of proteins and surfactants was investigated. The emulsions consisted of 5% v/v walnut oil, 0.5% w/v whey protein isolate (WPI), and 0 to 0.4% w/v Tween 20 (pH 3 and pH 7). The protein surface load, magnitude of the ξ-potential, and mean particle diameter of the emulsions decreased as the Tween 20 concentration was increased, indicating the whey proteins were displaced by this nonionic surfactant. The whey proteins were displaced from the lipid droplet surfaces more readily at pH 3 than at pH 7, which may have been due to differences in the conformation or interactions of the proteins at the droplet surfaces at different pH values. Emulsions stabilized by whey proteins alone had relatively low lipid oxidation rates when incubated in the dark at 45 °C for up to 8 days, as determined by measuring lipid hydroperoxides and 2-thiobarbituric acid-reactive substances (TBARS). Conversely, the whey proteins themselves were rapidly oxidized, as shown by carbonyl formation, intrinsic fluorescence, sulfhydryl group loss, and electrophoresis measurements. Displacement of whey proteins from the interface by Tween 20 reduced protein oxidation but promoted lipid oxidation. These results indicated that the adsorbed proteins were more prone to oxidation than the nonadsorbed proteins, and therefore, they could act as better antioxidants. Protein oxidation was faster, while lipid oxidation was slower at pH 3 than at pH 7, which was attributed to a higher antioxidant activity of whey proteins under acidic conditions. These results highlight the importance of interfacial composition and solution pH on the oxidative stability of emulsions containing mixed emulsifiers.