Circular dichroism and infrared spectroscopic characterization of secondary structure components of protein Z during mashing and boiling processes

High hydrostatic pressure reduces inflammation induced by litchi thaumatin-like protein via altering active domain

Thaumatin-like proteins (TLP), existing in various fruits, have allergenic and pro-inflammatory activities. The current research attempts to reduce the pro-inflammatory activity of litchi TLP (LcTLP) through high hydrostatic pressure (HHP). This study demonstrated that HHP (250-500 MPa, 5-10 min) was a potential technique to reduce the pro-inflammatory activity of LcTLP, which was attributed to the irreversible destruction of the active domain, ie., V-cleft. SDS-PAGE showed no change in the protein profile. Continuous HHP treatment promoted LcTLP unfolding and then reassembling (400 MPa was the transition pressure), and the content of β-sheets decreased from 35.4% to 31.1%. HHP treatment could mitigate inflammatory responses of LcTLP, as confirmed by ELISA and western blot. Molecular dynamics simulations showed significant changes in the residue network under HHP, thereby affecting the V-cleft. These findings provide a theoretical explanation and structural insights into the HHP-induced reduction of pro-inflammatory activity of LcTLP.

Comparison of recombinant protein Z with natural protein Z derived from malt: From structure to functional properties

Protein Z (PZ) is a prominent albumin found in the endosperm of barley seeds with a molecular weight of approximately 40 kDa. Its multifaceted functional attributes, including trypsin- and thrombin-inhibiting bioactivities and superior foaming properties, have garnered significant attention in research. Considering the post-translational modifications of PZ natural in barley malt, we tried to express recombinant protein Z (rPZ) in E. coli. The present study aims to undertake a comparative analysis between natural PZ and rPZ in order to elucidate their respective characteristics. After spectral analysis, there are significant differences in their secondary and tertiary structures. In addition, rPZ showed superior foamability and foam stability. As for the serpin-like activity, the inhibition rate of rPZ is much higher than that of PZ. In contrast with the inhibition activity, the digestability of rPZ is much lower than that of PZ. As for the cargo carrier properties, rPZ showed an excellent ability to stabilize astaxanthin at 37 °C. These results suggest that rPZ is more suitable as protein carrier, due to the high foamability, serpin-like activity and low digestive stability, which not only give a brief view of recombinant protein, but also give a direction for PZ in cargo delivery.

Self-assembled Abietic acid encapsulated nanoparticles to improve the stability of Proanthocyanin B2

Procyanidin B2 (Pac B2) has attracted much attention due to its strong antioxidant activity, but poor in vivo stability limits its wide application in food and medicine. In this paper, composite nanoparticles (NPs) were constructed using abietic acid (AA) as a carrier, which significantly enhanced Pac B2 stability. A spherical morphology and average diameter of 396.05 nm were observed in AA-Pac B2 NPs synthesized by solvent co-precipitation. Pac B2 encapsulation was 11.28 %, and thermal stability is improved. Infrared, Ultraviolet spectrum, and MD (molecular dynamics) spectroscopy revealed hydrogen bonding and hydrophobic interaction between AA and Pac B2. For up to 2 h at 37 °C, Pac B2 can be sustainably released in simulated gastric and intestinal fluids. In vitro, AA-Pac B2 NPs at the same concentration exhibited higher bioavailability and uptake efficiency than free Pac B2. The data demonstrate the potential of AA NPs for improving polyphenol thermal stability and bioavailability.

Comparative Study on Protein Composition and Foam Characteristics of Barley and Wheat Beer

Protein is an important component of beer, and its type, content and molecular weight directly affect the quality of beer, especially the foam quality of beer. Different brands of wheat beer and barley beer available in the market were used for this analysis. The differences in protein composition and foam performance between multi-sample barley and wheat beer were analyzed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and high-pressure size exclusion chromatography. Protein significantly influences beer quality, particularly its foam properties. Wheat beer (WB) has 9.52-84.10% more total protein content than barley beer (BB). The primary proteins in both beers are 6.9-20.1 kDa, with WB having 1.04 g/L more of this protein, 60.11% higher than that of BB. It is one of the main different proteins between WB and BB. WB also contains 66.67% more 20.1-32.4 kDa protein compared to BB. This is one of the main differences between WB and BB proteins. Both 6.9-20.1 kDa and 20.1-32.4 kDa proteins enhance beer viscosity and foam properties. Additionally, WB's > 32.4 kDa protein content is 246.67% higher than BB's, significantly improving beer hydrophobicity and foam performance. These protein differences are key factors in the superior foam quality of WB.

Insight into the mechanism of alkali-thermal pretreatment of food-waste solid residue through fluorescence spectroscopy coupled with parallel factor analysis

Food-waste solid residue is the remaining solid after food waste treatment, with high yield, high solid content, high protein and fiber content. Effective pretreatment is necessary to improve the efficiency of hydrolysis and acidification for anaerobic digestion of food-waste solid residue. In this study, fluorescence spectroscopy coupled with parallel factor analysis were used to insight into the mechanism of food-waste solid residue during three pretreatments (alkali, thermal and alkali-thermal). Pretreatments increased the solubility of lignocellulosic substrate and destroyed structure of starch, while lignocellulosic analogs were effectively cracked, changing the composition and improving the degradability. Soluble chemical oxygen demand, soluble protein and soluble polysaccharide concentrations were increased by 144.60%, 350.57% and 138.72% after pretreatment under the condition of 120 °C + 2% CaO, respectively. Three-dimensional fluorescence spectra showed the region of maximum fluorescence intensity under alkali-thermal pretreatments, indicating chemical bonds (such as OC-C) were easier broken and the solubility of organic substances were increased. Three main fluorescence components were obtained by parallel factor analysis, which were humic acid-like, lignocellulose-like and protein-like, respectively, while the lignocellulose-like had the maximum Fmax value. The fluorescence intensity of samples under alkali-thermal pretreatment varied in the range from 59.48 × 105 to 13.18 × 106, which was an increase of 174.27%-507.74% over the control (21.68 × 105), indicating that alkali-thermal pretreatment observably accelerated the breaking of chemical bonds, and thus promoted the dissolution of organic matter. This study deeply revealed the mechanism of alkali-thermal pretreatment of food-waste solid residue, which is of great significance for efficient resource utilization of food waste and food-waste solid residue.

The changes induced by hydrodynamic cavitation treatment in wheat gliadin and celiac-toxic peptides

Hydrodynamic cavitation (HC) is thought weaken the allergenicity of beer gluten proteins. However, the mechanism of action has not been thoroughly studied. In this study, an HC device was used to treat wheat gliadin and two specific celiac-toxic peptides, P1 and P2. FT-IR, MFS, HPLC, and CD were used to monitor the structural characteristics of gliadin and the two peptides. HC reduced the abundance of the coeliac toxic peptides P1 and P2 in solution and the contents of secondary structure β-turns and PPII, which are related to reduced allergen immunoreactivity. This meant that both the primary and secondary structures of P1 and P2 were affected by HC, leading to fewer allergic reactions. This study was focused on the impact of HC on the secondary structures of allergens produced from gluten raw materials, and it has positive implications for reducing product allergenicity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13197-024-05973-7.

Effects of Glycosylation Combined with Phosphate Treatment on the Allergenicity and Structure of Tropomyosin in Litopenaeus vannamei

Tropomyosin (TM) is the main allergen in shrimp (Litopenaeus vannamei). In this study, the effects of allergenicity and structure of TM by glycosylation (GOS-TM), phosphate treatment (SP-TM), and glycosylation combined with phosphate treatment (GOS-SP-TM) were investigated. Compared to GOS-TM and SP-TM, the IgG/IgE binding capacity of GOS-SP-TM was significantly decreased with 63.9 ± 2.0 and 49.7 ± 2.7%, respectively. Meanwhile, the α-helix content reduced, surface hydrophobicity increased, and 10 specific amino acids (K30, K38, S39, K48, K66, K74, K128, K161, S210, and K251) were modified by glycosylation on six IgE linear epitopes of GOS-SP-TM. In the BALB/c mice allergy model, GOS-SP-TM could significantly reduce the levels of specific IgE, IgG1, and CD4+IL-4+, while the levels of IgG2a, CD4+CD25+Foxp3+, and CD4+IFN-γ+ were increased, which equilibrated Th1 and Th2 cells, thus alleviating allergic symptoms. These results indicated that glycosylation combined with phosphate treatment can provide a new insight into developing hypoallergenic shrimp food.

Effects of ultrasound and thermal treatment on the interaction between hyaluronic acid and lactoferrin: Preparation, structures and functionalities

Complexes of polysaccharides and proteins have superior physicochemical and functional properties compared to single proteins or polysaccharides. In this study, lactoferrin-hyaluronic acid (LF-HA) complexes were prepared by both ultrasonic and thermal treatment. Appropriate preparation conditions, including ultrasonic and thermal treatment conditions, have been established. The complexes formed by different methods were structurally characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis, fourier transform infrared spectroscopy, and circular dichroism spectroscopy. Ultrasound formed non-covalent binding, while thermal treatment generated covalent bonding, altering the structure of LF. The LF-HA complexes showed improved heat stability, foaming stability, emulsifying activity and antioxidant capacity, but deceased foaming ability. Iron binding ability could only be improved by HA through thermal treatment. Moreover, the in vitro digestibility of LF-HA complexes decreased to below 80 % compared to LF.

Exploring the binding mechanisms of thermally and ultrasonically induced molten globule-like β-lactoglobulin with heptanal as revealed by multi-spectroscopic techniques and molecular simulation

This work employed the model protein β-lactoglobulin (BLG) to investigate the contribution of microstructural changes to regulating the interaction patterns between protein and flavor compounds through employing computer simulation and multi-spectroscopic techniques. The formation of molten globule (MG) state-like protein during the conformational evolution of BLG, in response to ultrasonic (UC) and heat (HT) treatments, was revealed through multi-spectroscopic characterization. Differential MG structures were distinguished by variations in surface hydrophobicity and the microenvironment of tryptophan residues. Fluorescence quenching measurements indicated that the formation of MG enhanced the binding affinity of heptanal to protein. LC-MS/MS and NMR revealed the covalent bonding between heptanal and BLG formed by Michael addition and Schiff-base reactions, and MG-like BLG exhibited fewer chemical shift residues. Molecular docking and molecular dynamics simulation confirmed the synergistic involvement of hydrophobic interactions and hydrogen bonds in shaping BLG-heptanal complexes thus promoting the stability of BLG structures. These findings indicated that the production of BLG-heptanal complexes was driven synergistically by non-covalent and covalent bonds, and their interaction processes were influenced by processes-induced formation of MG potentially tuning the release and retention behaviors of flavor compounds.

Nanoparticle encapsulation using self-assembly abietic acid to improve oral bioavailability of curcumin

This research constructed composite nanoparticles (NPs) using abietic acid (AA) as a carrier for significantly enhancing the bioavailability of curcumin (CCM). CCM-loaded AA NPs were synthesized using a low-energy microemulsification method, and the obtained nanoparticles had a spherical morphology with an average diameter of 458.66 nm, a narrow size distribution and a negative surface charge of -19.13 mV. The encapsulation efficiency of CCM was 17.98 %, while its solubility was 20-fold that of free curcumin. FITR, UV, and MD revealed hydrogen bonds and hydrophobic forces between AA and CCM. Thein-vitrorelease profile showed sustainable release of CCM in simulated gastric and intestinal fluids up to 2 h at 37 °C. In cellular studies, CCM-loaded AA NPs with the same CCM concentration exhibited greater bioaccessibility and bioavailability than free CCM. These data suggested a possible utilization of AA NPs in improving water solubility, bioavailability and activity of lipophilic bioactive food factors.

Interactions between humulinone derived from aged hops and protein Z enhance the foamability and foam stability

Foam is one of the important characteristics of beer, including foamability, foam stability and foam texture. Protein Z (PZ) is considered to be an important component of beer foam. In this study, the interaction between PZ and humulinone, a widespread compound in aged hops, and the effect on foam properties of PZ were investigated. The fluorescence spectra showed that the stoichiometric ratio of humulinone to PZ was 4.25 ± 0.48: 1, and the binding constant was (1.64 ± 0.17) × 105 M-1. MD and FTIR results showed that the main force of interaction between PZ and humulinone was hydrogen bond, and the possible sites were Asn-37, Ser-292, Lys-290 and Pro-395. Moreover, the addition of humulinone greatly reduced the surface tension of PZ solution, and changed the secondary structure of PZ, which is beneficial for the foam stability. Under the influence of humulinone, the foamability, foam stability and foam texture of PZ all increased.

Influence of linoleic acid on the immunodetection of shrimp (Litopenaeus vannamei) tropomyosin and the mechanism investigation via multi-spectroscopic and molecular modeling techniques

The effect of linoleic acid (LA) on the IgG/IgE recognition, in vitro digestibility and immunodetection of shrimp tropomyosin (TM) was investigated. Subsequently, the simultaneous binding of LA-TM was explored using multi-spectroscopic and molecular modeling techniques. Our findings reveled that the addition of LA significantly reduced TM's IgG/IgE immunoreactivity, digestibility, and immunodetection. Further analysis using multi-spectroscopic and molecular modeling techniques indicated that while TM's secondary structure remained largely unchanged, its 3-D structure showed significant alterations such as increased particle size and hydrophobic surface area, and a higher number of buried hydrophobic residues exposed due to the binding of LA to TM. These structural changes rendered it difficult for target antibodies and digestive enzymes to interact with related epitopes and cleavage sites buried inside the molecule. The results obtained in this study provide valuable insights into the molecular mechanism of poor immunodetection caused by food matrix interference.

Chicoric acid inserted in protein Z cavity exhibits higher stability and better wound healing effect under oxidative stress

Oxidative stress is one of the limiting factors that inhibit wound healing. Phytochemicals especially chicoric acid have the potential to act as an antioxidant and scavenge reactive oxygen species, thereby promoting wound healing. However, most of the phytochemicals were easy to be degraded during storage or using due to the oxidative status in wound site. Herein, we introduce a high stable protein Z that can encapsulate chicoric acid during foaming. TEM results showed that the size of protein Z-chicoric acid is in the range of nanoscale (named PZ-CA nanocomposite), and protein Z encapsulation can significantly improve the stability of chicoric acid under oxidative stress. Moreover, PZ-CA nanocomposite exhibited favorable antioxidant properties, biocompatibility, and the ability to promote cell migration in vitro. The role of PZ-CA nanocomposite in skin regeneration was explored by a mice model. Results in vivo suggest that the PZ-CA nanocomposite promotes wound healing with a faster rate as compared with a commercial spray solution, mostly through attenuating the oxidative stress, promoting cell proliferation and collagen deposition. This work not only provides a delivery vector for bioactive molecules, but also develops a kind of nanocomposite with the property of promoting wound healing.

Investigation of the allergenicity alterations of shrimp tropomyosin as glycated by glucose and maltotriose containing advanced glycation end products

Tropomyosin (TM) is the major allergen in shrimp that is known to be the primary trigger for shrimp-induced food allergy. Our previous reports suggest that glycation could reduce the allergenicity of TM and the reduction of allergenicity is largely dependent on the sources of saccharides. This investigation aimed to investigate the glycation of TM by glucose and maltotriose as well as the effects of glycation on the allergenicity of TM. Compared to TM, the IgG-binding capacity and IgE-binding capacity of tropomyosin glycated by glucose (TM-G) was greatly reduced with a longer glycation time, the release of allergic mediators from RBL-2H3 mast cells was reduced in a time-dependent manner, and weaker allergic reactions were induced in BALB/c mice. Conversely, tropomyosin glycated by maltotriose (TM-MTS) exhibited a stronger allergenicity after 48 hours of glycation due to the generation of neoallergens that were derived from the advanced glycation end products (AGEs). In conclusion, glucose could be used to desensitize the shrimp TM-induced food allergy via glycation, which could significantly reduce the allergenicity and alleviate allergic symptoms. This work could provide a novel approach to reduce the allergenicity of shrimp tropomyosin and prevent the shrimp tropomyosin-induced food allergy.

Modification mechanism of protein in rice adjuncts upon extrusion and its effects on nitrogen conversion during mashing

The traditional production of wort with adjunct-introduced was achieved by double mashing procedure, which hindered the utilization of proteins in adjunct and led to a deficiency of nitrogen in wort. In this study, the modification mechanism of the extrusion pretreatment on the structure characterization of rice flour protein was investigated. The decoction mashing procedure was performed to enhance the nitrogen conversion of the extruded rice adjunct. Decreased solubility along with disrupted secondary and tertiary structures of rice protein were observed after extrusion. As a result, the total nitrogen, free amino nitrogen, and free amino acids content of wort with extruded rice adjunct-introduced were improved by 23.28 %, 34.67 %, and 7.33 %, respectively, which could be verified by the electrophoretic patterns of the wort protein. The application of extrusion as a pretreatment of adjuncts can promote the protein availability of adjuncts in the decoction mashing stage.

Insight into the conformational and allergenicity alterations of shrimp tropomyosin induced by Sargassum fusiforme polyphenol

Tropomyosin (TM) is the main allergen in shrimp food. Algae polyphenol reportedly could affect the structures and allergenicity of shrimp TM. In this study, the alterations of conformational structures and allergenicity of TM induced by Sargassum fusiforme polyphenol (SFP) were investigated. Compared to TM, the conjugation of SFP to TM induced conformational structure instability, the IgG-binding capacity and IgE-binding capacity of TM gradually decreased with more conjugation of SFP to TM, and the conjugation of SFP to TM could significantly reduce degranulation, histamine secretion and release of IL-4 and IL-13 from RBL-2H3 mast cells. Therefore, the conjugation of SFP to TM led to conformational instability, significantly decreased the IgG-binding capacity and IgE-binding capacity, weakened the allergic responses of TM-stimulated mast cell, and performed in vivo anti-allergic properties in BALB/c mouse model. Therefore, SFP could serve as candidate natural anti-allergic substances to reduce shrimp TM-induced food allergy.

Ultrasound improves the thermal stability and binding capacity of ovomucin by promoting the dissociation of insoluble ovomucin aggregates

Ovomucin (OVM) is a natural glycoprotein with various biological activities but poor solubility. This study aimed to enhance the solubility of OVM by using an ultrasonic-assisted method. The effect of ultrasound (US) on the structure, thermal stability and biological functions of OVM aggregates was evaluated. It was found that insoluble OVM aggregates were dissociated and the solubility increased significantly to 90.0 % after US under 400 W for 45 min. US also improved the onset temperature (To) and denaturation temperature (Td) of OVM. More importantly, the cholesterol binding capacity of both OVM and its digestion products were significantly improved after US (p < 0.05). The gastrointestinal digestion products of US-OVM also showed higher α-amylase and α-glucosidase inhibition than native OVM aggregates. US-induced dissociation of OVM aggregates and the conversion of β-sheet and β-turn to random coil, resulting in the exposure of hydrophobic binding sites may be an important reason for the enhanced stability and adsorption capacity. These findings suggested that US was an effective method for preparing soluble OVM and improved its adsorption capacity, which can further facilitate the application of OVM in the food industry.

Inhibition of Iron Release from Donkey Spleen Ferritin through Malt-Derived Protein Z-Ferulic Acid Interactions

Protein-small molecule interactions naturally occur in foodstuffs, which could improve the properties of protein and small molecules. Meanwhile, they might affect the bioavailability and nutritional value of proteins. Ferritin, as an iron-storage protein, has been a focus of research. However, the complexity of foodstuffs enables the interaction between ferritin and food components, especially polyphenols, which can induce iron release from ferritin. Thus, the application of ferritin in food is limited. Inspired by the natural-occurring, strong protein-polyphenol interactions in beer, to inhibit the iron release of ferritin, the malt-derived protein Z (PZ) was chosen to interact with ferulic acid (FA), an abundant reductant in malt, beer, and other foodstuffs. The analysis of the interaction between PZ and FA was carried out using fluorescence spectroscopy, the results of which suggest that one PZ molecule can bind with 22.11 ± 2.13 of FA, and the binding constant is (4.99 ± 2.13) × 10⁵ M^-1. In a molecular dynamics (MD) simulation, FA was found to be embedded in the internal hydrophobic pocket of PZ, where it formed hydrogen bonds with Val-389 and Tyr-234. As expected, compared to iron release induced by FA, the iron release from donkey spleen ferritin (DSF) induced by FA decreased by 86.20% in the presence of PZ. Meanwhile, based on the PZ-FA interaction, adding PZ in beer reduced iron release from DSF by 40.5% when DSF:PZ was 1:40 (molar ratio). This work will provide a novel method of inhibiting iron release from ferritin.

Characterization of Peanut Protein Hydrolysate and Structural Identification of Umami-Enhancing Peptides

Umami peptides are naturally found in various foods and have been proven to be essential components contributing to food taste. Defatted peanut powder hydrolysate produced by a multiprotease (Flavorzyme, Alcalase, and Protamex) was found to elicit an umami taste and umami-enhancing effect. The taste profiles, hydrolysis efficiency, amino acids, molecular weight distribution, Fourier transform infrared spectroscopy (FT-IR), and separation fractions obtained by ultrafiltration were evaluated. The results showed that peanut protein was extensively hydrolyzed to give mainly (up to 96.84%) free amino acids and peptides with low molecular weights (<1000 Da). Furthermore, β-sheets were the major secondary structure. Fractions of 1−3000 Da and <1000 Da prominently contributed to the umami taste and umami enhancement. To obtain umami-enhancing peptides, these two fractions were further purified by gel filtration chromatography, followed by sensory evaluation. These peptides were identified as ADSYRLP, DPLKY, EAFRVL, EFHNR, and SDLYVR by ultra-performance liquid chromatography (UPLC), and had estimated thresholds of 0.107, 0.164, 0.134, 0.148, and 0.132 mmol/L, respectively. According to the results of this work, defatted peanut powder hydrolysate had an umami taste and umami-enhancing effect, and is a potential excellent umami peptide precursor material for the food industry.

Insight into IgG/IgE binding ability, in vitro digestibility and structural changes of shrimp (Litopenaeus vannamei) soluble extracts with thermal processing

The effects of six kinds of thermal processing on soluble protein recovery, potential allergenicity, in vitro digestibility and structural characteristics of shrimp soluble proteins were evaluated. Obtained results confirmed soluble protein recovery and IgG/IgE reactivity of shrimp soluble extracts were markedly suppressed by various thermal treatments with enhanced digestibility depended on the extent and type of heating applied, which correlated well with the structural alterations and modification. The maximum reduction of IgG/IgE-binding capacity and digestive stability were observed in the autoclaved shrimps because of unfolding of protein and hydrophobic residues exposed. Notably, tropomyosin (TM) and sarcoplasmic calcium-binding protein (SCP) were still IgG/IgE-reactive in various heat-processed shrimps, even higher IgG reactivity were found in heat-treated shrimps TM according to TM antiserum western-blotting and indirect ELISA results. Shrimp TM and SCP maintains its IgE/IgG-binding capacity after various cooking methods, thus most probably initiating allergic sensitization to both raw and cooked shrimps.

Effect of processing technologies on the digestibility of egg proteins

Egg and egg products are a rich source of highly bioavailable animal proteins. Several processing technologies can affect the structural and functional properties of these proteins differently and can influence their fate inside the gastrointestinal tract. The present review examines some of the processing technologies for improving egg protein digestibility and discusses how different processing conditions affect the digestibility of egg proteins under gastrointestinal digestion environments. To provide up-to-date information, most of the studies included in this review have been published in the last 5 years on different aspects of egg protein digestibility. Digestibility of egg proteins can be improved by employing some processing technologies that are able to improve the susceptibility of egg proteins to gastrointestinal proteases. Processing technologies, such as pulsed electric field, high-pressure, and ultrasound, can induce conformational and microstructural changes that lead to unfolding of the polypeptides and expose active sites for further interactions. These changes can enhance the accessibility of digestive proteases to cleavage sites. Some of these technologies may inactivate some egg proteins that are enzyme inhibitors, such as trypsin inhibitors. The underlying mechanisms of how different technologies mediate the egg protein digestibility have been discussed in detail. The proteolysis patterns and digestibility of the processed egg proteins are not always predictable and depends on the processing conditions. Empirical input is required to tailor the optimization of processing conditions for favorable effects on protein digestibility.

Degradation of 2,4-dichlorophenol contaminated soil by ultrasound-enhanced laccase

In this paper, ultrasound was used to enhance the degradation effect of laccase for 2,4-dichlorophenol (2,4-DCP) in soil. The degradation effect and mechanism of the ultrasound-enhanced laccase were investigated. From the results, the degradation rate of 2,4-DCP can reach as high as 51.7% under the following conditions: reaction period was 21 h, pH = 5.5, ultrasound power was 240 W, duty cycle was 50%, and moisture content was 50%. Using the ultrasound-enhanced laccase, the degradation rate of 2,4-DCP was significantly higher than that using only laccase or only ultrasound. In addition, when ultrasound was used, the optimum pH for the degradation of 2,4-DCP using laccase was increased, making the degradation technology more practical. The analysis results from high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) revealed the degradation pathway of 2,4-DCP in soil: first, 2,4-DCP gradually became phenol through dechlorination, then the small molecular organic matter was generated from the hydroxyl radical or laccase reaction.

Purification, secondary structure and antioxidant activity of metallothionein zinc-binding proteins from Arca subcrenata

Zinc-binding proteins named MT-M-I and MT-M-II were obtained after purification from metal-exposed hairy clams (Arca subcrenata) using gel permeation and ion-exchange chromatography. MT-M-I and MT-M-II were resolved by ion-exchange chromatography, and they were found to have similar molecular weights. MT-M-I and MT-M-II can bind 6 and 7 equivalents of Zn²⁺ in vitro, and they showed unusual migration behaviors in Tricine sodium dodecyl sulfate polyacrylamide gel electrophoresis (Tricine-SDS-PAGE). Such migration behaviors may be due to themetal thiolate clusters in these proteins. In terms of amino acid composition, the proportion of cysteine in MT-M-I and MT-M-II was approximately 30%, and glycine accounted for approximately 15%, where as aromatic amino acids were absent. Considering the performance in Tricine-SDS-PAGE and the amino acid compositions, MT-M-I and MT-M-II conform to the molecular characteristics of the metallothionein proteins. The structures were explored using circular dichroism (CD) and Fourier-transform infrared spectroscopy (FTIR). Also determined the antioxidant activities in terms of DPPH radical scavenging ability, hydroxyl radical (·OH) scavenging ability, and ferric-reducing/antioxidant power. The antioxidant activities of MT-M-I were found to be stronger than those of MT-M-II.

Effect of different drying methods on the physicochemical properties and phycobiliprotein structure of Porphyra haitanensis

This study explored the effects of four drying methods, namely vacuum freeze-drying (VFD), hot-air drying (HD), microwave drying (MD) and shade drying (SD) on the sensory quality, amino acids composition, phycobiliproteins structure and rehydration rate of Porphyra haitanensis. It showed that VFD dried P. haitanensis had the highest protein (35.44 ± 0.87%), polysaccharide (18.91 ± 0.64%), umami amino acids (484.67 ± 5.03 mg/100 g, dry weight) and essential amino acids (9.89 ± 0.27 g/100 g, dry weight) than another three dried products. Drying affected secondary structure of phycobiliproteins, and the phycobiliproteins from VFD laver contained the most α-helix structure and the least random coil. In addition, VFD processed laver was rich in water-soluble polysaccharides and hydrophilic amino acids, which resulted in its quick rehydration and high-water absorption capacity. The results showed that VFD was suitable for producing high-quality P. haitanensis with excellent flavor and high contents of nutritional compounds.

Effect of Soybean Soluble Polysaccharide on the Formation of Glucono-δ-Lactone-Induced Soybean Protein Isolate Gel

The effect of soybean soluble polysaccharide (SSPS) on the formation of glucono-δ-lactone (GDL)-induced soybean protein isolate (SPI) gel was investigated. Electrophoretic analysis showed the SSPS did not change the electrophoretic behavior of SPI during the formation of SPI gel. However, infrared analysis indicated the β-sheet content increased, and the contents of random coil and α-helix decreased in both cooked SPI and SPI gel. The SSPS and SPI might conjugate via the Maillard reaction according to the results of grafting degree, color change, and infrared analyses. The main interactions during the formation of SPI gel changed from non-covalent to electrostatic interaction after adding SSPS. Sulfhydryl group content also increased in both cooked SPI and SPI gel. The water-holding capacity and gel strength of SPI gel decreased as the SSPS concentration increased. Larger aggregate holes were observed in the microstructure of SPI gel at higher SSPS concentration. Thus, SSPS could covalently conjugate with SPI and influence the formation of hydrogen bonds, disulfide bonds, and electrostatic interaction among SPI molecules to eventually form a loose gel network.

Acidic electrolysed water delays browning by destroying conformation of polyphenoloxidase

BACKGROUND

Browning frequently occurs at fruits, vegetables and aquatic products during storage, and it drastically reduces the consumer's acceptability, with considerable financial loss. The objective of this paper was to investigate the effects of acidic electrolysed water (AEW) technology on polyphenoloxidase (PPO), which is an essential enzyme for browning.

RESULTS

AEW ice exhibited a good ability in delaying browning in shrimp. Kinetic study revealed that AEW exhibited the mixed type inhibition of PPO with a K_i value of 1.96 mmol L^-1 . Moreover, both the circular dichroism spectrum and Fourier transform infrared spectroscopy analyses revealed that the α-helix in PPO decreased whereas random coil increased which indicates that PPO conformation was destroyed.

CONCLUSION

Thus, this paper may provide a deeper understanding of the application of AEW technology for preventing browning in the food industry. © 2017 Society of Chemical Industry.

Comparative analysis of the effect of protein Z4 from barley malt and recombinant Pichia pastoris on beer foam stability: Role of N-glycosylation and glycation

This study aimed to elaborate the effect of N-glycosylation and glycation of protein Z₄ from barley malt and recombinant Pichia pastoris on beer foam stability. The malt protein Z₄ and recombinant protein Z₄ showed similar N-glycosylation patterns while recombinant protein Z₄ was glycosylated at a higher degree. In the simulated mashing and boiling, malt protein Z₄ and deglycosylated malt protein Z₄ preferred to glycate with glucose and maltose while recombinant protein Z₄ and deglycosylated recombinant protein Z₄ showed preference towards fructose. The addition of protein Z₄ and protein Z₄-saccharide complexes in finished beer showed that the addition of glycosylated protein Z₄ only slightly enhanced the beer foam stability while the addition of glycated protein Z₄ and protein Z₄ with both glycation and glycosylation could significantly increase the beer foam stability. Therefore, glycation instead of N-glycosylation of protein Z₄ played important roles in maintaining beer foam stability.