Effects of enzymatic deamidation by protein-glutaminase on structure and functional properties of alpha-zein

Purified protein glutaminase from Chryseobacterium proteolyticum enhances the properties of wheat gluten

Protein glutaminase (PG), originating from Chryseobacterium proteolyticum, can catalyze the deamidation of glutamine residues in plant proteins into glutamic acid, thus enhancing its functional properties. However, the low yield of PG limits its industrial production. In this study, the yield of PG in C. proteolyticum TM1040 increased by 121 %, up to 7.30 U/mL in a 15 L fermenter after medium optimization. Subsequently, purified PG was obtained by cation exchange chromatography (CEX) coupled with hydrophobic interaction chromatography (HIC). The degree of deamidation (DD) of wheat gluten after purified PG deamidation was 87.11 %, which is superior to chemical deamidation in safety and DD. The emulsifying and foaming properties of deamidated wheat gluten were 2.67 and 18.86 times higher, and the water- and oil-holding properties were 4.23 and 18.77 times higher, respectively. The deamidated wheat gluten with enhanced functional properties was used to improve the flavor and texture in baking cakes.

pH-induced interaction mechanism of zearalenone with zein: Binding characteristics, conformational structure and intermolecular forces

Zein-bound zearalenone (ZEN) complexes are naturally existed in maize by their spontaneous interaction, which significantly impacts the risk assessment of ZEN. Additionally, the pH levels in processing could affect the binding or release of zein-bound ZEN. In this study, pH-induced interaction mechanism of ZEN with zein were studied. Results showed that the acid conditions increased the binding constant (Ka) from 3.46 to 10.0 × 104 L/mol, binding energy from -17.38 to -43.49 kJ mol-1. By increasing hydrophobic interaction and hydrogen bond of ZEN with zein, the binding of ZEN with zein was promoted, forming zein-bound ZEN. Whereas, alkaline conditions decreased the Ka to 1.45 × 104 L/mol and binding energy to 148.48 kJ mol-1, weakened ZEN-zein interaction and stretched zein molecules, resulting the release of ZEN from zein. This study could provide important theoretical basis for perfecting risk assessment and controlling zein-bound ZEN during processing.

Effect of protein-glutaminase on the texture, rheology, microstructure and sensory properties of skimmed set-type yoghurt

The effects of enzymatic deamidation by protein-glutaminase (PG) on the texture, rheology, microstructure, and sensory properties of skimmed set-type yoghurt were studied. The proportion of small-particle size milk protein micelles (10-50 nm) increased significantly from 0 to 99.39% after PG deamidation. Cryo-SEM results revealed that PG-treated yoghurt had a denser and less open 3D structure. PG was effective at inhibiting post-acidification during storage at 4 ℃. The water holding capacity of PG-treated yoghurt (0.12 U·mL-1) increased by more than 15%. The fluidity and viscosity of yoghurt were significantly improved with increasing PG dose. Sensory evaluation revealed that PG (0.06 U·mL-1) significantly improved the smoothness and creaminess of skimmed set-type yoghurt, which corresponded to the pastiness in texture. In summary, PG can effectively address the problems of post-acidification, gel fracture, and flavors change in skimmed set-type yoghurt, providing new applications for PG in the food industry.

Protein-glutaminase improves water-/oil-holding capacity and beany off-flavor profiles of plant-based meat analogs

An unresolved challenge for plant-based meat analogs (PBMAs) is their lack of juiciness. Saturated fats significantly contribute to the juiciness of PBMAs, but there are concerns about the undesirable health effects related to saturated fats; thus, demand for their replacement with vegetable unsaturated oils has increased. Although many food additives are used to reduce the leakage of unsaturated oils, this solution cannot meet the clean-label requirements that have been trending in recent years. In this study, we aimed to develop better consumer-acceptable methods using protein-glutaminase (PG) to improve the juiciness of PBMA patties to meet clean-label trends. We found no significant difference between the visual surface of control and PG-treated textured vegetable proteins (TVPs). However, the microstructure of PG-treated TVP had a more rounded shape than that of the control TVP as observed under a scanning electron microscope. After grilling process, the PBMA patties composed of PG-treated TVP showed significantly higher liquid-holding capacities (a juiciness indicator) than the control patties. This suggested that PG treatment could potentially produce PBMA patties with increased juiciness. Interestingly, after the PG-treated TVP underwent the wash process, we found that PG treatment of TVP easily reduced the various beany off-flavor compounds by 58-85%. Moreover, the results of the in vitro protein digestion test showed that the amounts of free amino nitrogen released from PBMA patties composed of PG-treated TVP were 1.5- and 1.7-fold higher than those from control patties in the gastric and intestinal phases, respectively. These findings indicate that PG treatment of TVP could enhance the physical, sensory, and nutritional properties of PBMA patties and meet the clean-label requirements.

Enhancing Solubility and Reducing Thermal Aggregation in Pea Proteins through Protein Glutaminase-Mediated Deamidation

The limited solubility and stability of pea proteins hinder their utilization in liquid formulations. In this study, protein glutaminase (PG) was employed to modify pea protein isolates (PPIs) and obtain deamidated PPI with varying degrees of deamidation (DD, 10-25%). The solubility and thermal stability of these deamidated PPI samples were assessed, and a comprehensive analysis, including SDS-PAGE, zeta potential, FTIR, surface hydrophobicity, and intrinsic fluorescence, was conducted to elucidate the mechanism behind the improvement in their functional properties. The results reveal that PG modification greatly enhances the solubility and heat stability of PPI, with the most notable improvements observed at higher DD (>20%). PG modification increases the net charge of PPI, leading to the unfolding and extension of the protein structures, thus exposing more hydrophobic groups. These structural changes are particularly pronounced when DD exceeds 20%. This increased electrostatic repulsion between carboxyl groups would promote protein unfolding, enhancing interactions with water and hindering the aggregation of unfolded protein in the presence of salts at elevated temperatures (supported by high-performance size exclusion chromatography and transmission electron microscopy). Accordingly, PG-mediated deamidation shows promise in enhancing the functional properties of PPI.

Cricket Protein Isolate Extraction: Effect of Ammonium Sulfate on Physicochemical and Functional Properties of Proteins

Crickets are known to be a promising alternative protein source. However, a negative consumer bias and an off-flavor have become obstacles to the use of these insects in the food industry. In this study, we extracted the protein from commercial cricket powder by employing alkaline extraction-acid precipitation and including ammonium sulfate. The physicochemical and functional properties of the proteins were determined. It was found that, upon including 60% ammonium sulfate, the cricket protein isolate (CPI) had the highest protein content (~94%, w/w). The circular dichroism results indicated that a higher amount of ammonium sulfate drastically changed the secondary structure of the CPI by decreasing its α-helix content and enhancing its surface hydrophobicity. The lowest solubility of CPI was observed at pH 5. The CPI also showed better foaming properties and oil-holding capacity (OHC) compared with the cricket powder. In conclusion, adding ammonium sulfate affected the physicochemical and functional properties of the CPI, allowing it to be used as an alternative protein in protein-enriched foods and beverages.

Enhanced protein glutaminase production from Chryseobacterium proteolyticum combining physico-chemical mutagenesis and resistance screening and its application to soybean protein isolates

BACKGROUND

Protein glutaminase (PG) is a novel protein modification biotechnology that is increasingly being used in the food industry. However, the current level of fermentation of PG-producing strains still does not meet the requirements of industrial production. To obtain the mutant strains with high PG production, the atmospheric and room temperature plasma (ARTP) combined with LiCl chemical mutagen were used in mutagenesis of a PG producing Chryseobacterium proteolyticum 1003.

RESULTS

A mutant strain (WG15) was successfully obtained based on malonic acid resistance screening after compound mutagenesis of the starting strain C. proteolyticum 1003 using ARTP with LiCl, and it was confirmed to be genetically stable in PG synthesis after 15 generations. The protein glutaminase production of WG15 was 2.91 U mL^-1 after optimization of fermentation conditions, which is 48.69% higher than the original strain C. proteolyticum 1003. The PG obtained from fermentation showed good activities in deamidation of soy protein isolate. The solubility and foaming properties of the PG-treated soy protein isolate were significantly increased by 36.50% and 10.03%, respectively, when PG was added at the amount of 100 U mL^-1 . In addition, the emulsifying activity and emulsion stability of the treated soy protein isolate were improved by 12.44% and 10.34%, respectively, on the addition of 10 U mL^-1 PG. The secondary structure of the soy protein isolate changed after PG treatment, with an increased proportion of glutamate.

CONCLUSION

The results of the present study indicate that the PG produced by this mutant strain could improve the functional properties of soybean protein isolate and the C. proteolyticum mutant WG15 has great potential in food industry. © 2023 Society of Chemical Industry.

Effect of Protein-Glutaminase on Calcium Sulphate-Induced Gels of SPI with Different Thermal Treatments

The effects of protein-glutaminase (PG) on calcium sulphate (CaSO₄)-induced gels of soy protein isolate (SPI) with different heat treatment levels were investigated. The time-dependent degree of deamidation showed that the mild denaturation of the protein favored the deamidation. The particle size distribution showed that the heat treatment increased the SPI particle size, and the particle size distribution of the SPI shifted to the right or increased the proportion of the large particle size component as the degree of deamidation increased for each sample. Rheological analysis showed that the deamidation substantially pushed up the gel temperature and decreased the value of G'. The gel strength and water-holding capacity showed that the higher the amount of enzyme added, the more significant the decrease in gel strength, while the gel water-holding capacity increased. In summary, the deamidation of PG and heat treatment can affect the gel properties of SPI synergistically.

L-Glutamine-, peptidyl- and protein-glutaminases: structural features and applications in the food industry

L-Glutaminases are enzymes that catalyze the cleavage of the gamma-amido bond of L-glutamine residues, producing ammonia and L-glutamate. These enzymes have several applications in food and pharmaceutical industries. However, the L-glutaminases that hydrolyze free L-glutamine (L-glutamine glutaminases, EC 3.5.1.2) have different structures and properties with respect to the L-glutaminases that hydrolyze the same amino acid covalently bound in peptides (peptidyl glutaminases, EC 3.5.1.43) and proteins (protein-glutamine glutaminase, EC 3.5.1.44). In the food industry, L-glutamine glutaminases are applied to enhance the flavor of foods, whereas protein glutaminases are useful to improve the functional properties of proteins. This review will focus on structural backgrounds and differences between these enzymes, the methodology available to measure the activity as well as strengths and limitations. Production methods, applications, and challenges in the food industry will be also discussed. This review will provide useful information to search and identify the suitable L-glutaminase that best fits to the intended application.

The characteristics of protein-glutaminase from an isolated Chryseobacterium cucumeris strain and its deamidation application

Protein-glutaminase (PG), a deamidation enzyme commercially derived from Chryseobacterium proteolyticum, is used to improve the solubility and other functional properties of food proteins. In this study, a new PG-producing strain, Chryseobacterium cucumeris ZYF120413-7, was isolated from soil, and it had a high PG yield and a short culture time. It gave the maximum PG activity with 0.557 U/ml on Cbz-Gln-Gly after 12 h of culture, indicating that it was more suitable for PG production. The enzyme activity recovery and purification fold were 32.95% and 161.95-fold, respectively, with a specific activity of 27.37 U/mg. The PG was a pre-pro-protein with a 16 amino acids putative signal peptide, a pro-PG of 118 amino acids, and a mature PG of 185 amino acids. The amino acid sequence identity of PG from strain ZYF120413-7 was 74 and 45%, respectively, to that of PG from C. proteolyticum 9670T and BH-PG. The optimum reaction pH and temperature of PG was 6 and 60°C, respectively. Enzyme activity was inhibited by Cu2+. The optimum PG substrate was Cbz-Gln-Gly, and the Km and Vmax values were 1.68 mM and 1.41 μM mg protein−1 min−1, respectively. Degree of deamidation (DD) of soy protein isolate (SPI) treated by purified PG was 40.75% within the first 2 h and 52.35% after 18 h. These results demonstrated that the PG from C. cucumeris ZYF120413-7 was a promising protein-deamidating enzyme for improving the functionality of food proteins.

Properties of thermoplastic maize starch-zein composite films prepared by extrusion process under alkaline conditions

This work investigates the effect of the addition of NaOH on the compatibility and material properties of thermoplastic starch-zein composite films produced by a twin-screw extruder. Thermoplastic starch-zein composite films were produced by melt extrusion of glycerol-plasticized starch and zein (3:1 ratio) treated with different concentrations of sodium hydroxide (NaOH) (0 M, 0.05 M, 0.1 M, and 0.2 M NaOH). Scanning Electron Microscope and Confocal laser Scanning Microscope revealed that the composite without NaOH formed a phase-separated morphology with large zein aggregates within the starch matrix. However, the increase in NaOH concentration reduced the size of zein aggregates within the starch-zein composite films, with 0.2 M NaOH having the smallest size of zein aggregates. Dynamic mechanical analysis showed a decrease in glass transition temperature (T_g) and storage modulus (E'), suggesting more molecular chain mobility and efficient plasticization of starch and zein. This efficient plasticization was also confirmed by Fourier-Transform Infrared spectroscopy (FTIR). As a result, there was an optimal increase of 28% in elongation at break in the starch-zein composite film with 0.2 M NaOH. In conclusion, compatible thermoplastic starch-zein composite films with improved elongation at break can be produced with a twin-screw extruder by adding 0.2 M NaOH.

Improving functional properties of pea protein through "green" modifications using enzymes and polysaccharides

Pea proteins have gained significant interest in recent years. The objective of this study was to enhance pea protein functional properties through enzymatic and/or conjugation modifications and understand the physicochemical properties of the modified proteins. Molecular changes of the proteins were characterized, and protein functionality, in vitro digestibility, and sensory properties were analyzed. The proteins crosslinked with transglutaminase showed significantly improved water holding capacity (5.2-5.6 g/g protein) compared with the control pea protein isolate (2.8 g/g). The pea proteins conjugated with guar gum showed exceptional emulsifying capacity (EC) and stability (ES) of up to 100% compared with the control protein (EC of 58% and ES of 48%). Some sequentially modified pea proteins, such as transglutaminase crosslinking followed by guar gum conjugation had multiple functional enhancement (water holding, oil holding, emulsifying, and gelation). The functionally enhanced pea proteins had comparable sensory scores as the control protein.

Tailoring protein intrinsic charge by enzymatic deamidation for solubilizing chicken breast myofibrillar protein in water

Inspired by the salt-in effect, the potential use of protein-glutaminase (PG) to increase the intrinsic charges of chicken breast myofibrillar proteins (CMPs) for enhanced water solubility was tested. The degree of deamidation (DD) and solubility of CMPs increased with PG reaction time. Over 60% of CMPs were soluble in water under a DD of 6.5% due to specific conversion of glutamine to glutamic acid. PG deamidation could remarkably increase the net charge of CMPs with a merit in maintaining most of the amino acid and protein subunit compositions. Such a high electrostatic repulsion exerted a transformation of β-sheet into α-helix, unfolded the structure to expose hydrophobic residues, and allowed the dissociation of myofibril and release of subunits (myosin, actin or their oligomers), leading to a stable colloidal state. This work may foster the engineering advances of protein micro-modification in the tailor manufacture of muscle protein-based beverages.

Fabrication of delayed release hard capsule shells from zein/methacrylic acid copolymer blends

Hard capsule shells with an inherent delayed release action are useful for oral administration of active ingredients, which are acid-labile and/or enzymatically degradable in the gastric environment, without the need of film coating. The objective of this study was to fabricate delayed release hard capsule shells by the dip coating method. The film coating formulations comprised blends of zein and methacrylic acid copolymer (Eudragit® L100-55), with and without the addition of the plasticizer, polyethylene glycol 1000. The rheology parameters (loss modulus (G'), storage modulus (G") and loss tangent (tan δ, G"/G')) of the film coating solution were measured to investigate the processability. Central composite design was used to investigate the main, interaction and quadratic effects of the proportion of methacrylic acid copolymer, solid content of the film formers and level of polyethylene glycol 1000 on the capsule wall thickness and mechanical strength. Multiple response optimization was further conducted, and the design space was established. The in vitro drug release in simulated gastric and intestinal fluids of three different formulations in the design space was compared. The results showed that the tan δ value after the gelation point should be < 0.9 in order to form a thin and sturdy capsule shell. The gelation time and viscosity of the coating solution were related to the thickness of the capsule shell. The study showed that drug release from the capsule with a specified thickness and mechanical strength can be modulated by varying the ratio of zein to methacrylic acid copolymer. The delayed drug release profile was achieved through the capsule shell fabricated from zein to methacrylic acid copolymer at the ratios of 75:25 and 83.2:16.8, with 10% polyethylene glycol 1000.

Oat Protein Concentrates with Improved Solubility Produced by an Enzyme-Aided Ultrafiltration Extraction Method

The aim of this study was to develop an extraction method to produce highly functional oat protein concentrates. We investigated the possibility of combining enzyme-aided slightly alkaline (pH 8.0) extraction with ultrafiltration and subsequent diafiltration for concentration of the extracted oat proteins. A further aim was to study how the deamidation of oat proteins with protein-glutaminase (PG) improves the solubility of proteins as a function of the following parameters: pH (6.0–9.0), enzyme dosage (4–20 U/g protein), and incubation time (1–4 h) with response surface methodology (RSM). Furthermore, we investigated selected functional properties, such as heat-induced gelation and solubility, of the oat protein concentrates. The chosen parameters for the enzymatic deamidation pre-treatment process by PG were as follows: pH 8.0, dosage 11.0 U/g protein, and an incubation time of 4 h (1 h at native pH and 3 h at pH 8.0). Two oat protein concentrates were produced, non-deamidated and ultrafiltered, and deamidated and ultrafiltered, with protein concentrations of 45.0 and 52.4%, respectively. The solubility of both oat protein concentrates was significantly improved at neutral and slightly alkaline pH compared to the solubility of proteins extracted from the starting material. Additionally, both oat protein concentrates produced equally strong heat-induced gel-like structures at a protein concentration of 10%.

Biocompatible artificial synapses based on a zein active layer obtained from maize for neuromorphic computing

Artificial synaptic devices based on natural organic materials are becoming the most desirable for extending their fields of applications to include wearable and implantable devices due to their biocompatibility, flexibility, lightweight, and scalability. Herein, we proposed a zein material, extracted from natural maize, as an active layer in an artificial synapse. The synaptic device exhibited notable digital-data storage and analog data processing capabilities. Remarkably, the zein-based synaptic device achieved recognition accuracy of up to 87% and exhibited clear digit-classification results on the learning and inference test. Moreover, the recognition accuracy of the zein-based artificial synapse was maintained within a difference of less than 2%, regardless of mechanically stressed conditions. We believe that this work will be an important asset toward the realization of wearable and implantable devices utilizing artificial synapses.

Protein deamidation to produce processable ingredients and engineered colloids for emerging food applications

With the ever-increasing demands for functional and sustainable foods from the general public, there is currently a paradigm shift in the food industry toward the production of novel protein-based diet. Food scientists are therefore motivated to search for natural protein sources and innovative technologies to modify their chemical structure for desirable functionality and thus utilization. Deamidation is a viable, efficient, and attractive approach for modifying proteins owing to its ease of operating, specificity, and cost-effective processes. Over the past three decades, the knowledge of protein deamidation for food applications has evolved drastically, including the development of novel approaches for deamidation, such as protein-glutaminase and ion exchange resin, and their practices in new protein substrate. Thanks to deamidation, enhanced functionalities of food proteins from cereals, legumes, milk, oil seeds and others, and thereby their processabilities as food ingredients have been achieved. Moreover, deamidated proteins have been used to fabricate engineered food colloids, including self-assembled protein particles, protein-metallic complexes, and protein-carbohydrate complexes, which have demonstrated tailored physicochemical properties to modulate oral perception, improve gastrointestinal digestion and bioavailability, and protect and/or deliver bioactive nutrients. Novel bioactivity, altered digestibility, and varied allergenicity of deamidated proteins are increasingly recognized. Therefore, deamidated proteins with novel techno-functional and biological properties hold both promise and challenges for future food applications, and a comprehensive review on this area is critically needed to update our knowledge and provide a better understanding on the protein deamidation and its emerging applications.

Mass production of active recombinant Chryseobacterium proteolyticum protein glutaminase in Escherichia coli using a sequential dual expression system and one-step purification

Protein glutaminase (PG) is an enzyme that specifically catalyzes the deamidation of glutamine residues on proteins or peptides, remarkably improving the solubility, emulsification and foaming properties of food proteins and, thereby, conferring great potential in food industry applications. PG is primarily produced from wild strains of Chryseobacterium proteolyticum and the low enzyme production yield restricts large-scale industrial applications. In this context, by evaluating different cleavage site insertions between the pro-region and mature domain of PG as well as different linkers flanking the cleavage site, an E. coli expression and purification protocol has been developed to produce active recombinant PG. To simplify the production workflow, we developed a sequential dual expression system. More than 15 mg of pure and active PG was obtained from 1 L of shaking-flask bacteria culture by one-step nickel affinity chromatography purification. The enzymatic characteristics of the recombinant PG protein were similar to those of native PG. For the deamidation effect of recombinant PG, the deamidation degree (DD) of gliadin reached up to 67% and the solubility increased 84-fold. Thus, this study provides a practical approach to mass producing active PG proteins and investigates its potential applications on food proteins.

Optimization of extraction and deamidation of edible protein from evening primrose (Oenothera biennis L.) oil processing by-products and its effect on structural and techno-functional properties

The optimization of ultrasound-assisted alkaline extraction and enzymatic deamidation by protein-glutaminase (PG) on evening primrose seed cake (EPSC) protein and its effect on structure (amino acid composition, secondary structure and electrophoresis pattern) and techno-functional properties (water-holding and oil-binding capacities, solubility, emulsifying and foaming properties) of EPSC protein were evaluated. The optimum conditions of the both processes were measured using response surface methodology (RSM). The maximum yield (26.4%) and protein content (86.1%) were reached at the optimized extraction conditions. Optimal conditions of PG deamidation based on reaching a high degree of deamidation (DD) with a simultaneously low degree of hydrolysis (DH). Under these conditions, DD and DH were 39.40 and 2.11%, respectively. Ultrasound-assisted alkaline extraction and enzymatic deamidation by PG have great potential to produce edible EPSC protein with modified techno-functional characteristics that can be used for several aims in the food and pharmaceutical applications.

Preparation and Evaluation of New Glycopeptides Obtained by Proteolysis from Corn Gluten Meal Followed by Transglutaminase-Induced Glycosylation with Glucosamine

New glycopeptides were generated by proteolysis from corn gluten meal (CGM) followed by transglutaminase (TGase)-induced glycosylation with glucosamine (GlcN). The glycopeptides exhibited desirable antioxidant and intracellular ROS-scavenging properties. The amount of conjugated GlcN quantified by high-performance liquid chromatography (HPLC) was 23.0 g/kg protein. The formed glycopeptides contained both glycosylated and glycation types, as demonstrated by the electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS/MS). The glycopeptides exhibited scavenging capabilities against free radical diphenylpicrylhydrazyl (DPPH) and hydroxyl radicals by reducing their power. The potential protection of glycopeptides against ethanol-induced injury in LO2 cells was assessed In Vitro based on methyl thiazole tetrazolium (MTT) testing and intracellular reactive oxygen species (ROS) scavenging capacity, respectively. Glycopeptide cytoprotection was expressed in a dose-dependent manner, with the glycopeptides exhibiting good solubility ranging from 74.8% to 83.2% throughout a pH range of 2-10. Correspondingly, the glycopeptides showed good emulsifying activity (36.0 m2/g protein), emulsion stability (74.9%), and low surface hydrophobicity (16.3). These results indicate that glycosylation of CGM significantly improved its biological and functional properties. Glycopeptides from CGM could be used as potential antioxidants as well as comprising a functional food ingredient.

Adsorptive removal of cholesterol by biodegradable zein-graft-β-cyclodextrin film

A novel bio-based zein-graft-β-cyclodextrin film was synthesized for cholesterol adsorption at room temperature. Immobilization of β-cyclodextrin (β-CD) to zein was achieved by the Maillard reaction and the zein-graft-β-CD powders showed higher glass transition temperature and higher solubility in water. Zein-graft-β-CD films, prepared by solvent evaporation casting, showed excellent capacity for cholesterol adsorption. The F_1:1 has the best adsorption properties, and the maximum adsorption capacity can reach 5.70 ± 0.56 mg cholesterol/g film. The adsorption cholesterol mechanism of zein-graft-β-CD film was correspond to the pseudo-first order kinetic model. In addition, the zein-graft-β-CD film retained an adsorption capacity of 3.10 ± 0.89 mg cholesterol/g film after three reuses. Using composite enzyme (1 mg/mL papain and 1 mg/mL amylase), the film (F_1:1) degradation reached 98.81% in 1 week. These results suggest that zein-graft-β-CD film has potential as a nature-based adsorbent for cholesterol adsorption and could be used in the food industry.

Enhancing the Usability of Pea Protein Isolate in Food Applications through Modifying Its Structural and Sensory Properties via Deamidation by Glutaminase

This study aimed to demonstrate the feasibility of improving the properties of pea protein isolate (PPI) related to food applications via deamidation with glutaminase. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier transform infrared (FT-IR) profiling revealed that the current glutaminase treatment did not change the basic protein subunit composition. However, it allowed a certain extent of protein unfolding and conformational reorganization to generate more flexible and extended proteins with reduced average particle size and more hydrophobic groups exposed. The underlying mechanisms might include the reduction of β-sheets and antiparallel β-sheets and the increase of the β-turn structure. Moreover, the treatment time was of importance. A 12 h treatment was generally better than a 24 h treatment, and PPI treated with glutaminase at 50 °C for 12 h to a degree of deamidation of 56.1% exhibited significantly improved solubility, homogeneity, dispersibility, and suspendability with reduced beany flavor, grittiness, and lumpiness (compared to those of the untreated PPI). Thus, the glutaminase treatment offers a promising approach for enhancing the usability and applicability of pea proteins.

Complete Genome Sequence and Characterization of a Protein-Glutaminase Producing Strain, Chryseobacterium proteolyticum QSH1265

Recently, an enzyme named protein-glutaminase (PG) has been identified as a new type of enzyme with significant potential for deamidation of food proteins. The enzyme is shown to be expressed as a pre-pro-protein with a putative signal peptide of 21 amino acids, a pro-sequence of 114 amino acids, and a mature PG of 185 amino acids. The microbial enzyme PG specifically catalyzes deamidation of proteins without protein hydrolysis pretreatment and only reacts with glutamine residues in the side-chains of proteins or long peptides. All these attributes suggest that it has a great potential for food industrial applications. However, until recently, there have been relatively few studies of the PG-producing strains. A strain named Chryseobacterium proteolyticum QSH1265 which can produce PG was isolated from a soil sample collected in Songjiang, Shanghai, China. Its enzyme activity was about 0.34 ± 0.01 U/mL when using carboxybenzoxy-Gln-Gly as a substrate. The strain can produce acid from D-glucose, maltose, L-arabinose sucrose, glycerol, and mannitol but not fructose, and it is also positive for indole production and urease. Here we describe the complete genome sequence of this strain via PacBio RSII sequencing. The C. proteolyticum QSH1265 genome consists of a circular chromosome with total length of 4,849,803 bp without any plasmids. All of 4563 genes were predicted including 4459 genes for protein-coding and 104 RNA-relative genes with an average G+C content of 36.16%. The KEGG and COG annotation provide information for the specific function of proteins encoded in the genome, such as proteases, chromoproteins, stress proteins, antiporters, etc. A highly conserved hypothetical protein shares a promoter with the gene encoding the protein-glutaminase enzyme. The genome sequence and preliminary annotation provide valuable genetic information for further study of C. proteolyticum.

The structure and amphipathy characteristics of modified γ-zeins by SDS or alkali in conjunction with heating treatment

γ-Zein was modified by SDS or alkali combined with heating treatments in water and in 70% ethanol to change its amphipathic properties and explore the relationship between amphipathic characteristic and structure. γ-Zein water-dispersibility was dramatically increased via alkali or SDS combined with heating treatments, but their ethanol-dispersibilities were significantly different during ethanol evaporation. High both water-dispersibility and ethanol-dispersibility were found from alkali modified γ-zein while high water-dispersibility but low ethanol-dispersibility were obtained from SDS modified γ-zein, indicating that alkali modified γ-zein had better amphipathic characteristic compared with SDS modified γ-zein. Alkali modified γ-zein with higher amphipathic characteristic possessed higher structural inversion ability since it was easy to recover its native state as solvent changing from water to ethanol, contrary to SDS modified γ-zeins whose amphipathic characteristic was not improved. Moreover, the higher structural inversion ability of alkali modified γ-zein depended on the recovery capability of α-helix structure as solvent altering.

The Interaction between Zein and Lecithin in Ethanol-Water Solution and Characterization of Zein-Lecithin Composite Colloidal Nanoparticles

Lecithin, a naturally small molecular surfactant, which is widely used in the food industry, can delay aging, enhance memory, prevent and treat diabetes. The interaction between zein and soy lecithin with different mass ratios (20:1, 10:1, 5:1, 3:1, 2:1, 1:1 and 1:2) in ethanol-water solution and characterisation of zein and lecithin composite colloidal nanoparticles prepared by antisolvent co-precipitation method were investigated. The mean size of zein-lecithin composite colloidal nanoparticles was firstly increased with the rise of lecithin concentration and then siginificantly decreased. The nanoparticles at the zein to lecithin mass ratio of 5:1 had the largest particle size (263 nm), indicating that zein and lecithin formed composite colloidal nanoparticles, which might aggregate due to the enhanced interaction at a higher proportion of lecithin. Continuing to increase lecithin concentration, the zein-lecithin nanoparticles possibly formed a reverse micelle-like or a vesicle-like structure with zein in the core, which prevented the formation of nanoparticle aggregates and decreased the size of composite nanoparticles. The presence of lecithin significantly reduced the ζ-potential of zein-lecithin composite colloidal nanoparticles. The interaction between zein and lecithin enhanced the intensity of the fluorescence emission of zein in ethanol-water solution. The secondary structure of zein was also changed by the addition of lecithin. Differential scanning calorimetry thermograms revealed that the thermal stability of zein-lecithin nanoparticles was enhanced with the rise of lecithin level. The composite nanoparticles were relatively stable to elevated ionic strengths. Possible interaction mechanism between zein and lecithin was proposed. These findings would help further understand the theory of the interaction between the alcohol soluble protein and the natural small molecular surfactant. The composite colloidal nanoparticles formed in this study can broaden the application of zein and be suitable for incorporating water-insoluble bioactive components in functional food and beverage products.

Controlled Release from Zein Matrices: Interplay of Drug Hydrophobicity and pH

Purpose

In earlier studies, the corn protein zein is found to be suitable as a sustained release agent, yet the range of drugs for which zein has been studied remains small. Here, zein is used as a sole excipient for drugs differing in hydrophobicity and isoelectric point: indomethacin, paracetamol and ranitidine.

Methods

Caplets were prepared by hot-melt extrusion (HME) and injection moulding (IM). Each of the three model drugs were tested on two drug loadings in various dissolution media. The physical state of the drug, microstructure and hydration behaviour were investigated to build up understanding for the release behaviour from a zein based matrix for drug delivery.

Results

Drug crystallinity of the caplets increases with drug hydrophobicity. For ranitidine and indomethacin, swelling rates, swelling capacity and release rates were pH dependent as a consequence of the presence of charged groups on the drug molecules. Both hydration rates and release rates could be approached by existing models.

Conclusion

The drug state and pH dependant electrostatic interactions are hypothesised to influence release kinetics. Both factors can potentially be used to influence release kinetics release, thereby broadening the horizon for zein as a tuneable release agent.

Electronic supplementary material

The online version of this article (doi:10.1007/s11095-015-1818-8) contains supplementary material, which is available to authorized users.