Plant protein-based fibers: Fabrication, characterization, and potential food applications.

Proteins from plants have been considered as safer, healthier, and more sustainable resources than their animal counterparts. However, incomplete amino acid composition and relatively poor functionality limit their applications in foods. Structuring plant proteins to fibrous architectures enhances their physicochemical properties, which can favor various food applications. This review primarily focuses on fabrication of fibers from plant proteins via self-assembly, electrospinning, solution blow spinning, wet spinning, and high-temperature shear, as well as on several applications where such fibrous proteins assemble in quality foods. The changes of protein structure and protein-protein interactions during fiber production are discussed in detail, along with the effects of fabrication conditions and protein sources on the morphology and function of the fibers. Self-assembly requires proteolysis and subsequent peptide aggregation under specific conditions, which can be influenced by pH, salt and protein type. The spinning strategy is more scalable and produces uniformed fibers with larger length scales suitable for encapsulation, food packaging and sensor substrates. Significant progress has been made on high-temperature shear (including extrusion)-induced fibers responsible for desirable texture in meat analogues. Structuring plant proteins adds values for broadened food applications, but it remains challenging to keep processes cost-effective and environmentally friendly using food grade solvents.

Rebuilding the lid region from conformational and dynamic features to engineering applications of lipase in foods: Current status and future prospects.

The applications of lipases in esterification, amidation, and transesterification have broadened their potential in the production of fine compounds with high cumulative values. Mostly, the catalytic triad of lipases is covered by either one or two mobile peptides called the "lid" that control the substrate channel to the catalytic center. The lid holds unique conformational allostery via interfacial activation to regulate the dynamics and catalytic functions of lipases, thereby highlighting its importance in redesigning these enzymes for industrial applications. The structural characteristic of lipase, the dynamics of lids, and the roles of lid in lipase catalysis were summarized, providing opportunities for rebuilding lid region by biotechniques (e.g., metagenomic technology and protein engineering) and enzyme immobilization. The review focused on the advantages and disadvantages of strategies rebuilding the lid region. The main shortcomings of biotechnologies on lid rebuilding were discussed such as negative effects on lipase (e.g., a decrease of activity). Additionally, the main shortcomings (e.g., enzyme desorption at high temperatre) in immobilization on hydrophobic supports via interfacial action were presented. Solutions to the mentioned problems were proposed by combinations of computational design with biotechnologies, and improvements of lipase immobilization (e.g., immobilization protocols and support design). Finally, the review provides future perspectives about designing hyperfunctional lipases as biocatalysts in the food industry based on lid conformation and dynamics.

Polyphenols Weaken Pea Protein Gel by Formation of Large Aggregates with Diminished Noncovalent Interactions.

Polyphenols are well-known native cross-linkers and gel strengthening agents for many animal proteins. However, their role in modifying plant protein gels remains unclear. In this study, multiple techniques were applied to unravel the influence of green tea polyphenols (GTP) on pea protein gels and the underlying mechanisms. We found that the elasticity and viscosity of pea protein gels decreased with increased GTP. The protein backbone became less rigid when GTP was present based on shortened T1ρH in relaxation solid-state NMR measurements. Electron microscopy and small-angle X-ray scattering showed that gels weakened by GTP possessed disrupted networks with the presence of large protein aggregates. Solvent extraction and molecular dynamic simulation revealed a reduction in hydrophobic interactions and hydrogen bonds among proteins in gels containing GTP. The current findings may be applicable to other plant proteins for greater control of gel structures in the presence of polyphenols, expanding their utilization in food and biomedical applications.

Atomistic Modeling of Peptide Aggregation and ß-Sheet Structuring in Corn Zein for Viscoelasticity.

The structure-function relationships of plant-based proteins that give rise to desirable texture attributes in order to mimic meat products are generally unknown. In particular, it is not clear how to engineer viscoelasticity to impart cohesiveness and proper mouthfeel; however, it is known that intermolecular ß-sheet structures have the potential to enhance the viscoelastic property. Here, we investigated the propensity of selected peptide segments within common corn α-zein variants to maintain stable aggregates and ß-sheet structures. Simulations on dimer systems showed that stability was influenced by the initial orientation and the presence of contiguous small hydrophobic residues. Simulations using eight-peptide ß-sheet oligomers revealed that peptide sequences without proline had higher levels of ß-sheet structuring. Additionally, we identified that sequences with a dimer hydrogen-bonding density of >22% tended to have a larger percent ß-sheet conformation. These results contribute to understanding how the viscoelasticity of zein can be increased for use in plant-based meat analogues.

Electrospinning Induced Orientation of Protein Fibrils.

Amyloid-like fibrils are prepared from protein in the lab by controlled heat treatments, yet these must be further assembled to match the desirable mechanical and structural properties of biological fibers. Here, ß-lactoglobulin fibrils were incorporated into poly(ethylene oxide) fibers of 40-180 nm diameter by electrospinning. Protein fibrils presented as short segments dispersed within electrospun fibers, with no change in fibril diameter after electrospinning. Imaging analysis revealed fibrils were aligned within 20° relative to the fiber long axis, and alignment was further confirmed by polarized FTIR and anisotropic SAXS/WAXS scattering patterns. The elastic modulus of fibers increased with protein fibril content from 0.8 to 2 GPa, which is superior to reported values of silk, collagen, and gelatin. The present setup allows for manufacture of large quantities of polymeric fibers containing protein fibrils with varied diameter and mechanical strength, endowing great potential for a variety of applications.

Microwave pasteurization of apple juice: Modeling the inactivation of Escherichia coli O157:H7 and Salmonella Typhimurium at 80-90 °C.

Although due to their acidity some fruit juices are considered safe, several outbreaks have been reported. For processing fruit juices, microwave heating offers advantages such as shorter come-up time, faster and uniform heating, and energy efficiency. Thus, it could be a beneficial alternative to conventional pasteurization. The objective of this study was to study the inactivation kinetics of Escherichia coli O157:H7 and Salmonella Typhimurium under microwave pasteurization at temperatures between 80 and 90 °C, i.e., at conditions that are employed in conventional pasteurization. Inoculated juices were treated at different power levels (600 W, 720 W) and treatment times (5s, 10s, 15s, 20s, 25s). Time-temperature profiles were obtained by fiber-optic sensors in contact with the samples allowing continuous data collection. The log-logistic and Arrhenius equations were used to account for the influence of the temperature history; thus, resulting in two different modeling approaches that were compared in terms of their prediction abilities. Survival kinetics including non-isothermal conditions were described by a non-linear ordinary differential equation that was numerically solved by the Runge-Kutta method (ode45 in MATLAB ®). The lsqcurvefit function (MATLAB®) was employed to estimate the corresponding survival parameters, which were obtained from freshly made apple juice, whereas the prediction ability of these parameters was evaluated on commercial apple juices. Results indicated that inactivation increased with power level, temperature, and treatment time reaching a microbial reduction up to 7 Log10 cycles. The study is relevant to the food industry because it provides a quantitative tool to predict survival characteristics of pathogens at other non-isothermal processing conditions.

Mutations in sorghum SBEIIb and SSIIa affect alkali spreading value, starch composition, thermal properties and flour viscosity.

KEY MESSAGE: Seven novel alleles of SBEIIb and one allele of SSIIa co-segregated with the ASV phenotype and contributed to distinct starch quality traits important for food-processing applications. Sorghum is an important food crop for millions of people in Africa and Asia. Whole-genome re-sequencing of sorghum EMS mutants exhibiting an alkali spreading value (ASV) phenotype revealed candidate SNPs in Sobic.004G163700 and Sobic.010G093400. Comparative genomics identified Sobic.010G093400 as a starch synthase IIa and Sobic.004G163700 as a starch branching enzyme IIb. Segregation analyses showed that mutations in Sobic.010G093400 or Sobic.004G163700 co-segregated with the ASV phenotype. Mutants in SSIIa exhibited no change in amylose content but expressed lower final viscosity and lower starch gelatinization temperature (GT) than starches from non-mutant plants. The sbeIIb mutants exhibited significantly higher amylose levels and starch GT and lower viscosity compared to non-mutant starches and ssIIa mutants. Mutations in SBEIIb had a dosage-dependent effect on amylose content. Double mutants of sbeIIb and ssIIa resembled their sbeIIb parent in amylose content, starch thermal properties and viscosity profiles. These variants will provide opportunities to produce sorghum varieties with modified starch end-use qualities important for the beer brewing and baking industries and specialty foods for humans with diabetes.

In Vitro Fecal Fermentation of High Pressure-Treated Fruit Peels Used as Dietary Fiber Sources.

Fruit by-products are being investigated as non-conventional alternative sources of dietary fiber (DF). High hydrostatic pressure (HHP) treatments have been used to modify DF content as well as its technological and physiological functionality. Orange, mango and prickly pear peels untreated (OU, MU and PPU) and HHP-treated at 600 MPa (OP/55 °C and 20 min, MP/22 °C and 10 min, PPP/55 °C and 10 min) were evaluated. Untreated and treated fruit peels were subjected to fecal in vitro fermentations. The neutral sugar composition and linkage glycosidic positions were related to the production of short chain fatty acids (SCFA) resulting from the fermentation of the materials. After HHP-treatments, changes from multibranched sugars to linear sugars were observed. After 24 h of fermentation, OP yielded the highest amount of SCFA followed by PPU and MP (389.4, 282.0 and 204.6 µmol/10 mg DF, respectively). HHP treatment increased the SCFA concentration of orange and mango peel by 7 and 10.3% respectively, compared with the untreated samples after 24 h of fermentation. The results presented herein suggest that fruit peels could be used as good fermentable fiber sources, because they yielded high amounts of SCFA during in vitro fermentations.

Molecular Dynamics Simulation for Mechanism Elucidation of Food Processing and Safety: State of the Art.

Molecular dynamics (MD) simulation is a useful technique to study the interaction between molecules and how they are affected by various processes and processing conditions. This review summarizes the application of MD simulations in food processing and safety, with an emphasis on the effects that emerging nonthermal technologies (for example, high hydrostatic pressure, pulsed electric field) have on the molecular and structural characteristics of foods and biomaterials. The advances and potential projection of MD simulations in the science and engineering aspects of food materials are discussed and focused on research work conducted to study the effects of emerging technologies on food components. It is expected by showing key case studies that it will stir novel developments as a valuable tool to study the effects of emerging food technologies on biomaterials. This review is useful to food researchers and the food industry, as well as researchers and practitioners working on flavor and nutraceutical encapsulations, dietary carbohydrate product developments, modified starches, protein engineering, and other novel food applications.

Electrostatic stabilization of ß-lactoglobulin fibrils at increased pH with cationic polymers.

In order to improve the stability of ß-lactoglobulin fibrils formed in acidic conditions to increased pH values (pH 3-7), formation of electrostatic complexes between fibrils and cationic polymers chitosan (CH), amine-terminated poly(ethylene glycol) (APEG), low molecular weight poly(ethylenimine) (LPEI), and high molecular weight poly(ethylenimine) (HPEI) was investigated by electrophoretic mobility, turbidimetry, and atomic force microscopy. Except for suspensions with APEG, addition of polycations increased ζ-potential values of the fibrils at pH 5, 6, and 7, verifying their interactions with fibrils. Maximal increase in ζ-potential at pH 7, indicating optimal electrostatic interactivity, occurred at concentrations (w/w) of 0.05, 0.01, and 0.01% (corresponding to 6.9, 50, and 4 µmol·kg(-1)) for CH, LPEI, and HPEI, respectively. Turbidity of fibril solutions at pH 5, indicating isoelectric instability, was decreased significantly with increasing concentration of CH, LPEI, and BPEI, but not with added APEG. Turbidity was increased at pH 7 with added polycation, except for suspensions containing ≥0.02% HPEI. Fibril length and resistance to aggregation, as observed by atomic force microscopy, were increased at pH 5 with increasing concentration of CH and LPEI, yet only HPEI was capable of maintaining the morphology of fibrils at pH 7. Calculated persistence lengths of the fibrils, as compared to pure fibrils at pH 3 (∼4 µm), were only slightly reduced at pH 5 with CH and at pH 7 with HPEI, but increased at pH 5 with LPEI and HPEI. Improvement in the stability of ß-lactoglobulin fibrils at higher pH conditions with the addition of polycations will contribute to their potential utilization in packaging, food, and pharmaceutical applications.

Effect of limited proteolysis and CaCl2 on the rheology, microstructure and in vitro digestibility of pea protein-carboxymethyl cellulose mixed gel.

Limited proteolysis, CaCl2 and carboxymethyl cellulose (CMC) have individually demonstrated ability to increase the gel strength of laboratory-extracted plant proteins. However, the syneresis effects of their combination on the gelling capacity of commercial plant protein remains unclear. This was investigated by measuring the rheological property, microstructure and protein-protein interactions of gels formed from Alcalase hydrolyzed or intact pea proteins in the presence of 0.1 % CMC and 0-25 mM CaCl2. Sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) showed the molecular weight of pea protein in the mixture were < 15 kDa after hydrolysis. The hydrolysates showed higher intrinsic fluorescence intensity and lower surface hydrophobicity than the intact proteins. Rheology showed that the storage modulus (G') of hydrolyzed pea protein (PPH)-based gels sightly decreased compared to those of native proteins. 5-15 mM CaCl2 increased the G' for both PP and PPH-based gels and decreased the strain in the creep-recovery test. Scanning electron microscopy (SEM) showed the presence of smaller protein aggregates in the PPH-based gels compared to PP gels and the gel network became denser, and more compact and heterogenous in the presence of 15 and 25 mM CaCl2. The gel dissociation assay revealed that hydrophobic interactions and hydrogen bonds were the dominant forces to maintain the gel structure. In vitro digestion showed that the soluble protein content in PPH-based gels was 10 âˆ¼ 30 % higher compared to those of the PP counterpart. CaCl2 addition reduced protein digestibility with a concentration dependent behavior. The results obtained show contrasting effects of limited proteolysis and CaCl2 on the gelling capacity and digestibility of commercial pea proteins. These findings offer practical guidelines for developing pea protein-based food products with a balanced texture and protein nutrition through formulation and enzymatic pre-treatment.

Effect of extrusion process conditions on extrudates enriched with carotenoids encapsulated by different methods using gum arabic and vegetable fat as carriers.

Bioactive compounds into extruded foods enhance their nutritional value but they are heat and shear labile and prone to oxidation. This study was aimed to examine the impacts of distinct encapsulation methods on the stability of carotenoids under typical extrusion conditions. The study presents innovative encapsulation methods and investigates the protection efficacy of carotenoids degradation, as well as the effects on the physicochemical characteristics of carotenoid-rich products. Thus, spray drying, spray chilling, and their combination were compared based on their ability to protect carotenoids. Processing temperatures were 110 °C and 140 °C, and shear rates 500 and 2000 1/s. Carotenoid retention was determined, ß- and α-carotene retention ranged from 17 to 44 % and 18 to 48 %, respectively. Upon storage at room temperature, the carotenoid content was stable for 15 days, followed by a marked reduction after 30 days. Extrudates enriched microparticles produced by spray chilling and the combined methods exhibited higher carotenoid protection during storage. They also showed better quality attributes, notably bulk density, high water absorption index, color properties, and carotenoid retention. These findings suggest that encapsulation can protect carotenoids during extrusion, and the protection can be tailored to optimize the attributes of the final products.

Enzymatic hydrolysis of soy and chickpea protein with Alcalase and Flavourzyme and formation of hydrogen bond mediated insoluble aggregates.

Food applications involving plant proteins require modification of their functionality to mimic the unique properties of animal proteins. Enzymatic hydrolysis is commonly used to alter the functionality of plant proteins, particularly to improve their solubility near the isoelectric point. Current methodological approaches mostly indicate improved solubility upon hydrolysis. However, published methods include the removal of insoluble material before analysis, and calculations are based on only the solubilized material as a percentage of the filtered protein. This approach artificially increases solubility estimation and gives an incorrect assessment of the efficacy of hydrolysis. By using the total amount of protein, this study aims to determine the effect of two microbial proteases, Flavourzyme and Alcalase, on the solubility and structural and thermal properties of soy and chickpea proteins. Protein isolates were first extracted from soy and chickpea flour and hydrolyzed from 0 to 3 h. Then, their degree of hydrolysis and solubility at a range of pHs were determined using the o-phthaldialdehyde (OPA) and Lowry methods, respectively. Proteins' electrophoretic mobility, protein-protein interactions, thermal properties, and protein secondary structures were also determined. Solubility decreased over time though the solubility of the hydrolysate improved near the isoelectric point. Soy Flavourzyme hydrolysates remained the most soluble and chickpea Flavourzyme hydrolysates showed the least solubility. Thermal data suggested that Alcalase reduced the protein denaturation temperature, leading to a loss of solubility upon thermal enzyme inactivation. The loss of solubility of hydrolysates was strongly associated with hydrogen bonding, which may result from the formation of polar peptide termini. These results challenge commonly accepted beliefs that hydrolysis inevitably improves solubility of plant proteins. Instead, it is shown that hydrolysis causes structural changes that result in aggregation, thus potentially limiting the application of enzymatic hydrolysis without the addition of further processing methods.

A Plant-Based Animal Fat Analog Produced by an Emulsion Gel of Alginate and Pea Protein.

As the market for plant-based meat analogs grows, the development of plant-based animal fat analogs has become increasingly important. In this study, we propose an approach by developing a gelled emulsion based on sodium alginate, soybean oil (SO), and pea protein isolate. Formulations containing 15% to 70% (w/w) SO were successfully produced without phase inversion. The addition of more SO resulted in pre-gelled emulsions with a more elastic behavior. After the emulsion was gelled in the presence of calcium, the color of the gelled emulsion changed to light yellow, and the formulation containing 70% SO exhibited a color most similar to actual beef fat trimming. The lightness and yellowness values were greatly influenced by the concentrations of both SO and pea protein. Microscopic images revealed that pea protein formed an interfacial film around the oil droplets, and the oil was more tightly packed at higher oil concentrations. Differential scanning calorimetry showed that lipid crystallization of the gelled SO was influenced by the confinement of the alginate gelation, but the melting behavior was like that of free SO. FTIR spectrum analysis indicated a potential interaction between alginate and pea protein, but the functional groups of SO were unchanged. Under mild heating conditions, gelled SO exhibited an oil loss similar to that observed in actual beef trims. The developed product has the potential to mimic the appearance and slow-rendering melting attribute of real animal fat.

Editorial on the Special Issue "Novel Gels for Food Product Development".

Recently gels have gained significant attention in the food industry due to their unique properties and potential applications [...].

Fabrication of phytoglycogen-derived core-shell nanoparticles: Structure and characterizations.

The objective of this work was to investigate the fabrication of core-shell nanoparticles using phosphorylase-catalyzed chain extension of phytoglycogen, and to analyze the changes of structure and characterizations in detail. During the glucosylation reaction, the inorganic phosphate increased substantially up to 2.3 mg/mL in the initial 12 h, and then increased incrementally to 2.5 mg/mL at 24 h. The similar to trends was observed for increasing Mw and Rz over time, due to glucosyl transfers on the surface chain to form a corona around the phytoglycogen core with a larger size. Phosphorylase modification increases the percentages of longer chain fractions and the average chain length increased from degree of polymerization (DP) 11.6 to DP 48.2. The modified phytoglycogen exhibited the characteristic of B-type crystalline structure, indicating that the specific core-shell nanoparticle with inner amorphous nature and outer crystalline layer. The above results revealed that the potentiality of enzymatic chain elongation of phytoglycogen to design novel core-shell nanoparticle with tailor-made structure and functionality.

Biomimetic synthesis of maltodextrin-derived dendritic nanoparticle and its structural characterizations.

The maltodextrin-derived dendritic nanoparticle was fabricated using microbial branching enzyme and its structural characterizations were investigated. During biomimetic synthesis, molecular weight distribution of maltodextrin substrate with 6.8 × 104 g/mol shifted to the narrower and uniform distribution region with the larger molecular weight up to 6.3 × 106 g/mol (MD12). The enzyme-catalyzed product had the larger size, higher molecular density as well as higher percentage of α-1,6 linkage, accompanying by more chain accumulations of DP 6-12 and disappearance of DP > 24, suggesting the biosynthesized glucan dendrimer had a compact tighter branched structure. The interaction of molecular rotor CCVJ and local structure of dendrimer was monitored, displaying there was a higher intensity related with the numerous nano-pockets at the branch points of MD12. The maltodextrin-derived dendrimers had the single spherical particulate shape with the size range of 10-90 nm. The mathematical models were also established to reveal the chain structuring during enzymatic reaction. The above results showed that the biomimetic strategy for novel dendritic nanoparticle with controllable structure arising from branching enzyme treated maltodextrin, which would help to enlarge the panel of available dendrimer.

Impact of ultra-shear technology on quality attributes of model dairy-pea protein dispersions with different fat levels.

This study investigated the impact of ultra-shear technology (UST) processing on dairy-pea protein dispersions with different fat levels. Raw milk, skim milk, and cream, as well as model dispersions with combinations of dairy products and pea protein (i.e., raw milk with pea protein, skim milk with pea protein, and cream with pea protein) were employed as test samples. UST experiments were conducted at a pressure of 400 MPa and 70 °C shear valve exit temperature. The UST treatment increased the viscosity of the dispersions and the increases depended on the fat level. Dairy-pea protein dispersions from raw milk and skim milk were shear thinning and mathematically described by the power-law model defined by the consistency coefficient, K (Pa·sn) and the flow behavior index, n. UST treated cream + pea protein dispersions produced structures with gel-like characteristics. Microstructure and particle size analysis determined by laser scanning microscope revealed a reduction in particle size after UST treatment in raw milk + pea protein and skim milk + pea protein dispersions up to 7.55 and 8.30 µm, respectively. In contrast, the particle mean diameter of cream + pea protein dispersions increased up to 77.20 µm after the UST treatment. Thus, the effect of UST on the particle size and rheological behavior of the dispersions depended on the fat level. UST-treated dispersions were stable with no visible phase separation or sedimentation upon centrifugation at 4000×g for 30 min (4 °C). Heat treatment and freeze-thaw treatment of UST-treated samples showed stable blends immediately after the treatments, but subsequent centrifugation showed solid separation. Results from the study suggest that UST is a potential technology to produce stable dairy + pea protein liquids foods with different rheological characteristics for diverse applications.

Microencapsulation of Carotenoid-Rich Extract from Guaraná Peels and Study of Microparticle Functionality through Incorporation into an Oatmeal Paste.

The peels of guaraná (Paullinia cupana) fruit contain abundant carotenoid content, which has demonstrated health benefits. However, these compounds are unstable in certain conditions, and their application into food products can be changed considering the processing parameters. This study aimed to encapsulate the carotenoid-rich extract from guaraná peels by spray drying (SD), characterize the microparticles, investigate their influence on the pasting properties of oatmeal paste, and evaluate the effects of temperature and shear on carotenoid stability during the preparation of this product. A rheometer with a pasting cell was used to simulate the extrusion conditions. Temperatures of 70, 80, and 90 °C and shear rates of 50 and 100 1/s were the parameters evaluated. Microparticles with a total carotenoid content between 40 and 96 µg/g were obtained. Over the storage period, carotenoid stability, particle size, color, moisture, and water activity varied according to the core:carrier material proportion used. Afterward, the formulation SD1:2 was selected to be incorporated in oatmeal, and the paste viscosity was influenced by the addition of this powder. ß-carotene retention was higher than that of lutein following the treatment. The less severe treatment involving a temperature of 70 °C and a shear rate of 50 1/s exhibited better retention of total carotenoids, regardless of whether the carotenoid-rich extract was encapsulated or non-encapsulated. In the other treatments, the thermomechanical stress significantly influenced the stability of the total carotenoid. These results suggest that the addition of encapsulated carotenoids to foods prepared at higher temperatures has the potential for the development of functional and stable products.

Pectin as a natural agent for reinforcement of pea protein gel.

Pectin has been used as a gel strengthening agent, but its role in pea protein gels remains unclear. The present study investigated the effects of low-methyl pectin on the physicochemical and rheological properties of pea protein gels at neutral pH and elucidated underlying gelling mechanisms. Pectin increased the stability and viscosity of pea protein dispersions and induced the formation of large protein aggregates. After heating, the storage modulus of pea protein gel containing 0.5 % pectin increased by nearly six times compared to those without pectin, and the gel microstructures became more heterogeneous and compact. Molecular docking revealed that pectin interacted with proteins via mainly electrostatic and hydrogen-bonding interactions. Solvent extraction found that pectin increased the hydrogen bonding, hydrophobic interactions, and disulfide bonds of the gel systems, thus boosting their strength. The current work provided a practical simple approach to increasing the strength of pea protein gels at a neutral pH.