Metal-organic frameworks-based moisture responsive essential oil hydrogel beads for fresh-cut pineapple preservation.

The preservation of fresh-cut fruits and vegetables has attracted attention to the shelf-life reduction caused by high humidity. Herein, alginate/copper ions cross-linking, in-situ growth and self-assembly techniques of metal-organic frameworks (MOFs) were utilized to prepare a moisture responsive hydrogel bead (HKUST-1@ALG). As the multistage porous structure formation, tea tree essential oil (TTO) load capacity in hydrogel bead (TTO-HKUST-1@ALG) was increased from 6.1% to 21.6%. TTO-HKUST-1@ALG had excellent moisture response performance, and the release rates of TTO increased from 33.89% to 70.98% with moisture increasing from 45% to 95%. Besides, TTO-HKUST-1@ALG exhibited excellent antimicrobial, antioxidant capacity, and biocompatibility. During storage, TTO-HKUST-1@ALG effectively improved the cell membrane integrity by maintaining the balance of reactive oxygen species metabolism. The degradation of cell wall structure and tissue softening were delayed by inhibiting the cell wall-degrading enzymes activity. Briefly, TTO-HKUST-1@ALG improved the storage quality and extended shelf-life of fresh-cut pineapple, which was a promising preservative.

Acid-induced pea protein gels pretreated with media milling: Gelling properties and the formation mechanism.

This study explored the effect of stirred media mill (SMM) processing on the acid-induced gelling properties of pea protein. Results showed that SMM treatment enhanced the gel strength from 75.06 g to 183.89 g and increased the water holding capacity from 46.64 % to 73.50 %. The minimum gelation concentration achieved for SMM-treated pea protein was 4 %, significantly lower than that of heat-pretreated pea protein (9 %). SMM decreased protein aggregate size from 104 µm to 180 nm. Microscopy analysis revealed that the small aggregates facilitated the formation of uniform gel networks with tight connections. Linear rheology indicated that small protein aggregates resulted in slower gelation rates with a higher G' for the formed gels. The SMM-pretreated protein gel showed strain hardening, shear thinning behaviors, and satisfactory stability to withstand large-amplitude oscillatory shear. Overall, SMM emerges as a promising technology for producing protein gel products with strong mechanical attributes and customizable rheological properties.

Development, characterization and Lactobacillus plantarum encapsulating ability of novel C-phycocyanin-pectin-polyphenol based hydrogels.

In this study, it was found that the enhancement in the viability of Lactobacillus plantarum under gastrointestinal conditions by encapsulating them within novel C-Phycocyanin-pectin based hydrogels (from 5.7 to 7.1 log/CFU). The hardness, the strength and the stability of the hydrogels increased when the protein concentration was increased. In addition, the addition of resveratrol (RES), and tannic acid (TA) could improve the hardness (from 595.4 to 608.3 and 637.0 g) and WHC (from 93.9 to 94.2 and 94.8 %) of the hydrogels. The addition of gallic acid (GA) enhanced the hardness (675.0 g) of the hydrogels, but the WHC (86.2 %) was decreased. During simulated gastrointestinal conditions and refrigerated storage, the addition of TA enhanced the viable bacteria counts (from 6.8 and 8.0 to 7.5 and 8.5 log/CFU) of Lactobacillus plantarum. Furthermore, TA and GA are completely encased by the protein-pectin gel as an amorphous state, while RA is only partially encased.

Characterization, Stability and Antioxidant Activity of Vanilla Nano-Emulsion and Its Complex Essential Oil.

As a natural flavoring agent, vanilla essential oil has a special aroma and flavor, but its volatility and instability limit its value. Therefore, in this study, vanilla essential oil was compounded with cinnamon essential oil to prepare nano-emulsions (composite nano-emulsions called C/VT and C/VM), and the stability of the composite essential oil emulsions was investigated. Transmission electron microscopy (TEM) images showed that the nano-emulsions were spherical in shape and some flocs were observed in C/VM and C/VT. The results showed that the average droplet sizes of C/VM and C/VT increased only by 14.99% and 15.01% after heating at 100 °C for 20 min, and the average droplet sizes were less than 120 nm after 24 days of storage at 25 °C. Possibly due to the presence of reticulated flocs, which have a hindering effect on the movement of individual droplets, the instability indices of C/VM and C/VT were reduced by 34.9% and 39.08%, respectively, in comparison to the instability indices of C/VM and C/VT. In addition, the results of antioxidant experimental studies showed that the presence of composite essential oil flocs had no significant effect on the antioxidant capacity. These results indicate that the improved stability of the composite essential oil nano-emulsions is conducive to broadening the application of vanilla essential oil emulsions.

Comparison and analysis of mechanism of ß-lactoglobulin self-assembled gel carriers formed by different gelation methods.

Based on the findings of our previous studies, a comprehensive comparative investigation of the quality and formation mechanism of gels obtained from protein self-assemblies induced by different methods is necessary. Self-assembled heat-induced gels had higher gel mechanical strength, and hydrophobic interactions played a greater role. Whether or not heat treatment was used to induce gel formation may play a more important role than the effect of divalent cations on gel formation. Hydrogen bonds played an important role in all gels formed using different gelation methods. Furthermore, Self-assembled cold-induced gels were considered to can load bioactive substances with different hydrophilicity properties due to the high water-holding capacity and the smooth, dense microstructure. Therefore, ß-lactoglobulin fibrous and worm-like self-assembled cold-induced gels as a delivery material for hydrophilic bioactive substances (epigallocatechin gallate, vitamin B2) and amphiphilic bioactive substance (naringenin), with good encapsulation efficiency (91.92 %, 97.08 %, 96.72 %, 96.52 %, 98.94 %, 97.41 %, respectively) and slow-release performance.

Effect of sustained-release tea tree essential oil solid preservative on fresh-cut pineapple storage quality in modified atmospheres packaging.

The quality and safety of fresh-cut pineapple deteriorate during handling and storage due to physicochemical and microbial changes, so its preservation has attracted extensive attention. This study prepared sustained-release tea tree essential oil (TTO) solid preservative (SP) with an encapsulation efficiency of 71.45% and applied it on fresh-cut pineapple in modified atmospheres packaging (MAP). Results showed that TTO adsorbed on nano silicon dioxide (SiO2) was embedded in the starch-carboxymethyl cellulose network structure by extrusion. The hydrogen bond and hydrophobic interaction resulted in compact structure and good sustained-release performance of SP. The SP improved sensory quality and reduced nutrient loss and microbial spoilage of fresh-cut pineapple, which extended its shelf-life to four days. In addition, antioxidant capacity was enhanced with increasing antioxidant enzyme activity, antioxidant content, and 2,2-diphenyl-1-picrylhydrazine scavenging capacity and decreasing MDA accumulation. Therefore, sustained-release TTO solid preservative has potential for the preservation of fresh-cut pineapple.

Improving shikonin solubility and stability by encapsulation in natural surfactant-coated shikonin nanoparticles.

It is significant to develop a colloidal delivery system to improve the water solubility, stability, and bioavailability of shikonin, which is a hydrophobic plant polyphenol with a variety of physiological activities. In this study, three kinds of natural surfactants (saponin, sophorolipid, and rhamnolipid) were used to prepare shikonin nanoparticles by the pH-driven method. The physicochemical and structural properties of the shikonin nanoparticles were characterized, including particle size, zeta potential, and morphology. The encapsulation efficiencies of shikonin nanoparticles coated with saponin and sophorolipid were 97.6% and 97.3%, respectively, which were much higher than that of rhamnolipid-coated shikonin nanoparticles (19.0%). Shikonin nanoparticles coated with saponin and sophorolipid showed good resistance to heat and light and maintained long-term stability during storage. Moreover, shikonin nanoparticles coated with saponin and sophorolipid improved their in vitro-bioavailability. PRACTICAL APPLICATION: These article results are of great importance for improving the stability and bioavailability of shikonin in functional foods, dietary supplements, or pharmaceutical preparations. Moreover, this study provided theoretical and practical guides for further research of shikonin nanoparticles and may promote the development of natural colloidal delivery systems.

Physicochemical, structural, and functional properties of protein fractions and protein isolate from jackfruit seeds.

The physicochemical, structural, and functional properties of albumin, globulin, glutelin, and protein isolate (JSPI) extracted from jackfruit seeds were investigated. Protein fractions and JSPI were rich in amino acids, which can be comparable to soy protein. Other essential amino acids except histidine met the FAO/WHO/UNO-recommended intake for infants and adults. Jackfruit seed proteins were mainly composed of 17-26 kDa polypeptides, ß-sheet, and random coil were the main secondary structures. Glutelin (572.55) and JSPI (246.14) have higher H0 under neutral conditions, consistent with the solubility and emulsification properties results. Albumin and globulin had good solubility and were mostly soluble under neutral or weak alkaline conditions. In general, protein fractions and JSPI exhibited good foaming and emulsification properties. Therefore, jackfruit seed proteins have the potential to be nutritious functional ingredients in the food industry. PRACTICAL APPLICATION: Jackfruit seed proteins had high essential amino acids content and good functional properties. They can be used as a new type of functional ingredients in the food industry, which can not only reduce the environment pollution of discarded seeds but also improve use of plant protein.

A new site-specific monoPEGylated ß-lactoglobulin at the N-terminal: Effect of different molecular weights of mPEG on its conformation and antigenicity.

A new method was investigated to decline the antigenicity of ß-Lactoglobulin (ß-LG) by site specifically conjugating ß-LG at the N-terminus with 5 kDa and 10 kDa monomethoxy polyethylene glycol propyl aldehyde (mPEG-ALD). The optimal reaction conditions were molar ratio of 1:10 (ß-LG:mPEG-ALD), reaction time for 16 h, and pH 5.0, and the content of mono-PEGylated ß-LG was 51.3%. The results showed that mono-PEGylated ß-LG with molecular mass of 23.2 kDa and 28.5 kDa. The peptide fragments of mPEG5kDa-ALD-ß-LG produced the same sequence pattern of ß-LG except for the absence of one peptides f(1-14), indicating that α-amino group at the N-terminal was selectively modified. Furthermore, the conformation of modified ß-LG underwent into slight change. The antigenicity of mPEG5kDa-ALD-ß-LG and mPEG10kDa-ALD-ß-LG decreased from 144.4 µg/mL to 66.7 and 39.0 µg/mL respectively. It was speculated that the steric hindrance effect of PEG was the main reason for the decline of antigenicity of ß-LG.

Site specific PEGylation of ß-lactoglobulin at glutamine residues and its influence on conformation and antigenicity.

ß-lactoglobulin (ß-LG) is one of the main allergens in milk. Polyethylene glycol (PEG) modification (PEGylation) was found to have the ability to reduce the antigenicity of proteins. To determine the effect of site specific PEGylation on ß-LG antigenicity and conformation, we applied 5 kDa methoxy polyethylene glycol-amine (mPEG-NH2) to modify ß-LG at glutamine (Gln) residues under the catalysis of transglutaminase. The antigenicity of ß-LG was measured using rabbit IgG antibodies by indirect competitive ELISA. The result indicated that the antigenicity of ß-LG was decreased from 72.2 µg/mL to 22.7 µg/mL after PEGylation. SDS-PAGE and MALDI-TOF-MS showed that the molecular mass of native ß-LG was about 18.3 kDa while the PEGylated ß-LG had a molecular mass of 23.4 kDa, which meant that mono-PEGylated ß-LG was obtained after PEGylation and purification by cation exchange chromatography. Additionally, the circular dichroism spectrum of the PEGylated ß-LG was approximately superimposed on that of ß-LG and the secondary structure content of ß-LG also had no significant changes after PEGylation, which indicated that the secondary structure of ß-LG was preserved. After PEGylation, the intrinsic fluorescence intensity of ß-LG decreased from 6361 to 5159 while the surface hydrophobicity increased, which indicated that the tertiary structure of ß-LG was slightly changed. PEGylation site analysis result showed that Gln 155 or Gln 159 might be the most possible binding site. In conclusion, the decrease of the antigenicity of ß-LG induced by the PEGylation is mainly due to the steric shielding effect of PEG chain rather than conformational changes of ß-LG.

Antigenicity of ß-lactoglobulin reduced by combining with oleic acid during dynamic high-pressure microfluidization: Multi-spectroscopy and molecule dynamics simulation analysis.

Some food components can modulate the antigenicity of ß-lactoglobulin (ß-LG). This study investigated the role of oleic acid (OA) in reducing the antigenicity of ß-LG. The results indicate the antigenicity of ß-LG gradually decreased from 15 (sample with no OA) to 9.86, 7.51, and 6.01 µg/mL when interacting with OA during dynamic high-pressure microfluidization treatment at 0.1, 80, and 160 MPa. Although binding sites (n) of ß-LG combined with OA at 0.1, 80, and 160 MPa decreased from 0.79 to 0.5 and 0.66, ß-LG had a higher binding affinity (Ka) to OA than that of untreated ß-LG. The values of Ka for ß-LG/OA at 0.1, 80, and 160 MPa were 5.51 × 106, 17.43 × 106, and 49.75 × 106M-1, respectively. The molecule dynamic simulation showed that the OA molecules located at both ß-barrel (site 1) interacted with Lys60, Glu62, and Lys69 and outer surface site 2 consisting of Tyr20, Tyr42, Ser21, Glu157, and His161. Additionally, when binding with OA during the dynamic high-pressure microfluidization treatment, the conformation of ß-LG changed, reflected by the decrease of fluorescence intensity and total sulfhydryl group content, the increase of surface sulfhydryl group content, and secondary structure changes of ß-LG. These results deduce that some epitopes may be masked by OA or modified by the conformational changes, resulting in the decline of antigenicity of ß-LG molecules.

Comparison of antigenicity and conformational changes to ß-lactoglobulin following kestose glycation reaction with and without dynamic high-pressure microfluidization treatment.

Previous work indicated that conformational changes of ß-lactoglobulin (ß-LG) induced by dynamic high pressure microfluidization (DHPM) was related to the increase of antigenicity. In this study, ß-LG glycated with 1-kestose and combined with DHPM decreased the antigenicity of ß-LG. The antigenicity of control, ß-LG-kestose (0.1 MPa) and ß-LG-kestose (80 MPa) were 100, 79 and 42 µg/mL respectively. The molecular weight of ß-LG conjugated to kestose increased from 18.4 to 19.6 kDa and its conformation scarcely changed. Conversely, combined with DHPM treatment (80 MPa), ß-LG conjugated to kestose formed two conjugates with molecular weight of 18.8 and 19.8 kDa, respectively. Furthermore, the unfolding of ß-LG as a result of the treatments is reflected by a decrease of intrinsic and synchronous fluorescence intensity and changes to the secondary structure. The conformational changes induced by DHPM and glycation treatments synergistically decrease the antigenicity of ß-LG due to more masked or disrupted epitopes.

Molecular and Functional Properties of Protein Fractions and Isolate from Cashew Nut (Anacardium occidentale L.).

Some molecular and functional properties of albumin (83.6% protein), globulin (95.5% protein), glutelin (81.3% protein) as well as protein isolate (80.7% protein) from cashew nut were investigated. These proteins were subjected to molecular (circular dichroism, gel electrophoresis, scanning electron microscopy) and functional (solubility, emulsification, foaming, water/oil holding capacity) tests. Cashew nut proteins represent an abundant nutrient with well-balanced amino acid composition and could meet the requirements recommended by FAO/WHO. SDS-PAGE pattern indicated cashew nut proteins were mainly composed of a polypeptide with molecular weight (MW) of 53 kDa, which presented two bands with MW of 32 and 21 kDa under reducing conditions. The far-UV CD spectra indicated that cashew proteins were rich in ß-sheets. The surface hydrophobicity of the protein isolate was higher than that of the protein fractions. In pH 7.0, the solubility of protein fractions was above 70%, which was higher than protein isolate at any pH. Glutelin had the highest water/oil holding capacity and foaming properties. Protein isolate displayed better emulsifying properties than protein fractions. In summary, cashew nut kernel proteins have potential as valuable nutrition sources and could be used effectively in the food industry.

Effectiveness of partially hydrolyzed rice glutelin as a food emulsifier: Comparison to whey protein.

The emulsifying properties of partially hydrolyzed rice glutelin (H-RG, 2% degree of hydrolysis) were compared to those of whey isolate protein (WPI), a commonly used protein-based emulsifier. The surface load of WPI (1% emulsifier, d32=167.5nm) was 2.8 times lower than that of H-RG (3% emulsifier, d32=159.0nm). Emulsions containing WPI-coated lipid droplets had better stability to pH changes (2-8), NaCl addition (0-500mM) and thermal processing (30-90°C, 0 or 200mM NaCl). Nevertheless, H-RG emulsions were stable over a range of conditions: pH 6-8; NaCl≤200 (pH 7); temperatures≤90°C in the absence of salt (pH 7); and temperatures≤50°C in the presence of 200mM NaCl (pH 7). This study indicates that H-RG may be utilized as a natural emulsifier in the development of label-friendly emulsion-based food products, but that further work is needed to increase the range of applications.

Effect of ultrasound combined with malic acid on the activity and conformation of mushroom (Agaricus bisporus) polyphenoloxidase.

Polyphenoloxidase (PPO) plays an important role in the browning of vegetables, fruits and edible fungi. The effects of ultrasound, malic acid, and their combination on the activity and conformation of mushroom (Agaricus bisporus) PPO were studied. The activity of PPO decreased gradually with the increasing of malic acid concentrations (5-60mM). Neither medium concentrations (10, 20, 30mM) malic acid nor individual ultrasound (25kHz, 55.48W/cm(2)) treatment could remarkably inactivate PPO. However, the inactivation during their combination was more significant than the sum of ultrasound inactivation and malic acid inactivation. The inactivation kinetics of PPO followed a first-order kinetics under the combination of ultrasound and malic acid. The conformation of combination treated PPO was changed, which was reflected in the decrease of α-helix, increase of ß-sheet contents and disruption of the tertiary structure. Results of molecular microstructure showed that ultrasound broke large molecular groups of PPO into small ones. Moreover, combined treatment disrupted the microstructure of PPO and molecules were connected together.

Purification and conformational changes of bovine PEGylated ß-lactoglobulin related to antigenicity.

ß-Lactoglobulin (ß-LG) was conjugated with monomethoxy polyethylene glycol-succinimidyl carbonates (mPEG-SC, 20 kDa) to investigate the relationship between the antigenicity and conformational changes of ß-LG. The effect of molar ratio of protein to mPEG-SC (1:3-1:6), pH (6-8) and time (4-24h) on the antigenicity of ß-LG was investigated. The lowest antigenicity of ß-LG was observed at the molar ratio of 1:3, pH 7.0, and reaction time for 8h, which was 70% lower than that of control ß-LG. At the optimal modification conditions, it was indicated that two fractions obtained after purification showed the tense and single band on the SDS-PAGE at the position of approximate 78 kDa and 58 kDa, which corresponded to the tri- and di-PEGylated conjugate, respectively. As conjugated number of mPEG-SC with ß-LG increased, the quenching of fluorescence and the content of ß-strands were increased gradually, which may contribute to the decrease of antigenicity from two aspects.

Different modes of inhibition for organic acids on polyphenoloxidase.

It is still unclear whether the inhibitory effect of organic acid on polyphenoloxidase (PPO) is due to the reversible inhibition or decrease of pH. In this study, cinnamic acid, citric acid and malic acid inhibited PPO in different modes. Results showed that the inhibition by cinnamic acid resulted from reversible inhibition, while the decrease of pH was the main cause for citric acid and malic acid. The kinetic results showed that cinnamic acid reversibly inhibited PPO in a mixed-type manner. Fluorescence emission spectra indicated that cinnamic acid might interact with PPO and quench its intrinsic fluorescence, while the decrease of the fluorescence intensity induced by citric acid or malic acid was due to the acid-pH. Cinnamic acid bound to PPO and induced the rearrangement of secondary structure. Molecular docking result revealed cinnamic acid inserted into the hydrophobic cavity of PPO by forming π-π stacking.

Binding interaction between rice glutelin and amylose: Hydrophobic interaction and conformational changes.

The interaction of rice glutelin (RG) with amylose was characterized by spectroscopic and molecular docking studies. The intrinsic fluorescence of RG increased upon the addition of amylose. The binding sites, binding constant and thermodynamic features indicated that binding process was spontaneous and the main driving force of the interaction was hydrophobic interaction. The surface hydrophobicity of RG decreased with increasing amount of amylose. Furthermore, synchronous fluorescence and circular dichroism (CD) spectra provided data concerning conformational and micro-environmental changes of RG. With the concentration of amylose increasing, the polarity around the tyrosine residues increased while the hydrophobicity decreased. Alteration of protein conformation was observed with increasing of α-helix and reducing of ß-sheet. Finally, a visual representation of two binding sites located in the amorphous area of RG was presented by molecular modeling studies.

Comparative study on the effects of nystose and fructofuranosyl nystose in the glycation reaction on the antigenicity and conformation of ß-lactoglobulin.

Our previous work indicated that the antigenicity of bovine ß-lactoglobulin (ß-LG) decreased after conjugation with fructo-oligosaccharides (FOS) which was related to its conformational changes. In attempt to unravel further changes of ß-LG antigenicity, nystose (GF3) and 1(F)-ß-fructofuranosyl nystose (GF4) of FOS were used to investigate the relationship between conformation and antigenicity. The antigenicity of ß-LG after conjugated with GF3 and GF4 decreased from 143.4 to 29.5 and 31.6 µg/mL, respectively. The results of mass spectrometry revealed that the molecular weight of ß-LG increased from 18.4 to 19.8 and 19.1 kDa after conjugation with GF3 and GF4, respectively. It was shown that the conformational changes of ß-LG after conjugation with GF3 were bigger than that with GF4, including quenching of fluorescence intensity, the red-shift of fluorescence spectra, and the increase in sulfhydryl content. However, there was no significant difference in the antigenicity between ß-LG-GF3 and ß-LG-GF4 conjugates (P>0.05).

Antigenicity and conformational changes of ß-lactoglobulin by dynamic high pressure microfluidization combining with glycation treatment.

The combined effect of previous dynamic high-pressure microfluidization treatment (40, 80, 120, and 160MPa) and subsequent glycation with galacto-oligosaccharides (GOS) on the antigenicity of ß-lactoglobulin (ß-LG) was investigated. The antigenicity of ß-LG-GOS decreased at relatively low pressure (≤120MPa). Surface sulfhydryl group content of ß-LG-GOS increased and surface hydrophobicity of ß-LG-GOS decreased. Additionally, protein unfolding in ß-LG-GOS samples was reflected by quenching of fluorescence intensity, the red-shift of fluorescence spectra, decreased UV absorption, and circular dichroism analysis, indicating tertiary and secondary structural changes of ß-LG. The conformational changes may contribute to the alteration of antigenicity.