•Hybrid liposomes composed of amphiphilic chitosan and phospholipid were prepared.•The hybrid liposomes exhibited excellent ionic and thermal stability.•Curcumin hybrid liposomes showed improved stability and sustained release.•Bioavailability of curcumin was improved when loaded in hybrid liposomes.Hybrid liposomes, composed of amphiphilic chitosan and phospholipid, were prepared and used to evaluate the effect of amphiphilic polymers on the properties of liposomes. Successful preparation of the hybrid liposomes was confirmed using physicochemical characteristics, including morphology, particle size and zeta potential. Physical stability studies (exposure to solutions of increasing ionic strength and heat treatment) indicated that the hybrid liposomes had better ionic stability than amphiphilic chitosan-based polymeric liposomes and higher thermal stability than traditional phospholipid liposomes. Curcumin was then encapsulated in the hybrid liposomes. Compared with phospholipid liposomes, the hybrid liposomes displayed better storage stability and more sustained curcumin release. Cellular uptake experiments showed that the hybrid liposomes significantly increased the bioavailability of curcumin. The study highlights the potential of well-designed stable hybrid liposomes that increase the stability and bioavailability of lipophilic bioactive, such as curcumin.

•Both high temperature-short time and mild temperature-long time can inactivate PPO.•PPO samples with the same activity were obtained by different thermal treatment.•PPO with the same activity might possess different conformations.•Mild temperature deformed PPO, while high temperature induced aggregation of PPO.This study investigated changes in the activity, conformation and microstructure of mushroom polyphenoloxidase (PPO) subjected to thermal treatment. The inactivation of PPO can be achieved by high temperature-short time or mild temperature-long time treatment. Circular dichroism and fluorescence spectra suggested that heating process induced the rearrangement of secondary structure and the disruption of tertiary structure. Red shifts of fluorescence spectra showed positive correlations with the inactivation rate of PPO. There were significant differences in the conformation and molecular microstructure among PPO samples with the same relative activity, which were obtained by treating PPO at 45, 55 and 65 °C for different times. In summary, PPO molecules were deformed at mild temperature, while higher temperature induced the formation of large aggregates. PPO with the same relative activity might exist in different forms.

The poor water solubility and bioavailability of curcumin can be improved by encapsulating it into liposomes. However, the existing encapsulation technologies, such as the thin film method and the ethanol injection method, are complex and require the use of organic solvents. In this study, an organic solvent-free and easily scalable encapsulation technique was studied by utilizing the pH-dependent solubility properties of curcumin. Phospholipid was dissolved in water to form liposomes. Curcumin was deprotonated and dissolved under alkaline conditions and then encapsulated into the liposomes after acidification. Morphological observation and X-ray diffraction analysis confirmed that curcumin liposomes had been successfully prepared. Curcumin liposomes prepared by the pH-driven method were stable during storage. During in vitro digestion, curcumin liposomes prepared by the pH-driven method showed similar bioaccessibility to those prepared by the thin film method and higher bioaccessibility than those prepared by the ethanol injection method. The pH-driven method, which is organic solvent-free and easily scalable for industrial production, is thus a promising method for the preparation of curcumin liposomes.

•Inhibitory effect of C3G on PPO was much stronger than that of GA.•GA reversibly inhibited PPO in mixed-type while C3G was an irreversible inhibitor.•C3G had stronger effects on thermal inactivation and conformation of PPO than GA.•GA bound to PPO by hydrogen bond, π–π stacking and van der Waals forces.•C3G irreversibly interacted with Cys or Met in PPO by covalent bonds.Gentisic acid and cyanidin-3-O-glucoside are important bioactive polyphenols which are widely distributed in many fruits and cereals. In this work, kinetic study, spectral analysis and computational simulation were used to compare the inhibitory effects and inhibition mechanisms of gentisic acid and cyanidin-3-O-glucoside on mushroom polyphenoloxidase (PPO). The inhibitory effect of cyanidin-3-O-glucoside on PPO was much stronger than that of gentisic acid. Gentisic acid inhibited PPO in a reversible mixed-type manner while cyanidin-3-O-glucoside was an irreversible inhibitor. Gentisic acid and cyanidin-3-O-glucoside made the thermal inactivation of PPO easier, and induced apparent conformational changes of PPO. Compared with gentisic acid, cyanidin-3-O-glucoside had stronger effects on the thermal inactivation and conformation of PPO. Molecular docking results revealed gentisic acid bound to the active site of PPO by hydrogen bonding, π–π stacking and van der Waals forces. However, cyanidin-3-O-glucoside might irreversibly interact with the Met or Cys in PPO by covalent bonds.

•Polyphenoloxidase activity was inhibited by apigenin in a mixed-type manner.•The thermosensitivity of polyphenoloxidase decreased after treating with apigenin.•The dimension of apigenin treated polyphenoloxidase molecules became larger.•The conformations of polyphenoloxidase changed after treating with apigenin.•Two docking simulation software verified that apigenin bound to polyphenoloxidase.It has been revealed that some polyphenols can prevent enzymatic browning caused by polyphenoloxidase (PPO). Apigenin, widely distributed in many fruits and vegetables, is an important bioactive flavonoid compound. In this study, apigenin exhibited a strong inhibitory activity against PPO, and some reagents had synergistic effect with apigenin on inhibiting PPO. Apigenin inhibited PPO activity reversibly in a mixed-type manner. The fact that inactivation rate constant (k) of PPO increased while activation energy (Ea) and thermodynamic parameters (ΔG, ΔH and ΔS) decreased indicated that the thermosensitivity and stability of PPO decreased. The conformational changes of PPO were revealed by fluorescence emission spectra and circular dichroism. Atomic force microscopy observation suggested that the dimension of PPO molecules was larger after interacting with apigenin. Moreover, computational docking simulation indicated that apigenin bound to PPO and inserted into the hydrophobic cavity of PPO to interact with some amino acid residues.

•Inhibition of PPO induced by citric or malic acid was due to the decrease of pH.•Cinnamic acid reversibly inhibited PPO in a mixed-type manner.•Citric acid, malic acid and cinnamic acid quenched fluorescence in different modes.•Cinnamic acid bound to PPO and induced the rearrangement of secondary structure.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.

•β-Lactoglobulin was conjugated with polyethylene glycol.•Two fractions obtained after purification were tri- and di-PEGylated conjugates.•Conformation changes of two conjugates may be related to its antigenicity.β-Lactoglobulin (β-LG) was conjugated with monomethoxy polyethylene glycol-succinimidyl carbonates (mPEG-SC, 20 kDa) to investigate the relationship between the antigenicity and conformational changes of β-LG. The effect of molar ratio of protein to mPEG-SC (1:3–1:6), pH (6–8) and time (4–24 h) on the antigenicity of β-LG was investigated. The lowest antigenicity of β-LG was observed at the molar ratio of 1:3, pH 7.0, and reaction time for 8 h, which was 70% lower than that of control β-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 β-LG increased, the quenching of fluorescence and the content of β-strands were increased gradually, which may contribute to the decrease of antigenicity from two aspects.

•Increase of polymer layers lead to monotonic changes in size, charge and morphology.•pH induced more alteration of double-layered liposomes in appearance and size.•High concentration of ion modified the structure but not the core of microencapsules.•Polymers decoration efficiently prevent VC release from liposomes during digestion.In this study, liposomes (LPs), chitosan (CH) coated LPs, sodium alginate (AL) and CH multilayered LPs (AL-CH-LPs) were developed based on the electrostatic interaction between charged polysaccharides at a certain pH. The increase of polymer layers on LPs led to a monotonic increase in size from ∼600 (LPs) to ∼1810 nm (AL-CH-LPs) and negative charge from −12.5 to −25.2 mV, regarded as a consequence of the formation of gradually expanded structures by cationic CH and anionic AL. The environmental stress including pH, storage and ionic strength (10–200 mM NaCl) had significant impact on the appearance and the particle size of the double-layered liposome (AL-CH-LPs). Furthermore, LPs showed the highest release rate of hydrophilic model ingredient (vitamin C) under gastrointestinal conditions, while the polymers had a capacity to reduce the vitamin C release in simulated intestinal fluid. This work provided useful information on the potential application of CH and AL based delivery systems.

•Aleurone layer (AL) slightly affected rice cooking quality.•AL remarkably affected texture and peak viscosity of rice.•Histological characters of AL during cooking were clearly showed in situ.•Channels formed in AL during cooking which facilitated the cooking of rice.•AL affected rice texture by forming a reinforced coated film on rice surface.Understanding how aleurone layer (AL) affects rice cooking behaviour is important for rice processing. Individual effects of AL on rice cooking behaviour were evaluated and histological characters of AL before and after cooking were investigated. AL slightly affected rice cooking quality (optimum cooking time, water absorption, volume expansion ratio and total solids loss) while remarkably affected rice texture (hardness and adhesiveness) and peak viscosity. Histological investigation showed that channels were formed in AL during cooking. The channels facilitated the penetration of water, which could explain why AL exhibited slight effects on rice cooking quality. In addition, thick cell walls and thermally stable aleurone grains were widely distributed in AL. Leached components accumulated on them and formed a reinforced coated film on rice surface during cooking, which may be a possible mechanism accounting for the remarkable effect of AL on rice texture. Histological characters of AL are closely related with rice cooking behaviour.

The potential for excipient emulsions to enhance the bioaccessibility and antioxidant activity of quercetin was determined in this study. Oil-in-water excipient emulsions containing two levels (4 or 10%) of small lipid droplets (d < 250 nm) were prepared from a long-chain triglyceride (corn oil). The solubilization of quercetin by the excipient emulsions was faster than by bulk corn oil or bulk water, and the solubilization rate was higher at 100 °C than at 30 °C. The bioaccessibility of quercetin samples was determined using an in vitro gastrointestinal model, and the bioactivity of quercetin was determined using a rat feeding study. The excipient emulsions were more effective at enhancing quercetin bioaccessibility and rat plasma antioxidant activity than either bulk oil or bulk water. This effect was attributed to the rapid digestion of the long chain triglycerides when they were in an emulsified form, which led to the rapid production of mixed micelles capable of solubilizing, protecting, and transporting quercetin.

The influence of oil type on the ability of excipient emulsions to improve the solubility, stability, and bioaccessibility of curcumin was examined. Oil-in-water emulsions were prepared using coconut, sunflower, corn, flaxseed, or fish oils. These excipient emulsions were then mixed with powdered curcumin and incubated at 30 or 100 °C. For all oils, more curcumin was transferred from powder to excipient emulsion at 100 °C (190–200 μg/mL) than at 30 °C (30–36 μg/mL), which was attributed to increased curcumin solubility with temperature. Oil type influenced the stability and bioaccessibility of curcumin when excipient emulsions were exposed to simulated gastrointestinal tract conditions, which was attributed to differences in the molecular composition and physicochemical properties of the oils. Overall, the use of fish oil led to the highest effective curcumin bioavailability (38 %). This study provides valuable information for optimizing excipient emulsions to increase curcumin bioavailability in food, supplement, or pharmaceutical applications.

Powdered curcumin was either dissolved in the lipid phase of a nanoemulsion delivery system or it was directly mixed with an excipient nanoemulsion. The influence of thermal treatment (30 or 90 °C) and protein addition (caseinate) on the bioaccessibility and transformation of curcumin was then investigated using a simulated gastrointestinal tract (GIT) model: mouth; stomach; small intestine. Curcumin solubility was high in nanoemulsion delivery systems exposed to both thermal treatments because it was already present in the lipid phase. Conversely, curcumin solubility of a powder mixed with an excipient nanoemulsion was appreciably lower when exposed to 30 °C than 90 °C. This effect was attributed to the greater transfer of curcumin to the lipid phase of the excipient nanoemulsions at elevated temperatures. For the heated samples, the bioaccessibility and transformation of curcumin was not greatly affected by original curcumin location or protein addition. However, curcumin bioaccessibility was appreciably higher in the presence of nanoemulsion lipid droplets than in their absence, which was attributed to an increase in the solubilization capacity of the mixed micelle phase. This study provides some useful information for improving the design of functional foods to improve the oral bioavailability profile of lipophilic nutraceuticals.

•Excipient emulsions were designed to increase curcumin bioavailability.•Curcumin transfer into emulsions increased with incubation temperature.•Curcumin bioaccessibility increased with decreasing lipid droplet size.•Excipient emulsions may improve oral bioavailability of nutraceuticals.The influence of lipid droplet size of excipient emulsions on the solubility and bioaccessibility of powdered curcumin was investigated. Corn oil-in-water emulsions with different initial mean droplet diameters were prepared: large (d32 ≈ 14 µm); medium (d32 ≈ 0.52 µm); small (d32 ≈ 0.18 µm). These excipient emulsions were mixed with powdered curcumin and the resulting mixtures were incubated at either 30 °C (to simulate a salad dressing) or 100 °C (to simulate a cooking sauce). The amount of curcumin transferred into the excipient emulsions after incubation was higher at 100 °C than at 30 °C, and increased with decreasing droplet size at the higher temperature. The curcumin concentration in the mixed micelle phase and total digesta depended on the droplet size of the original excipient emulsions: large > medium ≈ small. However, the bioaccessibility of curcumin did not depend strongly on size. These effects were attributed to the competing effects of the oil droplets on solubilization and chemical degradation of curcumin under simulated gastrointestinal conditions. This study shows the potential of designing excipient emulsions to increase the oral bioavailability of lipophilic nutraceuticals, which may be useful for incorporating curcumin into functional foods.

Excipient foods have compositions and structures specifically designed to improve the bioaccessibility of bioactive agents present in other foods coingested with them. In this study, an excipient emulsion was shown to improve the solubility and bioaccessibility of curcumin from powdered rhizome turmeric (Curcuma longa). Corn oil-in-water emulsions were mixed with curcumin powder, and the resulting mixtures were incubated at either 30 °C (to simulate a salad dressing) or 100 °C (to simulate a cooking sauce). There was an appreciable transfer of curcumin into the excipient emulsions at both incubation temperatures, but this effect was much more pronounced at 100 °C. The bioaccessibility of curcumin measured using a simulated gastrointestinal tract model was greatly improved in the presence of the excipient emulsion, particularly in the system held at 100 °C. This effect was attributed to the higher initial amount of curcumin solubilized within the oil droplets, as well as that solubilized in the mixed micelles formed by lipid digestion. This study highlights the potential of designing excipient food emulsions that increase the oral bioavailability of lipophilic nutraceuticals, such as curcumin.

•The retrogradation percentage of rice starch was low during storage after IECT.•The retrogradation rate of rice starch was low and Avrami exponent was high by IECT.•The pattern of rice starch changed from A-type to amorphous and B-type, respectively.•The results of XRD and FTIR confirmed retrogradation behaviour of rice starch by IECT.Native rice starch (NRS, amylose/28.9%) was gelatinized by improved extrusion cooking technology (IECT) and retrograded (RRS) after low temperature storage (4 °C). The retrogradation behaviour of RRS was changed to low retrogradation percentage and low retrogradation rate. The retrogradation resulted in a high compact morphology. The melt enthalpy change and percentage of retrogradation of RRS was 3.68 J/g and 37.7%, respectively, compared to those of NRS (9.75 J/g, 100%). The retrogradation percentage for RRS was low during storage as shown as a low retrogradation rate (0.21 d−1) and a high Avrami exponent (0.89). The pattern of rice starch changed from A-type to amorphous and B-type. Both the relative crystallinity of RRS (12.7%) by the X-ray diffractograms and the ratio of the band height (0.63) in the FTIR spectra were low. The analysis of retrogradation structure and short-range molecular order further confirmed the retrogradation behaviour of rice starch after IECT treatment.

•High speed shearing (HSS) may not eliminate aggregates of pectin very efficiently.•Disaggregation and degradation of pectin occurred during the whole HSS treatment.•A method was proposed to measure Mw of the pectin containing many large aggregates.•High speed shearing has no effect on the primary structure of pectin.The effect of high speed shearing (HSS) on disaggregation and degradation of pectin from creeping fig seeds was investigated. It was found that disaggregation and degradation occurred during the whole shearing process. When pectin solution was sheared at 24,000 rpm for less than 8 h, degradation happened but disaggregation was dominant during this period. After 8 h, degradation became obvious, however, a small amount of aggregates remained even after 24 h treatment, indicating that HSS may not eliminate aggregates efficiently. The presence of aggregates is one of the most probable causes for the inaccurate determination of molecular weight of pectin. A new method was proposed for calculating more accurately the molecular weight based on the change of the reducing sugar content and the variation of molecular weight. Determination of unsaturated uronide and FT-IR spectra analysis indicated that neither β-elimination nor demethoxylation occurred during the HSS, and no new functional group was formed during the HSS process.

Highlights•mPEG-SC modified unfolded trypsin showed higher thermal stability and lower autolysis than unmodified samples.•Modified unfolded trypsin had higher catalytic efficiency and affinity to substrate than unmodified samples.•The conformational change was reflected in UV, fluorescence and CD spectroscopy.•Thermal stability enhancement might be relevant to conformational change.The effect of succinimidyl carbonates activated methoxypolyethylene glycol (mPEG-SC) on the catalytic properties and conformation of native trypsin and dynamic high-pressure microfluidisation (DHPM) induced unfolded trypsin was studied. The thermal stability of unfolded trypsin was enhanced more significantly than that of native trypsin between 45 and 70 °C. The autolysis analysis indicated that modified unfolded trypsin was markedly more resistant to autolysis compared to modified native trypsin between 40 and 180 min. Upon mPEG-SC conjugation, the Km value of the enzyme decreased by about 2-fold, and the catalytic efficiency (Kcat/Km) increased by about 3–4-fold. Moreover, the increased thermal stability of unfolded trypsin might be due to the lower surface hydrophobicity and the higher hydrogen bond formation after mPEG-SC modification, which was reflected in the decrease of UV absorbance, the quenching and blue shift of fluorescence spectra, as well as the increase of β-sheet content.

Tea polyphenols are major polyphenolic substances found in green tea with various biological activities. To overcome their instability toward oxygen and alkaline environments, tea polyphenol nanoliposome (TPN) was prepared by combining an ethanol injection method with dynamic high-pressure microfluidization. Good physicochemical characterizations (entrapment efficiency = 78.5%, particle size = 66.8 nm, polydispersity index = 0.213, and zeta potential = −6.16 mv) of TPN were observed. Compared with tea polyphenol solution, TPN showed equivalent antioxidant activities, indicated by equal DPPH free radical scavenging and slightly lower ferric reducing activities and lower inhibitions against Staphylococcus aureus, Escerhichia coli, Salmonella typhimurium, and Listeria monocytogenes. In addition, a relatively good sustained release property was observed in TPN, with only 29.8% tea polyphenols released from nanoliposome after 24 h of incubation. Moreover, TPN improved the stability of tea polyphenol in alkaline solution. This study expects to provide theories and practice guides for further applications of TPN.

•High methoxyl and low methoxyl pectin coated vitamin C liposomes were prepared.•Pectin coated liposomes were mainly mediated by the hydrogen bonding interactions.•Storage stability of vitamin C liposomes was obviously enhanced by pectin coating.•Pectin coated liposomes could significantly improve skin permeation of vitamin C.•Low methoxyl pectin coated liposomes could be a promising transdermal drug carrier.A transdermal drug delivery system was prepared by high methoxyl pectin (HMP) or low methoxyl pectin (LMP) coated vitamin C liposomes. HMP coated vitamin C liposomes (HMP-L) and LMP coated vitamin C liposomes (LMP-L) exhibited an increase in average diameter (from 66.9 nm to 117.3 nm and 129.6 nm, respectively), a decrease in zeta potential (from −2.3 mV to −23.9 mV and −35.5 mV, respectively), and a similar entrapment efficiency (48.3–50.1%). Morphology and FTIR analysis confirmed that pectin was successfully coated on the surface of vitamin C liposomes mainly through the hydrogen bonding interactions. Besides, HMP-L and LMP-L exhibited an obvious improvement in storage stability, with lower aggregation, oxidation of lipid and leakage ratio of vitamin C from liposomes, and LMP-L showed better physicochemical stability than HMP-L. Moreover, skin permeation of vitamin C was improved 1.7-fold for HMP-L and 2.1-fold for LMP-L after 24 h, respectively, compared with vitamin C nanoliposomes. Therefore, this study suggested that pectin coated liposomes, especially the LMP-L, could be a promising transdermal drug delivery system with better storage stability and skin permeation.

Few reports have focused on the effect of citric acid on thermodynamics and conformation of polyphenoloxidase (PPO). In this study, variations on activity, thermodynamics and conformation of mushroom PPO induced by citric acid (1–60 mM) and relationships among these were investigated. It showed that with the increasing concentration of citric acid, the activity of PPO decreased gradually to an inactivity condition; inactivation rate constant (k) of PPO increased and the activation energy (Ea) as well as thermodynamic parameters (ΔG, ΔH, ΔS) decreased, which indicated that the thermosensitivity, stability and number of non-covalent bonds of PPO decreased. The conformation was gradually unfolded, which was reflected in the decrease of α-helix contents, increase of β-sheet and exposure of aromatic amino acid residuals. Moreover, two linear relationships of relative activities, enthalpies (ΔH) against α-helix contents were obtained. It indicated that changes of activity and thermodynamics might correlate to the unfolding of conformation.Highlights► PPO activity was not affected by low citric acid but inhibited by high citric acid. ► Decreases in activation energy indicated its thermosensitivity decrease. ► Low thermodynamic parameters indicated its low stability and non-covalent bond. ► The conformations of PPO were gradually unfolded with a decrease of α-helix. ► Both activity and enthalpy against α-helix content gave linear relationships.

To improve lipid membrane stability and prevent leakage of encapsulated food ingredients, a polyelectrolyte delivery system (PDS) based on sodium alginate (AL) and chitosan (CH) coated on the surface of nanoliposomes (NLs) has been prepared and optimized using a layer-by-layer self-assembly deposition technique. Morphology and FTIR observation confirmed PDS has been successfully coated by polymers. Physical stability studies (pH and heat treatment) indicated that the outer-layer polymers could protect the core (NLs) from damage, and PDS showed more intact structure than NLs. Further enzymic digestion stability studies (particle size, surface charge, free fatty acid, and model functional component release) demonstrated that PDS could better resist lipolytic degradation and facilitate a lower level of encapsulated component release in simulated gastrointestinal conditions. This work suggested that deposition of polyelectrolyte on the surface of NLs can stabilize liposomal structure, and PDS could be developed as a formulation for delivering functional food ingredients in the gastrointestinal tract.

•Milling and irradiation both reduced the activities of lipase and lipoxidase in rice.•Irradiation suppressed the generation of free fatty acids in rice during storage.•Irradiation decreased the enthalpy of gelatinization of brown and milled rice.•Microstructure of rice showed stress cracks and some explosion after irradiation.Effects of microwave irradiation on composition, structure, thermal and storage properties of rice with different milling degrees were investigated. Microwave irradiation partially inactivated the lipase and lipoxidase, damaged thiamine, and created puffed rice. In addition, the transition temperatures (To and TP) of rice were shifted to higher temperatures, and the enthalpy of gelatinization decreased after irradiation. The effect was more obvious when the power of microwave was increased. Microstructure analysis showed that stress cracks and some “explosion” were created in rice kernels after microwave irradiation. Storage property analysis indicated that free fatty acid content of all rice samples increased gradually in the process of storage. Microwave irradiation reduced the release of free fatty acids during storage. The higher the power, the lesser the free fatty acids generated. The results suggested that microwave irradiation was potentially applicable for improving storage properties of brown and milled rice.

•Superheated steam (SS) was effective for inactivation of rice peroxidase.•SS treatment could maintain the natural physicochemical properties of lightly milled rice (LMR).•SS treatment caused almost no fissures to LMR.•Texture of LMR may be related to fissures and micro-mechanical behavior.Superheated steam (SS) was used to inactivate peroxidase of lightly milled rice (LMR) in this study in order to extend shelf-life of LMR. Meanwhile, the effects of SS on physicochemical properties of LMR were evaluated. Compared with hot air (HA), SS could inactivate peroxidase of LMR within a shorter time and result in lesser reduction of moisture content. SS caused much less fissures and alteration of micro-mechanical behavior (intercellular and intracellular cleavage) to LMR than HA did. SS-stabilized LMR, of which peroxidase was inactivated by SS, maintained their natural physicochemical properties including appearance (whiteness of uncooked rice and morphology of cooked rice), cooking quality (water absorption, volume expansion ratio and total solids loss), and texture profile (hardness, adhesiveness chewiness and cohesiveness). Physicochemical properties of LMR were closely connected with fissures. The morphology and texture of cooked LMR might be partly explained by the micro-mechanical behavior of uncooked LMR. SS would be a promising technology for inactivating peroxidase and retaining natural physicochemical properties of LMR simultaneously.

•Combination of ultrasound and malic acid effectively inactivated PPO.•The inactivation kinetics of combination treated PPO followed a first-order kinetics.•Conformation of PPO was unfolded with change of secondary and tertiary structure.•Combined treatment disrupted structure of PPO and molecules were connected together.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 (5–60 mM). Neither medium concentrations (10, 20, 30 mM) malic acid nor individual ultrasound (25 kHz, 55.48 W/cm2) 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 β-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.

The combined effect of previous dynamic high-pressure microfluidization treatment (40, 80, 120, and 160 MPa) and subsequent glycation with galacto-oligosaccharides (GOS) on the antigenicity of β-lactoglobulin (β-LG) was investigated. The antigenicity of β-LG-GOS decreased at relatively low pressure (≤120 MPa). Surface sulfhydryl group content of β-LG-GOS increased and surface hydrophobicity of β-LG-GOS decreased. Additionally, protein unfolding in β-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 β-LG. The conformational changes may contribute to the alteration of antigenicity.