ROS production in homogenate from the body wall of sea cucumber Stichopus japonicus under UVA irradiation: ESR spin-trapping study

Encapsulated fucoxanthin improves the functional properties and storage stability of Undaria Pinnatifida and apple freeze-dried snack food during accelerated storage

Carotenoids, recognized for their antioxidant and anti-aging properties, are commonly used in functional foods. To enhance the application of fucoxanthin (FX) in the food industry, this study employed the ion gel method for encapsulating FX and combined it with raw materials such as Undaria pinnatifida homogenate and apple pieces to create freeze-dried crunchy chunks. The study evaluated the effects of encapsulated-FX on the functional and structural characteristics of the Undaria pinnatifida and apple freeze-dried chunks over accelerated storage period under high temperature and humidity. Various analyses were conducted, including physicochemical properties, texture analysis, color evaluation, sensory assessment, and simulated digestion analysis. The results demonstrated that the FX-rich freeze-dried crunchy chunks exhibited favorable structural properties and appealing flavor. Notably, after the accelerated storage period, the encapsulated-FX maintained significant antioxidant activity, along with excellent thermal and light stability, indicating high storage stability. Additionally, the main ingredients, sodium alginate (SAA) and pectin (PE), significantly enhanced the stability of FX during in vitro digestion. This study provided a straightforward approach for producing freeze-dried snack foods rich in stabled-FX, contributing to the diversity of value-added algae products. Furthermore, it laid a theoretical foundation and reference for the future development of nutritional products.

Effect of flaxseed oil cyclolinopeptides on lipid oxidation, protein oxidation, and lipid profile during in vitro digestion of high-fat beef

This study investigated the influence of flaxseed oil cyclolinopeptides (CLs) on lipid and protein oxidation during high-fat meat digestion. Fourteen CLs were identified in flaxseed oil through UHPLC-ESI-QTOF-MS/MS, with dominant CLA, CLB, CLE, and CLM. During in vitro digestion, CLs inhibited lipid oxidation products (lipid hydroperoxide, Malondialdehyde, and 4-hydroxynonenal) and protein carbonylation. Compared to other groups, the lipid (16.28 ± 0.35) and protein (17.5 ± 0.6) oxidation was significantly inhibited, and antioxidant activity was remarkably increased when the CLs content reached 200 mg/kg. Through untargeted lipidomic analysis using Q-Exactive, it was observed that CLs mitigated the formation of oxidized triglycerides (OxTG) products and enhanced the hydrolysis of lipids to generate sphingolipid and polyunsaturated fatty-acids enriched glycerophospholipids imparting nutritional value to meat. Electron spin-resonance and fluorescence quenching showed that primary radicals such as alkyl and alkoxy radicals during high-fat meat digestion with flaxseed oil CLs significantly mitigate their formation. These findings collectively indicate that consuming CLs enriched flaxseed oil could reduce lipid oxidation and enhance the nutritional value of high-fat meat during digestion.

The Effects of Cooking Methods on Gel Properties, Lipid Quality, and Flavor of Surimi Gels Fortified with Antarctic Krill (Euphausia superba) Oil as High Internal Phase Emulsions

In this study, silver carp surimi products enriched with Antarctic krill oil high internal phase emulsions (AKO-HIPEs) were cooked using steaming (STE), microwave heating (MIC), and air-frying (AIR), respectively. The gel and flavor properties, lipid quality and stability were investigated. Compared to the MIC and AIR groups, the STE surimi gel added with HIPEs had better texture properties, exhibiting higher water-holding capacity and a more homogeneous structure, while the air-frying treatment resulted in visually brighter surimi products. The degree of lipid oxidation during cooking was in an order of STE < MIC < AIR as determined by electron paramagnetic resonance spectrometer and thiobarbituric acid reactive substances. HIPE-added surimi gels retained more nutrients and flavor when cooked by AIR compared to STE and MIC. Results imply that the texture properties and lipid stability of surimi products fortified with AKO-HIPEs were better than those of the oil group under any cooking method. In conclusion, surimi products added with AKO-HIPEs had better gel properties and retained more fatty acids and flavor than AKO-SO.

A novel fucoxanthin enriched seaweed gummy: Physicochemical qualities and protective effect on UVB-induced retinal müller cells

Retinal disease has become the major cause of visual impairment and vision loss worldwide. Carotenoids, which have the potential antioxidant and eye-care activities, have been widely used in functional foods. Our previous study showed that fucoxanthin could exert photoprotective activity in UVB-induced retinal müller cells (RMCs). To extend the application of fucoxanthin in food industry, fucoxanthin, Undaria pinnatifida pulp (UPP), carrageenan, and other ingredients were mixed to prepare seaweed-flavoured photoprotective gummies in this study. The structural and functional properties of the gummies were then evaluated by physicochemical test and cell experiments. As a result, fucoxanthin enriched gummies presented favourable structural properties and flavour. The hydroxyl groups in fucoxanthin and κ-carrageenan are bonded through hydrogen bonds, forming the spatial network structure inside the gummies, enhancing its elasticity. The gummies showed significant antioxidant effect and alleviated the UVB oxidation damage in RMCs. Moreover, the main ingredients carrageenan and UPP improved the stability of fucoxanthin during in vitro digestion. The results enhance the application of fucoxanthin in functional food with photoprotective activity.

Whey protein and flaxseed gum co-encapsulated fucoxanthin promoted tumor cells apoptosis based on MAPK-PI3K/Akt regulation on Huh-7 cell xenografted nude mice

Fucoxanthin (FX), a non-provitamin-A carotenoid, is a well-known major xanthophyll contained in edible brown algae. The nanoencapsulation of FX was motivated due to its multiple activities. Here, nano-encapsulated-FX (nano-FX) was prepared according to our early method by using whey protein and flaxseed gum as the biomacromolecule carrier material, then in vivo antitumor effect and mechanism of nano-FX on xenograft mice were investigated. Thirty 4-week-old male BALB/c nude mice were fed adaptively for 7 days to establish xenograft tumor model with Huh-7 cells. The tumor-bearing mice consumed nano-FX (50, 25, and 12.5 mg kg-1) and doxorubicin hydrochloride (DOX, 1 mg kg-1) or did not consume (Control) for 21 days, n = 6. The tumor inhibition rates of nano-FX were as high as 54.67 ± 1.04 %. Nano-FX intervention promoted apoptosis and induced hyperchromatic pyknosis and focal necrosis in tumor tissue by down-regulating the expression of p-JNK, p-ERK, PI3Kp85α, p-AKT, p-p38MAPK, Bcl-2, CyclinD1 and Ki-67, while up-regulating the expression of cleaved caspase-3 and Bax. Nano-FX inhibited tumor growth and protected liver function of tumor bearing mice in a dose-dependent manner, up-regulate the level of apoptosis-related proteins, inhibit the MAPK-PI3K/Akt pathways, and promote tumor cell apoptosis.

Phycocyanin-phlorotannin complexes improve the structure and functional properties of yogurt

Adding natural bioactive ingredients to yogurt can improve the nutritional and physiological benefits. In this study, we used ultrasonic-assisted phlorotannin from Ascophyllum nodosum (A. nodosum) modified phycocyanin (PC) to form a complex (UPP) to produce a fortified fermented yogurt. The effects of PC and UPP on the structure, stability, and function of fermented yogurt within 7 days were assessed using physicochemical properties, texture analysis, rheological testing, 16S rDNA sequencing analysis, and lipidomics analysis. Molecular docking indicated that PC might bind to phlorotannin via ARG-77, ARG-84, LEU-120, ALA-81, CYS-82, and ASP-85 sites.When the mass ratio of the complex is 1:1, the ability of UPP1:1 to remove DPPH· scavenging ability in an acid environment increased by about 50 %. UPP1:1 with more acid stability changed the microstructure of the yogurt, enhanced the stability of the yogurt, improved the antioxidant properties, and inhibited the growth of harmful bacteria within 7 days. This work encouraged the extraction and use of phlorotannin from edible brown algae and offered a straightforward method for making yogurt supplemented with PC.

Formation of chlorophyll-anionic polysaccharide complex coacervates to improve chlorophyll color stability: Thermodynamic and kinetic stability studies

Chlorophyll (Chl) is the predominant pigment in green plants that can act as a food color and possesses various functional activities. However, its instability and rapid degradation on heating compromise the sensory qualities of its products. This study aimed to enhance the heat resistance of Chl by forming complex coacervates with two negatively charged polysaccharides, sodium alginate (SA) and K-carrageenan (KC). Dynamic light scattering and scanning electron microscopy analyses confirmed the formation of coacervates between Chl and the polysaccharides, whereas Fourier-transform infrared spectroscopy revealed that hydrogen bonding and electrostatic attraction were the primary forces behind complex formation. Electron spin resonance and thermodynamic studies further revealed that these complexes bolstered the thermal stability of Chl, with a maximum improvement of 70.38 % in t1/2 and a reduction of 50.72 % in the degradation rate constant. In addition, the antioxidant capacity of Chl was enhanced up to 35 %. Therefore, this study offers a novel approach to Chl preservation and suggests a viable alternative to artificial pigments in food products.

Effect of light treatmeat on oxidation and flavour of dry-cured Wuchang fish

Lighting conditions are an important factor affecting dry-cured products. This study investigated the effects of treatments with different light intensities (0 lx, 1000 lx, 25000 lx) and different light sources including red light, blue light, UV-light on oxidation leve and flavor change in dry-cured Wuchang fish. The results showed that dry-cured Wuchang fish exhibited an attractive brown-yellow color, the highest oxidation degree of myoglobin (Mb), the highest fat oxidation under the light conditions of 25000 lx light intensity and UV-light irradiation. This phenomenon was observed that the degree of Mb oxidation was increased, while the degree of fat oxidation was increased. At 25000 lx light intensity and UV-light irradiation, dry-cured Wuchang fish showed an ignificantly decreased fatty acid conten (especially oleic acid and linoleic acid), significantly increased characteristic volatile compound contents (22 for 25,000 lx light intensity and 27 for UV-light irradiation), which contributed to the improvement of quality stability of dry-cured Wuchang fish. Our findings provide theoretical support for the industrial application of exogenous light in dry-cured Wuchang fish.

Interaction mechanism and binding mode of phycocyanin to lysozyme: Molecular docking and molecular dynamics simulation

In this study, multispectral analysis and molecular simulations were performed to investigate the interaction mechanism between phycocyanin (PC) and lysozyme (Lys). The interaction was examined using surface plasmon resonance (SPR), and the structural changes were analyzed using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results suggest that the interaction between PC and Lys was primarily driven by electrostatic, hydrophobic, and hydrogen bonding forces. Molecular dynamics (MD) simulation revealed that Lys preferentially binds between the two subunits, alpha (α) and beta (β), of PC, with residues ASP-13, GLU-106, and GLU-115 on PC and ARG-119, ARG-107, and ARG-98 on Lys being the main contributors to the binding interaction. Additionally, the formation of the PC-Lys complex resulted in increased kinetic and improved thermal stability of PC, which have important implications for PC applications.

Effect of phlorotannin extracts from Ascophyllum nodosum on the textural properties and structural changes of Apostichopus japonicus

In this work, phlorotannin extracts (PhTEs) were isolated from Ascophyllum nodosum. The effects of PhTEs on the textural properties, structural changes and oxidation level of Apostichopus japonicus (A. japonicus) were investigated. The results showed that thermal treatment could lead to the dissolution of TCA-soluble peptides and free hydroxyproline and promote the degradation of A. japonicus. The chemical compositional changes and texture profile analysis results indicated that PhTEs could effectively inhibit the degradation of A. japonicus and improve the hardness and chewiness of A. japonicus. Analysis of multiple spectroscopic methods suggested that the secondary and tertiary conformations tended to be stable after PhTEs were added. In addition, electron spin resonance results indicated that PhTEs could reduce the oxidation level of A. japonicus. These results suggest that the degradation of A. japonicus during mild heat treatment can be regulated by PhTEs, which provides insights for quality control in A. japonicus heat treatment.

Detection of Simulated In Vitro Digestion Products of Fucoxanthin and Their Photodamage Alleviation Effect in Retinal Müller Cells Induced by Ultraviolet B Irradiation: A Proteomics Analysis

Our previous study reported that the marine dietary bioactive compound fucoxanthin (FX) has the potential to reduce the level of oxidation in retinal Müller cells (RMCs) induced by ultraviolet B (UVB) irradiation. However, the gastrointestinal environment can inhibit the bioavailability and absorption of FX in the cell systems. In the current study, FX was initially digested in a simulated in vitro gastrointestinal fluid. Nine main digestive products were identified, and the photoprotective activities of FX simulated in vitro gastrointestinal digestion products (FX-ID) were assessed in the same RMC model. FX-ID significantly reduced intracellular ROS and alleviated apoptosis. Western blot assays showed that FX-ID inhibited phosphorylated proteins in the MAPK and NF-κB signaling pathways. Our proteomics analysis revealed that the differentially expressed proteins were linked to biological networks associated with antioxidation and metabolic processes. The data may provide insight into the photoprotective mechanisms of FX-ID and promote the development of various functional foods to prevent retinal disorders.

Facilitating Pro-survival Mitophagy for Alleviating Parkinson's Disease via Sequence-Targeted Lycopene Nanodots

The pathogenesis of Parkinson's disease is closely linked to impaired mitochondrial function and abnormal mitophagy. Biocompatible natural antioxidants effectively protect dopaminergic neurons. However, the main challenge in using natural antioxidants for Parkinson's disease therapy is creating a delivery platform to achieve neuron-targeted enrichment. Herein, we synthesized rationally sequence-targeted lycopene nanodots using recombinant human H-ferritin nanocages with lycopene loading into the cavity and lipophilic triphenylphosphonium (TPP) coupling on the outer surface. The nanodots allow for the neural enrichment and mitochondrial regulation of lycopene through blood-brain barrier transcytosis and neuronal mitochondria-targeting capability. These anti-ROS nanodots protect neuronal mitochondrial function and promote PINK1/Parkin-mediated mitophagy in MPTP toxicity-induced neurons in vivo and in vitro, which favors the secretory efflux of pathogenic α-synuclein and the survival of dopaminergic neurons. Moreover, these nanodots restore the Parkinson-like motor symptoms in Parkinson's model mice. This noninvasive sequence-targeted delivery strategy with excellent biocompatibility for pro-survival mitophagy-mediated pathology alleviation makes it a promising approach for treating and preventing Parkinson's disease.

Nanoencapsulation Motivates the High Inhibitive Ability of Fucoxanthin on H2O2-Induced Human Hepatocyte Cell Line (L02) Apoptosis via Regulating Lipid Metabolism Homeostasis

This study reports an encapsulation system for fucoxanthin (FX) through simple affinity binding with gelatin (GE) and then coating with chitosan oligosaccharides (COS). The effects of FX before and after encapsulation on the human hepatocyte cell line (L02) were investigated. FX-GE and FX-GE-COS nanocomplexes exhibited a spherical shape with diameters of 209 ± 6 to 210 ± 8 nm. FX-GE-COS nanocomplexes were found to perform the best with the highest encapsulation efficiency (EE, 83.88 ± 4.39%), improved FX stability, and enhanced cellular uptake on the nanoscale. The cytotoxicity and cell mitochondrial damage of H₂O₂ exposure to L02 cells decreased with the increase of free-FX and FX-GE-COS nanocomplexes. FX-GE-COS nanocomplexes' intervention decreased the intracellular ROS and inhibited the apoptosis of L02 cells that was induced by H₂O₂ exposure in a concentration-dependent manner. Lipidomic analysis revealed that FX-GE-COS nanocomplexes could regulate the lipid metabolism disturbed by H₂O₂ and protected the mitochondrial function of L02 cells. These results suggested that nanoencapsulation enhanced the antioxidant activity of FX to L02 cells, and the constructed FX-GE-COS nanocomplexes have the potential to be an antioxidant nutritional dietary supplement.

Encapsulated fucoxanthin improves the structure and functional properties of fermented yogurt during cold storage

Fucoxanthin (FX) extracted from Undaria pinnatifida by an ultrasonic-assisted extraction (UAE) procedure was successfully added to the fermented yogurt through a stably nanoencapsulation. The physicochemical characteristics, texture analysis, rheological testing, sensory evaluation, simulated digestion analysis, and 16SrDNA sequencing analysis were used to evaluate the effect of encapsulated-FX on the function, structure and stability of the fermented yogurt during 7 days cold storage. Encapsulated-FX with a highly water dispersion, changed the microstructure of yogurt, making it more uniform and denser, enhanced the antioxidant activity, increased the stability of milk protein in simulated gastric environment in vitro and promoted the absorption of protein small molecule fragments in the intestine, and inhibited the growth of harmful bacteria during cold storage. This study provided a simple strategy for the production of FX-fortified yogurt by using an effective nanoencapsulation technology, and promoted the extraction and application of active ingredients of edible brown algae.

Polyphenol extracts from Ascophyllum nodosum protected sea cucumber (Apostichopus japonicas) body wall against thermal degradation during tenderization

To retard the protein degradation during sea cucumber processing, polyphenol extracts from Ascophyllum nodosum (PhE) was used as a potential antioxidant to maintain the structural integrity of sea cucumber body wall. Accordingly, the protection effects of PhE (0, 0.5, 1.0 and 1.5 mg PhE/g SFBW) against thermal degradation of the solid fragments of body wall (SFBW) have been investigated in order to evaluate their impact on the oxidation level and structural changes. Electronic Spin Resonance results showed that PhE could significantly inhibit the occurrence of oxidation by scavenging the free radicals. The effect of PhE on chemical analysis of soluble matters in SFBW was characterized by SDS-PAGE and HPLC. Compared with thermally treated SFBW, samples with PhE presented a decrease in protein dissolution. Thermal treatment resulted in the disintegration of collagen fibrils and fibril bundles in SFBW samples, while the density of collagen fibrils was increased, and the porosity decreased in samples with PhE. The results of FTIR and intrinsic tryptophan fluorescence confirmed that the structures of SFBW were modified by PhE. Besides, the denaturing temperature and decomposition temperature were both improved with the addition of PhE. These results suggested that PhE appeared to have a positive effect on lowering oxidation and improving thermostability and structural stability of SFBW, which could provide a theoretical basis for protecting sea cucumber body wall against degradation during thermal tenderization.

Photoprotective Mechanism of Fucoxanthin in Ultraviolet B Irradiation-Induced Retinal Müller Cells Based on Lipidomics Analysis

Long-term exposure to sunlight and/or blue light causes vision damage to people of all ages. Dietary pigments and polyphenols have been shown to have photoprotective potential for eyes; however, many unknowns regarding the protective mechanism remain. In this study, we used ultraviolet B (UVB) irradiation-induced retinal Müller cells (RMCs) to screen for dietary polyphenols and pigment compounds with effective photoprotective activity. Fucoxanthin (FX) was shown to have the best therapeutic effect, and the mechanism was evaluated via lipidomics analysis. Both intra- and extracellular ROS, mitochondrial depolarization, and DNA damage induced by UVB irradiation were inhibited by FX. Meanwhile, FX modulated the MAPK signaling pathway, which is correlated with apoptosis and inflammation. Our lipidomics data revealed that FX regulated lipid metabolism disorder and protected the membrane structure. These results confirm the effective photoprotective effects of FX, which may lead to new insights into FX-functionalized photoprotective foods.

Synergistic effects of UVA irradiation and phlorotannin extracts of Laminaria japonica on properties of grass carp myofibrillar protein gel

BACKGROUND

Oxidized phlorotannin can be used as a protein crosslinking agent to produce high-quality fish gel products. Phlorotannin can be easily induced to form quinone compounds in an oxidizing environment, while o-quinone has been proven to be a reactive, electrophilic intermediate that easily reacts with proteins to form rigid molecular crosslinking networks. The objective of this study was to investigate the synergistic effects of ultraviolet A (UVA) irradiation (1 h, 15 W m-2 ) and various concentrations of Laminaria japonica phlorotannin extracts (PTE) on the gel properties of grass carp myofibrillar protein (MP).

RESULTS

UVA treatment and PTE could synergistically improve the MP gel properties more than PTE alone (P < 0.05). At 625 mmol kg-1 MP PTE alone, the gel strength and cooking yield reached 3.10 ± 0.16 g cm and 47.45 ± 0.35%, respectively, while with the same level of PTE plus UVA they became 4.26 ± 0.19 g cm and 53.89 ± 1.54%, respectively. The three-dimensional network structure of the gel (with PTE + UVA) showed higher connectivity and tightness than that of the control group (no treatment).

CONCLUSIONS

The synergistic effects of PTE and UVA could effectively induce crosslinking of grass carp MP, which could lead to an improvement of MP gel quality. These findings would provide a new technical approach to produce high-quality protein gel products in the fish processing industry. © 2020 Society of Chemical Industry.

Metabolomic Approach for Characterization of Polyphenolic Compounds in Laminaria japonica, Undaria pinnatifida, Sargassum fusiforme and Ascophyllum nodosum

Profiling of polyphenolics in four types of brown macroalgae, namely Laminaria japonica (L. japonica), Undaria pinnatifida (U. pinnatifida), Sargassum fusiforme (S. fusiforme), and Ascophyllum nodosum (A. nodosum), and their effect on oxidation resistance were investigated for the first time. Polyphenolic extracts from marine brown macroalgae were shown to effectively remove oxidants from cells and cellular systems. A. nodosum showed the highest antioxidant activity among evaluated brown macroalgae, showing a better scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical and alleviating oxidative damage caused by hydrogen peroxide to human keratinocytes (HaCaT) cells. Through Q-Exactive HF-X mass spectrometry analysis, 12 polyphenolic compounds were preliminarily identified, including phlorotannins, phenolic acids, and flavonoids. Significant differences in content and variety of polyphenolics were found in evaluated brown macroalgae, which could be related to differences in antioxidant activity in vivo and in vitro. Moreover, the antioxidant activity might be related to the total phenolic content and the types of polyphenolics, especially phlorotannins. The findings presented in this study indicate that A. nodosum could be used as an important substitute for functional ingredients in foods and pharmaceutical preparations, as well as a raw material for phlorotannins research.

The dual effects of riboflavin and kelp polyphenol extracts on the gel properties of myofibrillar protein from Scomberomorus Niphonius under UVA irradiation

In the present study, effects of riboflavin (RF) and kelp polyphenol extracts (KPE) on mackerel (Scomberomorus Niphonius) myofibrillar protein (MP) gel were studied with or without ultraviolet A (UVA) irradiation treatment. The gel strength was increased with the addition of RF and KPE under UVA irradiation. Analysis of the proteins in the gel indicated that the carbonyl content increased, while the contents of total sulfhydryl and amino groups decreased. The proteins appeared to have no α-helix structures, and the endogenous tryptophan content appeared to decrease. The results of SDS-PAGE indicated that the RF and KPE treated samples under UVA irradiation showed massive MP cross-linking by covalent bonds. Electron spin resonance (ESR) results indicated that UVA irradiation generated free radicals in RF and KPE, which ultimately led to an improvement in MP gel properties. It also indicated that KPE could prevent the occurrence of peroxidation to improve the gel properties.

Enhancement of gel properties of Scomberomorus niphonius myofibrillar protein using phlorotannin extracts under UVA irradiation

The effect of phlorotannin extracts (PTE) (from sporophyll of Undaria pinnatifida) added at different levels (0, 25, 125, 625 µmol/g protein) on the gel properties of mackerel (Scomberomorus niphonius) myofibrillar protein (MP) was studied with and without ultraviolet A (UVA) irradiation. The results showed that the gel strength and cooking yield increased in a PTE dose-dependent manner, and at the level of 625 µmol/g protein PTE, the highest gel strength of 308.43 ± 8.12 (mN·cm) and cooking yield of 76.16 ± 1.40% were obtained in the samples treated with UVA irradiation. The same samples also showed increased carbonyl content, decreased total sulfhydryl, unwinding of α-helix, and quenching of fluorescence intensity of endogenous tryptophan, all of which indicated that elevated protein oxidation in these samples led to enhanced protein cross-linking. Results of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) indicated aggregation of myosin heavy chains (MHCs) in the UVA-treated gels with PTE, also evidenced by the dense three-dimensional network structure in these samples visualized by scanning electron microscopy (SEM). Electron spin resonance (ESR) and spin trapping results indicated that free radicals were produced during the gelation process, possibly originated from UVA-treated PTE, which played a critical role of oxidizing fish MPs, and eventually led to the improvement of the textural properties of the mackerel MP gel. PRACTICAL APPLICATION: Brown algae are a family of high-yield marine algae. Phlorotannin extracts are highly active natural substances extracted from brown algae that can have many applications. Ultraviolet A (UVA) as a green and environmentally friendly physical processing method has been widely used in food processing in recent years. The method proposed in this study could be utilized to improve properties of fish protein gel made from poorly performing low-priced fishes, and provide workable guidance for industry to expand the application of brown algae in food processing to better meet consumer's demand for high-quality marine foods.

Inhibitory effect of natural metal ion chelators on the autolysis of sea cucumber (Stichopus japonicus) and its mechanism

Live sea cucumbers (Stichopus japonicus) were stored in a solution containing oxalic acid and tea polyphenols as natural metal ion chelators. The inhibitory effects of these chelators on the autolysis phenomenon and the underlying mechanism of action were investigated for the first time by using scanning electron microscopy, differential scanning calorimetry, low-field nuclear magnetic resonance and confocal laser scanning microscopy. External stimuli cause autolysis through the release of calcium ions (Ca²⁺) from cells into the extracellular connective tissue, initiating activity of the matrix metalloprotease (MMP) in the sea cucumber body wall (SCBW). MMP subsequently degrades the microfibrillar networks, that support the interconnecting collagen fibres and the interfibrillar proteoglycan bridges linking the collagen fibrils, to release the water restricted within the interspaces between collagen fibres and collagen fibrils, ultimately causing mucoid degeneration of SCBW. The natural metal ion chelators significantly inhibited the activation of MMP by chelating Ca²⁺, consequently effectively preventing the autolysis of SCBW.

Improvement of myofibrillar protein gel strength of Scomberomorus niphonius by riboflavin under UVA irradiation

In this study, effects of different concentrations of riboflavin (0, 0.02, and 0.1 μmol/g protein) on myofibrillar protein (MP, Scomberomorus niphonius) gel were characterized. The gel structure and properties were studied with or without Ultraviolet A (UVA) irradiation. Electron spin resonance results showed that riboflavin produced ·OH under UVA irradiation, which subsequently oxidized the MP. Compared with the control group, the addition of riboflavin with UVA irradiation increased the strength of the MP gel. The rheological results showed that under UVA irradiation, addition of riboflavin facilitated the sol-gel transition between 45 and 52°C, indicating that oxidation led to significant structural changes which in turn resulted in a more compact and uniform gel network. The presence of riboflavin led to increased carbonyl content and decreased sulfhydryl and free amino groups, which decreased the protein solubility and promoted alpha-helical conformational loss in the secondary structure of the MP. These results all indicated that the MP has been oxidized. Electrophoresis revealed that myosin heavy chains were aggregated in the UVA-treated riboflavin-added MP gel, indicating that protein cross-linking has been induced. All the results indicated that the ·OH produced by riboflavin under UVA irradiation oxidized the MP, and improved protein crosslinking and gel properties.

Physiological and immunological responses of sea cucumber Apostichopus japonicus during desiccation and subsequent resubmersion

Desiccation is one of the extremely stressful situations experienced by aquatic animals, and sea cucumber usually suffers from desiccation stress during transportation without water. The present study was conducted to evaluate the effect of desiccation and subsequent resubmersion on physiological stress, oxidative damage, antioxidant status and non-specific immune response of Apostichopus japonicus, providing valuable information on the health management of sea cucumber culturing. Control and desiccation groups were set up, and each group has three replicates. After 1, 3 and 6 h of desiccation, individuals were resubmersed in aerated seawater for a 24 h recovery in three batches, which were represented as D1, D3 and D6, respectively. The results showed that glucose level in coelomic fluid of sea cucumber significantly decreased after desiccation, whereas lactate, cortisol and osmolality showed remarkable ascending trends. Thereafter, all stress parameters gently recovered towards normal levels as control group during 24 h resubmersion. The prolonged desiccation at D6 treatment induced the significant increases of malondialdehyde (MDA) and reactive oxygen species (ROS) contents, as well as relatively lower superoxide dismutase (SOD) and catalase (CAT) activities. During the period of desiccation and subsequent resubmersion, sea cucumber adjusted antioxidant defense to reduce the concentrations of MDA and ROS as a strategy for protecting against oxidative damage. Desiccation also had significant effects on non-specific immune parameters (total coelomocytes counts, TCC; complement C3; total nitric oxide synthase, T-NOS; lysozyme, LSZ; alkaline phosphatase, AKP) of A. japonicus, which could be recovered to some extent during resubmersion. In conclusion, less than 6 h of desiccation did not induce irreparable damage to sea cucumber, and was recommended for handling and shipping live sea cucumbers.

RNA Sequencing Analysis to Capture the Transcriptome Landscape during Tenderization in Sea Cucumber Apostichopus japonicus

Sea cucumber (Apostichopus japonicus) is an economically significant species in China having great commercial value. It is challenging to maintain the textural properties during thermal processing due to the distinctive physiochemical structure of the A. japonicus body wall (AJBW). In this study, the gene expression profiles associated with tenderization in AJBW were determined at 0 h (CON), 1 h (T_1h), and 3 h (T_3h) after treatment at 37 °C using Illumina HiSeq™ 4000 platform. Seven-hundred-and-twenty-one and 806 differentially expressed genes (DEGs) were identified in comparisons of T_1h vs. CON and T_3h vs. CON, respectively. Among these DEGs, we found that two endogenous proteases-72 kDa type IV collagenase and matrix metalloproteinase 16 precursor-were significantly upregulated that could directly affect the tenderness of AJBW. In addition, 92 genes controlled four types of physiological and biochemical processes such as oxidative stress response (3), immune system process (55), apoptosis (4), and reorganization of the cytoskeleton and extracellular matrix (30). Further, the RT-qPCR results confirmed the accuracy of RNA-sequencing analysis. Our results showed the dynamic changes in global gene expression during tenderization and provided a series of candidate genes that contributed to tenderization in AJBW. This can help further studies on the genetics/molecular mechanisms associated with tenderization.

Reaction of phenol with singlet oxygen

Photo-degradation of organic pollutants plays an important role in their removal from the environment. This study provides an experimental and theoretical account of the reaction of singlet oxygen O2(1Δg) with the biodegradable-resistant species of phenol in an aqueous medium. The experiments combine customised LED-photoreactors, high-performance liquid chromatography (HPLC), and electron paramagnetic resonance (EPR) imaging, employing rose bengal as a sensitiser. Guided by density functional theory (DFT) calculations at the M062X level, we report the mechanism of the reaction and its kinetic model. Addition of O2(1Δg) to the phenol molecule branches into two competitive 1,4-cycloaddition and ortho ene-type routes, yielding 2,3-dioxabicyclo[2.2.2]octa-5,7-dien-1-ol (i.e., 1,4-endoperoxide 1-hydroxy-2,5-cyclohexadiene) and 2-hydroperoxycyclohexa-3,5-dien-1-one, respectively. Unimolecular rearrangements of the 1,4-endoperoxide proceed in a facile exothermic reaction to form the only experimentally detected product, para-benzoquinone. EPR revealed the nature of the oxidation intermediates and corroborated the appearance of O2(1Δg) as the only active radical participating in the photosensitised reaction. Additional experiments excluded the formation of hydroxyl (HO˙), hydroperoxyl (HO2˙), and phenoxy intermediates. We detected for the first time the para-semibenzoquinone anion (PSBQ), supporting the reaction pathway leading to the formation of para-benzoquinone. Our experiments and the water-solvation model result in the overall reaction rates of kr-solvation = 1.21 × 104 M-1 s-1 and kr = 1.14 × 104 M-1 s-1, respectively. These results have practical application to quantify the degradation of phenol in wastewater treatment.

Effects of pulsed electric field on intracellular antioxidant activity and antioxidant enzyme regulating capacities of pine nut (Pinus koraiensis) peptide QDHCH in HepG2 cells

Effects of pulse electric field (PEF) on antioxidant activity of pine nut (Pinus koraiensis) peptide were discussed using H₂O₂-induced HepG2 cells and changes of peptide structures were measured by MIR, NMR and CD spectra. Using HPLC-MS/MS, a novel peptide was identified as QDHCH. After PEF treatment the DPPH and ABTS radical inhibition, and CAA values of QDHCH were increased to 85.13%±0.17%, 95.45%±0.12%, and 4670.10μmol of quercetin equivalents/100g. The PEF-treated QDHCH has better protective oxidative stress inhibitory of 74.22±3.70%, and the T-SOD, CAT, GSH-Px and GSH-Rx activities in cells were significantly increased by 91.92, 7.98, 18.5 and 18.79U/mg prot, while the MDA content was decreased to 8.45±0.71U/mg prot compared with H₂O₂ damaged group. In addition, the hydroxyl radical scavenging activity of QDHCH was increased by 10.53%; the basic structure was not changed by PEF, while the influenced secondary structures may induce the antioxidant activity improvement in HepG2 cells.

Apoptosis induction is involved in UVA-induced autolysis in sea cucumber Stichopus japonicus

Autolysis easily happens to sea cucumber (Stichopus japonicus, S. japonicus) for external stimulus like UV exposure causing heavy economic losses. Therefore, it is meaningful to reveal the mechanism of S. japonicas autolysis. In the present study, to examine the involvement of apoptosis induction in UVA-induced autolysis of S. japonicas, we investigated the biochemical events including the DNA fragmentation, caspase-3 activation, mitogen-activated protein kinases (MAPKs) phosphorylation and free radical formation. Substantial morphological changes such as intestine vomiting and dermatolysis were observed in S. japonicus during the incubation after 1-h UVA irradiation (10W/m(2)). The degradation of the structural proteins and enhancement of cathepsin L activity were also detected, suggesting the profound impact of proteolysis caused by the UVA irradiation even for 1h. Furthermore, the DNA fragmentation and specific activity of caspase-3 was increased up to 12h after UVA irradiation. The levels of phosphorylated p38 mitogen activated protein kinase (MAPK) and phosphorylated c-Jun.-N-terminal kinase (JNK) were significantly increased by the UVA irradiation for 1h. An electron spin resonance (ESR) analysis revealed that UVA enhanced the free radical formation in S. japonicas, even through we could not identify the attributed species. These results suggest that UVA-induced autolysis in S. japonicas at least partially involves the oxidative stress-sensitive apoptosis induction pathway. These data present a novel insight into the mechanisms of sea cucumber autolysis induced by external stress.