Effects of protein concentration, ionic strength, and heat treatment on the interfacial and emulsifying properties of coconut (Cocos nucifera L.) globulins.

This research aimed to investigate the effects of protein concentration (0.2 %-1.0 %), ionic strength (100-500 mM NaCl), and heat treatment (temperature: 80 and 90℃; time: 15 and 30 min) on the interfacial and emulsifying properties of coconut globulins (CG). When protein concentration was set at 0.2-0.6 %, the interfacial adsorption increased with the increasing of protein concentration. However, the lowest interfacial viscoelasticity was found when CG concentration was 0.6 %. When the protein concentration was higher than 0.6 %, the dilatational viscoelasticity increased with the increasing of protein concentration. The protein concentration showed positive effect on the emulsion stability of CG. The ionic strength showed positive effect on the interfacial adsorption but negative effects on the interfacial viscoelasticity and emulsion stability. Higher temperature and longer heating time brought worse interface behavior. The heated CG (90℃, 30 min) had the worst interfacial behavior but the best emulsion stability.

Comprehensive Analyses of Breads Supplemented with Tannic Acids.

Tannic acid (TA) has been recently considered as a new dough additive for improving the bread-making quality of wheat. However, the effects of TA supplementation on the sensory quality parameters (color, crumb grain structure, and sensory properties) of bread have not been studied. Further, the potential of TA supplementation in bread-making quality improvement has not been evaluated by using commercial flour. In the present study, three commercial wheat flours (namely, XL, QZG, and QZZ) with different gluten qualities were used to evaluate the effects of TA supplementation (in concentrations of 0.1% and 0.3%, respectively). TA supplementation did not change the proximate composition of the breads but increased the volumes and specific volumes of XL and QZG breads. TA supplementation enhanced antioxidant activities, with 0.3% TA significantly increasing the antioxidant capacities of bread made from all three flour samples by approximately four-fold (FRAP method)/three-fold (ABTS method). Positive effects of TA on the reduction in crumb hardness, gumminess, and chewiness were observed in the XL bread, as determined by the texture profile analysis. For the analyses on visual and sensory attributes, our results suggest that TA did not affect the crust color, but only slightly reduced the L* (lightness) and b* (yellowness) values of the crumb and increased the a* (redness) value. TA supplementation also increased the porosity, total cell area, and mean cell area. Satisfactorily, the sensory evaluation results demonstrate that TA-supplemented breads did not exhibit negative sensory attributes when compared to the non-TA-added breads; rather, the attributes were even increased. In summary, TA-supplemented breads generally had not only better baking quality attributes and enhanced antioxidant activities, but, more importantly, presented high consumer acceptance in multiple commercial flour samples. Our results support the commercial potential of TA to be used as a dough improver.

The additive interactions between high-molecular-weight glutenin subunits and tannic acid improve the wheat quality.

Wheat gluten proteins, especially high-molecular-weight glutenin subunits (HMW-GS), are the main contributor to flour processing quality. Tannic acid (TA) consisting of a central glucose unit and ten gallic acid molecules is a phenolic acid that improves the processing quality. However, the underlying mechanism of TA's improvement remains largely unknown. Here, we showed that TA's improving effects on gluten aggregation, dough-mixing and bread-making properties were directly associated with the kinds of HMW-GS expressed in wheat seeds in HMW-GS near-isogenic lines (NILs). We established a biochemical framework, elucidated the additive effects of HMW-GS-TA interaction and discovered that TA cross-linked specifically with wheat glutenins but not gliadins, and reduced gluten surface hydrophobicity and SH content depending on the kinds of expressed HMW-GS in the wheat seeds. We also demonstrated that hydrogen bonds play an essential role in TA-HMW-GS interactions and improvement of wheat processing quality. Additionally, the effects of TA on the antioxidant capacity and on nutrient (protein and starch) digestibility were also investigated in the NILs of HMW-GS. TA increased antioxidant capacity but did not affect the digestion of starches and proteins. Our results revealed that TA more effectively strengthened wheat gluten in the presence of more HMW-GS kinds, highlighting TA's potential as an improver toward healthy and quality bread and demonstrating that manipulating hydrogen bonds was a previously overlooked approach to improve wheat quality.

Effect of water change on quality deterioration of Pacific white shrimp (Litopenaeus vannamei) during partial freezing storage.

The correlation between water changes and quality deterioration of Litopenaeus vannamei during partial freezing storage was evaluated in this study. Significant increases in cross-sectional area and equivalent diameter are detected, but the roundness and longiness of the ice crystals show irregular growth. Within the extension of storage, the bound water (T2b) and immobilized water (T21) decreased significantly. However, the free water (T22) increased significantly. Quality determination showed significant decrease in total sulfhydryl and Ca2+-ATPase, but significant increase in disulfide bonds during storage. Correlation analysis revealed that cross-sectional area showed significant negative correlation with total sulfhydryl and Ca2+-ATPase, while significant positive correlation with disulfide bonds, respectively. The correlation between water distribution index and Ca2+-ATPase, disulfide bonds was significant, respectively. Predicted models for the growth of ice crystals with respect to cross-sectional area and equivalent diameter size have been developed with the help of the Arrhenius model.

Quality changes and indicator proteins of Litopenaeus vannamei based on label-free proteomics analysis during partial freezing storage.

Litopenaeus vannamei are known to deteriorate in quality during low-temperature storage. This study demonstrated the potential protein indicators of partial freezing of stored shrimp by traditional quality parameters and label-free based proteomic techniques. The carbonyl content and myofibril fragmentation index (MFI) of shrimp increased from 0.56 ± 0.03 to 2.14 ± 0.03 nmol/mg and 13.09 ± 0.14 to 54.93 ± 0.96, respectively. Within the extension of storage, the trichloroacetic acid (TCA), cooking loss and whiteness significantly increased. A total of 240 proteins changed in abundance at 10, 20, and 30 days compared to fresh samples. Projectin, ribosomal protein and histone were potential biomarkers for protein denaturation and oxidation in shrimp muscle. Myosin heavy chain and glyceraldehyde-3-phosphate dehydrogenase corresponded with the degradation of muscle proteins. Myosin light chain, tubulin alpha chain, and heat shock protein correlated with tenderness and water holding capacity; meantime, malate dehydrogenase and hemocyanin can serve as color indicators. Further study of the properties of these indicator proteins can inform their exploitation as quality indicator proteins during partial freezing storage.

Proteomics study of mitochondrial proteins in tilapia red meat and their effect on color change during storage.

The underlying mechanism of the role of mitochondria in color changing of tilapia fillet during 0-4 d storage is not completely clear. A total of 209 differentially significant expressed proteins (DSEPs) were identified by using label-free mitochondrial proteomics, with 56 proteins up-regulated in T2 and 61 proteins (up-regulated) in T3. Protein-Protein interaction reveled proteins which participate in TCA cycles (Citrate synthase (cs)), Oxidoreductase (Malate dehydrogenase (mdh1, mdh2), Succinyl-CoA (Oxct1), Hydroxyacyl-coenzyme a dehydrogenase (hadh), Dehydrogenase/reductase (SDR family) member 1 (dhrs1)) interacted strongly with each other. In turn, they can increase the level of mitochondrial respiration and mitochondrial function, leading to color changing of tilapia fillet. The heat shock 60kD protein 1 (chaperonin, hspd1) interacted with metabolic enzymes (cs and mdh2) and had important effects on color. These results could help researchers better understand the color changing mechanism on the surface of tilapia fillet during the storage.

Unraveling the effect of the combination of modified atmosphere packaging and ε-polylysine on the physicochemical properties and bacterial community of greater amberjack (Seriola dumerili).

The combined effect of ε-polylysine (PL) and modified atmosphere packaging (MAP; 60% CO2/40% N2) on the bacterial community of greater amberjack filets and their physicochemical properties was evaluated at 4°C. The total viable counts (TVC), psychrotrophic bacterial count, sensory index, texture analysis, and total volatile basic nitrogen (TVB-N) revealed that PL, MAP, and MAP + PL treatment delayed the deterioration of greater amberjack filets. These treatment groups also showed decreased accumulation of biogenic amines. High-throughput 16S rRNA gene sequencing results indicated that these treatments suppressed the growth of Pseudomonas in greater amberjack filets. Furthermore, the MAP + PL treatment group was observed to be more effective than the PL and MAP groups, extending the shelf life of greater amberjack filets by 6 days. This investigation showed that the combination of PL and MAP has the potential to retain the quality and extend the shelf life of greater amberjack.

Antioxidant Activity of Gracilaria lemaneiformis Polysaccharide Degradation Based on Nrf-2/Keap-1 Signaling Pathway in HepG2 Cells with Oxidative Stress Induced by H2O2.

The objective of this research was to investigate the antioxidant activity of Gracilarialemaneiformis polysaccharide degradation and its underlying mechanism involved in the Nrf-2/Keap-1 signaling pathway in HepG2 cells with oxidative stress induced by H2O2. The result of the scavenging ability of free radicals showed that GLP-HV (polysaccharide degraded by H2O2-vitamin C (Vc)) performed a better scavenging ability than GLP (G.lemaneiformis polysaccharide). Moreover, the scavenging ability of polysaccharide to these free radicals from strong to weak was as follows: superoxide radical, ferric ion, ABTS+, and DPPH radical, and their IC50 values were 3.56 ± 0.0028, 4.97 ± 0.18, 9.62 ± 0.35, and 23.85 ± 1.78 mg/mL, respectively. Furthermore, GLP-HV obviously relieved oxidative stress in HepG2 cells, which strengthened the activity of T-AOC, CAT, GSH-PX, and SOD, and diminished the intensity of MDA, intracellular ROS, and calcium ion based on the Nrf-2/Keap-1 signaling pathway. The PCR result revealed that polysaccharide upregulated the expression of the genes Nrf-2, HO-1, NQO-1, and ZO-1 and downregulated Keap-1. The correlation between chemical properties and antioxidant mechanism of GLP-HV was evaluated via a heat map. The results illustrated that reducing sugar and active groups presented a positive correlation, and molecular weight and viscosity exhibited a negative relation with antioxidant activity.

Effects of Modified Atmosphere Packaging with Different Gas Ratios on the Quality Changes of Golden Pompano (Trachinotus ovatus) Fillets during Superchilling Storage.

The quality changes of golden pompano fillets in air packaging (AP) and modified atmosphere packaging (MAP) with 30% CO2/70% N2, 50% CO2/50% N2, and 70% CO2/30% N2 were evaluated under superchilling (−3 °C). The results showed that the whiteness of fillets decreased during storage. The rate of pH increase of MAP was significantly slower than in AP groups, in which MAP with 70% CO2/30% N2 effectively suppressed the PH. Interestingly, the hardness decreased on day five following the treatments, followed by a relatively stationary trend. MAP could greatly suppress the increase of total volatile basic nitrogen (TVB-N) contents of fillets compared to fillets packed in AP. All MAP groups of fillets maintained first-grade freshness throughout storage, while the AP samples decreased to second-grade freshness on about the 25th day. MAP with 70% CO2/30% N2 and MAP with 50% CO2/50% N2 had the best results in inhibiting protein degeneration and explanation. Unexpectedly, drip loss of fillets in MAP far exceeded the AP group during storage, which causes sensory discomfort. Anaerobic plate count (APC) of fillets in AP exceeded the consumption limit of 6.7 log CFU/g on day 26 (6.75 log CFU/g on the 26th day), whereas the MAP was still microbiologically acceptable after 30 days of storage (6.43, 6.41, 6.22 log CFU/g, respectively). Considering physicochemical and microbiological parameters, the shelf life of fillets packed in AP was 25 days. MAP treatments could prolong the shelf life of fillets by ~4−5 days compared to AP. Overall, MAP with 70% CO2/30% N2 gas ratio was best for inhibiting the quality deterioration of fillets. Furthermore, principal component analysis (PCA) was performed to evaluate the critical indicators of quality deterioration of the fillets. Two principal components were determined by dimensionality reduction, in which the contribution of the first principal component was centrifugal loss > hardness > TVB-N > APC > CO2 solubility > TBARs > drip loss > pH, which mainly reflected the degree of microbial proliferation, protein hydrolysis, and oxidation. The contribution of the second principal component was pH > TBRAs > drip loss > APC > CO2 solubility > TVB-N > hardness > centrifugal loss, indicating a high correlation between lipid oxidation and microbial proliferation index.

Novel Antioxidant Peptides from Grateloupia livida Hydrolysates: Purification and Identification.

Grateloupia livida protein was hydrolyzed with various proteases (alkaline protease, Protamex and neutral protease) to obtain anti-oxidative peptides. Antioxidant activity of the enzymatic hydrolysates was evaluated by the DPPH radical scavenging, ABTS radical scavenging and reducing power assays. The results suggested that hydrolysates obtained by neutral protease 1 h hydrolysis displayed the highest antioxidant activity (DPPH IC50 value of 3.96 mg/mL ± 0.41 mg/mL, ABTS IC50 value of 0.88 ± 0.13 mg/mL and reducing power of 0.531 ± 0.012 at 8 mg/mL), and had low molecular weight distribution (almost 99% below 3 kDa). Three fractions (F1-F3) were then isolated from the hydrolysates by using semi-preparative RP-HPLC, and the fraction F3 showed the highest antioxidant ability. Four antioxidant peptides were identified as LYEEMKESKVINADK, LEADNVGVVLMGDGR, LIDDSFGTDAPVPERL, and GLDELSEEDRLT from the F3 by LC-MS/MS. Online prediction showed that the four peptides possessed good water solubility, non-toxic and non-allergenic characteristics. Moreover, the LYEEMKESKVINADK exhibited the highest antioxidant ability. Molecular docking revealed that these peptides could all well bind with Kelch-like ECH-associated protein 1 (Keap1), among which LYEEMKESKVINADK had the lowest docking energy (-216.878 kcal/mol). These results demonstrated that the antioxidant peptides from Grateloupia livida could potentially be used as natural antioxidant.

Insight of the Functional and Biological Activities of Coconut (Cocos nucifera L.) Protein by Proteomics Analysis and Protein-Based Bioinformatics.

Coconut (Cocos nucifera L.) is one of the most critical economic crops in the tropics and sub-tropics. Although coconut protein has attracted more and more attention due to its nutritional potential, the lack of proteomic information has limited its practical application. The present study aimed to investigate the coconut meat proteome by shotgun proteomics and protein-based bioinformatic analysis. A grand total of 1686 proteins were identified by searching the National Center for Biotechnology Information (NCBI) protein database and self-constructed C. nucifera transcriptome repository. Among them, 17 and 9 proteins were identified as antioxidant proteins and globulins, respectively. Network analysis of the globulins referred to the sub-works of Cupin and Oleosin, and the antioxidant proteins were related to the sub-networks of glutathione metabolism and peroxisome. The bioactive peptides acquired by in-silico digestion of the targeted proteins have the potential to be applied as antioxidants and emulsifiers for both healthcare and food stabilization.

Comparison of the Physicochemical Properties of Carboxymethyl Agar Synthesized by Microwave-Assisted and Conventional Methods.

The microwave-assisted carboxymethylation of agar to improve its physicochemical properties was investigated. Microwave power, reaction time, and temperature, ethanol concentration, and amounts of chloroacetic acid and sodium hydroxide were assessed for their effects on synthetic yield and degree of substitution (DS). All factors were positively correlated with DS within a certain range. Using optimized conditions, samples with different DS were prepared, and the physicochemical properties of unmodified and carboxymethyl agars prepared by microwave and conventional methods were compared. Carboxymethylation significantly changed the physicochemical properties of the agar, improving gel transparency and reducing dissolution temperature, gel strength, gel hardness, molecular weight, and molecular size; DS was the key factor. Specifically, higher DS values resulted in greater changes. The microwave-assisted method significantly shortened the reaction time and preserved molecular weight, gel strength, and texture hardness of the agar. Therefore, as an environmentally friendly method, microwave-assisted synthesis shows great promise for producing carboxymethyl agar.

Insights on preparation, structure and activities of Gracilaria lemaneiformis polysaccharide.

Gracilaria lemaneiformis is a kind of edible economic red algae, which is rich in polysaccharide, phycobiliprotein, pigments, minerals and other nutrients and functional components. Polysaccharide is one of the main active components of Gracilaria lemaneiformis, which has been reported to present various physiological bioactivities, including regulation of glycolipid metabolism, immune, anti-tumor, anti-inflammatory and other biological activities. This paper aims to provide a brief summary of extraction, purification, structural characteristics, and physiological activities of Gracilaria lemaneiformis polysaccharide (GLP). This article is able to provide theoretical basis for the future research and exploitation of GLP, and improve its potential development to promote the healthy and sustainable processing and high value utilization industry of Gracilaria lemaneiformis.

Degradation of Codium cylindricum polysaccharides by H2O2-Vc-ultrasonic and H2O2-Fe2+-ultrasonic treatment: Structural characterization and antioxidant activity.

In this study, two degraded polysaccharides were obtained by H2O2-Vc-ultrasonic and H2O2-Fe2+-ultrasonic treatment from Codium cylindricum. The basic structure of polysaccharides was characterized and the relationship between structure and antioxidant activity was studied. FTIR spectrum indicated that the degraded polysaccharides had similar functional groups (OH, CH, CO group) with ordinary polysaccharides. LC-MS analysis showed that the degraded polysaccharides were composed of the same monosaccharide units (mannose, galactose, arabinose, glucose, ribose) with Codium cylindricum polysaccharides, but the molar ratio was different. Meanwhile, the molecular weight and morphological feature of polysaccharides had been changed after degradation. Additionally, the antioxidant activity assay revealed that two degraded polysaccharides with lower molecular weight possessed better antioxidant property than ordinary polysaccharides. These results suggested that the basic structure of polysaccharides had not been damaged by two degradation methods, while the antioxidant activity was significantly enhanced.

Purification and Characterisation of Two Novel Pigment Proteins from the Carapace of Red Swamp Crayfish (Procambarus clarkii).

Pigment proteins play a vital role in the red colour change of the red swamp crayfish (Procambarus clarkii) shell after cooking. In this study, two red-change-related pigment proteins with molecular weights of approximately 170 and 43 kDa-denoted as F1 and F2, respectively-were purified by ammonium sulphate salting-out and size exclusion chromatography. F1 and F2 entirely comprised homomultimeric protein complexes composed of 21 kDa subunits. LC-MS/MS analysis showed that the 21 kDa protein subunit belonged to the crustacyanin family, named P. clarkii crustacyanin A2 (PcCRA2). The full-length cDNA of PcCRA2 was cloned, which encoded 190 amino acid residues and was highly homologous (91.58%) with Cherax quadricarinatus crustacyanin A. The predicted 3D structure showed that PcCRA2 had a ß-barrel structure for pigment encapsulation. The colour change of F1 was first detected at 40 °C, and the red change occurred upon heating above 60 °C. Additionally, with increasing temperature, its ß-sheet content increased, and its α-helix content reduced. Correlation analysis showed that the redness value of F1 was significantly related to the heating temperature and the ß-sheet content.

Red color-related proteins from the shell of red swamp crayfish (Procambarus clarkii): Isolation, identification and bioinformatic analysis.

Two water-soluble red color-related proteins with the molecular masses of 24 and 73 kDa were purified from the shell of Procambarus clarkii. Initial color changes of these two proteins were detected at 30 °C and the large amount of red precipitate were obtained at 80 °C. PAGE analysis showed that the 24 kDa protein was the monomer, while the 73 kDa protein was the trimer. Identification revealed that these two proteins belonged to the hemocyanin subunit 2 family. With respect to the amino acid sequence similarity, the red color-related proteins shared the highest sequence identity with the hemocyanin derived from giant freshwater prawn (Macrobrachium rosenbergii). The phylogenetic tree analysis also clearly supported this finding. The shell-derived red color-related proteins show potential use as the edible thermal-sensitive indicator in food processing field.

Degradation of sulphated polysaccharides from Grateloupia livida and antioxidant activity of the degraded components.

Degradation of sulphated polysaccharides from Grateloupia livida (GLP) was studied using H2O2-Vc combined with microwave treatment. Optimal conditions were determined after the Box-Behnken response surface analysis. The best degradation conditions were as follows: microwave power 250 W, microwave temperature 54 °C, the concentration of H2O2 3 mM, degradation time 33 min. Under these conditions, the DPPH scavenging activity of the degraded GLP (DGLP) was 71.39 ± 0.17% at a concentration of 6.0 mg/mL. The degradation method is fast and effective, which is beneficial to improve the antioxidant activity of polysaccharides. Two sulphated polysaccharide constituents (DGLP-1 and DGLP-2) were isolated from DGLP and characterized, and their antioxidant activities were determined. The two polysaccharides had high sulphate content (sulphate content: 25.18-25.26%), contained galactose as the major monosaccharide, and had molecular weights of 158.49 ± 0.43 and 18.06 ± 0.92 kDa, respectively. Antioxidant assays suggested that DGLP-1 and especially DGLP-2 possessed good antioxidant properties.

Purification, characterization and antibacterial activities of red color-related protein found in the shell of kuruma shrimp, Marsupenaeus japonicus.

The well-known red color change plays a significant role in consumer acceptability of crustacean species. In this study, we described the purification of the red color-related protein named MjRCP75 from the shell of Marsupenaeus japonicus. It was a homogeneous monomer with molecular mass of 75 kDa and rich in α-helix conformation. The α-helix content decreased within the increasing of heating temperature and was transformed dominantly to ß types. Identification and structural analysis revealed that MjRCP75 belonged to hemocyanin family. The released pigment from heated MjRCP75 showed a λmax at 483 nm in acetone. MjRCP75 showed clearly antibacterial activity against Escherichia coli, Staphylococcus aureus, and Vibrio parahaemolyticus. These findings identify MjRCP75 as the red color-related protein in M. japonicus shell and reveal its involvement in antibacterial activities.

Effect of low-temperature preservation on quality changes in Pacific white shrimp, Litopenaeus vannamei: a review.

Shrimp has been widely accepted as an excellent resource for white meat due to its high-protein and low-fat content, especially low cholesterol. However, shrimps are highly perishable during preservation and retailing procedures due to the activities of enzymatic proteolysis, lipid oxidation, and microbial degradation. With increasing knowledge of and demands for safety, nutrition, and freshness of shrimp products, energy efficient, quality, maintained, and sustainable preservation technologies are needed. Low-temperature preservation, a practical processing method for improving the shelf life of food products, is widely used in the aquatic industry. This review focuses on the effects of low-temperature preservation on the quality changes in Litopenaeus vannamei. It considers physicochemical properties, sensory evaluation, melanosis assessment, and microbiological analysis. The perspectives of non-protein-based techniques on quality analysis of shrimps during preservation are also discussed. © 2019 Society of Chemical Industry.

Functional and structural properties of red color-related pigment-binding protein from the shell of Litopenaeus vannamei.

BACKGROUND: A novel red color-related pigment-binding protein named LvPBP75 isolated from the shell of Litopenaeus vannamei has recently been identified as hemocyanin. However, information on the functional and structural properties of LvPBP75 is insufficient. This study aimed to elucidate the thermal properties and pigment-binding ability of LvPBP75. RESULTS: LvPBP75 showed significant red color change after heat treatment with high concentrations of NaCl (>0.1 mol L-1 ), acidic (<5) or alkaline (>9) pH values and alcohols. LvPBP75 mRNA expression analysis revealed that expression level was highest in hepatopancreas and weakest in muscle. Reconstruction and structural analysis revealed that astaxanthin could bind to hemocyanin derived from the shell of L. vannamei but not to hemocyanins derived from the hepatopancreas or hemolymph of other invertebrates. Three-dimensional models of hemocyanin monomer displayed significant structural differences between native LvPBP75 and hemocyanin derived from shrimp hepatopancreas. CONCLUSION: The results suggest a novel function of hemocyanin as binding with pigment and its involvement in L. vannamei shell color change. The pigment-binding ability of hemocyanins has species and tissue specificity, and their unique structural features play an important role in binding ability. © 2018 Society of Chemical Industry.