Mechanism of color change in Antarctic krill oil during storage.

Antarctic krill oil (AKO) is reddish-orange in color but undergoes changes during storage. To investigate the color deterioration and potential mechanisms involved, the changes in color, endogenous components (astaxanthin, fatty acids, and phospholipids), and reaction products (aldehydes, α-dicarbonyl compounds, and pyrroles) of AKO upon storage were determined. Although the visual color of AKO tended to darken upon storage, the colorimetric analysis and ultraviolet-visible spectrum analysis both indicated a fading in red and yellow due to the oxidative degradation of astaxanthin. During storage of AKO, lipid oxidation led to the formation of carbonyl compounds such as aldehydes and α-dicarbonyls. In addition, phosphatidylethanolamines (PEs) exhibited a faster loss rate than phosphatidylcholines. Moreover, hydrophobic pyrroles, the Maillard-like reaction products associated with primary amine groups in PEs accumulated. Therefore, it is suggested that the Maillard-like reaction between PEs and carbonyl compounds formed by lipid oxidation contributed to color darkening of AKO during storage.

Characterization of Oyster Protein Hydrolysate-Iron Complexes and their In Vivo Protective Effects against Iron Deficiency-Induced Symptoms in Mice.

Iron is one of the trace mineral elements, and iron deficiency is a common phenomenon that negatively influences human health. Food-derived iron supplements were considered excellent candidates for improving this syndrome. In this work, oyster-protein hydrolysates (OPH) and ferrous chloride successfully formed the OPH-Fe complex (6 mg/mL, 40 °C, 30 min), where the main binding sites involved were the carboxyl and amino groups. The OPH-Fe complex showed no obvious changes in the secondary structure, while the iron changed the morphological appearance and also showed fluorescence quenching, an ultraviolet shift, and an increase in size distribution. The OPH-Fe complex showed better dynamic absorption of iron (64.11 µmol/L) than ferrous sulfate (46.90 µmol/L), and the medium dose had better protective effects against iron-deficiency anemia in vivo. Three representative peptides (DGKGKIPEE, FAGDDAPRA, and VLDSGDGVTH) that were absorbed intact were identified. This experiment provided a theoretical foundation for further study of the digestion and absorption of the OPH-Fe complex.

In Vitro Gastrointestinal Digestion and Microbial Hydrolysis of Hydroxytyrosol-SCFA and Tyrosol-SCFA Acyl Esters: Controlled-Release of SCFAs and Polyphenols.

Phenolipids such as hydroxytyrosol-SCFA acyl esters (HTy-SEs) and tyrosol-SCFA acyl esters (TYr-SEs) with various alkyl chains lengths (C1-C4) and different isomers (branched-chain and straight-chain) were successfully synthesized. All esters were hydrolyzed by pancreatic lipase to produce polyphenols (HTy and TYr) and SCFAs (iso-butyric acid, acetic acid, propionic acid, and n-butyric acid). Moreover, HTy-SEs (and TYr-SEs) could also be hydrolyzed to free HTy (and TYr) and SCFAs by gut microbiota and Lactobacillus from mice feces. Especially, the hydrolysis rates showed positive correlation with the carbon skeleton length, and the hydrolysis degree (DH) of ester with a branched-chain fatty acid was weaker than that of ester with a straight-chain fatty acid. Besides, the DH values of TYr -SEs were significantly higher than those of HTy-SEs. Therefore, through regulating the structures of polyphenols, carbon skeleton lengths, and isomers, controlled-release of polyphenols and SCFAs from phenolipids will be easily achieved.

Effects of Addition of Tea Polyphenol Palmitate and Process Parameters on the Preparation of High-Purity EPA Ethyl Ester.

High-purity eicosapentaenoic acid (EPA) ethyl ester (EPA-EE) can be produced from an integrated technique consisting of saponification, ethyl esterification, urea complexation, molecular distillation and column separation. In order to improve the purity and inhibit oxidation, tea polyphenol palmitate (TPP) was added before the procedure of ethyl esterification. Furthermore, through the optimization of process parameters, 2:1 (mass ratio of urea to fish oil, g/g), 6 h (crystallization time) and 4:1 (mass ratio of ethyl alcohol to urea, g/g) were found to be the optimum conditions in the procedure of urea complexation. Distillate (fraction collection), 115 °C (distillation temperature) and one stage (the number of stages) were found to be the optimum conditions for the procedure of molecular distillation. With the addition of TPP and the above optimum conditions, high-purity (96.95%) EPA-EE was finally obtained after column separation.

Effects of Tea Polyphenol and Its Combination with Other Antioxidants Added during the Extraction Process on Oxidative Stability of Antarctic Krill (Euphausia superba) Oil.

Antarctic krill (Euphausia superba) oil contains high levels of marine omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA), including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). In industrial production, krill oil is usually extracted from krill meals by using ethanol as a solvent. Water in the krill meal can be easily extracted by using ethanol as an extraction solvent. During the extraction process, the EPA and DHA are more easily oxidized and degraded when water exists in the ethanol extract of krill oil. Based on the analysis of peroxide value (POV), thiobarbituric acid-reactive substances (TBARS), fatty acid composition, and lipid class composition, the present study indicated that the composite antioxidants (TP-TPP) consist of tea polyphenol (TP) and tea polyphenol palmitate (TPP) had an excellent antioxidant effect. By contrast, adding TP-TPP into ethanol solvent during the extraction process is more effective than adding TP-TPP into krill oil after the extraction process.

Preparation and Hepatoprotective Activities of Peptides Derived from Mussels (Mytilus edulis) and Clams (Ruditapes philippinarum).

Low molecular weight (<5 kDa) peptides from mussels (Mytilus edulis) (MPs) and the peptides from clams (Ruditapes philippinarum) (CPs) were prepared through enzymatic hydrolysis by proteases (dispase, pepsin, trypsin, alcalase and papain). Both the MPs and the CPs showed excellent in vitro scavenging ability of free radicals including OH, DPPH and ABTS in the concentration range of 0.625−10.000 mg/mL. By contrast, the MPs hydrolyzed by alcalase (MPs-A) and the CPs hydrolyzed by dispase (CPs-D) had the highest antioxidant activities. Furthermore, MPs-A and CPs-D exhibited protective capabilities against oxidative damage induced by H2O2 in HepG2 cells in the concentration range of 25−800 µg/mL. Meanwhile, compared with the corresponding indicators of the negative control (alcohol-fed) mice, lower contents of hepatic MDA and serums ALT and AST, as well as higher activities of hepatic SOD and GSH-PX were observed in experiment mice treated with MPs-A and CPs-D. The present results clearly indicated that Mytilus edulis and Ruditapes philippinarum are good sources of hepatoprotective peptides.

Effects of different antioxidants and their combinations on the oxidative stability of DHA algae oil and walnut oil.

Through monitoring Rancimat induction time (RIT), peroxide value (POV), and thiobarbituric acid-reactive substances (TBARS) of docosahexaenoic acid (DHA) algae oil and walnut oil during accelerated storage, the effects of the single and the combinations of seven kinds of antioxidants involving ascorbyl palmitate (AP), phytic acid (PA), vitamin E (VE), antioxidant of bamboo leaves (AOB), rosemary extract, tea polyphenols (TP), and tea polyphenol palmitate (TPP) against lipid oxidation were evaluated. RIT, POV, and TBARS results showed that the DHA algae oil sample containing 600 mg/kg TPP revealed the strongest stability and the walnut oil sample containing 450 mg/kg TPP and 100 mg/kg TP revealed the strongest stability. Then, the shelf lives of two oils were predicted from the extrapolation of the linear regression model between Log RIT and temperature. Our results indicated that the optimal antioxidant could prolong the shelf lives of DHA algae oil and walnut oil by 2.31- and 7.74-fold, respectively.

Antioxidative Effect of Chlorella Pyrenoidosa Protein Hydrolysates and Their Application in Krill Oil-in-Water Emulsions.

Chlorella pyrenoidosa is an excellent source of protein, and in this research, we assessed the antioxidant and emulsifying effects of Chlorella protein hydrolysate (CPH) using neutral proteases and alkaline proteases, as well as the properties of CPH-derived krill oil-in-water (O/W) emulsions. The CPHs exhibited the ability to scavenge several kinds of free radicals, including 1,1-diphenyl-2-picrylhydrazyl (DPPH), O2-, hydroxyl, and ABTS. Additionally, the CPHs (5 mg/mL) scavenged approximately 100% of the DPPH and ABTS. The CPHs showed similar emulsifying activities to Tween 20 and excellent foaming activities (max FS 74%), which helped to stabilize the krill oil-in-water emulsion. Less than 10 mg/mL CPHs was able to form fresh krill oil-in-water emulsions; moreover, the CPHs (5 mg/mL) in a krill O/W emulsion were homogenous, opaque, and stable for at least 30 days. Based on their inhibitory effects on the peroxide value (POV) and thiobarbituric acid reactive substances (TRABS), the CPHs were found to be able to inhibit lipid oxidation in both emulsifying systems and krill O/W emulsions. Thus, the CPHs could improve superoxide dismutase (SOD) activities by 5- or 10-fold and decrease the high reactive oxygen species (ROS) level caused by the addition of H2O2 in vitro. In conclusion, health-promoting CPHs could be applied in krill oil-in-water emulsions as both emulsifiers and antioxidants, which could help to improve the oxidative and physical stability of emulsions.

Effects of antioxidants of bamboo leaves on protein digestion and transport of cooked abalone muscles.

The effects of oxidation on protein digestion and transport in cooked abalone muscles were investigated using a combination of simulated digestion and everted-rat-gut-sac models for the first time. Boiling heat treatments caused protein oxidation in the abalone muscles, reflected by increases in the carbonyl group and disulfide bond contents, protein hydrophobicity and aggregation degree, as well as decreases in the free sulfhydryl group and amino acid contents. Protein oxidation significantly inhibited the degree of hydrolysis, digestion rate, and digestibility of the abalone muscles in the simulated digestion model. The results from the everted-rat-gut-sac model showed that amino acid and peptide transport levels from the digestion products of the cooked abalone muscles were lower than those of the uncooked samples. In contrast, the addition of antioxidants of bamboo leaves mitigated heat-treatment-induced protein oxidation, aggregation and increased hydrophobicity, and consequently improved abalone muscle protein digestibility and transport levels.

Characterization of a synthetic zinc-chelating peptide from sea cucumber (Stichopus japonicus) and its gastrointestinal digestion and absorption in vitro.

BACKGROUND: Zinc absorption in intestinal system could be strongly affected by the gastrointestinal digestion and absorption of zinc-chelating peptides serving as zinc carriers. In this study, a novel zinc-chelating sea cucumber synthetic peptide (SCSP) was synthesized to estimate its gastrointestinal digestion and promotive effect of zinc absorption in vitro. RESULTS: Analysis of isothermal titration calorimetry suggested that the binding of SCSP and zinc (N ≈ 1) was exothermic, with relatively weak binding affinity (K = 1.0 × 10-3  mol L-1 ). The formation of SCSP-Zn complexes brought morphological changes to the peptides confirmed by scanning electron microscopy (SEM), which also indicated 6.88% of the existence of zinc element. In addition, the SCSP-Zn complexes remained stable under simulated human gastrointestinal digestion. In an in vitro study, the SCSP-Zn complex could successfully transport through the intestinal membrane in the model of everted rat gut sacs (nearly 7.5 µM cm-2 ) as well as Caco-2 cells where the zinc transport reached 0.0014 mg mL-1 carried by SCSP. Fluorescence staining experiments revealed free zinc accumulation inside the tissues and cells treated with the SCSP-Zn complex. CONCLUSIONS: The chelation SCSP-Zn had the promotion ability of zinc absorption in vitro and ex vivo experiments, which suggested a theoretical basis for the design and production of effective zinc chelating peptides as zinc carriers to improve zinc bioavailability. © 2022 Society of Chemical Industry.

Distribution of tyrosol fatty acid esters in the gastrointestinal tracts of mice and their hydrolysis characteristics by gut microbiota.

Phenolic lipids have been approved as safe and effective antioxidants, and are a potential ingredient for functional foods. However, the characteristics of gastrointestinal distribution and microbial hydrolysis in the gastrointestinal tract (GI) are not clear. In this study, the above characteristics of tyrosol-myristic acid ester (T-C14:0), tyrosol-palmitic acid ester (T-C16:0) and tyrosol-stearic acid ester (T-C18:0) were estimated by an in vivo mice model and in vitro anaerobic fermentation model. HPLC-UV measurements indicate that tyrosol (TYr) was rapidly and almost completely absorbed in the small intestine. By contrast, oral T-C14:0, T-C16:0 and T-C18:0 were remarkably stable in the stomach environments of the mice, and could be further hydrolyzed to free TYr by gut microbiota including Lactobacillus johnsonii, Lactobacillus reuteri and Lactobacillus gasseri (in the colon and cecum). Further, the liberated TYr and fatty acids can participate in regulating the composition of the gut microorganisms, which may lead to some additional health benefits. Therefore, the production of phenolic lipids such as tyrosol fatty acid esters provides a new approach to prolong the action time of polyphenol in vivo, and could also lead to additional health benefits including the regulation of gut microorganisms.

Effects of roasting temperature and time on aldehyde formation derived from lipid oxidation in scallop (Patinopecten yessoensis) and the deterrent effect by antioxidants of bamboo leaves.

This study aimed to investigate the effects of roasting temperature and time on aldehyde formation derived from lipid oxidation in scallop, and the deterrent effect of natural antioxidants extracted from bamboo leaves (AOB). Results showed that roasting process significantly increased the peroxide value (PV), thiobarbituric acid-reactive substances (TBARS), p-Anisidine value (p-AV), and total oxidation (TOTOX) in scallop lipids. Besides, 16 different aldehydes in scallop lipids were detected using an HPLC-ESI-MS/MS method. Among them, the content of hexanal, pentanal, nonanal, trans, trans-2,4-octadienal, and 4-hydroxy-2-hexenal increased in a time- and temperature-dependent manner during the roasting process. After roasting at 210 °C for 40 min, their content increased by 1.23, 0.81, 1.44, 0.59, and 2.12 folds compared with the unroasted group, respectively. However, pretreatment with AOB effectively prevented aldehyde formation in roasted scallops by reducing the oxidation of polyunsaturated fatty acids and scavenging free radicals.

Gastrointestinal digestion and absorption characterization in vitro of zinc-chelating hydrolysate from scallop adductor (Patinopecten yessoensis).

BACKGROUD: Zinc (Zn) is an essential catalytic element in the human health system but its absorption in the intestinal system can be strongly affected by gastrointestinal (GI) digestion. In this study, the food-derived potential Zn carrier, scallop adductor hydrolysates (SAHs), was produced and characterized. RESULTS: During temporary storage at 4 °C, SAH decreased in Zn-chelating capacity in the aqueous phase, whereas the SAH-Zn complex exhibited high stability. Moreover, the secondary structure of SAH had no significant alteration. Zn morphologically altered the surface structures of SAH, which was involving in carboxyl group of SAH. Results of in vitro GI digestion suggested that the SAH-Zn maintained good stability in GI system and only proportion of high molecular weight cleaved. In addition, SAH could successfully carry and transport Zn while the fluorescence staining revealed free Zn accumulation inside the tissue. Finally, three representative absorbed peptides (around 600 Da) were identified and synthesized. Three synthetic peptides exhibit higher Zn-chelating capacity than SAH and could also successfully transported through the intestine. CONCLUSION: This study provided a theoretical basis for the investigation of digestion and absorption of marine animal-derived peptides as Zn carriers. © 2021 Society of Chemical Industry.

Lipid oxidation and aldehyde formation during in vitro gastrointestinal digestion of roasted scallop (Patinopecten yessoensis) - the role of added antioxidant of bamboo leaves.

This study investigated lipid oxidation and aldehyde formation in roasted scallop during in vitro gastrointestinal digestion, and the effects of co-digestion of antioxidant of bamboo leaves (AOB) on this process. The results showed that the contents of lipid hydroperoxides (LOOH), conjugated dienes (CD), and Schiff bases (SB) were increased during gastrointestinal digestion. Besides, malondialdehyde (MDA) levels and total aldehyde formation decreased initially at the gastric stage but increased at the intestinal stage. The results of HPLC-ESI-MS/MS analysis showed that the contents of hexanal (HEX), trans, trans-2,4-octadienal (ODE), trans, trans-2,4-decadienal (DDE), 4-hydroxyhexenal (HHE) and 4-hydroxynonenal (HNE) in the digestive juices were all initially decreased and then increased during gastrointestinal digestion. Meanwhile, the content of acrolein, propanal, and trans-2-pentenal at the end of intestinal digestion was lower than that in the initial stage of gastric digestion. Additionally, the digestion of roasted scallop caused significant oxidation of polyunsaturated fatty acids (PUFAs) and release of free fatty acids (FFA) in the intestinal phase, which were positively related to aldehyde production. However, co-digestion of AOB significantly reduced lipid oxidation and formation of lipid oxidation products (LOOH, CD, SB, and aldehyde) during gastrointestinal digestion, indicating that the addition of AOB was effective in reducing gastrointestinal lipid oxidation.

MicroRNA­15b­5p exerts its tumor repressive role via targeting GDI2: A novel insight into the pathogenesis of thyroid carcinoma.

Thyroid carcinoma (THCA) is a malignant tumor of the endocrine system. Previous studies have revealed the vital roles of microRNAs (miRNAs/miRs) in THCA procession. The present study aimed to explore the effects of miR­15b­5p on the progression of THCA and its targeting mechanism. The data of THCA and healthy samples were firstly collected from starbase2.0 and used to analyze the relationship of miR­15b­5p with THCA. Dual­luciferase assay was performed to detect the direct interaction between miR­15b­5p and the predicted target gene GDP dissociation inhibitor 2 (GDI2). The effects of miR­15b­5p and GDI2 on the overall survival of patients with THCA were analyzed using Kaplan­Meier analysis with log rank test. Cell Counting Kit­8 and Transwell assays were conducted to assess the impacts of miR­15b­5p and GDI2 on the proliferation and invasion of THCA cells. Reverse transcription­quantitative PCR and western blot analyses were performed to analyze the expression levels of the related miRNAs and proteins, respectively. miR­15b­5p was found to be downregulated both in THCA tissues and cells, and the low expression of miR­15b­5p was associated with the short overall survival time of patients. Moreover, the upregulation or downregulation of miR­15b­5p could inhibit or enhance the proliferation and invasion of THCA cells, respectively. miR­15b­5p reduced the protein expression levels of matrix metalloproteinase (MMP)2 and MMP9, which were related to cell invasion. Furthermore, GDI2, which was enhanced in THCA and related to the poor prognosis of patients with THCA, was identified as the target gene of miR­15b­5p and negatively regulated by miR­15b­5p. Additional experiments demonstrated that GDI2 overexpression could significantly reduce the antitumor effect of miR­15b­5p and its inhibitory action on the expression levels of MMP2 and MMP9. Thus, the results indicated a potential tumor suppressive role of miR­15b­5p in THCA, which was mainly exerted by targeting GDI2 and modulating MMP2 and MMP9. These findings will increase the understanding on the pathogenesis of THCA and provide novel candidates for THCA therapy.

Oxidation kinetics of polyunsaturated fatty acids esterified into triacylglycerols and phospholipids in dried scallop (Argopecten irradians) adductor muscles during storage.

The difference between the oxidative susceptibility of polyunsaturated fatty acids (PUFAs) esterified into triacylglycerols (TAG) and phospholipids (PL) and the effects of polyphenolic antioxidants on such susceptibility in dried seafood were investigated. Lipid fractions containing TAG and PL were extracted from dried scallops stored for various times, and their fatty acid contents were determined. The changes in contents of four representative PUFAs, including α-linolenic acid (ALA), arachidonic acid (AA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) esterified into TAG or PL, were used to fit kinetic models to obtain the reaction rate constant (k), which reflects the oxidation rates of different lipid classes. The results indicated that the oxidation of PUFAs (ALA, AA, EPA, and DHA) esterified into TAG or PL at two storage temperatures (15 °C and 25 °C) followed the first-order kinetic model, and TAG had a greater oxidation rate than PL under the experimental conditions. The results further showed that natural phenolics could effectively inhibit the oxidation of PUFAs esterified into PL and TAG, while retaining the nutritional value of dried scallops during long term storage. Furthermore, PL could be protected by the polar polyphenolic antioxidant better than TAG. This study shows that monitoring substrate loss and using kinetic models of PUFAs esterified into different lipid classes can provide insights into further chemical and nutritional studies on food systems containing complex lipid class compositions.

Improving the oxidative stability and lengthening the shelf life of DHA algae oil with composite antioxidants.

Based on various antioxidant mechanisms, four kinds of antioxidants including ascorbyl palmitate (AP), vitamin E (VE), phytic acid (PA) and one of the polyphenols (antioxidant of bamboo leaves, tea polyphenol palmitate or tea polyphenols (TP)) were used in combination to improve oxidative stability of docosahexaenoic acid (DHA) algae oil. To achieve the best effect, the formulations and mixture ratios of the antioxidant combinations were optimized. The effects were monitored by peroxide value, thiobarbituric acid-reactive substances, acid value, free radicals, Rancimat induction time and fatty acid composition of DHA algae oil undergoing accelerated storage. Finally, the DHA algae oil containing 80 mg/kg AP, 80 mg/kg VE, 40 mg/kg PA and 80 mg/kg TP had the highest oxidative stability. Furthermore, the shelf life of DHA algae oil containing the optimum composite antioxidant was predicted by using accelerated shelf life testing coupled with Arrhenius model, which was 3.80-fold longer than the control sample.

Zinc-Chelating Mechanism of Sea Cucumber (Stichopus japonicus)-Derived Synthetic Peptides.

In this study, three synthetic zinc-chelating peptides (ZCPs) derived from sea cucumber hydrolysates with limited or none of the common metal-chelating amino-acid residues were analyzed by flame atomic absorption spectroscopy, circular dichroism spectroscopy, size exclusion chromatography, zeta-potential, Fourier transform infrared spectroscopy, Raman spectroscopy and nuclear magnetic resonance spectroscopy. The amount of zinc bound to the ZCPs reached maximum values with ZCP:zinc at 1:1, and it was not further increased by additional zinc presence. The secondary structures of ZCPs were slightly altered, whereas no formation of multimers was observed. Furthermore, zinc increased the zeta-potential value by neutralizing the negatively charged residues. Only free carboxyl in C-terminus of ZCPs was identified as the primary binding site of zinc. These results provide the theoretical foundation to understand the mechanism of zinc chelation by peptides.

Mechanism of antioxidant action of natural phenolics on scallop (Argopecten irradians) adductor muscle during drying process.

Lipid hydrolysis and oxidation occurred in Argopecten irradians adductor muscle during hot air drying. Using an in vivo imaging system, we found that antioxidants of bamboo leaves (AOB) could diffuse into the adductor muscle upon marinating. Both tea polyphenols (TP) and AOB efficiently retarded lipid oxidation but had a slight effect on lipid hydrolysis during drying process. The in situ antioxidant mechanisms of AOB as well as TP were revealed, including quenching of free radicals detected by electron spin resonance, chelating metal ions determined by confocal laser scanning microscopy and inhibiting lipoxygenase. Less than 8% of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in AOB and TP marinated adductor muscle were decreased compared to more than 28% decrease in control adductor muscle during the drying process. Overall, these natural antioxidants, TP and AOB, efficiently maintained high nutritive value of adductor muscle, especially, their lipid quality.

Hydrolysis and Transport Characteristics of Tyrosol Acyl Esters in Rat Intestine.

Lipophenols such as palmitoyl esters of green-tea polyphenols (GTP) have been allowed for use as food additives for oxidation control. However, their digestive absorption remains unexplored. In this paper, the hydrolysis and transport characteristics of tyrosol acyl esters (TYr-Es) with various fatty acids (C12:0, C14:0, C16:0, C18:0, C18:1, and C18:2) were evaluated using the everted-rat-gut-sac model for the first time. HPLC-UV measurements demonstrated that TYr-Es were hydrolyzed to TYr, which contributed significantly to TYr transport across the sacs. The hydrolysis and transport rates correlated negatively with the chain lengths of their lipid moieties but showed a positive correlation with the degree of unsaturation. In general, all TYr-Es exhibited sustained-release behavior; therefore, the production of TYr-Es may serve as a useful way to prolong the duration of action and further improve the bioactivities of TYr.