Purification and characterization of antioxidant peptides from yak (Bos grunniens) bone hydrolysates and evaluation of cellular antioxidant activity.

In this study, papain and alcalase were used to generate antioxidant peptides from yak bone protein. The antioxidant activities of hydrolysates in vitro were evaluated by 2,2'-azinobios-(3-ethylbenzothiazoline-6-sulphonic acid) radical scavenging activity, total reducing power, ferrous ion chelating ability and hydroxyl radical scavenging activity. The hydrolysates generated by alcalase possessed the best antioxidant activity among unhydrolyzed protein and samples treated by papain, but the antioxidant activity decreased after simulated gastrointestinal digestion in vitro. The products of simulated gastrointestinal digestion were separated by ultrafiltration and high performance liquid chromatography, and the amino acid sequences of peptides were identified by mass spectrometry. The digestion sites within peptides were predicted by a bioinformatics strategy, and ten peptides were selected for synthesis. Among 10 synthetic peptides, Gly-Phe-Hyp-Gly-Ala-Asp-Gly-Val-Ala, Gly-Gly-Pro-Gln-Gly-Pro-Arg and Gly-Ser-Gln-Gly-Ser-Gln-Gly-Pro-Ala possessed strong antioxidant activities, among which Gly-Phe-Hyp-Gly-Ala-Asp-Gly-Val-Ala had a significant cytoprotective effect in Caco-2 cells under oxidative stress induced by H2O2, which reduced the formation of reactive oxygen species and malondialdehyde, and improved the activity of antioxidant enzymes in cells. These results showed that yak bone peptides exhibited strong antioxidant activity and have a potential value as a new type of natural antioxidant.

Physicochemical and functional properties of Maillard reaction products derived from cod (Gadus morhua L.) skin collagen peptides and xylose.

To improve the utilization of cod skin collagen peptides (CSCP), we heated them with xylose at 80 °C, 100 °C, and 120 °C for up to 150 min to prepare xylose-CSCP Maillard reaction products (MRPs), and then investigated their physicochemical and functional properties. The results showed that Arg, Lys, Phe, and Asp were the major amino acids involved in the Maillard reaction. After being heated at 120 °C for 150 min, the ABTS scavenging activity and reducing power of xylose-CSCP MRPs were 99.59% and 0.887 absorbance units, respectively. Xylose-CSCP MRPs had better emulsifying properties and foaming properties than CSCP. Furthermore, 26 volatile compounds, including 2,5-dimethyl-pyrazine and 2-ethyl-3,5-dimethylpyrazine, were identified from xylose-CSCP MRPs by gas chromatography-ion mobility spectrometry. Newly formed heterocyclic compounds might be responsible for the flavor and antioxidant capacity of xylose-CSCP MRPs. These results suggest the potential for xylose-CSCP MRPs to serve as functional food ingredients.

Modification of gelatin hydrolysates from grass carp (Ctenopharyngodon idellus) scales by Maillard reaction: Antioxidant activity and volatile compounds.

Fish scales are usually discarded or used to produce fish meal, etc. In order to enhance their utility, we produced the gelatin hydrolysates from fish scales (FSGH) and they were heated with glucose, xylose, and ribose to prepare sugar-FSGH Maillard reaction products (MRPs). The antioxidant capacity and sensory property of MRPs were evaluated. The results showed that ribose-FSGH MRPs exhibited higher antioxidant capacity than glucose- and xylose-FSGH MRPs. After simulated gastrointestinal digestion, the DPPH and ABTS scavenging activity of ribose-FSGH MRPs were 25.32 µM and 193.37 µM Trolox equivalent/g sample, respectively, and the reducing power was 0.509. Flavor compounds (such as butanal, benzaldehyde, 2-methyl-3-furanthiol, and maltol) of ribose-FSGH MRPs were produced in abundance after 5 h of heating and ribose-FSGH MRPs exhibited flavor enhanced effect on caramel-like and mouthfulness sensory attributes. These results suggest that ribose-FSGH MRPs can be potentially used as food antioxidants.

Changes in Quality and Microbial Succession of Lightly Salted and Sugar-Salted Blunt Snout Bream ( Megalobrama amblycephala) Fillets Stored at 4°C.

The effect of a low concentration of salt and sugar on the quality and microbial succession in blunt snout bream ( Megalobrama amblycephala) fillets was assessed by sensory analysis, total volatile basic nitrogen, biogenic amines, K value, total viable counts, 16S rRNA gene analysis, and Illumina MiSeq PE300 high-throughput sequencing. Fish samples were left untreated (control), treated with 1.8% salt (T1), or treated with 1.8% salt plus 0.9% sugar (T2). Consequently, salted and sugar-salted treatments extended the shelf life of bream fillets by 2 days, which retarded the increase of total volatile basic nitrogen, putrescine, cadaverine, and total viable counts. The putrescine and cadaverine concentrations of T2 were significantly ( P < 0.05) higher than T1 after day 10. Brachybacterium was the major initial microbiota of bream fillets. As storage time progressed, Pseudomonas and Shewanella were major genera in the spoiled control group. Pseudomonas, Shewanella, and Pseudoalteromonas became the main spoilers in the T1 and T2 groups.

Influence of heat processing on the volatile organic compounds and microbial diversity of salted and vacuum-packaged silver carp (Hypophthalmichthys molitrix) fillets during storage.

Ready-to-eat products have become popular with most of the busy people in modern cities. Heat processing combined with vacuum-packaging is one of the most common methods to make ready-to-eat products with an extended shelf-life. In this study, the influence of heat processing [80 °C (LT) and 98 °C (HT) in water bath] on the quality of salted and vacuum-packaged silver carp (Hypophthalmichthys molitrix) fillets, stored at 20 ± 1 °C, was investigated by sensory analysis, biochemical analysis, and microbial diversity. SPME-GC/MS indicated the presence of 27 volatile organic compounds (VOCs) in fillets, and major VOCs were aldehydes and alcohols. Acids tended to increase during storage and caused a fetid odor at the end of storage. Culture-dependent method indicated that Bacillus dominated the spoiled LT and HT samples. In addition, Bacillus was identified as the main spoiler of deteriorated heated fillets by high-throughput sequencing. Sphingomonas and Brevibacillus dominated the indigenous bacteria of fresh raw fillets. After heat processing, LT samples exhibited higher organoleptic quality than HT samples on day 0. HT samples showed extended shelf-life at 20 °C storage compared to LT samples.

Effect of transglutaminase on quality and gel properties of pork and fish mince mixtures.

Transglutaminase (TGase) is widely applied in the meat industry, and mixing of meat from various sources is an efficient way to enhance the quality of meat products. In this study, sensory scores, color, gel properties, water holding capacity and microstructure of mince mixtures, treated with 0.4% TGase, were determined to investigate the effect of TGase and mixing ratios (pork/fish, 10:0, 7:3, 5:5, 3:7, 0:10) on quality and gel properties of mince mixtures composed of pork and silver carp (Hypophthalmichthys molitrix). Results indicated that the mixture improved the sensory quality and gel properties of meat products compared to control group. The addition of TGase significantly (p < .05) increased the gel strength, especially at 7:3 ratio of pork and silver carp, in which gel strength reached its maximum and was 10.26%, 64.15% greater than pork with TGase and without TGase respectively, and water holding capacity were greater, and microstructure became more compact. The results suggest the synergetic interaction between proteins of pork and silver carp. TGase increased the interaction, especially for mixing proportion of 7:3 (pork/fish). Those results could be useful for the development of mixed and new meat products in the food industry. PRACTICAL APPLICATIONS: Pork and silver carp are two main meat in diet, and mince mixtures can improve the nutrition of meat product. TGase is usually used to enhance the texture and gel properties of meat in industry. The addition of TGase in pork/fish mince mixtures can not only improve the texture, but catalyze the synergetic interaction between proteins from different meat and further enhance gel properties of mice mixtures in a certain ratio. All of that will provide reference for meat processing and development of new meat product.

Biogenic Amines and Predictive Models of Quality of Rainbow Trout ( Oncorhynchus mykiss ) Fillets during Storage.

To estimate biogenic amines and changes in quality of rainbow trout ( Oncorhynchus mykiss ) fillets at different temperatures, we determined the sensory attributes, total volatile basic nitrogen (TVB-N), total viable counts (TVC), and biogenic amines (BAs) of samples that were untreated (CK) or dry cured with 1.8% salt (T). There was no significant difference between CK and T samples in terms of TVB-N, TVC, and BAs. TVB-N and TVC increased significantly (P < 0.05) with storage time at 3, 9, and 15°C. Putrescine (PUT) and cadaverine (CAD) increased significantly (P < 0.05) at -3, 3, 9, and 15°C during storage. Histamine formed more easily when storage temperatures were higher. The kinetic models of sensory scores for TVB-N, TVC, PUT, CAD, and the sum of PUT and CAD (PUT+CAD) in T samples versus storage time and temperature were developed based on the Arrhenius equation. High regression coefficients (R2 > 0.9) indicated the acceptability of the kinetic model for predicting changes in the quality of the rainbow trout fillets. Relative errors between predicted and experimental values of TVB-N, TVC, and PUT+CAD were all within 10% except for TVB-N on day 6. The prediction model based on TVB-N, TVC, and PUT+CAD can be applied to evaluate changes in quality of rainbow trout fillets from -3 to 15°C (270 to 288 K).

Quality Changes and Biogenic Amines Accumulation of Black Carp (Mylopharyngodon piceus) Fillets Stored at Different Temperatures.

Postmortem quality changes of black carp (Mylopharyngodon piceus) fillets stored at 20, 4, and 0°C (in ice) were determined in terms of pH value, K value, total volatile basic nitrogen, free amino acids, biogenic amines, drip loss, electrical conductivity (EC), sensory score, and microbial growth. The results showed that black carp fillets could maintain a good quality for 2, 9, and 12 days when stored at 20, 4, and 0°C, respectively. Pseudomonads, Aeromonas, and Enterobacteriaceae were the main spoilage bacteria in black carp. Tryptamine, 2-phenylethylamine, putrescine, cadaverine, and tyramine increased significantly (P < 0.05) during storage at the three temperatures, but not spermidine and spermine, among which tyramine and putrescine were the main biogenic amines in black carp fillets. A significantly higher concentration of histamine (132.05 mg/kg on the third day) was detected in the samples stored at 20°C (P < 0.01) than at 4 and 0°C (0.62 to 3.28 mg/kg) throughout storage, indicating storage of samples at 20°C favored the formation of histamine. The accumulations of tyramine, cadaverine, and histamine were highly correlated with the productions of tyrosine, lysine, and histidine, respectively. Correlations between EC and sensory, physical, chemical, and microbial parameters at the three storage temperatures showed that EC could be used as a better quality indicator to assess the overall quality of fish stored at 4 and 0°C (low temperature) than at 20°C.

Biogenic amine and quality changes in lightly salt- and sugar-salted black carp (Mylopharyngodon piceus) fillets stored at 4°C.

The effects of low salt and sugar dry-curing on the quality changes of black carp (Mylopharyngodon piceus) fillets stored at 4°C were evaluated by sensory, physical, chemical, and microbiological methods. Fish samples were left untreated (control), or were dry-cured with 1.5% salt (T1) or 1.5% salt+1.2% sugar (T2). Curing treatments reduced chemical changes reflected in HxR, Hx, pH, and total volatile base nitrogen (TVB-N); decreased cooking loss; and increased overall sensory quality of fish (p<0.05) compared to untreated samples. Significantly lower values of cadaverine and putrescine were observed in T1 and T2 compared to the control after the 2nd and 4th day, respectively (p<0.05). There were significant differences (p<0.05) between T1 and T2 for pH, TVB-N, total aerobic counts (TAC), and sensory characteristics. Sensory characteristics were significantly correlated with TAC, TVB-N, putrescine, and cadaverine in all samples (p<0.01).

[Determination of the contents of resveratrols and piceids in wines by high performance liquid chromatography with solid phase extraction].

A method has been developed for the determination of the contents of cis- and trans-resveratrols and piceids in wines by high performance liquid chromatography (HPLC) with solid phase extraction (SPE). The techniques of SPE including the activation of the SPE column, elimination of interference and elution conditions of samples were confirmed. The analytes were separated by using a Hypersil C18 column (4.6 mm i. d. x 250 mm, 5 microm) and acetonitrile-water as mobile phase with linear gradient elution. A photodiode array detector monitored at the detection wavelengths of 288 nm and 306 nm for cis- and trans-isomers, respectively. The external standard calibration curves were used in quantitation. There were good linear correlations between the concentrations and peak areas of the four components with the correlation coefficients of 0.9973-0.9999. The average recoveries were 97.4%-98.6% with relative standard deviations of 2.1%-3.2%. The detection limits were 0.002-0.005 mg/L. The method of SPE-HPLC eliminated a great deal of interferences in wines effectively by optimizing extraction conditions. The four isomers were well separated and the analytical results were improved well and truly. The results for determining 15 market wines showed that as an important bioactive substance, the resveratrol content has close relationships with brewing methods, varieties of grape and producing areas. The results also showed that it is a convenient, rapid, sensitive and accurate method. It can be used to analyze resveratrols and piceids in other natural samples.