Amino Acid Fraction Research Articles

Effect of extraction pH on the emulsion stability and surface protein structure of soybean oil body.

In this study, the pH was varied (6.0-11.0) during the extraction of soybean oil body (SOB), and the stabilities of the corresponding emulsions as well as the structural properties of SOB surface proteins were investigated. The extraction pH was found to affect both the SOB emulsion stability and surface protein structure. Micromorphological analysis showed that the degree of SOB dispersion was higher under alkaline conditions compared to other treatment conditions (acidic or neutral). Structural changes in the SOB surface proteins, as evaluated using changes in the α-helix and β-sheet contents and fluorescence intensity, were more pronounced when extraction was performed at pH11.0. Structural changes in SOB surface proteins also affected the amino acid fractions, surface hydrophobicity, and free sulfhydryl content. Overall, an extraction pH of 11.0 resulted in optimal SOB emulsion stability and had the greatest effect on the structural properties of the SOB surface proteins.

The simplicity of protein sequence-function relationships

How complex are the rules by which a protein’s sequence determines its function? High-order epistatic interactions among residues are thought to be pervasive, suggesting an idiosyncratic and unpredictable sequence-function relationship. But many prior studies may have overestimated epistasis, because they analyzed sequence-function relationships relative to a single reference sequence—which causes measurement noise and local idiosyncrasies to snowball into high-order epistasis—or they did not fully account for global nonlinearities. Here we present a reference-free method that jointly infers specific epistatic interactions and global nonlinearity using a bird’s-eye view of sequence space. This technique yields the simplest explanation of sequence-function relationships and is more robust than existing methods to measurement noise, missing data, and model misspecification. We reanalyze 20 experimental datasets and find that context-independent amino acid effects and pairwise interactions, along with a simple nonlinearity to account for limited dynamic range, explain a median of 96% of phenotypic variance and over 92% in every case. Only a tiny fraction of genotypes are strongly affected by higher-order epistasis. Sequence-function relationships are also sparse: a miniscule fraction of amino acids and interactions account for 90% of phenotypic variance. Sequence-function causality across these datasets is therefore simple, opening the way for tractable approaches to characterize proteins’ genetic architecture.

Amino acid composition of canned main dish increased food value

It is relevant to reduce the meat raw material in the composition of canned main dishes – porridge with meat due to the unsatisfactory state of livestock production in Ukraine. It is promising to use in the technology of canned main dishes – porridge with meat of non-traditional cereals – spelt, which is superior in terms of amino acid composition to certain types of traditionally used cereals. The purpose of the article is to study the amino acid composition of the canned main dish – porridge with meat containing spelt groats. The mass fraction of essential amino acids was determined by the chromatographic method. The amino acid score, the coefficient of its discrepancy and the biological value determined by calculation method. According to the results of determining the content of essential amino acids in porridge with meat containing spelt groats (experimental sample), their amount was lower compared to the control, namely isoleucine – by 44.74 %, lysine – by 23.75 %, leucine – by 14.64 %, threonine – by 11.36 %, valine – by 9.26 %, methionine – by 12.00 %, tryptophan – by 7.69 %, phenylalanine – by 2.17 %, histidine – by 8.57 %. The developed canned main dish – porridge with meat containing spelt groats is a source of leucine and lysine. The calculation of the amino acid score in experimental sample showed that all essential amino acids have a value of 100 % and above, and the limited amino acid is isoleucine, the score of which is 100 %, and the highest score belongs to histidine – 181 %. It was established that the coefficient of divergence of the amino acid score in experimental sample is higher by 2.56 %, and the indicator of biological value is lower by 2.57 % compared to the control, which is not significant. Thus, the reduction of meat raw materials in the recipe composition of porridge with meat made it possible to preserve the amino acid composition due to the use of spelt groats, and the finished product can be classified as a complete food product.

Dry deposition fluxes, source, and potential ecological impact of amino acids in the Danjiangkou Reservoir of China's South-to-North water transfer project

As a nitrogen source for biological growth, amino compounds can participate in global nitrogen cycle processes and directly impact ecosystems. Dry deposition samples were collected from September 2020 to August 2021 from the Danjiangkou Reservoir of the South-to-North Water Transfer Project. The dry deposition characteristics of amino acids in the reservoir area were analyzed, their sources were resolved, and the potential ecological impacts were evaluated. The results showed that the dry deposition flux of dissolved free amino acids was 0.48 kg N ha−1 yr−1 and that of dissolved combined amino acids was 1.09 kg N ha−1 yr−1 in Danjiangkou Reservoir. The dominant amino acid fractions were glutamic acid and aspartic acid. Agricultural activities, coal combustion, and primary biogenic particles influenced the amino acid deposition in the reservoir area. The potential source areas for amino acid deposition mainly influenced the northeast, southwest, northwest, and south of the reservoir. The amounts of amino acids entering the water bodies via dry deposition was 85.72 t N yr−1, contributing 0.83 g C m−2 yr−1 of new production to the reservoir water bodies. To summarize, this research depicted that the potential ecological impact of dry deposition of amino acids on artificial freshwater lakes should not be overlooked.

Химический состав и качественные показатели говядины бычков мясных пород

Purpose. To study the effect of the genotype of bulls on the chemical composition and commodity-technological parameters of beef. Materials and Methods. The object of research is 18–month-old crossbred bulls, obtained as a result of industrial crossing of Kazakh white-headed cattle bulls with heifers of Kalmyk breed (group I), Kazakh white-headed bulls with heifers of Hereford breed (group II) and Kazakh white-headed bulls with heifers of Aberdeen-Angus breed (group III). Purebred bulls of the Kazakh white-headed breed were used as a control group. The slaughter qualities of the experimental animals were determined by control slaughter of three bulls from each group. Chemical analysis of beef samples was carried out according to the following methods and GOST standards: moisture content was determined by drying the sample to a constant mass at a temperature of 100-105°C according to GOST 9793-2016; protein content – by the amount of protein nitrogen by the Kjeldahl method according to GOST 25011-2017; fat content – according to GOST 23042-2015; ash content – according to GOST 31727-2012; amino acid composition was determined according to the method of measuring the mass fraction of amino acids by the CE method on the Kapel-105M system, the concentration of hydrogen ions (pH) was determined according to GOST R 51478-99. Results. It was found that the highest slaughter qualities were possessed by crossbred bulls of the III experimental group. The highest dry matter content was in the average sample of meat of bulls of the III experimental group – 35.13%, which is 0.63% more than in the control; the difference in fat content was 0.23% in favor of the control group. In terms of protein content, the largest amount was recorded in the meat of bulls of the III experimental group – 20.07%, which is higher than in the samples of the control, I and II experimental groups, respectively, by 0.60, 0.84 and 0.77%. The protein-quality index in the samples ranged from 6.30 to 6.48. The pH value of the meat varied slightly – from 5.60 to 5.77. Conclusion. The conducted research has allowed us to establish that the industrial crossing of the Kazakh white-headed cattle with different meat breeds contributes to an increase in productivity, quality indicators, and the beef produced. This is explained by good compatibility of crossed breeds and high breed qualities of studied breeds.

Co-Immobilization of Alcalase/Dispase for Production of Selenium-Enriched Peptide from Cardamine violifolia.

Enzymatically derived selenium-enriched peptides from Cardamine violifolia (CV) can serve as valuable selenium supplements. However, the industrial application of free enzyme is impeded by its limited stability and reusability. Herein, this study explores the application of co-immobilized enzymes (Alcalase and Dispase) on amino resin for hydrolyzing CV proteins to produce selenium-enriched peptides. The successful enzyme immobilization was confirmed through scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and Fourier-transform infrared spectroscopy (FTIR). Co-immobilized enzyme at a mass ratio of 5:1 (Alcalase/Dispase) exhibited the smallest pore size (7.065 nm) and highest activity (41 U/mg), resulting in a high degree of hydrolysis of CV protein (27.2%), which was obviously higher than the case of using free enzymes (20.7%) or immobilized Alcalase (25.8%). In addition, after a month of storage, the co-immobilized enzyme still retained a viability level of 41.93%, showing fairly good stability. Encouragingly, the selenium-enriched peptides from co-immobilized enzyme hydrolysis exhibited uniform distribution of selenium forms, complete amino acid fractions and homogeneous distribution of molecular weight, confirming the practicality of using co-immobilized enzymes for CV protein hydrolysis.

Potential of Subcritical Water Hydrolysis to Valorize Low-Valued Ray-Finned Fish (Labeobarbus nedgia): Effects of Hydrolysis Temperature and Pressurization Agent.

Subcritical water (SCW) hydrolysis was applied to valorize the low-valued ray-finned fish (Labeobarbus nedgia) into valuable protein hydrolysates, employing N2 and CO2 as pressurization agents at varying temperatures (140, 160, 180, and 200 °C). The degree of hydrolysis (DH) and total free amino acid content increased with temperature for both pressurizing agents. The highest DH (54.5 ± 0.4%) and total free amino acid content (210 ± 1 mg/gprot) were observed at 200 °C when CO2 gas was used as the pressurizing agent. Predominantly, glycine and alanine were released for both pressurizing agents. The antioxidant activity, evaluated through three different assays, increased with temperature and was found to be the highest at 200 °C. This study illustrated the advantages of the intensified SCW technology by using CO2 as a pressurization agent in valorizing low-valued ray-finned fish (Labeobarbus nedgia), as animal residue rich in proteins, for the production of valuable protein hydrolysates with a high fraction of valuable free amino acids, which could offer potential applications as a functional ingredient in the food industry.

Extant Sequence Reconstruction: The Accuracy of Ancestral Sequence Reconstructions Evaluated by Extant Sequence Cross-Validation

Ancestral sequence reconstruction (ASR) is a phylogenetic method widely used to analyze the properties of ancient biomolecules and to elucidate mechanisms of molecular evolution. Despite its increasingly widespread application, the accuracy of ASR is currently unknown, as it is generally impossible to compare resurrected proteins to the true ancestors. Which evolutionary models are best for ASR? How accurate are the resulting inferences? Here we answer these questions using a cross-validation method to reconstruct each extant sequence in an alignment with ASR methodology, a method we term “extant sequence reconstruction” (ESR). We thus can evaluate the accuracy of ASR methodology by comparing ESR reconstructions to the corresponding known true sequences. We find that a common measure of the quality of a reconstructed sequence, the average probability, is indeed a good estimate of the fraction of correct amino acids when the evolutionary model is accurate or overparameterized. However, the average probability is a poor measure for comparing reconstructions from different models, because, surprisingly, a more accurate phylogenetic model often results in reconstructions with lower probability. While better (more predictive) models may produce reconstructions with lower sequence identity to the true sequences, better models nevertheless produce reconstructions that are more biophysically similar to true ancestors. In addition, we find that a large fraction of sequences sampled from the reconstruction distribution may have fewer errors than the single most probable (SMP) sequence reconstruction, despite the fact that the SMP has the lowest expected error of all possible sequences. Our results emphasize the importance of model selection for ASR and the usefulness of sampling sequence reconstructions for analyzing ancestral protein properties. ESR is a powerful method for validating the evolutionary models used for ASR and can be applied in practice to any phylogenetic analysis of real biological sequences. Most significantly, ESR uses ASR methodology to provide a general method by which the biophysical properties of resurrected proteins can be compared to the properties of the true protein.

Recycling of animal protein wastes in the formulation of feed for Labeo rohita and Mystus vittatus—a comparative evaluation

Lactic acid bacteria (LAB) are key players in the fermentation of organic wastes and their recycling as feedstuff for fish. Whey, a common dairy byproduct in India, is a cheap source of LAB and can be used to ferment animal byproducts. An experimental study was designed to explore whether the whey fermented animal protein blend (WFAPB) could be used as a fishmeal replacer in the formulation of feed for both stomach-less carp fish Labeo rohita and stomach-bearing catfish Mystus vittatus. Experiments were performed with five isoproteinous, isolipidous, and isoenergetic feeds with WFAPB replacing fishmeal (FM) by 0% (T1), 25% (T2), 50% (T3), 75% (T4), and 100% (T5). Fifteen days of laboratory experiments with these experimental feeds revealed that more than 50% FM replacement level could result in excess postprandial absorption (6 h) of some essential and non-essential amino acids in the plasma of both fish. The postprandial absorption was more in M. vittatus than L. rohita. Ninety-day experiments were conducted in outdoor cement vats to measure growths and deposition of amino acids (AA) in muscle. Regression analysis was performed to find the optimal FM replacement based on four growth parameters and fifteen AA deposition in muscle. A two-phase fuzzy methodology was used to obtain Pareto-optimal replacement levels for each fish. The results demonstrated that FM replacement levels were 7.63% and 36.79% respectively for L. rohita and M. vittatus when only four growth parameters were considered. However, based on the FM replacement level that maximized deposition of 15 amino acids and growth parameters, it was found that 12.23% and 40.02% replacement of FM by the WFAPB was ideal respectively for L. rohita and M. vittatus. The results revealed that only a fraction of both essential and non-essential amino acids absorbed in plasma could be converted into protein and deposited as bound amino acids in the muscle. It is concluded that fermentation by whey is an inexpensive, easily available, and environmentally sustainable technique to recycle animal protein in the formulation of feed for fish, and the stomach-bearing carnivorous fish are more efficient in utilizing fermented animal protein blend than the stomach-less carps.

Development of a Two-Dimensional Liquid Chromatographic Method for Analysis of Urea Cycle Amino Acids.

The urea cycle has been found to be closely associated with certain types of cancers and other diseases such as cardiovascular disease and chronic kidney disease. An analytical method for the precise quantification of urea cycle amino acids (arginine, ornithine, citrulline, and argininosuccinate) by off-line two-dimensional liquid chromatography (2D-LC) combined with fluorescence-based detection was developed. Before analysis, the amino acids were derivatised with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) to obtain NBD-amino acids. The first dimension involved the reversed-phase separation, in which NBD derivatives of urea cycle amino acids were completely separated from each other and mostly separated from the 18 NBD-proteinogenic amino acids. The samples were eluted with stepwise gradient using 0.02% trifluoroacetic acid in water-acetonitrile as the mobile phase. In the second dimension, an amino column was used for the separation of NBD-ornithine, -citrulline, and -argininosuccinate, while a sulfonic acid column was used to separate NBD-arginine. The developed 2D-LC system was used to analyse human plasma samples. The fractions of NBD-urea cycle amino acids obtained in the first dimension were collected manually and introduced into the second dimension. By choosing appropriate mobile phases for the second dimension, each NBD-urea cycle amino acid eluted in the first dimension was well separated from the other proteinogenic amino acids and interference from endogenous substance. This could not be achieved in the first dimension. The urea cycle amino acids in human plasma sample were quantified, and the method was well validated. The calibration curves for each NBD-urea cycle amino acid showed good linearity from 3 (ASA) or 15 (Orn, Cit, and Arg) to 600 nM, with correlation coefficients higher than 0.9969. The intraday and interday precisions were less than 7.9% and 15%, respectively. The 2D-LC system is expected to be useful for understanding the involvement of the urea cycle in disease progression.

Allosteric regulation in SARS-CoV-2 spike protein.

Allosteric regulation is common in protein-protein interactions and is thus promising in drug design. Previous experimental and simulation work supported the presence of allosteric regulation in the SARS-CoV-2 spike protein. Here the route of allosteric regulation in SARS-CoV-2 spike protein is examined by all-atom explicit solvent molecular dynamics simulations, contrastive machine learning, and the Ohm approach. It was found that peptide binding to the polybasic cleavage sites, especially the one at the first subunit of the trimeric spike protein, activates the fluctuation of the spike protein's backbone, which eventually propagates to the receptor-binding domain on the third subunit that binds to ACE2. Remarkably, the allosteric regulation routes starting from the polybasic cleavage sites share a high fraction (39-67%) of the critical amino acids with the routes starting from the nitrogen-terminal domains, suggesting the presence of an allosteric regulation network in the spike protein. Our study paves the way for the rational design of allosteric antibody inhibitors.

Elevated Plasma Tryptophan in Patients with Anorexia Nervosa Compared with Hypotrophic Controls

We hypothesized that anorexia nervosa (AN) is associated with pathological amino acid metabolism. This study aimed to identify amino acids exhibiting abnormal metabolism in patients with AN compared with those in low-nutrient controls. This was a single-center, retrospective, observational study that compared patients with AN with a low-nutrient control group. All participants were admitted to the Kitasato University Hospital Emergency Center between January 1, 2018, and January 31, 2021. Both the AN and low-nutrient control groups had five patients each. Plasma amino acid category testing was conducted at the same institution for both groups. Patient sex, age, height, weight, and comorbidities were retrospectively extracted. Plasma amino acid fractions, total amino acids, total essential amino acids, total nonessential amino acids, branched-chain amino acids (sum of valine, isoleucine, and leucine), and amino acid concentrations and ratios were compared between the two groups. Data were analyzed using the Mann-Whitney U test. Body mass index was lower in the AN group (p = 0.00794). Tryptophan levels were significantly higher in the AN group (p = 0.00794). Other amino acid values, the sum of amino acid values, and amino acid ratios were not significantly different between both groups. Serum tryptophan levels were higher in the AN group than in the low-nutrient group, and AN may be associated with abnormal amino acid metabolism.

Влияние генотипа крупного рогатого скота на химический состав говядины

Purpose. To study the slaughter qualities of mixed young cattle and the chemical composition of beef obtained from it. Materials and Methods. The object of research is 18-month-old crossbred bulls, obtained as a result of industrial crossing of Kazakh white-headed cattle bulls with heifers of the Simmental breed (group I), Hereford bulls with heifers of the Simmental breed (group II) and Kalmyk bulls with heifers of red steppe cattle (group III). Purebred bulls of the Kazakh white-headed breed were used as a control group. Chemical analysis of beef samples was carried out according to the following methods and GOST standards: moisture content was determined by drying the sample to a constant mass at a temperature of 100-105 °C according to GOST 9793-2016; protein content – by the amount of protein nitrogen by the Kjeldahl method according to GOST 25011-2017; fat content – according to GOST 23042-2015; ash content – according to GOST 31727-2012; the amino acid and vitamin composition was determined according to the method of measuring the mass fraction of amino acids and vitamins by the KE method on the Kapel-105M system, the concentration of hydrogen ions (pH) according to GOST R 51478-99. Calorie content of 100 g / meat was calculated using the formula of V. M. Aleksandrov. Results. To assess the meat productivity of crossbred steers, their control slaughter was carried out, which showed that the largest slaughter weight and slaughter yield were possessed by steers of the II experimental group – 312.4 kg and 61.0%. Beef samples from young animals of the II experimental group had the highest content of dry matter. The difference with peers from the control, I and III groups was 0.27, 0.21 and 0.63%, respectively. It was also noted that the crossbred young of the II experimental group surpassed purebred Kazakh white-headed bulls in protein content by 1.67%. The difference with the crossbreeds from group I and III is 1.38 and 2.3% respectively. A study of the vitamin composition of the beef of experimental young animals showed that the resulting beef was relatively rich in vitamins of group B. beef obtained from crossbred bulls of the II experimental group has a higher biological value (Protein qualitative indicator = 5.86 compared with the control 5.59). The increase in protein qualitative indicator is mainly due to the higher content of tryptophan in beef of the experimental group II – by 9.0% (494.40 mg% compared with 453.86 mg% in the control). The pH value of the water-meat extract in bulls of different genotypes is almost the same and ranged from 5.41 to 5.49. Conclusion. It has been established that the crossing of bulls of meat breeds of cattle with heifers of dairy and combined breeds contributes to the production of young offspring with excellent slaughter qualities, and beef obtained from such offspring has a high biological value.

15 Industry Perspective on the Value and Challenges of Amino Acid Feeding in Ruminants

Abstract The focus of this presentation is to provide a perspective on the value and challenges to meeting the amino acid needs of ruminant livestock based on experiences in the feed manufacturing and ruminant feeding industries. Monogastric nutritionists have demonstrated extensively the value of having an ideal amino acid profile from the point of growth, efficiency, and environmental stewardship. For the ruminant animal, the challenges of protein fractionation, deamination and re-synthesis of amino acids in the rumen create greater complexity both for research advancement as well as practical application to delivery of amino acid technology. In this presentation, amino acid supplies, protein synthesis, the impact of overlaid growth-promoting technologies, and return relative to investment of amino acid-feeding technology will be discussed. In addition to discussing the biological and economic aspects of amino acid feeding, thoughts on the means of delivering amino acid technology within the constraints of feed manufacturing and feeding practices common to ruminant livestock will be discussed. As genetics for improved lean growth in cattle continue to evolve, amino acid nutrition should be at the forefront of investigation of nutritional technologies which allow the improvement in genetic potential to be fully expressed. In addition to the potential value that amino acid feeding brings to ruminant livestock growth and efficiency, it also stands to merit environmental stewardship within this industry.

Raman Multi-Omic Snapshots of Koshihikari Rice Kernels Reveal Important Molecular Diversities with Potential Benefits in Healthcare.

This study exploits quantitative algorithms of Raman spectroscopy to assess, at the molecular scale, the nutritional quality of individual kernels of the Japanese short-grain rice cultivar Koshihikari in terms of amylose-to-amylopectin ratio, fractions of phenylalanine and tryptophan aromatic amino acid residues, protein-to-carbohydrate ratio, and fractions of protein secondary structures. Statistical assessments on a large number of rice kernels reveal wide distributions of the above nutritional parameters over nominally homogeneous kernel batches. This demonstrates that genetic classifications cannot catch omic fluctuations, which are strongly influenced by a number of extrinsic factors, including the location of individual grass plants within the same rice field and the level of kernel maturation. The possibility of collecting nearly real-time Raman "multi-omic snapshots" of individual rice kernels allows for the automatic (low-cost) differentiation of groups of kernels with restricted nutritional characteristics that could be used in the formulation of functional foods for specific diseases and in positively modulating the intestinal microbiota for protection against bacterial infection and cancer prevention.

Origin, distribution and spatial characteristics of dissolved organic matter in the Heilongjiang River

The Heilongjiang River Basin is a vast area with significant DOM sources and composition differences. The mechanism of DOM degradation under spatial variation remains unclear. This research investigated the degradation characteristics of DOM in different watersheds of the Heilongjiang River. DOM levels were higher in midstream waters, while DOM degradation rates were higher in midstream and downstream waters. The parallel factor analysis (PARAFAC) results showed that the upstream amino acid fraction was significantly depleted, the midstream was dominated by the degradation of DOM of terrestrial origin, and the downstream humic acid fraction was decreased considerably. Gene sequencing results indicated that the upstream, middle, and downstream water bodies' microbial community composition and structure differed significantly. The network analysis results revealed microorganisms in upstream water bodies mainly utilized amino acid-like substances and small molecule humic acids. Microorganisms in the middle and lower reaches of the water column were characterized by the utilization of humic acid-like fractions. In this study, we further screened the key driving microorganisms (e.g., Flavobacterium and Lacibacter) responsible for the difference in the DOM utilization function of upstream-to-midstream and midstream-to-downstream microorganisms in the Heilongjiang River. These findings will help identify the cycling process of DOM under spatial variation and predict the succession pattern of microbial communities.

Separation and fractionation of glutamic acid and histidine via origami isoelectric focusing

We demonstrated the fractionation of two amino acids, glutamic acid and histidine, separated via isoelectric focusing (IEF) on filter paper folded and stacked in an origami fashion. Channels for electrophoresis were fabricated as circular zones acquired via wax printing onto the filter paper. An ampholyte solution with amphiphilic samples was deposited on all the circle zones, which was followed by folding to form the electrophoresis channels. IEF was achieved by applying an electrical potential between the anodic and cathodic chambers filled with phosphoric acid and sodium hydroxide solutions, respectively. A pH gradient was formed using either a wide-range ampholyte with a pH of 3 to 10 or a narrow-range version with a pH of 5 to 8, which was confirmed by adding pH indicators to each layer. The origami IEF was used to separate the amino acids, glutamic acid and histidine, by mixing with the ampholytes, which were deposited on the layers. The components in each layer were extracted with water and measured by high-performance liquid chromatography using pre-column derivatization with dansyl chloride. The results indicated that the focus for glutamic acid and that for histidine were at different layers, according to their isoelectric points. The origami isoelectric focusing achieved the fractionation of amino acids in less than 3 min using voltage as low as 30 V.

Effect of Marinating Temperature of Atlantic Herring on Meat Ripening, Peptide Fractions Proportion, and Antioxidant Activity of Meat and Brine

The temperature has a significant effect on cathepsin activity, but the effect of temperature on the ripening of marinades, and the formation of protein hydrolysis products, is less studied than other technological factors. The results of this study showed that herring marinated at 2 °C showed a higher mass yield, but lower non-protein nitrogen (NPN), peptides, and free amino acid fraction content, than after marinating at 7 and 12 °C. The higher temperature increased the free amino acid content the most, and decreased the hardness, as measured via sensory assessment, of the marinated meat. This was confirmed by the hardness measurement in the texture profile analysis. The highest activity of cathepsins D and B in the meat was found at 7 °C, while cathepsin L was found at 2 °C. Increasing the temperature by 10 °C increased the diffusion/loss of nitrogenous substances from the meat to the brine by 36%. The meat and brine showed high antioxidant activity, which depended on the marinating temperature, and originated mainly from the 5–10 or <5 kDa fraction. The meat had a higher ABTS (2,2′-azinobis-3-ethylbenzothiazoline-6-sulfonate) activity than the brine, opposite to the DPPH (2,2-diphenyl-1-picrylhydrazyl radical) activity, while the FRAP (Ferric Reducing Antioxidant Power) capacity was similar for meat and brine. The fractionation of the meat and brine extracts increased the antioxidant potential of FRAP and ABTS only for the brine. The most hydrophobic peptides were released during marinating at 7 °C. The meat and brine were dominated by 2–4 kDa peptides, followed by 4–6 and 0.5–2 kDa. The higher temperature favored a higher proportion of <4 kDa than >4 kDa peptides in the brine.

Variations in the concentration of free amino acids during the early development of the Pacific red snapper Lutjanus peru

The free amino acids (FAAs) profile and its variations during the embryonic development and yolk-sac larvae of Pacific red snapper Lutjanus peru are described. The concentration of 15 FAAs (nine essentials and six non-essentials) was evaluated by reverse-phase high-performance liquid chromatography. The fertilized eggs of L. peru contain a small concentration of FAAs (4.77 ± 0.89 nmol ind-1). However, the variations in the FAAs pool during the early development are similar to the changes reported in other species with small pelagic eggs. The essential free amino acids are more abundant than the non-essential free amino acids throughout the studied period. During the egg stage, an increase in the FAAs was observed, and after hatching, isoleucine, leucine, lysine, and alanine were the FAAs that decreased the most during the yolk-sac larvae stage. The hatching rate was correlated with the total FAAs, the fraction of essential free amino acids, and the concentrations of glutamic acid, threonine, and valine in the egg stage, suggesting a possible role as a determinant in egg quality. Further studies are required to assess the role of FAAs in other aspects of egg development, like fertilization rate and egg buoyancy.

Synthesis and characterization of new nanocomposites-based polyimide/modified montmorillonite and their applications in gas separation

ABSTRACT This study reports synthesis of nanocomposite materials-based polyimide (PI) matrix and reactive modified montmorillonite (m-MMT) as a reinforcing agent. New diamine and PI derived from amino acid (L-phenylalanine) fractions in the structure as pendant group were synthesized. The best dispersion of m-MMT was observed for PI/m-MMT 3% nanocomposites, which resulted in the best mechanical performance with an increase of 56% in tensile modulus and 14% in yield strength, respectively compared to that of pure PI. The maximum ideal selectivity achieved was 15.89 with 3% loading at 4 bar pressure which is 42.52% higher than neat PI membrane.