Effects of increased supply of essential amino acids on the metabolism of the isolated perfused guinea-pig mammary gland.

The effects of high rates of infusion of essential amino acids on amino acid uptake by the isolated perfused guinea-pig mammary gland were studied. Infusion of methionine, tyrosine, phenylalanine, histidine and tryptophan (designated group 1) resulted in significant increases in the uptakes of tyrosine, phenylalanine and histidine. Methionine, tryptophan and other essential amino acids were not significantly affected. Infusion of threonine, valine, isoleucine, leucine, lysine and arginine (designated group 2) resulted in significant increases in uptake of all these amino acids. Group 1 amino acid uptake was not significantly affected. Infusion of all the essential amino acids (i.e. groups 1 and 2 together) resulted in significant increases in all their uptakes. Using as index 'the predicted rate of protein synthesis', infusion of group 1 and 2 together led to an apparent 27% increase in protein synthesis. The above results are discussed in relation to the control of milk protein synthesis by limiting essential amino acids.     

Photosensitized amino acid degradation in the presence of riboflavin and its derivatives

The addition of photosensitizers to water can accelerate disinfection in sunlight-based systems by enhancing oxidation of target compounds through direct reaction with the excited sensitizer or through production of another oxidant, such as singlet oxygen (1O?). The kinetics of the oxidation of selected amino acids in the presence of the sensitizer riboflavin (Vitamin B2), its primary photoproduct lumichrome, and its derivative riboflavin tetraacetate (2',3',4',5'-tetraacetylriboflavin; RTA) were quantified and the mechanisms of reaction were determined during exposure to 365 ± 9 nm light. 1O?-mediated reactions contributed to the rapid photodegradation of the four amino acids, but its contribution was sensitizer-dependent and varied from 5.4-10.2% for tyrosine, 7.1-12.4% for tryptophan, 18.7-69.0% for methionine, and 64.7-100.2% for histidine. Riboflavin was subject to rapid photodegradation (t? < 8 min), while the half-lives of lumichrome and RTA were 100 and 30 times longer, respectively. Lumichrome and RTA also were more efficient 1O? sensitizers (quantum yield (Φ) = 0.63 and 0.66) compared to riboflavin (Φ = 0.48). Of the three flavin-based compounds, RTA shows the most promise as a sensitizer in sunlight-based disinfection systems because it absorbs both visible and UV light, is an efficient 1O? sensitizer, is a strong oxidant in its triplet state, and exhibits greater photostability.     

Effect of amino acids on the formation of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in creatinine/phenylalanine and creatinine/phenylalanine/4-oxo-2-nonenal reaction mixtures

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) formation in mixtures of creatinine, phenylalanine, amino acids and 4-oxo-2-nonenal was studied, to analyse the role of amino acids on the generation of this heterocyclic aromatic amine. When oxidised lipid was absent, cysteine, serine, aspartic acid, threonine, asparagine, tryptophan, tyrosine, proline, and methionine increased significantly (p < 0.05) the amount of PhIP formed in comparison to the control. When lipid was present, only the addition of methionine, glycine, and serine increased significantly (p < 0.05) the amount of PhIP produced, while histidine, cysteine, lysine, tryptophan, tyrosine, and alanine reduced significantly (p < 0.05) PhIP. These results may be a consequence of the different competitive reactions that occur. Thus, in the absence of lipids, thermal decomposition of the amino acids produced reactive carbonyls that converted phenylalanine into phenylacetaldehyde as a key step in the formation of PhIP. When oxidised lipid was present, amino acids competed with phenylalanine for the lipid, and amino acid degradation products were formed, among which alpha-keto acids seemed to play a role in these reactions. These results suggest that PhIP can be produced by several alternative reaction pathways from all major food components, including amino acids and lipids, in addition to carbohydrates.     

Effects of restriction of amino acid supply to the isolated perfused guinea-pig mammary gland.

When individual essential amino acids were omitted for periods of 40--100 min from the infusate substrate solution in isolated perfused guinea-pig mammary gland experiments, uptake of methionine, tyrosine, phenylalanine, histidine and tryptophan (group 1) was significantly depressed by a mean of 49.8%, whereas the remaining essential amino acids (group 2) showed no significant decrease in uptake. During depletion periods oxidation of [14C]amino acids was increased. The possible significance of the differences in absorption between the 2 groups of amino acids is discussed.     

Interaction between whey proteins and lipids during light-induced oxidation

Dairy products are a suitable group for polyunsaturated fatty acid (PUFA) fortification, but are very susceptible to light-induced oxidation. In this study, the combined effect of light and PUFA fortification on the stability of milk proteins and on the formation of protein-lipid complexes was studied. Therefore, emulsions were prepared containing whey proteins and lipids with a different degree of unsaturation (olive, soybean, fish and algae oil). PUFA stimulated the protein oxidation process, even after complete degradation of the photosensitizer. First order reaction kinetics were established for riboflavin and tryptophan degradation, as well as the formation of N-formylkynurenine, a tryptophan degradation product. Oxidation was further characterised by degradation of the essential amino acids lysine, histidine, methionine and tyrosine. Protein-lipid adduct formation, measured fluorometrically and by the protein-bound carbonyl groups, could be linked with a decreased extractability of the unsaturated lipids from the emulsion, but also caused the formation of protein aggregates of high molecular mass.     

Amino acids as modulators of lipoxygenase oxidation mechanism. The identification and structural characterization of spin adducts intermediates by electron spin resonance and tandem mass spectrometry

Antioxidant activity is displayed by amino acids, such as tryptophan (Trp), tyrosine (Tyr) and histidine (His) in the spontaneous oxidation of linoleic acid (LA). In addition, when Trp was incubated with soybean lipoxygenase (LOX 1) and LA, a modulating effect was observed. The elucidation of the reaction pathways was achieved through the identification, by electron spin resonance (ESR) spectroscopy, of α-[4-pyridyl 1-oxide]-N-t-butyl nitrone (POBN) adducts with the selected amino acids. The latter, when electrosprayed (ESI) were detected in the gas-phase as radical cations. They were structurally characterized by tandem mass spectrometry (MS/MS) through collision-induced dissociation (CID) of the adducts. The kinetic data obtained from selected model systems suggested a reversible radical scavenging activity of tryptophan on the intermediate dienyl radical formed in the lipids lipoxygenase cascade.     

Effect of Amino Acids and Peptides on Mixing and Frozen Dough Properties of Wheat Flour

Free amino acids, peptides, and vital wheat gluten were investigated to determine their effect on the mixing and frozen dough baking properties of wheat flour. Addition of 1% cysteine and aspartic acid decreased and glutamic acid, histidine, arginine, and lysine increased the mixing tolerance of flour. Cystine, methionine, tryptophan, and phenylalanine increased but isoleucine, histidine, glycine, arginine, glutamic acid, aspartic acid, and lysine decreased loaf volume of nonfrozen dough breads. However cystine, methionine, tryptophan, and phenylalanine did not increase loaf volume of bread prepared from frozen dough. Vital wheat gluten increased mixing tolerance and bread loaf volume only for the nonfrozen dough. However, wheat gluten hydrolysate, corn, and bonito peptides decreased mixing tolerance after optimum mixing time and were effective in increasing loaf volume for both frozen and nonfrozen dough. As the amount of corn and bonito peptide increased, specific loaf volumes also increased. Addition of 2.5% corn peptide was most effective in increasing loaf volume of frozen dough bread. Crust browning and crumb stickiness increased, whereas crumb softness decreased with addition of peptides. Addition of less than 1% peptide did not adversely affect the aftertaste and off‐flavor of bread. These results suggest that addition of peptides are effective for improving the baking quality of frozen dough, whereas amino acids and gluten have no effect.     

美拉德反应制备蛋糕香精及成分分析

研究了蛋黄酶解液的氨基酸组成,其含有可通过美拉德反应产生蛋糕香气的脯氨酸、蛋氨酸、赖氨酸等氨基酸。优化以蛋黄酶解液为前体原料,添加氨基酸、还原糖等通过美拉德反应制备蛋糕香精的条件,并分析产物的组成成分。结果表明,在反应温度110℃、反应时间60min、反应体系pH为6,物料配比为蛋黄液酶解物8.00%、葡萄糖0.40%、木糖0.20%、蛋氨酸0.02%、赖氨酸0.14%、脯氨酸0.04%、精氨酸0.04%、组氨酸0.02%、天冬氨酸0.02%、缬氨酸0.02%、水分14.50%、丙二醇76.60%,所得产物含有29种呈味物质,具有浓郁的蛋糕香味。     

Damage of Amino Acid Residues of Proteins after Reaction with Oxidizing Lipids: Estimation by Proteolytic Enzymes

A mixture of casein and methyl linoleate was stored at 50°C and 80% relative humidity for 0 - 14 days and damage to amino acid residues assessed. The damage was estimated by determining the amino acid composition of the hydrolysate by using proteolytic enzymes (pepsin-pancreatin digestion, followed by aminopeptidase-prolidase hydrolysis). The damage to amino acid residues was the most extensive in methionine, followed by tryptophan, histidine, and lysine. The degree of damage to these amino acids was also determined by chemical methods without using proteolytic enzymes. The efficiency of detecting damage by the present enzymatic method was close to that of the chemical methods.     

Amino acid pattern of the Egyptian apricot fruits (Hamawy)

Apricot fruits were subjected to acid hydrolysis and the amino acids were separated and quantitatively determined by paper chromatography. The analysis revealed the presence of 19 amino acids, predominantly glutamic acid, aspartic acid, histidine, arginine and tyrosine. The results also demonstrated that the concentrations of cystine, methionine and hydroxyproline were relatively small.     

Determination of the first-limiting amino acid for milk production in dairy cows consuming a diet of grass silage and a cereal-based supplement containing feather meal

Lactating dairy cows consuming a diet of grass silage and a cereal-based supplement containing feather meal were given intravenous infusions of amino acids to determine the first-limiting amino acid for milk production, methionine having been shown to be not-limiting in a previous experiment. The three infusion treatments were a mixture of methionine, lysine, histidine and tryptophan (4AA); the mixture without lysine (-Lys); and the mixture without histidine (-His). The 4AA treatment markedly increased the yield of milk protein by about 18% and this response was not diminished by omission of lysine. However, exclusion of histidine produced no response over basal, confirming histidine as the first-limiting amino acid. In a second experiment, lactating cows receiving a similar basal diet were used to examine the effects on milk production of progressively substituting avian blood meal (rich in histidine and poor in methionine) for part of the feather meal. Blood meal was substituted for 0, 0.10, 0.20 and 0.40 of the feather meal in the supplement. The yield of milk protein was increased by about 15% by the first level of inclusion of blood meal, but there was no further response beyond the first level of inclusion. The results of the feeding trial confirm that dietary addition of protein rich in histidine and of low ruminal degradability substantially increased milk production with this basal diet, although it should be noted that the calculated supply of all the essential amino acids were also increased, by varying degrees, by substitution of blood meal. The results of the two experiments are discussed in relation to the likely importance of histidine as a limiting amino acid in dairy cows consuming diets typical of those used in practice. © 1999 Society of Chemical Industry     

烟叶中游离氨基酸与化学成分派生值之间的关系

系统地分析了烤烟烟叶中游离氨基酸与化学成分派生值的关系。参试材料３１份,每个样品鉴定２６项指标。对试验数据分别进行简单相关分析、逐步回归和偏相关分析以及典型相关分析。简单相关分析结果表明,游离氨基酸组分与化学成分派生值之间均存在一定的相关关系。其中丝氨酸、甘氨酸、缬氨酸含量较高,钾／氯比值较高,则烟叶品质较好。逐步回归和偏相关分析系统地分析了游离氨基酸组分对化学成分派生值贡献的大小。其中对施木克值的贡献,以蛋氨酸最大,甘氨酸、丙氨酸和色氨酸次之;对于氧化钾与氯的比值来说,贡献最大的是丝氨酸。典型相关分析结果表明,游离氨基酸与化学成分派生值间的典型相关主要是由组氨酸、酪氨酸、脯氨酸、苯丙氨酸、亮氨酸、丙氨酸、苏氨酸、胱氨酸、天冬氨酸、氨与施木克值、两糖差及糖／碱比值相关显著引起的。     

Changes during ensilage in the nitrogenous components of fresh and additive treated ryegrass and lucerne

The changes in the major nitrogenous components of herbage during the ensilage of lucerne and Italian ryegrass, with and without the addition of 85% formic acid and 40% formaldehyde at the rates of 3.2 and 7.4 g kg^?1 fresh herbage respectively, were studied. Both herbages were of similar amino-N composition except for asparagine which was about 10% of total nitrogen (TN) in lucerne and only 0.2% of TN in Italian ryegrass. After 90 days ensiling about 90% of the sum of protein-, peptide-, amino- and amide-N was preserved in the additive-treated silages while only 58% was recovered in the untreated lucerne (butyrate) silage. Recoveries of these compounds in the untreated ryegrass (lactate) silage was 83%. In the butyrate silage, the branched chain amino acids, valine, leucine and isoleucine were well preserved. In addition to these, proline, phenylalanine, glycine, methionine and threonine were well preserved in the lactate silages. Both the untreated silages contained more alanine than in their original respective herbages. Most of the losses from the amine-forming amino acids were recovered as their corresponding amines. Alpha-amino butyric acid and δ-amino valeric acid were found in both the untreated silages and the quantity present was dependent on the silage quality. In both the additive-treated silages, recoveries of amino acids, other than sulphur amino acids, lysine, histidine, tyrosine and tryptophan, were ca 90% or greater. The losses of these amino acids, excluding the sulphur amino acids, can be attributed mainly to the direct effects of formaldehyde in preventing their estimation following freeze drying or acid hydrolysis.     

COMBINATION OF BLACK BEAN (PHASEOLUS VULGARIS) AMYLASE INHIBITOR WITH MODIFIED PANCREATIC α-AMYLASE

Several amino acid residues important for the action of porcine pancreatic α-amylase on starch were modified using specific reagents: histidine groups by photooxidation with rose bengal or by diethylpyrocarbonate; cysteine by dithiobis nitrobenzoic acid; tryptophan by N-bromosuccimide and tyrosine by hydroxyl acetylation with N-acetylimidazole. These modifications, with the exception of cysteine, reduced the amylase activity but none of them alone was able to alter significantly the inhibition of the enzyme by a purified black bean (Phaseolus vulgaris) amylase inhibitor. Only by photooxidation that can modify several groups at the same time was the inhibitor action eliminated. The results suggested that the histidine of the amylase active site and tyrosine of the substrate binding site are not important for binding to the bean inhibitor. The terminal sugars of the amylase inhibitor were identified as mannose and xylose. Periodate oxidation of the carbohydrate moiety caused total loss of activity. The treatment of the inhibitor with α-mannosidase did not alter its inhibitor action on α-amylase.     

Effects of Trolox and ascorbic acid on the riboflavin photosensitised oxidation of aromatic amino acids

The effects of 0, 100, 250, 500, 750 or 1000 ppm Trolox and ascorbic acid on the singlet oxygen oxidation of aromatic amino acids viz. phenylalanine, tryptophan, tyrosine in the presence of 25 ppm riboflavin were determined by measuring depleted headspace oxygen by gas chromatography and aromatic amino acid content by high performance liquid chromatography. The coefficients of variations (CVs) for headspace oxygen analysis and HPLC analysis of aromatic amino acids were 1.4% and 4.7%, respectively. Samples were stored under light (1000 lux) at 30 °C for 10 h. Both Trolox and ascorbic acid acted as antioxidants. As the concentration of Trolox and ascorbic increased from 0 to 1000 ppm, the head space oxygen depletion increased. This was due to the oxidation of Trolox and ascorbic acid along with amino acids in the presence of riboflavin. High performance liquid chromatography analysis of the samples clearly indicated that both Trolox and ascorbic acid minimised the degradation of phenylalanine, tryptophan, tyrosine significantly (p < 0.05), but did not prevent their oxidation completely. Trolox acted as a better antioxidant than ascorbic acid in protecting phenylalanine, tryptophan and tyrosine. Type-I mechanism was mainly responsible for riboflavin photosensitised degradation of aromatic amino acids.     

The effects of intravenous supplements of amino acids on the milk production of dairy cows consuming grass silage and a supplement containing feather meal

Two experiments were carried out to identify the limiting amino acids for milk production in dairy cows consuming diets based on grass silage and a cereal-based supplement containing feather meal as the only high-protein ingredient. In the first experiment, the yield of protein in milk was increased by 26% in response to intravenous infusion of a mixture of histidine, lysine, methionine and tryptophan. In the second experiment, omission of methionine from the infused mixture led to no reduction in the milk response compared with that seen with the mixture of four amino acids, confirming that methionine was not limiting milk production from the basal diet. The results have important implications for the choice of complementary proteins to blend with feather meal in diets for ruminants.     

Chemical,amino acid and fatty acid composition of Sterculia urens L. seed

The chemical, amino acid and fatty acid compositions of Sterculia urens seeds are reported. The cotyledons were found to be rich in protein (30.88%) and lipids (39.2%). The major amino acids in defatted Sterculia urens cotyledon flour (DSCF) were determined as glutamic acid, arginine and aspartic acid. Cysteine, methionine, tyrosine and histidine were observed in minor quantities. The ratio of essential to non-essential amino acids was observed to be 0.45. Among the essential amino acids, isoleucine was found to be higher than the reported FAO/WHO requirements. The GC-FID and GC–MS analysis revealed that the major fatty acids of the total lipid were stearic acid (31.72%), linoleic acid (28.83%) and palmitic acid (26.79%). Eicosadienoic acid (4.98%) and eicosatrienoic acid (2.96%) were also found in the total lipid.     

Study of the White Film Developed on the Cut Surface of Vacuum-packed Dry-cured Ham Slices

Scanning electron microscopy of the white film developed on the cut surface of some vacuum-packed dry-cured ham slices showed a fibrous structure composed of protein materials. Gradient SDS-PAGE revealed the main components in the film were proteins with molecular weight in the range 26000–87000, but especially 37000, 41000, 56000, and 65000. Free amino acids were also in the film in low proportions (250 μg total free amino acids per mg of protein). The main amino acids were proline methionine, isoleucine, leucine, phenylalanine, histidine and tyrosine. 11.7% of the total free amino acids was tyrosine, thus indicating its minor role in formation of white film.     

Covalent interactions between amino acid side chains and oxidation products of caffeoylquinic acid (chlorogenic acid)

BACKGROUND: Physicochemical properties and digestibility of proteins can be modified by covalent interactions with oxidized phenolic compounds, i.e., quinones. In order to control these interactions in food products, the covalent interactions between quinones from caffeoylquinic acid (CQA) and amino acid side chains were studied with mass spectrometry using N‐terminally protected amino acids. RESULTS: The addition of two molecules of CQA, presumably in the form of a pre‐formed dimer, was observed for lysine, tyrosine, histidine and tryptophan. A monomer of CQA seemed to be able to react with histidine and tryptophan, whereas no interaction with a CQA monomer was observed for lysine and tyrosine. Serine and threonine showed no covalent interactions with CQA. Cross‐linking between CQA and the side chains of two molecules of lysine is likely to occur also in proteins. The results show that protein cross‐linking may also be expected to occur via two tyrosine residues in the absence of other phenolic substrates. The side chains of lysine and tyrosine are more reactive than that of histidine and tryptophan. CONCLUSIONS: These results show that covalent protein modification by oxidized phenolics occurs preferentially via an initial dimerization and encompasses not only lysine and cysteine residues. Copyright © 2008 Society of Chemical Industry     

Amino acid pattern in eggs as influenced by supplementation of dopamine agonists and antagonists in laying hens

A total of thirty laying hens divided into 3 equal groups was used. The 1st group served as control and was fed a basal ration. The 2nd and 3rd groups received L-Dopa and reserpine, respectively. The goal of the study was devoted to determine the effects of these additives on the rate of egg production, weights of eggs and yolks as well as yolk proteins and their amino acid pattern. In the reserpine-treated hens the rate of egg production was increased whereas in the L-Dopa-treated group, the weights of eggs and yolks, food intake as well as the amino acids aspartate, glutamate, glycine, alanine and methionine were significantly increased. The levels of tyrosine and histidine were decreased in both treatments while methionine was decreased by reserpine only. The addition of dopamine antagonist to a ration containing lysine and leucine in concentrations of 0.55% and 0.9% did not influence their levels in eggs. The increment of methionine, aspartate, glutamate and glycine by the dopamine agonist and their decrease by antagonist revealed that these amino acids are excitatory neurotransmitters in brain.