BIOCHEMICAL RESPONSES OF ASPARAGUS TO CONTROLLED ATMOSPHERE STORAGE AT 20C

In seeking to understand the beneficial effects of controlled atmosphere (CA) storage at 20C on asparagus (Asparagus officinalis L.), biochemical responses of spear tips stored in air were compared with those of spears stored under CA (2% O₂, 10% CO₂). CA storage prevented the rapid loss of sucrose, increased acid invertase activity and asparagine accumulation observed in the tips of spears stored in air. CA storage also delayed changes in the levels of glutamine, malic, citric and fumaric acids, compared with those in tips of air-stored spears. Elongation observed in water-fed spears in air was reduced by CA. It is proposed that CA acted by depressing metabolism to such an extent that sucrose levels were maintained in the spear tip and this, in turn, prevented the cascade of metabolic events that contribute to spear deterioration in air.     

Ammonium exposure and pyruvate affect the amino acid metabolism of bovine blastocysts in vitro

The accumulation of ammonium is a major artefact of in vitro embryo culture. This study has examined ammonium production and potential mechanisms of disposal in preimplantation bovine blastocysts. Embryos were produced by in vitro maturation and fertilisation of oocytes, and cultured in synthetic oviduct fluid containing amino acids and BSA (SOFaaBSA). Ammonium/urea concentrations were determined enzymatically. Amino acid appearance/disappearance 'profiles' of single blastocysts were determined at 0, 1.25 and 2.5 mM NH(4)Cl (with or without 0.33 mM pyruvate), and with or without 10 mM dipicolinic acid (DPCA; a glutamate dehydrogenase (GLDH) inhibitor) or 2 mM amino-oxyacetate (AOA; a transaminase inhibitor). Free ammonium was produced at a rate of 4.281 (+/-0.362) pmol/embryo/h, while urea production was undetectable. The presence/absence of pyruvate affected amino acid profiles, especially alanine appearance (P < 0.001), glutamate disappearance (P < 0.05) and overall turnover (the sum of appearance and disappearance) (P < 0.001). GLDH inhibition with DPCA had no effect on amino acid overall disappearance, but glutamate disappearance increased, while that of arginine decreased (P < 0.05). The transaminase inhibitor, AOA, depressed turnover (P < 0.05), aspartate and glutamate disappearance, and alanine appearance. Thus, bovine blastocysts release ammonium as free ions or fix them, not as urea, but as alanine, possibly glutamine and, less likely, arginine. An active role for GLDH and transaminases in regulating blastocyst amino acid metabolism was demonstrated.     

Amino acid composition of wheat grain. 1: Changes during development

The changes in the composition of free and total amino acids in wheat grain during development are described: the experiment was performed in a growth chamber with three varieties of winter wheat (Triticum aestivum L.): Splendeur, Hobbit and Maris Huntsman. The changes in the total composition of amino acids of the grain as development progressed were consistent with an increase in the proportion of storage proteins. At 15 days after anthesis, the relative amount of glycine increased, suggesting that at this moment the proportion of gliadins was relatively low. The relative amount of arginine increased in mature grain, showing that at times close to maturity the relative proportion of synthesis of a protein fraction rich in this amino acid increased. Free glutamate, proline and arginine decreased at 15 days to a greater extent than the other amino acids and was present in low relative amounts during the period of maximum protein synthesis in the grain; these three amino acids could be the most limiting for protein synthesis in grain. In the free fraction the following showed a similar pattern of change during grain development: aspartate, arginine and histidine on the one hand, and on the other alanine, valine, leucine, isoleucine, threonine, phenylalanine and tyrosine; moreover both groups were inversely correlated. Glycine and lysine were directly related to each other and inversely to glutamate.     

Postharvest changes in physicochemical characteristics and free amino acids content of immature vegetable soya bean (Glycine max L.) grains

The aim of this study was to investigate the changes in physicochemical characteristics and free amino acid profile occurring in immature vegetable soya bbean during postharvest storage under three temperatures [5, 10 and 20 (control), ±1 °C] for 7 days. The results showed that a lower temperature provided an effective control in reducing weight loss, maintained firmness, delayed changes in the pod colour and soluble sugars concentration. Twenty‐two free amino acids in immature soya beans also identified by the ¹H NMR spectroscopy were strongly affected by postharvest temperature, and there were time‐specific differences in the concentration. Those significant differences in free amino acids concentration among storage conditions were closely associated with aspartate and glutamate degradation. Additionally, after 7‐day storage at 5 and 10 °C, the soya bean grains accumulated the highest amount of some essential and flavour amino acids, which revealed storage conditions selected should be dictated by the goal.     

Supplementation of amino acids in apple must for the standardization of volatile compounds in ciders

The aim of this study was to identify the main amino acids responsible for the production of esters in ciders. The experiments were carried out in apple must and synthetic must. The amino acids were analysed by high‐performance liquid chromatography and the volatile compounds by gas chromatography. Aspartate, asparagine and glutamate positively influenced the production of esters in the cider models and were used in the experiments with mixtures. The response surface generated by the proposed model yielded two regions that maximized the production of esters. In addition, the combination of aspartate and glutamate predicted a higher production. The optimal suggested concentrations were 43.4% of aspartate and 56.6% of glutamate for 120 mg/L of total nitrogen. The apple must supplemented with these two amino acids resulted in four times more esters than in the same cider without supplementation, demonstrating the effectiveness of the proposed model.     

Changes in free amino acids and biogenic amines of Egyptian salted-fermented fish (Feseekh) during ripening and storage

The aim of this study was to investigate changes in the formation of amino acids and biogenic amines in Egyptian salted-fermented fish (Feseekh) during ripening (20 days) and storage (40–60 days). The total concentration of free amino acids increased from 8 (dry weight; DW) to 72 g/kg (DW) after 60 days of storage. The predominant free amino acids were leucine, glutamic acid, lysine, alanine, valine, aspartic acid, isoleucine and citrulline. Their concentrations accounted for 68% of the total concentration of amino acids after 60 days. The total contents of biogenic amines ranged from 84 to 1633 mg/kg (DW) during the investigated period. Cadaverine was the major amine detected in Feseekh at all sampling stages and its concentration varied between 21 and 997 mg/kg (DW). The histamine content (211 mg/kg DW) only exceeded the maximum tolerance level (200 mg/kg) after 60 days. It could be concluded that Feseekh can be consumed without any health risks between 20 and 40 days but it can be hazardous after 60 days due to the biogenic amine content.     

C- and N-catabolic utilization of tricarboxylic acid cycle-related amino acids by Scheffersomyces stipitis and other yeasts

Scheffersomyces stipitis and the closely related yeast Candida shehatae assimilated the L-amino acids glutamate, aspartate and proline as both carbon and nitrogen sole sources. We also found this rarely investigated ability in ascomycetous species such as Candida glabrata, C. reukaufii, C. utilis, Debaryomyces hansenii, Kluyveromyces lactis, K. marxianus, Candida albicans, L. elongisporus, Meyerozyma guilliermondii, C. maltosa, Pichia capsulata and Yarrowia lipolytica and in basidiomycetous species such as Rhodotorula rubra and Trichosporon beigelii. Glutamate was a very efficient carbon source for Sc. stipitis, which enabled a high biomass yield/mole, although the growth rate was lower when compared to growth on glucose medium. The cells secreted waste ammonium during growth on glutamate alone. In Sc. stipitis cultures grown in glucose medium containing glutamate as the nitrogen source the biomass yield was maximal, and ethanol concentration and specific ethanol formation rate were significantly higher than in glucose medium containing ammonium as the nitrogen source. Mainly C-assimilation of glutamate but also N-assimilation in glucose-containing medium correlated with enhanced activity of the NAD-dependent glutamate dehydrogenase 2 (GDH2). A Δgdh2 disruptant was unable to utilize glutamate as either a carbon or a nitrogen source; moreover, this disruptant was also unable to utilize aspartate as a carbon source. The mutation was complemented by retransformation of the GDH2 ORF into the Δgdh2 strain. The results show that Gdh2p plays a dual role in Sc. stipitis as both C- and N-catabolic enzyme, which indicates its role as an interface between the carbon and nitrogen metabolism of this yeast.     

Influence of Storage on the Composition of Clarified Apple Juice Concentrate

The effect of storage on apple juice concentrate was determined by following changes in composition during a period of 111 days at 37°C. Results showed that storage caused an 87% loss in the total free amino acids, which was mostly due to decreases in glutamic acid, asparagine and aspartic acid. The forml titration method was inadequate for determining the amino compounds involved in Maillard-type reactions. Sucrose was hydrolyzed under these conditions at a rate corresponding to a fist order process. The reducing sugars increased at a rate determined by the inversion of sucrose; no consumption attributable to browning reaction was detected. Reduction of organic acids was 9% while apparent phenolic compounds increased from 0.149 to 0.215 g/100g. A maximum accumulation of HMF was observed after 100 days of storage.     

Hepatic effects of rumen-protected branched-chain amino acids with or without propylene glycol supplementation in dairy cows during early lactation

Essential amino acids (EAA) are critical for multiple physiological processes. Branched-chain amino acid (BCAA) supplementation provides energy substrates, promotes protein synthesis, and stimulates insulin secretion in rodents and humans. Most dairy cows face a protein and energy deficit during the first weeks postpartum and utilize body reserves to counteract this shortage. The objective was to evaluate the effect of rumen-protected BCAA (RP-BCAA; 375 g of 27% l-leucine, 85 g of 48% l-isoleucine, and 91 g of 67% l-valine) with or without oral propylene glycol (PG) administration on markers of liver health status, concentrations of nonesterified fatty acids (NEFA) and β-hydroxybutyrate (BHB) in plasma, and liver triglycerides (TG) during the early postpartum period in dairy cows. Multiparous Holstein cows were enrolled in blocks of 3 and randomly assigned to either the control group or 1 of the 2 treatments from calving until 35 d postpartum. The control group (n = 16) received 200 g of dry molasses per cow/d; the RP-BCAA group (n = 14) received RP-BCAA mixed with 200 g of dry molasses per cow/d; the RP-BCAA plus PG (RP-BCAAPG) group (n = 16) received RP-BCAA mixed with 200 g of dry molasses per cow/d, plus 300 mL of PG, once daily from calving until 7 d in milk (DIM). The RP-BCAA and RP-BCAAGP groups, on average (± standard deviation), were predicted to receive a greater supply of metabolizable protein in the form of l-Leu 27.4 ± 3.5 g/d, l-Ile 15.2 ± 1.8 g/d, and l-Val 24.2 ± 2.4 g/d compared with the control cows. Liver biopsies were collected at d 9 ± 4 prepartum and at 5 ± 1 and 21 ± 1 DIM. Blood was sampled 3 times per week from calving until 21 DIM. Milk yield, dry matter intake, NEFA, BHB, EAA blood concentration, serum chemistry, insulin, glucagon, and liver TG and protein abundance of total and phosphorylated branched-chain ketoacid dehydrogenase E1α (p-BCKDH-E1α) were analyzed using repeated measures ANOVA. Cows in the RP-BCAA and RP-BCAAPG groups had lower liver TG and lower activities of aspartate aminotransferase and glutamate dehydrogenase during the first 21 DIM, compared with control. All cows, regardless of treatment, showed an upregulation of p-BCKDH-E1α at d 5 postpartum, compared with levels at 21 d postpartum. Insulin, Met, and Glu blood concentration were greater in RP-BCAA and RP-BCAAPG compared with control during the first 35 DIM. Therefore, the use of RP-BCAA in combination with PG might be a feasible option to reduce hepatic lipidosis in dairy cows during early lactation.     

Content of amino acids and the quality of protein in as‐eaten green asparagus (Asparagus officinalis L.) products

The content of amino acids in fresh green spears and in three as‐eaten products was considered, i.e., in fresh asparagus after cooking and in two products obtained from frozen asparagus stored for 12 months at ?20 °C. One of the frozen products was obtained using the traditional method (blanching–freezing–frozen storage) and then cooked. The other was obtained using the modified technology (cooking–freezing–frozen storage); after the storage period the product was defrosted and heated to consumption temperature in a microwave oven. The limiting amino acid of the first order was methionine with cystine, and of the second order leucine. Essential amino acids constituted 40–43% of the total amino acid content. The dominant amino acids were aspartic acid and glutamic acid. The culinary and technological procedures applied brought about a drastic decrease (50–56% in 16 g N) in tyrosine content.     

Nitrate modifies the assimilation pattern of ammonium and urea in wheat seedlings

BACKGROUND: In certain plant species, ammonium or urea nutrition can cause negative effects on plant development which can result in toxic symptoms. Some authors suggest that the presence of nitrate can alleviate these symptoms by increasing ammonium and urea assimilation, avoiding its accumulation. In order to study this hypothesis, wheat (Triticum aestivum L.) seedlings were grown with various nitrogen supplies containing the main nitrogen forms (ammonium, nitrate and urea). Amino acids content and the activity of the three main enzymes involved in nitrogen assimilation (nitrate reductase, glutamine synthetase and urease) were studied. RESULTS: The application of nitrate along with urea and/or ammonium was not associated with a time‐sustained increase in the activity of glutamine synthetase and urease. Amino acid analysis revealed that nitrate induced changes in amino acid metabolism enhancing its concentration. Likewise the content of protein was also higher in nitrate‐treated plants. CONCLUSION: These results suggest that the effect of nitrate is compatible with a rapid and transient increase in the activity of glutamine synthetase and urease during the first hour after the onset of treatments. Nevertheless, a possible effect of nitrate reducing ammonium accumulation through the activation of alternative metabolic pathways different from that involving glutamine synthetase cannot be ruled out. Finally, nitrate effects on amino acid concentration indicate that, whereas ammonium assimilation takes place principally in the root, urea and nitrate assimilation occurred in the shoot, under the conditions of the experiment. Copyright © 2009 Society of Chemical Industry     

采后苯并噻重氮处理对‘玉金香’甜瓜氨基酸代谢酯类香气物质及其代谢机理的影响

以‘玉金香’甜瓜为材料,采后常温贮藏期间分析其氨基酸含量、谷丙转氨酶（glutamate pyruvic transaminase,GPT）、谷草转氨酶（glutamic oxaloacetic transaminase,GOT）、丙酮酸脱羧酶（pyruvate decarboxylase,PDC）、丙酮酸脱氢酶（pyruvate dehydrogenase,PDH）活力及其代谢产物酯类香气物质含量的 变化,探讨采后苯并噻重氮（benzothiadiazole,BTH）诱抗处理对酯类香气物质氨基酸代谢途径影响的机理。结 果表明：BTH诱抗处理可延迟样品酯类香气物质释放高峰出现,抑制其释放,总含量比CK组（未经任何处理） 低19.10%。15 种游离氨基酸被分离确定,CK组氨基酸总含量峰值（14 597 μg/g）出现在第6天,BTH组峰值出现 在第8天,低于CK组9.47%（P＜0.05）。BTH处理抑制了贮藏期间GOT、PDC和PDH活力,与CK组相比,BTH处 理组果皮GOT、PDC和PDH活力峰值分别降低31.80%、16.86%和24.30%,果肉峰值分别降低19.10%、14.70%和 25.56%,果皮GOT活力被显著抑制（P＜0.05）;不同处理组间GPT活力差异不显著（P＞0.05）。氨基酸总含量、 GOT活力与酯类香气物质含量呈极显著正相关（P＜0.01）。水处理对氨基酸含量、代谢酶活力及其产物酯类香气 物质释放均有影响,但无明显作用规律。由此可见,BTH处理会减少氨基酸含量,抑制相关代谢酶活力,进而改变 其产物酯类香气物质的释放。     

Towards a freshness test for asparagus: spear tip asparagine content is strongly related to post-harvest accumulated heat-units

The shelf-life of asparagus (Asparagus officinalis L.) is strongly related to the post-harvest accumulated heat-units; the greater the number of accumulated heat-units (degree-h >0°C) experienced by the spears the lower the residual shelf-life. The potential of using asparagine and/or amino acid content as markers of freshness for asparagus spears was assessed by determining the relationship between the concentrations of these metabolites in the spear tips of two cultivars (‘Limbras 10’ and ‘Jersey Giant’) and the post-harvest age of the spears in terms of accumulated heat-units. There was a strong quadratic relationship between spear tip asparagine content and degree-h (R² = 0.878) that was independent of cultivar (P = 0.16). Free amino acid content was also correlated quadratically with degree-h (R² = 0.788 and 0.813 for ‘Limbras 10’ and ‘Jersey Giant’, respectively) but this was cultivar dependent (P = 0.002). Spear tip asparagine concentration has potential as a marker of freshness for asparagus but requires the development of an asparagine assay suitable for use in packhouses or by exporters.     

Whole blood and plasma amino acid uptakes by lactating bovine mammary glands

The objective of the experiment was to determine the contribution of red blood cells to transport of individual amino acids to lactating bovine mammary glands. Blood samples were collected from coccygeal and subcutaneous abdominal veins of 21 lactating Holstein cows on d 35, 70, 105, and 126 of lactation. Samples were collected every 20 min for 12 h. Subsamples of whole blood and plasma were pooled by hour and day. Hourly plasma samples and daily whole blood and plasma samples were analyzed for amino acid concentration. Plasma glutamate concentration was stable throughout the 12-h collection period, indicating that sample collection did not perturb amino acid homeostasis. Therefore, data from pooled daily samples were used for subsequent comparisons. Whole blood arteriovenous differences of phosphoserine, aspartate, glutamate, hydroxyproline, phosphoethanolamine, serine, asparagine, glycine, glutamine, taurine, histidine, citrulline, threonine, alanine, beta-aminoisobutyrate, carnosine, arginine, proline, alpha-aminobutyrate, tyrosine, valine, methionine, cystine, isoleucine, leucine, phenylalanine, tryptophan, ornithine, and lysine differed significantly from plasma arteriovenous differences. Uptakes of individual amino acids from plasma were poorly correlated with uptake from whole blood. These data clearly indicate that uptake data derived from plasma do not adequately represent whole blood amino acid uptake.     

Varietal differences in amino acid composition of wheat (Triticum aestivum L) grain

The differences in the amino acid composition of the developing grain between the three winter wheat (Triticum aestivum L) varieties Splendeur, Hobbit and Maris Huntsman were analysed in a growth-room experiment. At 15 days after anthesis, Maris Huntsman, the variety with the fastest leaf senescence, had a larger proportion of glutamate and smaller levels of threonine, glycine, alanine, valine, methionine and isoleucine in the total amino acid fraction; at later dates these differences were in general less pronounced, particularly compared with Splendeur. This suggests that, in the variety with the fastest leaf senescence, rapid gliadin synthesis in the grain occurs earlier. At any given percentage of nitrogen in the mature grain, Hobbit had a smaller proportion of glutamate and greater proportions of lysine, arginine and alanine; Splendeur, the only bread-making variety, had smaller levels of aspartate and lysine; and Maris Huntsman had the greatest relative amount of phenylalanine. The possible differences among the varieties in the relative proportion of some protein fractions are discussed. Until 25 days after anthesis Maris Huntsman had smaller relative proportions of free alanine, valine, leucine, isoleocine and threonine, in particular when compared with Splendeur. In Maris Huntsman, the relative amount of aspartate increased from 15 days after anthesis onwards, whereas in Hobbit it only did so in mature grains.     

Magnesium nutrition on accumulation and transport of amino acids in tea plants

BACKGROUND: Free amino acids in young tea shoots are important chemical constituents, remarkably influencing the quality of green teas. Nutrient solution, soil pot and field experiments were conducted to investigate the effect of magnesium nutritional status on accumulation and transport of free amino acids in tea plants ( Camellia sinensis (L.) O. Kuntze). RESULTS: A sufficient supply of Mg in nutrient solution increased biomass production and concentrations of free amino acids, notably theanine in young shoots and roots, without affecting total N in the leaves, absorption rates of inorganic N and glutamine synthetase activity. Amino acids in xylem saps and phloem exudates or total sugars in phloem exudates of tea plants from pot and field experiments showed their highest levels in bud breaking and shoot extension in early spring (March and early April). Application of Mg increased the amounts of amino acids and total sugars in the xylem saps and phloem exudates. CONCLUSION: Adequate supply of Mg nutrient promoted the synthesis of theanine in roots and its accumulation in the young shoots of tea plants. Magnesium nutritional status was an important factor influencing the mobility of amino acids and sugars via xylem and phloem especially when N and C reserves remobilized to support spring growth of young shoots. Copyright © 2011 Society of Chemical Industry     

Changes in amino acid and fatty acid composition during shelf‐life of marinated fish

Quality aspects of marinated fish were examined over a 120 day period. Nutritional quality parameters (proximate composition, fatty acid profile and amino acid profile) were determined. Changes in amino acids and fatty acids were examined in the muscle of marinated fish during storage. Aspartic acid, threonine, proline, glycine, tyrosine and lysine concentrations in marinated anchovy and rainbow trout greatly influenced their quality. Polyunsaturated fatty acid concentrations decreased significantly (p < 0.05) in marinated anchovy but not (p > 0.05) in marinated rainbow trout, while total saturated fatty acid concentrations increased significantly (p < 0.05) in both marinated fish during storage. These changes in fatty acid and amino acid concentrations were found to be useful as an index of freshness and decomposition of marinated fish in storage. Copyright © 2005 Society of Chemical Industry     

Possible regulatory role of phenylalanine ammonia‐lyase in the production of anthocyanins in asparagus (Asparagus officinalis L)

The regulatory role of phenylalanine ammonia‐lyase (PAL) in the light‐induced accumulation of anthocyanins in the epidermis of asparagus spears has been analysed. A correlation between the stimulation of PAL activity and the rise in total anthocyanin content has been observed. Light radiation induced PAL activity, which in turn stimulated anthocyanin accumulation, a hypothesis which has been confirmed by treating asparagus spears with S‐carvone, an inhibitor of PAL activity. A marked delay was observed in the rise in PAL activity and total anthocyanin content in asparagus spears treated with this compound during light irradiation. PAL activity and anthocyanin synthesis continued when the spears were stored in darkness for 5 days after being subjected to light, but the inhibitory effect of S‐carvone remained during this storage. When the asparagus spears were immersed in water for 20 h, no PAL activity could be detected and scarcely any total anthocyanin content was measured. However, after 5 days of storage in darkness a sharp upsurge in PAL activity was found, which was not translated into a parallel increase in total anthocyanin content. Copyright © 2005 Society of Chemical Industry     

Use of unusual storage temperatures to improve the amino acid profile of potatoes for novel flavoring applications

To investigate the potential of potato culls as a source of novel flavorings, free amino acid profiles of juice from tubers stored at 0°C, 12°C or 24°C were analysed by gas chromatography/mass spectrometry after separation on cation exchange resin and derivatization with N-methyl-t-butyl-dimethyl-silyl-trifluoroacetamide. Juices were also incubated for 42 h with or without a commercial protease for comparison. Storage at all three temperatures increased glutamine concentration. The relative percentages of asparagine and glutamine decreased while several other amino acids increased in the juice of potatoes stored at 0°C and 24°C. Small shifts in free amino acid profile, increasing alanine, valine, aspartic acid, asparagine and arginine levels, were obtained by incubating juice from potatoes stored at 0°C without added protease while the protease produced substantial increases but with emphasis on leucine and isoleucine and phenylalanine, which increased bitterness. Since storage alone increased the concentration of single amino acids such as alanine, methionine and phenylalanine by several fold, it may be the preferred means of improving potato culls for novel flavor applications where bitterness must be minimized.     

储藏条件对花生的氨基酸和脂肪酸组成及风味的变化影响

花生在储藏过程中易走油霉变,分析花生在贮藏过程中的氨基酸和脂肪酸含量变化是研究花生品质的重要内容。将花生在低温常湿、常温低湿和常温常湿环境下储藏12个月,利用高效液相色谱和气相质谱联用仪测定不同储藏条件下花生的氨基酸与脂肪酸随储藏时间的变化情况,结合电子鼻和傅里叶变换红外吸收光谱对花生品质进行分析。研究结果显示:低温冷藏环境下花生中氨基酸总量由233.42 mg/g降至215.41 mg/g,常温常湿的条件下降至197.85 mg/g;脂肪酸变化最明显的是油酸和亚油酸的含量,低温冷藏12个月后O/L值从0.94上升至0.96,而常温低湿条件下达到1.54,亚油酸遭到严重破坏;红外谱图中蛋白质和脂肪酸的特征峰1653 cm^-1和1744 cm^-1均减弱,常温常湿条件下最明显。低温冷藏是最佳贮藏条件。