Nucleotide Degradation Products Research Articles

Evolution of the biochemistry underpinning purine alkaloid metabolism in plants.

Purine alkaloids are naturally occurring nitrogenous methylated derivatives of purine nucleotide degradation products, having essential roles in medicine, food and various other aspects of our daily lives. They are generated through convergent evolution in different plant species. The pivotal reaction steps within the purine alkaloid metabolic pathways have been largely elucidated, and the convergent evolution of purine alkaloids has been substantiated through bioinformatic, biochemical and other research perspectives within S-adenosyl-ʟ-methionine-dependent N-methyltransferases. Currently, the biological and ecological roles of purine alkaloids, further refinement of the purine alkaloid metabolic pathways and the investigation of purine alkaloid adaptive evolutionary mechanisms continue to attract widespread research interest. The exploration of the purine alkaloid metabolic pathways also enhances our comprehension of the biochemical mechanism, providing insights into inter-species interactions and adaptive evolution and offering potential value in drug development and agricultural applications. Here, we review the progress of research in the distribution, metabolic pathway elucidation and regulation, evolutionary mechanism and ecological roles of purine alkaloids in plants. The opportunities and challenges involved in elucidating the biochemical basis and evolutionary mechanisms of the purine alkaloid metabolic pathways, as well as other research aspects, are also discussed. This article is part of the theme issue 'The evolution of plant meta-bolism'.

Effect of gamma irradiation on microbial growth, physicochemical properties, and non‐volatile flavour of chicken sausages during storage

SummaryEffects of 60Co‐γ ray irradiation on physicochemical properties and non‐volatile flavour changes of chicken sausage during storage were investigated. Gamma irradiation at high doses effectively inhibited microbial growth and retarded physicochemical deterioration of chicken sausages throughout the storage period. The total fatty acid, saturated, and polyunsaturated fatty acids increased and decreased with increasing irradiation dose. In contrast, the monounsaturated acid content decreased with increasing irradiation dose. The free amino acid content exhibited a reduction of 4.27% following irradiation at a dose of 6 kGy and this decrease was further intensified during storage. Tartaric acid and pyruvate were chicken sausage's main organic acids and the most important taste‐active compounds. The irradiation dose had no significant effect on the organic acid content of chicken sausages, which continued to decrease during storage. The degradation products of nucleotides in irradiated chicken sausages demonstrated a noteworthy reduction in AMP and IMP, with no significant alterations observed in the remaining products. Thus, appropriate irradiation treatment (3 kGy) could effectively prolong the shelf life of chicken sausages without affecting their overall quality and had no adverse effects on the non‐volatile flavour compounds.

Mouse tissue harvest-induced hypoxia rapidly alters the in vivo metabolome, between-genotype metabolite level differences, and 13C-tracing enrichments

ObjectiveMetabolomics as an approach to solve biological problems is exponentially increasing in use. Thus, this a pivotal time for the adoption of best practices. It is well known that disrupted tissue oxygen supply rapidly alters cellular energy charge. However, the speed and extent to which delayed mouse tissue freezing after dissection alters the broad metabolome is not well described. Furthermore, how tissue genotype may modulate such metabolomic drift and the degree to which traced 13C-isotopologue distributions may change have not been addressed. MethodsBy combined liquid chromatography (LC)- and gas chromatography (GC)-mass spectrometry (MS), we measured how levels of 255 mouse liver metabolites changed following 30-second, 1-minute, 3-minute, and 10-minute freezing delays. We then performed test-of-concept delay-to-freeze experiments evaluating broad metabolomic drift in mouse heart and skeletal muscle, differential metabolomic change between wildtype (WT) and mitochondrial pyruvate carrier (MPC) knockout mouse livers, and shifts in 13C-isotopologue abundances and enrichments traced from 13C-labled glucose into mouse liver. ResultsOur data demonstrate that delayed mouse tissue freezing after dissection leads to rapid hypoxia-driven remodeling of the broad metabolome, induction of both false-negative and false-positive between-genotype differences, and restructuring of 13C-isotopologue distributions. Notably, we show that increased purine nucleotide degradation products are an especially high dynamic range marker of delayed liver and heart freezing. ConclusionsOur findings provide a previously absent, systematic illustration of the extensive, multi-domain metabolomic changes occurring within the early minutes of delayed tissue freezing. They also provide a novel, detailed resource of mouse liver ex vivo, hypoxic metabolomic remodeling.

Metabolomic Analysis Reveals That the Moor Frog Rana arvalis Uses Both Glucose and Glycerol as Cryoprotectants.

Simple SummaryThe moor frog Rana arvalis can tolerate freezing to low temperatures, up to −16 °C. We performed metabolomic analysis of the liver and hindlimb muscles of frozen and control R. arvalis. We found that the moor frog synthesizes glucose and glycerol in similar concentrations as low molecular weight cryoprotectants. This is the first such case reported for the genus Rana, which was believed to use glucose only. We found that freezing upregulates glycolysis, with the accumulation of several end products: lactate, alanine, ethanol, and, possibly, 2,3-butanediol. To our knowledge, this is also the first report of ethanol as an end product of glycolysis in terrestrial vertebrates. We observed highly increased concentrations of nucleotide degradation products, implying high level of stress. We found almost no signs of adaptations to reoxygenation stress, with overall low levels of antioxidants. We also performed metabolomics analysis of subcutaneous ice that was found to contain glucose, glycerol, and several other substances.The moor frog Rana arvalis is one of a few amphibians that can tolerate freezing to low temperatures, up to −16 °C. In this study, we performed metabolomic analysis of the liver and hindlimb muscles of frozen and control R. arvalis. We found that the moor frog synthesizes glucose and glycerol in similar concentrations as low molecular weight cryoprotectants. This is the first such case reported for the genus Rana, which was believed to use glucose only. We found that freezing upregulates glycolysis, with the accumulation of several end products: lactate, alanine, ethanol, and, possibly, 2,3-butanediol. To our knowledge, this is also the first report of ethanol as an end product of glycolysis in terrestrial vertebrates. We observed highly increased concentrations of nucleotide degradation products, implying high level of stress. The Krebs cycle arrest resulted in high concentrations of succinate, which is common for animals. However, we found almost no signs of adaptations to reoxygenation stress, with overall low levels of antioxidants. We also performed metabolomics analysis of subcutaneous ice that was found to contain glucose, glycerol, and several other substances.

Biochemical Response to Freezing in the Siberian Salamander Salamandrella keyserlingii.

Simple SummaryThe Siberian salamander is a unique amphibian that is capable to survive long-term freezing at −55 °C. We used 1H-NMR analysis to study quantitative changes of multiple metabolites in liver and hindlimb muscle of the Siberian salamander in response to freezing. For the majority of molecules we observed significant changes in concentrations. Glycerol content in frozen organs was as high as 2% w/w, which confirms its role as a cryoprotectant. No other putative cryoprotectants were detected. Freezing resulted in increased concentrations of glycolysis products: lactate and alanine. Unexpectedly, we detected no increase in concentrations of succinate, which accumulates under ischemia in various tetrapods. Freezing proved to be a dramatic stress with high levels of nucleotide degradation products. There was also significant increase in the concentrations of choline and glycerophosphocholine, which may be interpreted as the degradation of biomembranes. Thus, we found that freezing results not only in macroscopical damage due to ice formation, but also to degradation of DNA and biomembranes.The Siberian salamander Salamandrella keyserlingii Dybowski, 1870 is a unique amphibian that is capable to survive long-term freezing at −55 °C. Nothing is known on the biochemical basis of this remarkable freezing tolerance, except for the fact that it uses glycerol as a low molecular weight cryoprotectant. We used 1H-NMR analysis to study quantitative changes of multiple metabolites in liver and hindlimb muscle of S. keyserlingii in response to freezing. For the majority of molecules we observed significant changes in concentrations. Glycerol content in frozen organs was as high as 2% w/w, which confirms its role as a cryoprotectant. No other putative cryoprotectants were detected. Freezing resulted in ischemia manifested as increased concentrations of glycolysis products: lactate and alanine. Unexpectedly, we detected no increase in concentrations of succinate, which accumulates under ischemia in various tetrapods. Freezing proved to be a dramatic stress with reduced adenosine phosphate pool and high levels of nucleotide degradation products (hypoxanthine, β-alanine, and β-aminoisobutyrate). There was also significant increase in the concentrations of choline and glycerophosphocholine, which may be interpreted as the degradation of biomembranes. Thus, we found that freezing results not only in macroscopical damage due to ice formation, but also to degradation of DNA and biomembranes.

Metabolic profiling of epidermal and mesophyll tissues under water-deficit stress in Opuntia ficus-indica reveals stress-adaptive metabolic responses.

Cactus pear (Opuntia ficus-indica) is a high productivity species within the Cactaceae grown in many semiarid parts of the world for food, fodder, forage, and biofuels. O. ficus-indica utilises obligate crassulacean acid metabolism (CAM), an adaptation that greatly improves water-use efficiency (WUE) and reduces crop water usage. To better understand CAM-related metabolites and water-deficit stress responses of O. ficus-indica, comparative metabolic profiling was performed on mesophyll and epidermal tissues collected from well-watered and water-deficit stressed cladodes at 50% relative water content (RWC). Tissues were collected over a 24-h period to identify metabolite levels throughout the diel cycle and analysed using a combination of acidic/basic ultra-high-performance liquid chromatography/tandem mass spectrometry (UHPLC/MS/MS) and gas chromatography/mass spectrometry (GC/MS) platforms. A total of 382 metabolites, including 210 (55%) named and 172 (45%) unnamed compounds, were characterised across both tissues. Most tricarboxylic acid (TCA) cycle and glycolysis intermediates were depleted in plants undergoing water-deficit stress indicative of CAM idling or post-idling, while the raffinose family oligosaccharides (RFO) accumulated in both mesophyll and epidermal tissues as osmoprotectants. Levels of reduced glutathione and other metabolites of the ascorbate cycle as well as oxylipins, stress hormones such as traumatic acid, and nucleotide degradation products were increased under water-deficit stress conditions. Notably, tryptophan accumulation, an atypical response, was significantly (24-fold) higher during all time points in water-deficit stressed mesophyll tissue compared with well-watered controls. Many of the metabolite increases were indicative of a highly oxidising environment under water-deficit stress. A total of 34 unnamed metabolites also accumulated in response to water-deficit stress indicating that such compounds might play important roles in water-deficit stress tolerance.

Effect of Chilled Ageing Conditioning at 4°C in Lamb Longissimus Dorsi Muscles on Water-Soluble Flavour Precursors as Revealed by a Metabolomic Approach

The objective of this study was to investigate, by a metabolomic approach, the effects of chilled ageing conditioning at 4°C in lamb longissimus dorsi (LD) muscles on water-soluble flavour precursors. The results showed that the content of nucleotide degradation products significantly increased (P<0.05) due to the adjusted biosynthesis of alkaloids derived from histidine and purine from day 0 to day 4. Additionally, the content of glycolytic compounds significantly increased (P<0.05) due to enhanced glycolysis, and the content of organic acid increased (P<0.05) because of the altered tricarboxylic acid cycle (TCA) from day 0 to day 4. In addition, the content of total free amino acids significantly increased (P<0.05), owing to the altered biosynthesis of amino acids from day 4 to day 8. These results are significant proof that there were quantitative changes observed in lamb flavour precursors during chilled ageing.

Metabolome analysis of Saccharomyces cerevisiae and optimization of culture medium for S-adenosyl-L-methionine production.

S-Adenosyl-l-methionine (SAM) is a fine chemical used as a nutritional supplement and a prescription drug. It is industrially produced using Saccharomyces cerevisiae owing to its high SAM content. To investigate the optimization of culture medium components for higher SAM production, metabolome analysis was conducted to compare the intracellular metabolite concentrations between Kyokai no. 6 (high SAM-producing) and laboratory yeast S288C (control) under different SAM production conditions. Metabolome analysis and the result of principal component analysis showed that the rate-limiting step for SAM production was ATP supply and the levels of degradation products of adenosine nucleotides were higher in Kyokai 6 strain than in the S288C strain under the l-methionine supplemented condition. Analysis of ATP accumulation showed that the levels of intracellular ATP in the Kyokai 6 strain were also higher compared to those in the S288C strain. Furthermore, as expected from metabolome analysis, the SAM content of Kyokai 6 strain cultivated in the medium without yeast extract increased by 2.5-fold compared to that in the additional condition, by increasing intracellular ATP level with inhibited cell growth. These results suggest that high SAM production is attributed to the enhanced ATP supply with l-methionine condition and high efficiency of intracellular ATP consumption.Electronic supplementary materialThe online version of this article (doi:10.1186/s13568-016-0210-3) contains supplementary material, which is available to authorized users.

Comparative studies of quality changes in white and dark muscles from common carp (Cyprinus carpio) during refrigerated (4 °C) storage

SummaryDifferences between white and dark muscles from common carp (Cyprinus carpio) in sensory assessment, total viable counts (TVC), total volatile basic nitrogen (TVB‐N), pH, electrical conductivity (EC), biogenic amines (BAs), nucleotide degradation products and colours were investigated under air and vacuum conditions during refrigerated (4 °C) storage. Compared with white muscle, dark muscle had a higher lipid content, but lower crude protein and moisture content. TVC, TVB‐N, pH, and L* value were higher in white muscle, while K value and a* value were higher in dark muscle. Under both conditions, white and dark muscles had significant (P < 0.05) differences in tyramine and cadaverine content. Although dark muscle was significantly (P < 0.05) lower in ATP content, it had higher rate of IMP degradation and K value increase. Taking sensory and microbial indexes into consideration, dark muscle appeared to have a longer shelf life than white muscle under both conditions.

가열 한우육 및 호주산우육 스테이크에서 심부온도에 따른 glucose, lactate 및 핵산 분해 물질 함량 비교

본 연구는 가열 한우육 및 호주산우육 스테이크에서 심부온도에 따른 glucose, lactate 및 핵산 분해 물질 함량을 비교하고자 실시하였다. 시료로 한우육(거세우, 1등급) 및 호주산우육(Bos indicus, 100일 곡류 비육)의 등심(M. longissimus dorsi)과 우둔(M. semimembranosus)를 약 2 cm 두께로 절단하여 각각 세 그룹으로 나누고, <TEX>$180^{\circ}C$</TEX> 오븐에서 심부온도가 각각 50, 70 및 <TEX>$90^{\circ}C$</TEX>가 되도록 가열하였다. Glucose 함량은 심부온도에 관계없이 한우육 스테이크가 호주산우육 스테이크에 비해 현저하게 높았다(P<0.05). 이와 반대로 lactate 함량은 한우육 스테이크가 호주산우육 스테이크보다 낮았다(P<0.05). 핵산 분해 물질 중 Hx 함량은 모든 심부온도에서 한우육 스테이크가 호주산우육 스테이크보다 낮았던 반면(P<0.05), GMP, IMP 및 inosine 함량은 한우육 스테이크가 높았다(P<0.05). 심부온도가 증가함에 따라 쇠고기 스테이크의 glucose 함량은 감소하는 경향을 보였으나, lactate 함량은 일정한 경향을 보이지 않았다. 또한 핵산 분해 물질 함량은 심부온도의 증가에 따라 유의적인 변화를 보이지 않았다. 따라서 가열 한우육 스테이크의 단맛 및 감칠맛 관련 풍미 전구물질 함량이 호주산우육 스테이크보다 높았다. This study was conducted to compare the glucose, lactate, and nucleotide degradation products content of cooked beef steaks from Korean Hanwoo (quality grade: 1) and Australian cattle (Bos indicus, grain-fed for 100 d) by internal temperature. The loins (M. longissimus dorsi) and top rounds (M. semimembranosus) from two cattle breeds were cut into about 2 cm thickness and then cooked in a <TEX>$180^{\circ}C$</TEX> electronic oven until internal temperature attained to 50, 70, or <TEX>$90^{\circ}C$</TEX>. Regardless of internal temperature, glucose content was higher (P<0.05) in cooked loin and top round steaks from Hanwoo compared to those from Australian cattle. Lactate content was shown to be lower (P<0.05) in cooked steaks from Hanwoo than in those from Australian cattle. Lower (P<0.05) hypoxanthine and higher (P<0.05) guanosine 5'-monophosphate, inosine 5'-monophosphate, inosine contents were observed in cooked steaks from Hanwoo. Furthermore, glucose content tended to be decreased by internal temperature but nucleotide degradation products content was not changed by internal temperature. Therefore, these findings suggest that cooked Hanwoo beef steaks had higher flavor precursors related to sweet and umami tastes than cooked Australian beef steaks

Modeling Quality Changes in Brined Bream (Megalobrama amblycephala) Fillets During Storage: Comparison of the Arrhenius Model, BP, and RBF Neural Network

To evaluate and predict the freshness of brined bream (Megalobrama amblycephala) fillets stored at different temperatures, changes in quality [nucleotide degradation products (IMP, HxR, Hx), K value, sensory assessment (SA), total aerobic counts (TAC), thiobarbituric acid reactive substances (TBARS), and total volatile base nitrogen (TVB-N)] were investigated. The Arrhenius model, back-propagation neural network (BP-NN), and radial basis function neural network (RBF-NN) were established and compared. The RBF-NN predicted changes of SA, TAC, K value, TVB-N, TBARS, and HxR of brined fillets during storage with relative errors all within ±5 %, while the BP-NN values were all within ±10 % (except for the values at day 2 for K value, day 2 and day 4 for HxR). For the Arrhenius model, the relative errors of TVB-N were all within ±10 %, and those of SA, TAC, K value, TBARS, and HxR ranged from 0.58 to 44.37 %. Thus, RBF-NN is a promising method for predicting the changes in the quality of bream during storage at 270–282 K.

Chemical Quality Indices for Freshness Evaluation of Fish

The compounds formed in fish spoilage process have been frequently used to assess the quality of different species. Quality indices based mainly on the concentration of the products of nucleotide degradation and biogenic amine content have been proposed. However, these indicators must be calculated considering intrinsic and extrinsic factors that may affect both, biogenic amine formation and nucleotide degradation rate and pattern. In relation to the analytical methods, regardless the methodology chosen, the extraction stage is critical. High performance liquid chromatography is the technique indicated for both, biogenic amine analysis and determination of nucleotide degradation products.

Freshness and quality attributes of cold stored Atlantic bonito (Sarda sarda) gravad

SummaryQuality and safety parameters of Atlantic bonito gravad during 42 days of storage at 7 ± 1 °C were analysed using monitoring sensory quality, microbial contamination, nucleotide degradation products, biogenic amines (BA), trimethylamine (TMA) and thiobarbituric acid reactive substances (TBARS). The shelf‐life of vacuum packed Atlantic bonito gravad was found to be 28 days. Total viable count (TVC) did not exceed 6 log CFU g−1. Malonodialdehyde (MDA) content did not surpass 10 mg kg−1. Nine biogenic amines were detected. Histamine level at the end of the storage was 355.3 mg kg−1. TMA increased from 53.9 to 619.1 mg kg−1. Among indicators based on the products of nucleotide degradation, the H value is best correlated with the sensory assessment. It can be concluded that the storage temperature of bonito gravad must be below 7 °C to prevent the threat to safety and quality posed by biogenic amines, especially histamine.

Nucleotide degradation products of gamma‐irradiated sea bream (Sparus aurata) stored in ice

SummaryNucleotide degradation products of irradiated sea bream stored up to 19 days in ice were investigated. Irradiation had significant effect on the nucleotide concentrations in sea bream muscle (P &lt; 0.05). The results showed that the highest value of inosine monophosphate (IMP) was observed in irradiated sea bream at 5 kGy, followed by at 2.5 kGy. Initial inosine (INO) concentration in irradiated sea bream at 5 kGy was 4.26 μmoles g−1, which reached maximum value of 8.83 μmoles g−1 when fish completely spoiled (19 days). When the fish reached the limit of acceptability, the mean values of K, Ki, H and G were 86.8%, 90.3%, 59.8% and 213.9% for unirradiated sea bream, 85.2%, 87.8%, 56.8% and 197.8% for irradiated sea bream at 2.5 kGy and 88.4%, 90.9%, 57.8%, 211.5% for irradiated sea bream at 5 kGy, respectively. The results of this study indicated that nucleotide degradation was more rapid in unirradiated sea bream than those irradiated. K, Ki, H and G value in irradiated fish can be used as a freshness index because there is a good linear relationship between values and storage time of fish.

Post-mortem Changes in Farmed Spotted Babylon Snail (Babylonia areolata) During Iced Storage

Post-mortem changes in farmed spotted Babylon snail stored in ice for 7 days were evaluated using nucleotide degradation products, K-value, total volatile base nitrogen (TVB-N), trimethylamine nitrogen (TMA-N), organic acid, free amino acids and biogenic amines. During a 7-day ice storage, K-value, TVB-N, TMA-N and organic acids contents increased with increasing storage time (p < 0.05). Changes in free amino acid, such as aspartic acid, serine, glutamic acid, glycine, arginine and proline were observed throughout the ice storage (p < 0.05), while total free amino acids were found to decrease significantly (p < 0.05). Biogenic amines found in snail muscle during ice storage were tyramine, putrescine, cadaverine, agmatine and histamine. Bacteria counts of snail muscle exceeded 7 log CFU/g, which was considered as the limit for acceptability after 7 days of iced storage. This result initiates the use of ice storage as a preliminary treatment for snails transported from farms.

Brain purine metabolism and xanthine dehydrogenase/oxidase conversion in hyperammonemia are under control of NMDA receptors and nitric oxide

In hyperammonemia, a decrease in brain ATP can be a result of adenine nucleotide catabolism. Xanthine dehydrogenase (XD) and xanthine oxidase (XO) are the end steps in the purine catabolic pathway and directly involved in depletion of the adenylate pool in the cell. Besides, XD can easily be converted to XO to produce reactive oxygen species in the cell. In this study, the effects of acute ammonia intoxication in vivo on brain adenine nucleotide pool and xanthine and hypoxanthine, the end degradation products of adenine nucleotides, during the conversion of XD to XO were studied. Injection of rats with ammonium acetate was shown to lead to the dramatic decrease in the ATP level, adenine nucleotide pool size and adenylate energy charge and to the great increase in hypoxanthine and xanthine 11 min after the lethal dose indicating rapid degradation of adenylates. Conversion of XD to XO in hyperammonemic rat brain was evidenced by elevated XO/XD activity ratio. Injection of MK-801, a NMDA receptor blocker, prevented ammonia-induced catabolism of adenine nucleotides and conversion of XD to XO suggesting that in vivo these processes are mediated by activation of NMDA receptors. The in vitro dose-dependent effects of sodium nitroprusside, a NO donor, on XD and XO activities are indicative of the direct modification of the enzymes by nitric oxide. This is the first report evidencing the increase in brain xanthine and hypoxanthine levels and adenine nucleotide breakdown in acute ammonia intoxication and NMDA receptor-mediated prevention of these alterations.

An alternative freshness index method for modified atmosphere packaged abalone using an artificial neural network

An alternative freshness index method for abalone ( Haliotis asinina) muscle packaged under atmospheric air (Air) and modified atmosphere (MA) of 40% CO 2: 30% O 2: 30% N 2 packaging conditions and stored at 2 ± 1 °C was developed. Biochemical indices covering pH, total volatile basic nitrogen (TVB-N), trimethylamine (TMA) and nucleotide degradation products, as well as instrumental texture and color of the packaged abalones, were determined. Sensory characteristics including odor, color and appearance were evaluated and then summarized into overall freshness scores (freshness index). The biochemical and instrumental analyses were then calibrated with the freshness index, using an artificial neural network algorithm. The neural network was shown to be capable of correlating biochemical and instrumental analyses with the freshness index. A useful prediction was possible, as measured by a low mean square error (MSE = 0.092) and a regression coefficient ( R 2 = 0.98) between true and predicted data.

Nucleotide degradation and biogenic amine formation of wild white grouper (Epinephelus aeneus) stored in ice and at chill temperature (4 °C)

Sensory (cooked and uncooked), chemical (proximate composition, TVB-N, nucleotide degradation products and biogenic amines) and microbiological quality (TVC and total coliform) changes were investigated during storage of ungutted white grouper kept in ice and at chill temperature (4°C). According to the sensory assessment, the shelf life of white grouper was 16 days in ice and 4 days for fish stored at chill temperature. TVB-N values increased with storage time. Amines found in white grouper stored in ice were TMA, putrescine, cadaverine, 2-phenylethylamine, dopamine, agmatine, tryptamine and serotonin. Histamine, spermine, spermidine were never detected with either storage condition. The acceptability limit in terms of microbial count was exceeded at 8 days in ice and at 4 days for fish stored at chill temperature. Total coliform count was 2.8log10cfu/ml at 1 day and reached 105cfu/ml for both storage conditions.

Water-soluble precursors of beef flavour. Part II: Effect of post-mortem conditioning

Changes in glycolytic metabolites, nucleotide degradation products, free amino acids and other amino compounds were monitored in beef muscle ( M. longissimus lumborum), stored for 21 days at 4 °C, in order to evaluate how post-mortem conditioning may affect flavour formation in beef. The major effects observed in sugar-related substances were the dephosphorylation of the phosphates of glucose, fructose and mannose, to yield their free sugars, as well as the breakdown of inosine 5′-monophosphate, to give a sixfold increase in ribose. Total reducing sugars increased by only 15% during conditioning, while glycogen levels remained unchanged from 2 days post-slaughter. Free amino acids increased during conditioning, particularly between days 7 and 14. Phenylalanine, methionine, lysine, leucine and isoleucine were the amino acids showing the greatest increase with conditioning time, with methionine, in particular, showing a sevenfold increase during the conditioning period. The effects of these precursor changes on cooked beef flavour are discussed.

Effects of aluminium foil and cling film on biogenic amines and nucleotide degradation products in gutted sea bream stored at 2±1 °C

Biogenic amines and nucleotide degradation products of sea bream stored in ice, wrapped in aluminium foil (WAF) and in cling film (WCF) at 2±1 °C were investigated by using a rapid HPLC method. Results obtained from this study showed that for household purposes packing fish in different materials has a little effect on the biogenic amines formation and nucleotide degradation products. The highest decrease of IMP content was observed for sea bream in WAF, followed by WCF. INO values showed a fluctuation and remained below the levels of 5.5 μmol/g for all storage conditions. Hx value constantly increased with the storage time during chilled storage. For all of the storage condition, K and Ki value increased linearly with storage time. At the end of the storage period, K, Ki, H and G value reached 60–76%, 65–81%, 30–54% and 89–173%, respectively. Among biogenic amines, (trimetylamine) TMA, putrescine, cadaverine, spermidine, spermine, tryptamine, tyramine, β-phenylalanine and histamine were detected during storage period. TMA and putrescine were observed to increase linearly during storage period. Histamine production was only found at the end of storage period. The highest histamine values for fish wrapped in aluminium foil were 6.4 mg/100 g and fish wrapped in cling film was 4.6 mg/100 g.