ATP Metabolites During Aging of Exudative and Nonexudative Pork Meats

ABSTRACT: The content of nucleotide metabolites in the muscle L.dorsi from 9 exudative and 9 acceptable quality pork carcasses was determined during 7 d of aging in order to establish a period postmortem for detecting exudative meats. Hypoxanthine and inosine levels in exudative meats were different (p < 0.05) from those of normal meats up to 3 days of aging, while 5'-inosine monophosphate (IMP) and 5'-adenosine triphosphate (ATP) contents only differed during the 1st 4 and 6 h postmortem, respectively. The IMP/ATP ratio was only different (p < 0.05) at 2 h. Thus, 2 h postmortem is proposed as the optimal sampling time for the detection of exudative pork meats.     

Biochemical changes in freshwater rainbow trout (Oncorhynchus mykiss) during chilled storage†

The sensory characteristics and biochemical freshness-indicator contents of rainbow trout (Oncorhynchus mykiss) stored for up to 12 days (a) in ice without previous gutting (group A), (b) in ice after gutting (group B) and (c) under refrigeration (4–5 °C) after gutting and vacuum-packing (group C) were compared. Acceptable freshness was maintained for five days in groups A and C, and for six days in group B. The results indicate that the hypoxanthine ratio ie hypoxanthine content: (inosine monophosphate + inosine + hypoxanthine content) and K₁ ie (inosine + hypoxanthine content): (inosine monophosphate + inosine + hypoxanthine content) are both useful indicators of the freshness of trout stored in ice, regardless of whether or not they have been gutted beforehand. © 1999 Society of Chemical Industry     

Effective and repeatable chromatographic separation of 5 nucleotides in infant formula milk powder by ion-pair high-performance liquid chromatography–ultraviolet

A robust method using HPLC-UV was developed to improve the accuracy and repeatability of a quantitative method to detect 5 nucleotides (cytidine-monophosphate, uridine monophosphate, adenosine monophosphate, guanine monophosphate, and inosine monophosphate) in infant formulas. The results showed that efficient separation could not be achieved without strict conditions. The proposed method displayed a strong linear relationship (R² > 0.9999) of single nucleotide in infant formula milk powder in the range of 10 to 1,000 mg/kg, a steady recovery (80.0% ～110.0%) with relative standard deviation from 0.5% to 3.5%, under strict conditions of hydrophilic C₁₈ column with di-isopropyl at 62.5 ± 2.5°C (± standard deviation), 0.65 ± 0.1 mg/mL tetrabutylammonium bisulfate, and mobile phase of pH of 2.75 ± 0.02. By applying this method on a series of milk products in the Chinese market, we found a few of them exceeded the legal limits of nucleotides.     

反相高效液相色谱法测定中国对虾肉中的呈味核苷酸

核苷酸5＇-CMP、5＇-UMP、5＇-GMP、5＇-IMP、5＇-AMP 等是食品重要的鲜味物质。采用C18 高效液相色谱柱,以甲醇与0.05mol/L KH2PO4 溶液1:1(V/V)为流动相,梯度洗脱,能将其很好地分离。DAD 检测器在260nm处检测,各呈味核苷酸的测定标准曲线在0.00～0.10mg/ml 的范围内呈很好的线性关系,R2 分别在0.9902～1.0000之间。对中国对虾肉中的呈味核苷酸进行测定,结果表明：加标回收率在99.96%～100.34% 之间,变异系数在0.04%～0.4% 之间。方法的精密度和准确度均较高,可应用于食品中呈味核苷酸的分析检测。     

Concentration of Umami Compounds in Pork Meat and Cooking Juice with Different Cooking Times and Temperatures

This study examined the concentrations of umami compounds in pork loins cooked at 3 different temperatures and 3 different lengths of cooking times. The pork loins were cooked with the sous vide technique. The free amino acids (FAAs), glutamic acid and aspartic acid; the 5′‐nucleotides, inosine‐5′‐monophosphate (IMP) and adenosine‐5′‐monophosphate (AMP); and corresponding nucleoside inosine of the cooked meat and its released juice were determined by high‐performance liquid chromatography. Under the experimental conditions used, the cooking temperature played a more important role than the cooking time in the concentration of the analyzed compounds. The amino acid concentrations in the meat did not remain constant under these experimental conditions. The most notable effect observed was that of the cooking temperature and the higher amino acid concentrations in the released juice of meat cooked at 80 °C compared with 60 and 70 °C. This is most likely due to the heat induced hydrolysis of proteins and peptides releasing water soluble FAAs from the meat into the cooking juice. In this experiment, the cooking time and temperature had no influence on the IMP concentrations observed. However, the AMP concentrations increased with the increasing temperature and time. This suggests that the choice of time and temperature in sous vide cooking affects the nucleotide concentration of pork meat. The Sous vide technique proved to be a good technique to preserve the cooking juice and the results presented here show that cooking juice is rich in umami compounds, which can be used to provide a savory or brothy taste.     

Applications of Polarography for Assessment of Fish Freshness

Fish freshness was assessed with an enzymatic method using a polarographic probe at 0.7 volt (platinum vs silver) to monitor degradation of inosine monophosphate (IMP), inosine (H × R), and hypoxanthine (Hx). The K-value, a ratio of H × R + Hx/IMP + H × R + Hx, was determined in Sockeye salmon, Pacific cod and Pacific herring in ice and at 12°C. Results were compared with those from HPLC and sensory scores. K-values by polarography correlated well with HPLC. Loss of freshness accompanied rise in K-value in all studies. Sensory scores correlated relatively well with K-values in Sockeye salmon and Pacific herring but less with Pacific cod. K-value did not reflect eating quality of Pacific cod.     

Concentration of Creatine Phosphate, Adenine Nucleotides and Their Derivatives in Electrically Stimulated and Nonstimulated Beef Muscle

The concentration of creatine phosphate (CP), adenosine tri-, di- and monophosphate (ATP, ADP and AMP, respectively), inosine monophosphate (IMP) and inosine in longissimus muscle removed from electrically stimulated (ES) and nonstimulated (NS) beef sides was enzymatically determined. After aging the carcass 7 days, steaks were removed for flavor evaluation. R values (absorbance ratios) were obtained from muscle samples removed over time from both sides. Data indicate more rapid catabolism of CP, ATP, and ADP in ES samples, with subsequent fluctuations in IMP and inosine concentration. At 12 and 24 hr post-stimulation, ES samples had more inosine; however, this difference did not exist after aging. Flavor differences were not observed after the 7-day aging period. R values parallel the degradation of adenine nucleotides and indicate rapid onset of rigor mortis in ES muscle.     

Microbial growth in vacuum packaged frankfurters produced in Spain

The effects of storage temperature and time on the microflora of vacuum packed frankfurters were analysed. Total aerobic counts, lactic acid bacteria, Brochothrix thermosphacta and yeast and moulds, were determined as functions of time. Statistically significant differences were observed (P ≤0·001) amongst the counts obtained at 2 and 7°C. At the end of the controlled storage period (42 days) the sausages kept at 7°C showed signs of spoilage. The appearance of superficial slime occurred after 28 days in samples with lactic acid bacteria at counts higher than 10⁸ cfu g⁻¹. The swelling of the pack showed after 42 days in those samples which had a level higher than 5 × 10⁸ cfu g⁻¹. On the contrary, the samples kept at 2°C did not show the aforesaid spoilage signs during the period of controlled storage. Basing our conclusions on the results obtained, a period of shelf life of 28 days was established at 7°C, whilst at 2°C a minimum shelf life of 42 days was obtained.     

Hypoxanthine Ratio Determination in Fish Extract Using Capillary Electrophoresis and Immobilized Enzymes

Fish freshness was assessed using capillary electrophoresis and an immobilized enzyme procedure to monitor degradation of inosine-5′-monophosphate (IMP), inosine (HxR) and hypoxanthine (Hx). The enzymatic method used an amperometric probe at + 0.7 V (platinum vs silver/silver chloride) with immobilized xanthine oxidase, catalase, nucleoside phosphorylase, and nucleotidase for converting Hx, HxR or IMP to uric acid. Capillary electrophoresis resolved IMP, inosine and Hx by migration rates resulting from an applied electric field (416 V/cm, 50 μA). Components were detected at 250 nm. The H ratio of Hx/[IMP + HxR + Hx] and simplified K value of [HxR + Hx]/ [IMP + HxR + Hx] were determined in cod, salmon and trout stored on ice (0-4°C) and at 20°C. The two procedures agreed and for all species H ratio and K values increased with storage time.     

Influence of storage temperature on the quality of beef liver; pH as a reliable indicator of beef liver spoilage

The development of the microbial flora specifically involved in the spoilage of sliced beef livers packaged and stored under aerobic conditions at 0 and 3 °C for 14 days was studied. Changes in the pH value of the product were also determined. The possibility that pH value could be considered as a quick and reliable indicator of incipient spoilage was particularly considered. All microbial groups (except micrococci) showed differences in their rates of growth between 0 and 3 °C. Pseudomonads and lactic acid bacteria were the main components of the spoilage flora. When the 37 °C aerobic plate counts (APCs) reached 10⁵–10⁶ CFU g⁻¹ and the 20 °C APCs and pseudomonad counts reached 10⁶–10⁷ CFU g⁻¹, visible surface colonies (VSCs) were observed. The presence of VSCs is the most important criterion to determine organoleptic beef liver spoilage and has hence enabled us to establish a shelf-life of up to 8–10 and 5.5–6.5 days for samples stored at 0 and 3 °C respectively. Our study shows that the determination of pH, which is simple, economical and rapid, is capable of giving a reliable estimate of the spoilage status of beef livers. pH values lower than 6.15 may be considered as indicative of beef liver spoilage. © 1999 Society of Chemical Industry     

Sensory Changes in Umami Taste of Inosine 5'-Monophosphate Solution after Heating

Discrimination in umami taste of inosine 5′-monophosphate (IMP) solution caused by thermal degradation was investigated by sensory evaluation. The difference threshold of umami taste of 0.005% IMP solution in the presence of 0.05% monosodium glutamate (MSG) was 0.002%. The difference threshold of a 0.005% IMP solution decreased by about one half when heated at 95°C for 15 h. Inosine, one of the main products of the thermal degradation of IMP, had a bitter taste. The detection threshold of inosine varied widely among panelists. Heating a 0.005% IMP solution at 95°C for 15 h formed inosine at about one tenth of its lowest detection threshold.     

Thermal Degradation of Flavor Enhancers, Inosine 5'-monophosphate, and Guanosine 5'-monophosphate in Aqueous Solution

The mechanism of thermal degradation of inosine 5′-monophosphate (IMP) and guanosine (GMP) was investigated kinetically in aqueous solution as a function of pH and temperature. The degradation of IMP and GMP followed first order kinetics. The rate constants were considerably affected by pH and temperature. The half-life times at 100°C were: IMP, 8.7 hr (pH 4.0), 13.1 hr (pH 7.0), 46.2 hr (pH 9.0); GMP, 6.4 hr (pH 4.0), 8.2 hr (pH 7.0), 38.5 hr (pH 9.0). These times were shortened to about one-third by raising the temperature 10°C. The predominant degradation products were nucleosides and phosphoric acid, indicating that the main reaction of the thermal degradation was the hydrolysis of the phosphoric ester bond in the nucleotides.     

Spore-forming bacteria in commercial cooked,pasteurised and chilled vegetable purées

In commercial purées of broccoli, carrot, courgette, leek, potato and split pea, pasteurized in their final packaging and analysed at two periods, Bacillus spp. were the dominant aerobic mesophilic bacteria (AMB). Initial numbers were generally lower than 2 log cfu g⁻¹. They increased up to 6–8 log cfu g⁻¹after about 20 days of storage at 10°C. At 4°C, numbers of AMB after 20 days were lower than 3 log cfu g⁻¹in potato purée, lower than 4 log cfu g⁻¹in leek purée, and between 3 and 6 log cfu g⁻¹in other products. Strict anaerobes were in markedly lower numbers than AMB. At all storage temperatures tested courgette purée usually showed the most rapid bacterial growth and spoilage. On this product, an increase in storage temperature from 4°C to 10°C resulted in a threefold reduction in time to 5 log cfu g⁻¹, and time to spoilage. Growth kinetics of AMB in courgette purée at 20°C, 15°C, 10°C, 6·5°C and 4°C were determined using a mathematical model. Three hundred and forty eight isolates were identified using the API system. Bacillus circulans, B. macerans and B. polymyxa were among the main species isolated from products stored at 4°C and 10°C, while B. subtilis and B. licheniformis were the dominant species in product stored at abuse temperature. Bacillus cereus was isolated from all storage conditions, but mostly from products stored at abuse temperature.     

Monitoring the sensorial and microbiological quality of pasteurized white asparagus at different storage temperatures

Changes in sensory quality and proliferation of pathogenic and spoilage microorganisms in pasteurized white asparagus were measured as a function of storage temperature. The main sensorial attributes studied with regard to storage time were the general appearance of the product, turgidity and package swelling. There was a significant correlation between the deterioration in sensorial quality and microbial evolution, which was even more marked at higher temperatures. After 13 days at 4°C, 6 days at 10°C, 5 days at 20°C and 84 h at 30°C organoleptic deterioration and, consequently, the end of shelf life were detected. A significant growth of spoilage flora was observed, which might be responsible for the drop in pH levels during the final period of analysis (from 6.3 to 3.5–4 until 148 h). There was greater lactic acid bacteria (LAB) growth as the temperature and CO₂ concentration increased, reaching a final concentration of approximately 10⁸ CFU g^?1 at all temperatures. We found no positive samples of Clostridium spp at 10 and 4°C. Among the species isolated at 20–30°C Clostridium septicum and in lower proportions Clostridium perfringens were encountered. The possible presence of Listeria monocytogenes was analyzed, but there were no positive samples in the final product. Pasteurized white asparagus maintains good organoleptic characteristics with a relatively long shelf‐life at low temperatures, which leads to an adequate acceptance among consumers. Copyright © 2006 Society of Chemical Industry     

Nucleotide Catabolism: Influence on the Storage Life of Tropical Species of Fish from the North West Shelf of Australia

The storage life of four species of fish from the North West Shelf was examined by means of nucleotide catabolism and sensory evaluation. It was found that the shelf life was related to the rate of inosine monophosphate (IMP) breakdown rather than to bacterial spoilage, because the endemic mesophilic bacteria were unable to adapt to ice storage conditions. The results indicated that the IMP level was fundamentally related to both flavor intensity, and acceptability, and was not merely circumstantially related to time of storage.     

Spoilage changes in the deep water fish, smooth oreo dory during storage in ice

Smooth oreo dory ( Pseudocyttus maculatus ), a deep water fish, was monitored for changes during storage in ice. Based on the sensory evaluation of the cooked flesh the storage life was 8 days for acceptable quality fish.
Bacterial counts of flesh and surface, the loss of inosine monophosphate (IMP) and the K value showed significant changes during the storage life. Therefore these were found to be useful for monitoring loss of freshness and development of spoilage. After 13 days there were off flavours in the cooked fish, dephosphorylation of IMP had levelled off, and the K value had reached 70%.
The changes that occurred during storage of this deep water species in ice were similar to those changes commonly observed in demersal species from shallow temperate coastal waters.     

Effects of Frozen Storage on Survival of Staphylococcus aureus and Enterotoxin Production in Precooked Tuna Meat

This study investigated the survival of Staphylococcus aureus in precooked tuna meat for producing canned products during frozen storage (?20 ± 2 °C) as well as its growth and enterotoxin production at 35 to 37 °C after the storage. Samples (50 ± 5 g) of precooked albacore (loin, chunk, and flake) and skipjack (chunk and flake) tuna were inoculated with 5 enterotoxin‐producing strains of S. aureus at a level of approximately 3.5 log CFU/g and individually packed in a vacuum bag after 3 h incubation at 35 to 37 °C. Vacuum‐packed samples were stored in a freezer (?20 ± 2 °C) for 4 wk. The frozen samples were then thawed in 37 °C circulating water for 2 h and incubated at 35 to 37 °C for 22 h. Populations of S. aureus in all precooked tuna samples decreased slightly (<0.7 log CFU/g) after 4 wk of storage at ?20 ± 2 °C, but increased rapidly once the samples were thawed and held at 35 to 37 °C. Total S. aureus counts in albacore and skipjack samples increased by greater than 3 log CFU/g after 6 and 8 h of exposure to 35 to 37 °C, respectively. All samples became spoiled after 10 h of exposure to 35 to 37 °C, while no enterotoxin was detected in any samples. However, enterotoxins were detected in albacore loin and other samples after 12 and 24 h of incubation at 35 to 37 °C, respectively. Frozen precooked tuna meat should be used for producing canned tuna within 6 to 8 h of thawing to avoid product spoilage and potential enterotoxin production by S. aureus in contaminated precooked tuna meat.     

Pasteurization of Pacific Oysters by Radiation: Post-Mortem Changes in Nucleotides During Storage at 0-2°C

SUMMARY: The concentration of nucleotides was lower in the adductor muscle of the oyster (1.64 μmoles/g) than in the remaining dark tissues of the oyster (2.75 μmoles/g). The concentration was less in the whole oyster meats (2.87 μmoles/g) than is usually found in fish muscle, or other marine invertebrates.
In addition to the adenine nucleotides and inosine monophosphate, uridine triphosphate, guanosine triphosphate, guanosine diphosphate, guanosine monophosphate and guanosine diphosphate-mannose were found in the fresh oysters. Samples collected in summer had greater concentrations of nucleotides than similar winter samples. lnosine monophosphate formed rapidly from adenosine triphosphate during storage at 0°–2°C, while the turnover rate of inosine monophosphate was slow and reflected low 5'-nucleotidase activity. Hypoxanthine, inosine, guanosine, guanine and uracil were formed during ice storage. The nucleotide breakdown in oysters was not changed by 2 mrads of radiation dose. Total nucleosides and free bases increased during storage of both unirradiated and irradiated samples. During the latter part of the storage period the concentrations of nucleosides and free bases were considerably greater in the irradiated samples. This difference probably is due to the utilization of these compounds by bacteria in the un-irradiated samples. After 15 days of storage bacteria had increased to more than 10'organisms per g, while the counts for irradiated samples were very low (less than 103 per g).     

The effect of storage temperature on histamine production and the freshness of yellowfin tuna (Thunnus albacares)

The present study was undertaken to assess the effect of storage temperatures on the shelf life and safety of yellowfin tuna (Thunnus albacares) by studying the changes in microbial, chemical, and organoleptical attributes. Shelf life of yellowfin tuna was determined through changes in total aerobic mesophilic and psychrotrophilic bacterial plate counts, K values, and organoleptic properties, whereas one aspect of its safety was determined through histamine development during storage at 0, 8, and 20 °C. The K value increased linearly at a slow rate (2.4%/day, r² = 0.90, p < 0.05) during storage at 0 °C. Based on K value indices, yellowfin tuna maintained an acceptable shelf life for 12, 5 and 1 day at 0, 8, and 20 °C, respectively. However, yellowfin tuna were rejected earlier by the sensory panelists than their K value indicated. Histamine development was found to be lower than the Food and Drug Authority (FDA) safety level of 5 mg/100 g fish during storage at 0 °C for 17 days. Yellowfin tuna stored at 8 and 20 °C became unsafe for human consumption, reaching unacceptable histamine levels after 4 and 1 day, respectively. Aerobic mesophilic bacteria initially dominated the microflora on yellowfin tuna, however, as storage time increased, aerobic psychrotrophic bacteria became dominant at cold storage but the numbers did not exceeded the International Commission on Microbiological Specifications for Foods (ICMSF) limit of 10⁷ cfu/g.     

Probability of growth and toxin production by nonproteolytic Clostridium botulinum in rockfish fillets stored under modified atmospheres

Whether toxin production by Clostridium botulinum precedes or follows spoilage of fish stored under modified atmospheres (MA), remains unclear. In this factorial design study we inoculated a pool of nonproteolytic C. botulinum spores (5 type E, 4 type B, and 4 type F strains) at 6 levels (10⁴ to 10⁻¹) between two rockfish fillets and then incubated the fillets at 4, 8, 12 and 30°C under vacuum, 100% CO₂ and 70% CO₂+30% air for 21 days. The probability of toxigenesis by one spore was significantly affected (P<0.005) by temperature (T) and storage time (S_t), and not (P>0.1) by MA, MA×T or MA×S_t. At the 10° spore/sample level, the earliest time to detect toxin production at 4,8,12 and 30°C under all MAs was >21, 15–21, 6–9 and 2 days, respectively. No toxin production was detected at 4°C. Only type B toxin was present in the toxic samples. At 30°C storage, spoilage of fillets followed toxigenesis. Using linear and logistic regression models, equations were derived that could estimate the lag phase and predict the probability of one spore initiating growth under a particular storage condition.