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.     

Bacterial and Autolytic Changes in Water Retention and Adenosine Nucleotides of Cod Mince

Water uptake ability (WUA), expressible moisture (EM), hypoxanthine (Hx), and inosine (HxR) were monitored in cod mince stored at 0, ?2, ?3°C, with or without bacterial inactivation using NaOCl. Hx and HxR increased (p < 0.05) in all samples during the first 9-10 days. Bacterial inactivation reduced Hx and HxR build up. Beyond day 10, Hx and HxR decreased in all samples. The decrease was slower in samples in which bacterial had been inactivated. Bacterial inactivation deterred WUA increases and EM decrease.     

Effect of Adenosine-Nucleotides and Their Derivatives on the Denaturation of Myofibrillar Proteins in vitro during Frozen Storage at −20°C

To investigate the effect of adenosine-nucleotides and their derivatives on the denaturation of myofibrillar proteins, 235 nmoles/mL adenosine-5′-diphosphate (ADP), adenosine-5′-monophosphate (AMP), inosine-5′-monophosphate (IMP), inosine (HxR), or hypoxantine (Hx), was added to 3 mg/mL actomyosin (AM) solution suspended in 0.10M KC1 solution and stored at ?20°C for 12 wk. The AM was extracted from milktish dorsal muscle. Protein denaturation was evaluated by measuring solubility, Ca-ATPase and Mg(EGTA)-ATPase activity of AM, by analyzing changes in electrophoretic profiles and transmission electron microscopy. Inosine and hypoxanthine accelerated protein denaturation compared to control samples. Infrared spectrum analyses indicated that negatively charged groups of these nucleotides interacted with amino or imino groups on AM after addition. ADP, AMP, and IMP had a protective effect on denaturation of AM during frozen storage at ?20°C.     

Effects of freshness on ATP-related compounds in retorted chub mackerel Scomber japonicus

To examine the usefulness of measurement of adenosine triphosphate (ATP)-related compounds for estimation of the quality of canned and/or retorted fishes, we investigated the ATP-related compounds, in sashimi (for raw-eating)-grade and for-cooking-grade chub mackerel Scomber japonicus before and after retort process (121 °C for 30 min) by HPLC method. By the deterioration (storage time) and retort process, inosine monophosphate (IMP), an umami-taste compound, was decreased and inosine (HxR), hypoxantine (Hx) and the K-value, an index of fish freshness defined as the ratio of the sum of HxR and Hx to the sum of ATP-related compounds, were increased. By the retorting, the K-values of sashimi-grade, for-cooking-grade and unacceptable-grade meats were increased from 9.9%, 26.6% and 70% to 36%, 46% and 81%, respectively. These results suggest that the measurement of ATP-related compounds in retorted fish products may estimate the freshness in raw materials, the product quality and/or the good manufacture practices.     

不同贮藏条件下鸡肉肌苷酸含量的变化规律

为了探讨肌苷酸在冷藏和冷冻期间产生和降解规律,以70日龄黄羽肉鸡为实验材料,连续7 d测量4 ℃冷藏期间胸肌IMP、HxR、Hx、ADP、AMP和IMPc含量以及-20 ℃不同冷冻时间鸡肉IMP及其代谢物含量。结果显示:冷藏第2 d和第5 d IMP含量有显著降解,分别为屠宰后4 h的66%和45%。Hx含量在第2 d和第5 d极显著增加,分别为屠宰后4 h的2.6倍和4.6倍。HxR含量第4 d达到最大值,之后快速下降。IMPc含量从第5 d开始降解趋势明显。冷冻1周内IMP、Hx和HxR含量变化均不大。IMP含量冷冻1个月、210 d和540 d后分别为屠宰后4 h的65%、41%和6%,冷冻1个月到4个月之间变化不大。Hx和HxR含量分别在冷冻30 d和300 d时最高。IMPc含量冷冻210 d和540 d时下降极显著,分别为屠宰后4 h的84%和42%。因此,建议鸡肉4 ℃冷藏保存时货架期4 d为宜;-20 ℃冷冻保存时1周最宜,鸡肉冷冻保存时间最好不超过4个月。     

低分子质量壳寡糖对鲢鱼冷藏过程中鱼肉品质及菌相的影响

分析低分子质量壳寡糖（分子质量≤1 000 Da,脱乙酰度≥90%）对鲢鱼片4 ℃冷藏过程中菌相组成及品质变化的影响。将鲢鱼片随机分为对照组与壳寡糖（0.5 g/100 mL）处理组,测定其感官评分、菌落总数、总挥发性盐基氮含量、三磷酸腺苷关联物含量及K值等指标,并采用Illumina MiSeq高通量测序技术分析菌相组成,评价壳寡糖对鲢鱼片的保鲜作用。结果表明：壳寡糖能够改变鲢鱼冷藏过程中的菌相组成且抑制其优势腐败菌属假单胞菌和气单胞菌的生长;壳寡糖处理能够显著抑制鱼肉菌落总数和挥发性盐基氮的生成,同时显著延缓肌苷酸及次黄嘌呤核苷酸的降解,进而减少次黄嘌呤的生成。壳寡糖能够显著提高鲢鱼贮藏过程中的品质,这主要通过抑制优势腐败菌属的生长实现。     

冻结方式对不同部位草鱼呈味物质的影响

以草鱼腹肉、背肉和红肉为研究对象,采用－40?℃速冻、－20?℃乙醇液体冻结和－20?℃静止空气冻结对草鱼进行冻结处理,采用高效液相色谱法、氨基酸自动分析法以及电子舌测定不同冻结方式的鱼肉中呈味物质含量变化,并测定各部位鱼肉的乳酸含量。结果表明,冻结方式对鱼肉的鲜度和呈味物质含量有一定影响。肌苷酸（inosine monphosphate,IMP）和一磷酸腺苷（adenosine monophosphate,AMP）含量、游离氨基酸总量与冻结速率呈正相关,但乳酸、次黄嘌呤核苷（insoine,HxR）和次黄嘌呤（hypoxanthine,Hx）的含量与冻结速率呈负相关,在－20?℃冻藏条件下贮藏3?d后,－40?℃速冻组K值最小,－20?℃静止空气冻结组K值最大。红肉部分IMP、AMP含量低,而HxR和Hx含量较高,其滋味和鲜度较差,3?种冻结方式中红肉的K值分别为28.99%、40.92%、46.58%;腹肉与背肉中游离氨基酸含量相近,且高于红肉部位,但红肉中天冬氨酸、谷氨酸含量明显高于腹肉和背肉;红肉中乳酸含量显著高于腹背肉,且不同冻结方式对其影响较大。电子舌能有效区分不同冻结方式和不同部位的草鱼肉。     

Effects of retort conditions on ATP-related compounds in pouched fish muscle

To examine the usefulness of high-temperature short time (HTST) process on quality of retorted fish products, adenosine triphosphate (ATP)-related compounds in raw fishes and retorted fish models (10 g/pouch) heated at 115 °C for 90 min (common retort (CR) process) or 125 °C for 9 min (HTST process) were analyzed by HPLC method. The raw materials used in this study were fresh chub mackerel Scomber japonicus for sashimi (raw eating), frozen-thawed yellowfin tuna Thunnus albacares for sashimi, frozen-thawed pink salmon Oncorhynchus gorbuscha for cooking and frozen-thawed pink shrimp Pandalus borealis for sashimi. In all the fish samples, the level of inosine monophosphate (IMP), an umami-taste compound, was higher in HTST fishes than in CR fishes. On the other hand, inosine (HxR) and hypoxanthine (Hx), no-taste and bitter taste compounds, was high in CR fishes. K-value, an index of fish freshness defined as the ratio of the sum of HxR and Hx to the sum of ATP-related compounds, was high in CR fishes. In sensory test of pink salmon by the paired difference test, umami and sweetness in the HTST fish were stronger than the ones of the CR fish. The bitterness was stronger in the CR fish rather than in the HTST fish. These results indicated that HTST is a favorable process for retorted fish product and measurement of ATP-related compounds is useful for the quality check of retorted fishes.     

Patterns of Nucleotide Catabolism as Freshness Indicators in Flatfish from the Gulf of Alaska

Hypoxanthine was the major catabolite of adenosine triphosphate (ATP) in rock, yellowfin, flathead and Dover soles examined from the Gulf of Alaska. Inosine monophosphate (IMP)/hypoxanthine (Hx) ratios were as effective as K₁ values for assessing freshness. In contrast, inosine (HxR) was the end catabolite in rex sole and hypoxanthine was barely detectable. The gradual accumulation of hypoxanthine in rock and yellowfin soles made this catabolite a useful freshness indicator for these species.     

滤纸电泳分析检测鱼的鲜度 K 值

为了监控鱼类的鲜度水平,本文建立了简单的鱼肉鲜度K值的滤纸电泳检测方法。样品经1N HCl提取、混匀后,经高速离心机（8000 xg）离心15 min,取上清液10 μL于直径6 mm的滤纸片上,然后把含样品液的滤纸片放置在用醋酸吡啶缓冲液浸润的（醋酸：啶：＝10：1：289,pH＝3.7）电泳用滤纸上,经800 V 20 in的滤纸电泳分离后,在254 nm的紫外光视觉化处理下,观察到ATP＋ADP＋IMP, AMP, HxR＋Hx有效的分离,样品经数据处理软件处理后进行定量分析。标准品ATP＋ADP＋IMP, AMP, HxR＋Hx在0.001 umol至0.01 μmol浓度之间,有良好的线性关系线,线性关系系数均为0.99。鱼肉样品分别添加0.3 μmol ATP及其分解产物,其平均回收率为98%、96%、103%,相对标准偏差为0.75-5.8%。结果表明该方法具有快速、简便、准确的优点,并且不需要昂贵的设备,适合鱼肉鲜度K值的现场测定。     

Characterization of Quality Deterioration in Yellowfin Tuna

The spoilage pattern of thawed yellowfin tuna carcasses was examined. After five days storage at 10° and 18°C, bacterial counts were low (< 10³) although visible softening of the flesh was apparent. Direct measurement of ethanol as an indicator of pre-process spoilage also failed to reflect differences among carcasses which were aged for up to five days. Analysis of nucleotides by high performance liquid chro-matography suggested that the ratio of inosine monophosphate (IMP) to other nucleotides may be a valuable indication of spoilage time where the IMP ratio decreased linearly with time after thawing. Average recoveries of adenosine monophosphate, inosine monophosphate, inosine and hypoxanthine were 50%, 75%, 64% and 92%, respectively, from spiked tuna which had been cooked at 122°C for 67 min.     

ELECTRON BEAM IRRADIATION,OXYGEN, AND TEMPERATURE EFFECTS ON NUCLEOTIDE DEGRADATION IN STORED AQUACULTURE HYBRID STRIPED BASS FILLETS1

Skinless fillets from commercially-grown aquaculture hybrid striped bass (Morone saxatilis x M. chrysops) were electron beam-irradiated in the presence of air or vacuum-packaged and stored at 4C and -20C for 14 days. A mean low dose level of 2.0 or 3.0 kGy (± 0.5 kGy) and high dose level of 20 kGy (± 4 kGy) were used for irradiated samples. Hypoxanthine (Hx) concentrations, K_i- values {[(1NO + Hx)/(IMP + INO + Hx)] × 100}, and H-values {[(Hx)/(IMP + INO + Hx)] × 100} indicated that irradiation did not influence the rate of nucleotide degradation compared with nonirradiated controls at either refrigerated or frozen temperatures. Vacuum packaging or freezing of stored samples resulted in lower H-values and Hx contents compared with nonirradiated controls regardless of irradiation treatment.     

酵母提取物和迷迭香提取物对鲈鱼风味的影响

以酵母提取物和迷迭香提取物混合腌制大口黑鲈背部鱼肉,通过单因素试验、正交试验探究最佳腌制时间、调味料比例、料液比,确定了最佳加工工艺,并分析了腌制前后风味差异。结果表明:在4 ℃下,当0.15%酵母提取物与0.2%迷迭香提取物混合配制腌制液比例为1:3,鱼肉与腌制液料液比为1:4,浸泡50 min时感官评分最高;通过电子鼻分析表明,经腌制处理的鲈鱼与对照组气味差异明显;且在此配方处理下,脂质氧化分解产生的醛、酮、醇类化合物含量明显减少,去腥效果明显;处理组鱼肉中IMP(次黄嘌呤核苷酸)、AMP(腺嘌呤核苷酸)2种主要呈味核苷酸含量增加,Hx(次黄嘌呤)、HxR(次黄嘌呤核苷)2种核苷酸含量下降,鲜味提升。     

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.     

南美白对虾在微冻保藏期间的鲜度变化

以南美白对虾(Penaeus vannamei)为研究对象,在-3℃的微冻条件下对其进行保藏试验。通过高效液相色谱法对不同保藏期间虾肌肉中的腺苷三磷酸(ATP)及其降解的关联产物如肌苷酸(IMP)、肌苷(HxR)和次黄嘌呤(Hx)等进行分析,进而了解鲜度指标K值的变化趋势;另一方面,结合细菌总数和总挥发性盐基氮(TVBN)的测定以及感官评分的结果,对南美白对虾在微冻保藏条件下的鲜度和品质变化的规律进行考察,旨在为其保鲜提供理论依据。结果表明:微冻保藏至18 d时虾肌肉中IMP达到最高值、Hx和HxR仍维持在较低水平,而K值为23.5%,证明微冻保藏至18 d时,南美白对虾仍能保持其原有的风味和鲜度。根据细菌总数及其相关的TVBN测定和感官评分的结果,发现微冻保藏至26 d时,虾肌肉中的细菌总数、TVBN值和感官评分仍未超过腐败临界值;而保藏至26～30 d时,虽然细菌总数和TVBN值尚未超标,但感官上已失去食用价值,据此,可以认为南美白对虾在微冻保藏条件下的保质期约为26 d。     

Muscle High-Energy Phosphates and Stress Affect K-Values during Ice Storage of Atlantic Salmon (Salmo salar)

Initial levels of white muscle high-energy phosphates, IMP, ATP:IMP-ratio, adenylate energy charge and pH were used as indicators of handling stress when Atlantic salmon were slaughtered. Ante-mortem handling included fish that were either anesthetized (baseline), quickly netted and killed by a blow to the head (unstressed) or chased to exhaustion in the holding tank (stressed). During subsequent storage in ice, freshness was evaluated in terms of IMP, HxR, Hx and K-values. HPLC showed initial differences in distribution of metabolites induced by struggling gradually fell during storage. K-values were different only for 2 days post mortem, but the effect of handling stress was discernible as higher mean K-values and different IMP and HxR contents for up to 7 days post mortem.     

A study of chemical characteristics of soy sauce and mixed soy sauce: chemical characteristics of soy sauce

Mixed soy sauce is one among the Korean traditional fermented soy sauces consumed as condiment for cooking in Korea, especially mixed soy sauce is made of the fresh seafood and the meat different from the soy sauce. Therefore, mixed soy sauce provides the strong and complicated umami taste, which is stronger than that of soy sauce. The objective of this study was to investigate for the chemical characteristics changes of mixed soy sauce in comparison with soy sauce during fermentation process (0, 120, 240 and 360 days) at different fermentation temperatures (4 and 20 °C), change in moisture, total nitrogen, crude fat, ash, pH, titratable acidity, total acidity, salt content and reducing sugar of mixed soy sauce in comparison with soy sauce. Especially, histidine, arginine, threonine, methionine, phenylalanine, and lysine, essential amino acid and among adenosine triphosphate (ATP)-related compounds, inosine (HxR) and hypoxantine (Hx) were prominent in mixed soy sauce at 20 °C. Otherwise, 2,4-dinitrophenylhydrazine (DNPH) derivative and 3DG content were prominent in soy sauce at 20 °C. The content of 2,4-DNPH derivative and 3DG in soy sauce is correlated with its browning intensity.     

NUCLEOTIDE CATABOLISM IN COLD STORED ADDUCTOR MUSCLE OF SCALLOP (ZYGOCHLAMYS PATAGONICA)

The postmortem catabolism of adenosine triphosphate (ATP) in cold stored scallop adductor muscles was examined. The change In the pH of stored muscles was also investigated. The ATP content increased for a short time after death and afterwards decreased up to 24 h of storage. Thereafter, the nucleotide level remained unchanged up to 120 h of storage. The ADP content slightly decreased up to 48 h and after that remained unchanged. The AMP slowly accumulated to around 15% of the total nucleotide concentration when the ATP decreased. Small amounts of IMP were detected in all samples. Conversely, adenosine (Ado) was not detected. Inosine (HxR) slightly increased after 48 h of storage and hypoxanthine (Hx.) significantly increased after 24 h. The 260/250‐absorbance ratio of muscle extracts and the pH of stored muscles fell sharply up to 24 h and then decreased slowly. The Hx contents were positively correlated (P < 0.01) with both the Hx/AMP ratios and the K values.     

Effect of ginger extract and vinegar on ATP metabolites,IMP‐related enzyme activity,reducing sugars and phosphorylated sugars in silver carp during postslaughter storage

This study aimed to investigate the utilisation of ginger extract and vinegar for retarding decomposition of inosine monophosphate (IMP), and IMP‐related enzyme activity (the activity of acid phosphatase (ACP) and alkaline phosphatase (ALP)) in salted silver carp (Hypophthalmichthys molitrix) during early postslaughter and chilled storage. We also quantified the decomposition pathway of ATP‐related compounds, the reducing and phosphorylated sugar, and free amino acids (FAAs) in samples. Rapid glycolysis in control occurred during postmortem storage. Vinegar and ginger extract inhibited the activity of ACP and ALP, thereby inhibiting the decomposition of IMP and the increase in hypoxanthine (Hx). IMP concentrations in treated sample were significantly higher than those of the control. Moreover, vinegar and ginger extract promoted the increase in FAAs. Therefore, vinegar and ginger extract could inhibit ACP and ALP activities and contributed to the accumulation of IMP and FAAs in silver carp during chilled storage.     

Quality changes and microbiological spoilage analysis of air‐packed and vacuum‐packed silver carp (Hypophthalmichthys molitrix) fillets during chilled storage

The effects of air‐packed (AP) and vacuum‐packed (VP) on quality and microbial characteristics of silver carp (Hypophthalmichthys molitrix) fillets during chilled storage (4 ± 1 °C) were investigated. The fillets were analyzed for sensory scores, total volatile basic nitrogen (TVB‐N), ATP‐related compounds (ATP, IMP, HxR, and Hx), K value, and biogenic amines (BAs). The results proved that VP inhibited the increase of microorganisms, TVB‐N, Hx, and putrescine in silver carp, and slowed the reduction in sensory score. Therefore, VP can be applied for preservation of the silver carp fillets to improve its quality. For identification, 16S rRNA genes of the isolated pure strains were sequenced and analyzed. On the initial day of storage, Chryseobacterium was the dominant bacterial genus. At the end of shelf life, Pseudomonas was the most common group in AP fillets and Aeromonas followed by Yersinia were found mainly in VP samples.

Practical applications

Silver carp (Hypophthalmichthys molitrix) are distributed widely in fresh water systems. The world aquaculture production of silver carp was 4,354,638 tons, and it ranked second highest among freshwater fish species in 2015, but they are perishable during storage because of microbial spoilage and biochemical reactions. Vacuum packaging (VP) has proved to be effective for extending the shelf‐life of aquatic products by excluding oxygen that prevents the growth of spoilage bacterial. However, little information is available on the microbial succession of VP silver carp. Therefore, this work was to determine the differences of microbiological succession on chilled silver carp fillets under air‐packed (AP) and VP conditions using a combination of culture‐based and 16S rRNA gene analysis methods. Furthermore, this study will give valuable information about development and spoilage of VP silver carp fillets.