Combined effect of antimicrobial edible coatings with reduction of initial microbial load on the shelf-life of fresh hake (Merluccius merluccius) medallions

Two distinct strategies were combined to preserve fresh fish (Merluccius merluccius) under refrigeration at 4 °C for 12 days: (i) the application of an antimicrobial edible coating enriched with oregano essential oil (OEO) or carvacrol (CV) and (ii) the reduction of initial microbial load by good handling practise and the use of sodium hypochlorite (NaOCl). The action of antimicrobial coatings alone retarded the growth of Enterobacteriaceae, lactic acid bacteria (LAB) and H₂S producing bacteria on fish samples. The reduction of initial microbial load by itself only affected the evolution of LAB, but not the rest of the bacterial groups. When using both techniques combined, edible antimicrobial coatings were significantly more effective with additional and significant delays in the growth of mesophilic, psychrotrophic and Pseudomonas bacteria. Thus, the use of both strategies combined resulted in a reduction of the counts of all bacterial groups after 12 days of storage which ranged from 1.5 log and 8 log, in Pseudomonas and H₂S producing bacteria, respectively. Moreover, no significant differences were observed when comparing the microbiological evolution of samples treated with OEO compared to those only treated with CV.     

Suitability of Volatile Amines as Freshness Indexes for Iced Mediterranean Hake

Batches of gutted Mediterranean hake (Merluccius merluccius var. Mediterraneus) were stored, in different seasons of the year, for up to 20 d in ice. Changes in trimethylamine (TMA‐N), total volatile bases (TVB‐N), P‐ratio and trimethylamine oxide (TMAO) were measured; sensory evaluation of raw and cooked hake samples was also carried out. Similar profiles were observed between the different trials for all the parameters studied. TVB‐N was not correlated with the time of ice storage, and proved to be better as a spoilage index than a freshness one. In contrast, TMA‐N appears to be a good index of hake quality, and the value of 5 mg/100g offish seems an appropriate limit of acceptability. P‐ratio was a poorer index of freshness than was TMA‐N.     

Effect of frozen storage of hake,sardine and mixed minces on natural actomyosin extracted in salt solutions

Natural actomyosin extracted in salt solutions from mixtures of hake and sardine minces (3:1; 1:1 and 1:3 w/w) stored frozen for up to 1 year differed in the amount extracted and in the characteristics of the extracts. In the mixed minces the amount of natural actomyosin extracted decreased during frozen storage at a higher rate than that theoretically corresponding to the amount of hake in the mixes. With increasing storage time and proportion of sardine a lower percentage of myosin heavy chain and actin was observed by electrophoresis. An increased size of aggregates was also observed by electrophoresis and transmission electron microscopy. The stability of emulsions was enhanced when aggregates appeared in the extracts. The decrease in the amount of natural actomyosin extracted does not explain the changes observed in the texture of the minces during frozen storage. This may indicate that the size of the aggregates unextractable in salt solutions, independently of the type of bonds that bind the proteins in the aggregates, plays an important role in the textural changes observed. Copyright © 2003 Society of Chemical Industry     

Development of a Quality Index Method for Frozen Hake (M. capensis and M. paradoxus)

A quality index method (QIM) consisting of 9 parameters with a total of 17 sensory points was developed for frozen hake (M. capensis and M. paradoxus). The score sheet was divided into 2 parts. The 1st, including 7 parameters with up to 13 sensory points, was directly related to loss of quality during storage at ?20 °C. Multivariate analysis confirmed the relevance of these parameters for prediction of storage time. The 2nd part contained 2 additional parameters scoring up to 4 sensory points. These parameters are commercially important but not directly linked to storage time.     

坪北地区高分辨率层序分析与等时对比

以高分辨率层序地层学理论体系为指导思想，通过基准面旋回结构和叠加样式的沉积动力学分析，采用多级次基准面旋回划分方案研究陕北坪北地区上三叠统长4 5油层组高分辨率层序地层学特征，通过钻井岩心与测井资料的综合分析，从该油层组中识别出三个级别的基准面旋回界面，以界面的成因和级别为依据，将长4 5油层组划分为短期、中期、长期三个级次的旋回层序。根据多级次旋回层序划分结果，运用旋回等时对比法寸各级次旋回层序进行等时对比并建立不同尺度的时间一地层格架，讨论了不同时间尺度的层序地层格架在油气勘探开发各阶段的研究意义，     

Validation of the rancimat test for the assessment of the relative stability of fish oils

The induction periods for the peroxidation of various fish oils at 55–90°C were studied by the Rancimat test. The natural logarithms of the induction periods varied linearly with respect to temperature, with a mean coefficient of −7.5×10⁻²°C⁻¹, which was significantly different from that reported for vegetable oils. The activation energy for the formation of volatile acids had a mean value of 38.9 kJ/mol and was independent of the fish oil source. Peroxide formation under Rancimat test conditions followed first-order kinetics. The same kinetics were followed under Schaal Oven test conditions (forced-air oven, 60°C). On the basis of the results obtained, the Rancimat test appears to be useful in determining the relative stabilities of fish oils without the change in peroxide decomposition kinetics that may occur at elevated temperatures.     

Extra-Cold Storage of Hake and Mackerel Fillets and Mince

Extra-cold storage (?30 and ?40°C) of mackerel (Scomber scombras) mince and fillets showed lower free fatty acid formation. Extra-cold storage (-30°C) of white hake (Urophycti tenuis) fillets produced fish with better quality based on sensory and chemical indices. The colder the storage temperature, the less firm the hake mince and fillets. Ascorbic acid accelerated cohesiveness development of mackerel mince and fillets. Over time, the quality of the hake and mackerel decreased according to sensory and chemical indices. They became tougher and generally more cohesive.     

Cross-Linking of Myosin Heavy Chains from Cod, Herring and Silver Hake During Thermal Setting

Cross-linking of myofibrillar proteins extracted from cod (Gadus morhua), herring (Clupea harengus) and silver hake (Merluccius bilinearis) was studied in 0.6M NaCl, pH 6.5 at 40°C and evaluated turbidimetrically and by SDS polyacrylamide gel electrophoresis coupled with l-ethyl-3-(3-dimethylaminopropyl) carbodiimide as a zero-length crosslinker. Turbidities of heat-treated cod and silver hake myofibril/myosin solutions were significantly higher than those of herring. Electrophoretic results showed that the myosin heavy chain (MHC) was the principal myofibrillar protein cross-linked to form a polymerized complex during the heat treatment. Cross-linking ability of MHC from the three fish species was different; herring MHC formed only small polymers (n≦3) but cod and silver hake MHC formed both small and large polymers (n≦6).     

Endotoxin and biogenic amine levels in Atlantic mackerel (Scomber scombrus), sardine (Sardina pilchardus) and Mediterranean hake (Merluccius merluccius) stored at 22 °C

Whole Atlantic mackerel (Scomber scombrus), sardine (Sardina pilchardus) and Mediterranean hake (Merluccius merluccius) from the Croatian Adriatic were stored at 22 °C and changes in histamine, putrescine, tyramine and cadaverine levels were monitored in relation to bacterial endotoxin. After 12 h, histamine levels in sardine were above the legal limit of 50 mg kg^?1, set by the US Food and Drug Administration, and an increase in putrescine content preceded the increase in histamine. After 24 h, histamine contents in mackerel and sardine reached 1090 ± 101 and 577 ± 275 mg kg^?1, respectively, which exceeded the toxic threshold of 500 mg kg^?1. At the same time, the putrescine content was also high in both fish (353–420 mg kg^?1). The time-course of endotoxin production was similar in all fish species stored at 22 °C. A high correlation was found between endotoxin and histamine, and between endotoxin and putrescine in mackerel and sardine. On the other hand, high endotoxin levels in hake, after 24 h, were associated with the low histamine and putrescine content (40–60 mg kg^?1).     

Production of Biogenic Amines and Their Potential Use as Quality Control Indices for Hake (Merluccius merluccius, L.) Stored in Ice

ABSTRACT: The production of tyramine, histamine, putrescine, cadaverine, agmatine, and spermidine was studied for use as quality indices in muscle of gutted hake stored in ice for 25 d. The changes in biogenic amine concentrations were correlated with trimethylamine nitrogen levels. All concentrations except for spermidine, increased progressively throughout storage. During storage, cadaverine reached 72.14 mg/kg while there were no significant increases in histamine and tyramine. The levels of free amino acids, which may be metabolized into biogenic amines, were not correlated to respective biogenic amines levels. The production of cadaverine and agmatine occurred prior to spoilage and these biogenic amines may indicate freshness of hake stored in ice.