Microbiological and Sensorial Quality Assessment of Ready-to-Cook Seafood Products Packaged under Modified Atmosphere

ABSTRACT:  The effects of modified atmosphere packaging (MAP) (30:40:30 O₂:CO₂:N₂ and 5:95 O₂:CO₂) on the quality of 4 ready-to-cook seafood products were studied. In particular, the investigation was carried out on hake fillets, yellow gurnard fillets, chub mackerel fillets, and entire eviscerated cuttlefish. Quality assessment was based on microbiological and sensorial indices determination. Both packaging gas mixtures contributed to a considerable slowing down of the microbial and sensorial quality loss of the investigated seafood products. Results showed that sensorial quality was the subindex that limited their shelf life. In fact, based primarily on microbiological results, samples under MAP remained acceptable up to the end of storage (that is, 14 d), regardless of fish specie. On the other hand, results from sensory analyses showed that chub mackerel fillets in MAP were acceptable up to the 6th storage d, whilst hake fillets, yellow gurnard fillets, and entire cuttlefish became unacceptable after 10 to 11 d. However, compared to control samples, an increase in the sensorial shelf life of MAP samples (ranging from about 95% to 250%) was always recorded.
Practical Application: Modified atmosphere packaging (MAP) is an inexpensive and uncomplicated method of extending shelf life of packed seafood. It could gain great attention from the fish industrial sector due to the fact that MAP is a practical and economic technique, realizable by small technical expedients. Moreover, there is great attention from the food industry and retailers to react to the growing demand for convenience food, thus promoting an increase in the assortments of ready-to-cook seafood products.     

Stress corrosion cracking of cold-worked austenitic stainless steels

Stress corrosion cracking (SCC) of AISI 304L and AISI 316L stainless steels, cold-worked under various conditions (i.e. at different degrees of deformation obtained by drawing and rolling at room temperature and at liquid nitrogen temperature) has been carried out in H₂O containing 1000 ppm Cl^? at 250°C and in a boiling MgCl₂ solution. The effect of heat treatments at 400 and 900°C on the SCC of previously cold-worked steels has also been studied. Particular attention was directed towards heat treatment at 400°C. In steels deformed at room temperature, it increases the SCC resistance. By contrast, for steels deformed at liquid nitrogen temperature, heat treatment at 400°C reduces the SCC resistance if carried out for short periods of time (1–6 h). Hardness measurements, structural analyses via X-rays, scanning and transmission electron microscopy (SEM and TEM), as well as modified Strauss tests, seem to prove that reduced stress corrosion resistance is not to be related to the chromium-rich carbides precipitation which could have been accelerated by the presence of α′-martensite. Instead, they tend to suggest that perhaps this phenomenon is connected to an increase in the level of internal micro-stresses which are generated by a reciprocal re-ordering of the α′ and γ structural phases.     

Aziridide-based inhibitors of cathepsin L: synthesis, inhibition activity, and docking studies

A comprehensive screening of N-acylated aziridine (aziridide) based cysteine protease inhibitors containing either Boc-Leu-Caa (Caa=cyclic amino acid), Boc-Gly-Caa, or Boc-Phe-Ala attached to the aziridine nitrogen atom revealed Boc-(S)-Leu-(S)-Azy-(S,S)-Azi(OBn)(2) (18 a) as a highly potent cathepsin L (CL) inhibitor (K(i)=13 nM) (Azy=aziridine-2-carboxylate, Azi=aziridine-2,3-dicarboxylate). Docking studies, which also accounted for the unusual bonding situations (the flexibility and hybridization of the aziridides) predict that the inhibitor adopts a Y shape and spans across the entire active site cleft, binding into both the nonprimed and primed sites of CL.     

Total mercury,methylmercury and selenium in mercury polluted areas in the province Guizhou,China

The province of Guizhou in Southwestern China is currently one of the world's most important mercury production areas. Emissions of mercury from the province to the global atmosphere have been estimated to be approximately 12% of the world total anthropogenic emissions. The main objective of this study was to assess the level of contamination with Hg in two geographical areas of Guizhou province. Mercury pollution in the areas concerned originates from mercury mining and ore processing in the area of Wanshan, while in the area of Quingzhen mercury pollution originates from the chemical industry discharging Hg through wastewaters and emissions to the atmosphere due to coal burning for electricity production. The results of this study confirmed high contamination with Hg in soil, sediments and rice in the Hg mining area in Wanshan. High levels of Hg in soil and rice were also found in the vicinity of the chemical plant in Quingzhen. The concentrations of Hg decreased with distance from the main sources of pollution considerably. The general conclusion is that Hg contamination in Wanshan is geographically more widespread, due to deposition and scavenging of Hg from contaminated air and deposition on land. In Quingzhen Hg contamination of soil is very high close to the chemical plant but the levels reach background concentrations at a distance of several km. Even though the major source of Hg in both areas is inorganic Hg, it was observed that active transformation of inorganic Hg to organic Hg species (MeHg) takes place in water, sediments and soils. The concentration of Hg in rice grains can reach up to 569 microg/kg of total Hg of which 145 microg/kg was in MeHg form. The percentage of Hg as MeHg varied from 5 to 83%. The concentrations of selenium can reach up to 16 mg/kg in soil and up to 1 mg/g in rice. A correlation exists between the concentration of Se in soil and rice, indicating that a portion of Se is bioavailable to plants. No correlation between Hg and Se in rice was found. Exposure of the local population to Hg may occur due to inhalation of Hg present in air (in particular in Hg mining area) and consumption of Hg contaminated food (in particular rice and fish) and water. Comparison of intake through these different routes showed that the values of Hg considerably exceed the USA EPA Reference Concentration (RfC) for chronic Hg exposure (RfC is 0.0004 mg/m(3)) close to the emission sources. Intake of Hg through food consumption, particularly rice and fish, is also an important route of Hg exposure in study area. In general, it can be concluded that the population mostly at risk is located in the vicinity of smelting facilities, mining activities and close to the waste disposal sites in the wider area of Wanshan. In order to assess the real level of contamination in the local population, it is recommended that biomonitoring should be performed, including Hg and MeHg measurements in hair, blood and urine samples.     

Transformations of mercury in the terrestrial isopod Porcellio scaber (Crustacea)

The biological cycle of mercury in the terrestrial isopod Porcellio scaber was investigated. Testing the possibility of in vivo Hg(2+) methylation was divided into two methodologically different parts. Firstly, concentrations of total mercury and MeHg in isopods P. scaber and their environment from a Hg-unpolluted area were measured by the use of validated methods (CV AAS, CV AFS). The data obtained show that the percentage of MeHg in leaves, soil and faeces was less than 1%. In contrast, the percentage of MeHg in gut and hepatopancreas was increased to 14 and 77%, respectively, indicating methylation of Hg(2+) in the gut and its further accumulation in glands. To confirm this assumption, the second methodology was applied-a radiotracer technique with 203Hg(2+) of high specific activity. There are few radiotracer techniques for Hg-methylation assays; for our work we chose the method of Czuba et al. which includes alkaline leaching of Hg species, their extraction into dithizone-toluene, followed by specific separation of Hg dithizonates by thin-layer chromatography and gamma counting. All steps of the analytical protocol were checked and optimised by the use of aqueous solutions of 203Hg(2+) and Me(203)Hg(+). The most important finding was that cleaning-up the extract through a florisil column is not appropriate, because the column retains different percentages of Hg(2+) and MeHg(+) and consequently affects the accuracy of the final result. This optimised protocol was then applied to Hg transformation studies in the terrestrial isopod P. scaber. Leaching Hg species from P. scaber fed with 203Hg(2+) or Me(203)Hg(+) dosed food was completely efficient only at elevated temperatures. Preliminary results of methylation/demethlytion studies are rather variable but they show that both processes (Hg(2+)<-->MeHg(+)) take place in the isopod P. scaber. Additionally, an assessment of the mass balance of Hg in isopods P. scaber exposed to 203Hg(2+) indicates that volatile Hg species are also formed.     

Whey protein nanoparticles prepared with desolvation with ethanol: Characterization,thermal stability and interfacial behavior

Whey protein isolate (WPI) nanoparticles were prepared by diluting an alkaline solution of protein in ethanol at concentrations varying between 50 and 80%. The nanoparticles were then immediately diluted in buffer. While the nanoparticles were not stable at pH 7, they showed no changes in size when diluted at pH 3. When 75–80% ethanol was added during preparation, the size of the WPI nanoparticles ranged between 10 and 100 nm, with no change in size after dilution and storage at pH 3 for 96 h at 22 °C. When heating was applied, particle aggregation occurred, and large aggregates (>1 μm) were observed at temperatures > 60 °C. The particle size of the heat-induced aggregates could be reduced by homogenization. The nanoparticles prepared by desolvation showed interfacial pressure values similar to those of the corresponding protein solutions, indicating similar interfacial properties and the potential to be used to stabilize emulsions but as supramolecular aggregates of WPI.     

Inactivation of Spoiling Yeasts of Fruit Juices by Pulsed Ultrasound

This paper reports on the use of ultrasound (US) as a suitable strategy to control the growth of spoiling yeasts in fruit juices. In a first phase, US technique was tested towards Saccharomyces cerevisiae inoculated in different juices (strawberry, orange, apple, pineapple and red-fruits): the treatment was performed by modulating the level of the power (20–60 %), the duration of the treatment (2–6 min) and the pulse (2–6 s), according to a fractional design. Then, the best treatment was applied against some other spoiling yeasts (Pichia membranifaciens, Wickerhamomyces anomalus, Zygosaccharomyces bailii, Zygosaccharomyces rouxii, Candida norvegica). Finally, a challenge test for a commercial beverage (red-fruit juice), inoculated with Z. bailii and containing a citrus extract, was conducted evaluating the effect of US on the sensory scores of the beverage. The results showed that the effect of US was mainly influenced by the power and the duration of the treatment; on the other hand, the effect of pulse was less significant and slight. The highest reduction of S. cerevisiae was found in the following combination of the design: power 60 %/time 4 min/pulse 2 s and power 60 %/time 6 min/pulse 6 s; this result was confirmed for the other spoiling yeasts. US and citrus extract could be combined to prolong the shelf life of the red-fruit juice and control the growth of Z. bailii. The two hurdles exerted a different role and acted in different times: US reduced the initial contamination, whilst citrus extract controlled the yeast within the storage.     

Single-electron transfer living radical copolymerization of SWCNT-g-PMMA via graft from approach

The sidewall functionalization of single-walled carbon nanotubes (SWCNTs) was established by poly (methyl methacrylate) (PMMA) using controlled radical polymerization (CRP) method. A bromide functionalized SWCNT (SWCNT-Br) has been used as an initiator for the synthesis of SWCNT-graft-PMMA (SWCNT-g-PMMA). The efficiency of the sacrificial initiator (S) was monitored during the polymerization process. The obtained polymers possess a uniform distribution of molecular weight with a lower polydispersity index of 1.36. The SWCNTs-based initiator acts as an efficient medium for the controlled growth of polymer on the SWCNTs surfaces. The presence of bimodal gel permeation chromatographic (GPC) curve for the SWCNT-g-PMMA(S) obtained through sacrificial initiator (S) confirms uncontrolled behavior. However, the clear sharp peak for SWCNT-g-PMMA obtained without sacrificial initiator shows its well-controlled process of polymerization, which acts as a mimic to bone cement. The efficiency of the functionalization of SWCNT and the controlled formation of SWCNT-g-PMMA composites were characterized by TGA, Raman, TEM, NMR, XPS and dispersion measurements.     

HDL3-mediated cholesterol efflux from cultured enterocytes: The role of apoproteins A-I and A-II

High density lipoproteins (HDL) were recently demonstrated in an enterocyte model (CaCo-2 cells) to mediate reverse cholesterol transport by retroendocytosis. The present study was carried out to define the role of the major HDL apoproteins (apo) A-I and apo A-II in this pathway. HDL₃ was fractionated by heparin affinity chromatography into the two main fractions containing either apo A-I only (fraction A) or both apo A-I and apo A-II (fraction B). In addition, liposomes were reconstituted from purified apo A-I or apo A-II and dimyristoyl phosphatidylcholine. The cell binding properties and cholesterol efflux potential were studied in the lipoprotein fractions and the liposomes. Both fractions exhibited similar maximal binding capacities of 4427 (A) and 5041 (B) ng/mg cell protein, but their dissociation constants differed (40.5 and 167.7 μg/mL, respectively). Fraction A induced cholesterol efflux and stimulated cholesterol synthesis more than did fraction B. Fraction A mobilized both cellular free and esterified cholesterol, whereas fraction B preferentially mobilized cholesteryl esters. Liposomes, containing either apo A-I or apo A-II, showed specific binding, endocytosis and endosomal transport, and were released as intact particles. Apo A-I liposomes also mediated cholesterol efflux. In conclusion, there is evidence that the HDL₃ subfractions A and B, as well as reconstituted liposomes containing either apo A-I or apo A-II, were specifically bound and entered a retroendocytosis pathway which was directly linked to cholesterol efflux. Quantitatively, the apo A-I subfraction appeared to play the dominant role in normal enterocytes. The apo A-II content of fraction B was related to the mobilization of cholesteryl esters.