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The states of protons within food items are highly related to their physical attributes. In this study, the effect of cooking methods including boiling, steaming, roasting and frying on proton dynamics, physicochemical parameters and microstructure of Spanish mackerel was assessed by low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) techniques. The treatment of cooking resulted in a significant reduction of proton mobility and declined freedom of protons. The state changes of protons can be monitored easily in an intuitive and non-destructive manner during various cooking process. The treatments of boiling, steaming, roasting and frying resulted in different cooking loss and similar water-holding capability. A significant increase of total carbonyl content and thiobarbituric acid reactive substances was found, while a decrease of the values for free thiols and surface hydrophobicity was observed. The analysis of circular dichroism spectroscopy and cryo-scanning electron microscopy showed significant structural change. The correlation coefficients of R cal 2 and R cv 2 from partial least squares (PLS) regression models were more than 0.980, suggesting good correlation between LF-NMR data and hardness, resilience, springiness, chewiness, gumminess, and adhesiveness. Good recoveries and a relatively small coefficient of variation (CV) were obtained from the PLS regression models, indicating good reliability and accuracy in predicting texture parameters for mackerel samples.Foods 2020, 9, 364 2 of 16 and texture characteristics. However, it is a challenge to characterize the water dynamics, protein denaturation and lipid oxidation during various thermal processes of Spanish mackerel. Therefore, it is vital to determine the effect of different cooking methods on protein and lipid state changes in Spanish mackerel. The states of protons from water, proteins, lipid and polysaccharide are highly related to fish muscle destruction and protein denaturation during thermal processes. Most of the protons coming from the water within the fish meat can be reflected through monitoring relaxation parameters by radio frequency with the low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) techniques [3]. The protons are chemically exchanged back and forth from water to macromolecules in fish meat, so that their transverse component of the magnetization vector can be measured by the spin-to-spin relaxation time (T 2 ). Different food samples have different relaxation time T 2 , and therefore the parameters of T 2 can reflect the change of physical attributes [4]. In addition, the MRI can provide visualized internal information of the food items during processing and storage [5]. At present, the non-destructive LF-NMR and MRI technology has exhibited prominent superiority in assessing food proton change during various food-processing methods, such as rehydration of sea cucumbers [6], drying of surf calm and chicken [7], cooking change of striped snakehead fish, and evalua...

The distribution of hexachlorocyclohexanes (HCHs) and dichlorodiphenyltrichloroethanes (DDTs) in the surface seawater and sediment of Jincheng Bay mariculture area were investigated in the present study. The concentration of total HCHs and DDTs ranged from 2.98 to 14.87 ng L −1 and were < 0.032 ng L −1 , respectively, in surface seawater, and ranged from 5.52 to 9.43 and from 4.11 to 6.72 ng g −1 , respectively, in surface sediment. It was deduced from the composition profile of HCH isomers and DDT congeners that HCH residues derived from a mixture of technical-grade HCH and lindane whereas the DDT residues derived from technical-grade DDT and dicofol. Moreover, both HCH and DDT residues may mainly originate from historical inputs. The hazard quotient of α-HCH, β-HCH, γ-HCH and δ-HCH to marine species was 0.030, 0.157, 3.008 and 0.008, respectively. It was estimated that the overall probability of adverse biological effect from HCHs was less than 5%, indicating that its risk to seawater column species was low. The threshold effect concentration exceeding frequency of γ-HCH, p,p '-DDD, p,p'-DDE and p,p'-DDT in sediment ranged from 8.3% to 100%, and the relative concentration of the HCH and DDT mixture exceeded their probable effect level in sediment. These findings indicated that the risk to marine benthos was high and potentially detrimental to the safety of aquatic products, e.g., sea cucumber and benthic shellfish.

The major hazard of arsenic in living organisms is increasingly being recognized. Marine mollusks are apt to accumulate high levels of arsenic, but knowledge related to arsenic detoxification in marine mollusks is still less than sufficient. In this study, arsenic bioaccumulation as well as the role of glutathione S-transferase omega (GSTΩ) in the process of detoxification were investigated in the Ruditapes philippinarum clam after waterborne exposure to As(III) or As(V) for 30 days. The results showed that the gills accumulated significantly higher arsenic levels than the digestive glands. Arsenobetaine (AsB) and dimethylarsenate (DMA) accounted for most of the arsenic found, and monomethylarsonate (MMA) can be quickly metabolized. A subcellular distribution analysis showed that most arsenic was in biologically detoxified metal fractions (including metal-rich granules and metallothionein-like proteins), indicating their important roles in protecting cells from arsenic toxicity. The relative mRNA expressions of two genes encoding GSTΩ were up-regulated after arsenic exposure, and the transcriptional responses were more sensitive to As(III) than As(V). The recombinant GSTΩs exhibited high activities at optimal conditions, especially at 37 °C and pH 4-5, with an As(V) concentration of 60 mM. Furthermore, the genes encoding GSTΩ significantly enhance the arsenite tolerance but not the arsenate tolerance of E. coli AW3110 (DE3) (ΔarsRBC). It can be deduced from these results that GSTΩs play an important role in arsenic detoxification in R. philippinarum.