The quality changes of shelled Pacific oysters (Crassostrea gigas) were examined in relation to the effects of superchilling storage at -1 °C for 28 days by measuring changes in biochemical properties (microbial analysis, ATP-related compounds, pH, free amino acids) and sensory evaluations in this study. The results indicated that microorganism growth was significantly inhibited during superchilling storage. Adenosine diphosphate (ADP) and adenosine monophosphate (AMP) accumulated while ATP rapidly decreased in the adductor muscle. Adenosine triphosphate (ATP) and ADP were the primary components in the other 3 tissues including mantle, gill, and body trunk of oysters, and they remained relatively stable over time. The pH and adenylate energy charge (AEC) in the adductor muscle could be utilized as freshness indicators for shelled oysters. However, there were no significant differences (P >0.05) among the free amino acids during whole storage. According to the sensory evaluations, oysters could be alive and tolerated up to 21 days at -1 °C storage. The study demonstrated that superchilling storage at -1°C could better maintain the eating quality of shelled oysters and the shelf life was extended to 21 days.
Scallop adductor muscle has a great popularity for raw consumption in Japan, but conventionally shucking live scallops with high vitality by knife needs skill and is time-consuming. Flash-boil shucking is a convenient shucking method in sushi restaurants for live scallops. However, it is not clear about the effects of this treatment on the quality of its main edible part, adductor muscle. This study was conducted to investigate the impact of flash-boil shucking on the quality raw-edible scallop adductor muscle, focusing on flavor-enhancing components and ultrastructure. Thermal treatment could contribute to the formation of flavor-enhancing nucleotides in the external layer of adductor muscle. Adenosine monophosphate content increased with the boiling time, which significantly increased to 1.47 ± 0.42 µmol/g in the 30 s-boiled group compared with 0.38 ± 0.13 µmol/g in the control group (p ˂ 0.05). The rapid adenosine monophosphate accumulation after boiling resulted in a faster accumulation of inosine and hypoxanthine during subsequent refrigeration, which could bring bitterness to aquatic products. Flash-boil shucking had no discernible effect on the proportion of free amino acids relevant to the flavor of scallop adductor muscle, despite the possibility of a reduction in total free amino acids. The external layer of scallop adductor muscle could be hardened after flash-boil shucking. At the ultrastructural level, muscle fibers tend to aggregate transversely and contract longitudinally depending on the heating time. Flash-boil shucking is ideal for consuming the raw-edible scallop adductor muscle promptly. Flash-boil shucking treatment is recommended for households, restaurants, and small factories for treating scallops with high vitality.
The changes of sensory and biochemical characteristics on the fresh and frozen‐thawed scallop adductor muscle during storage at 4°C were discussed in this study. The Quality Index Method (QIM) scheme for evaluating scallop adductor muscle as raw materials for sashimi was proposed for the first time. The results of sensory evaluation showed that frozen‐thawed scallop adductor muscle within zero to one day of refrigeration can be happily accepted by consumers, indicating the superiority of freezing for long‐distance transportation, although the triangle test confirmed that there are still sensorial differences between fresh and frozen‐thawed scallop adductor muscle. The microscopic observation of myofibrils extracted from scallop adductor muscle suggested that the myofibrillar protein which constitutes myofibrils has suffered some extent change due to freezing and thawing, even though the head region of myosin remained stable judging by the fact that there was no significant difference in Ca2+‐ATPase activity (p > 0.05). The changes of adenosine triphosphate (ATP) and its related compounds, and pH value during storage can be regarded as indicators to differentiate fresh and frozen‐thawed scallop adductor muscle. The changes of Mg2+‐ATPase activity indicated that the interaction between myosin and actin was weakened by the freezing and thawing process.
Practical Application: The QIM scheme can be used to evaluate the scallop adductor muscle as raw materials for sashimi. The mechanism of quality changes in the frozen‐thawed scallop adductor muscle was discussed in combination with the destruction of myofibrils, ATP degradation and the decrease of pH value. This study has positive significance for improving the quality of frozen‐thawed scallop adductor muscle by combining the changes of sensory and biochemical characteristics.
In this study, the impacts of deacetylation degree and molecular weight on the rheological and adhesive properties of chitosan (CS) including shear viscosity, initial viscosity, and peel strength of tobacco leaves have been studied. The effect of different dissolution solvents such as acetic acid (HAC) and lactic acid (HL) on chitosan adhesives was also investigated. The results revealed that the adhesive properties increased first and then decreased with the increase of deacetylation degree, while chitosan with higher molecular weight showed higher initial adhesiveness and peel strength values. Chitosan sample III with a medium deacetylation degree of 80.5%
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