Studies on the quality control of the Japanese scallop [Mizuhopecten yessoensis] adductor muscle

In recent years, the price of the Japanese scallop Mizuhopecten yessoensis is declining with increasing production. On the other hand, although the requirement of the consumers is severe to the freshness and the quality, there is little research on the relation between the quality of products and the components in the scallop adductor muscle, compared with fish. The rigor of the adductor muscle comes into question, as the surface of the adductor muscle becomes blackish and tough. Therefore, the purposes of this study are to grasp the property for high quality of scallop adductor muscle products, to develop the distribution system for the high quality, to improve the added value, and to expand the consumption. In the chapter 1, seasonal variation of growth and components were examined in the scallop adductor muscle. The weight of adductor muscle was highest in August. Glycogen content increased from spring to autumn (highest in August, 3.6% ) , and protein content increased from spring to autumn (highest in October, 19.8%). The content of glycogen and protein per piece of adductor muscle was highest in August The relation between glycogen and protein contents on the dry matter basis showed a converse correlation. The content of ash varied between 1.5% and 1.6% and decreased from spring to autumn. The level of potassium was highest and ranged from 420 to 480 mg/100 g . The total amounts of ATP and its related compounds increased from spring to summer (highest in July, 9.3 micro mol/g) . Scallop adductor muscle has two peaks in April and October (highest, 410mg/100 g ) in arginine level, and also two peaks in March and November (highest, 102mg/100g ) in octopine level, respectively. The total amounts of free amino acids ranged between 2000 and 2600mg/100 g and increased from spring to summer. Taurine and glycine were main free amino acids and over 60% of the total amounts of free amino acids. As for taste active free amino acids, glycine, alanine and glutamic acid were contained in large amounts. The level of glutamic acid was highest in the spawning season (132mg/lOO g in May) . Glycine and alanine levels were highest in August (857mg/lOO g and 264mg/lOO g , respectively) . In the chapter 2, the influences of storage temperatures, washing methods and fishing seasons on the rigor of scallop adductor muscle were examined from the rheological and biochemical viewpoints. During storage at - 3, O and 5 deg C the rigor of adductor muscle progressed fastest at - 3 deg C , followed by O deg C) . The ratio of adductor muscle in rigor reached 100% after 4 days at - 3 deg C and after 6 days at 0 and 5 deg C, respectively. Therefore, the storage at - 3 deg C was unsuitable for quality control. In the adductor muscle in rigor, breaking strength and pH value were low, and K value. was high, compared with normal adductor muscle. It was observed that the rigor occurred when K value exceeded 20% and pH value decreased below 6.5. In the adductor muscle of scallop washed in distilled water breaking strength, ATP concentration and pH value decreased, and K value increased remarkably during storage at 0 deg C, while not remarkably in the adductor muscle washed in artificial seawater or without washing. The ratio of scallop adductor muscle in rigor was 100% after 2 days by washing in distilled water and after 5 days by washing in artificial seawater or without washing. The washing treatment of scallop adductor muscle with fresh water was unsuitable even for a short time, and that with seawater was desirable. Decrease in ATP concentration and pH value, development of rigor and accumulation of octopine progressed much faster during storage at 0 deg C in the adductor muscle of scallop caught in September than that in April. Fishing seasons influenced the quality of scallop. In the chapter 3, quality control with gas packagings and antibacterial sheet was examined in the scallop adductor muscle. Packaging with N2 gas accelerated rigor and initial decomposition. In the adductor muscle packed with mixture of 02 and C02, initial decomposition was delayed but rigor was developed, as C02 concentration increased. On the other hand, in the adductor muscle packed with 02 gas it was observed that the decrease in ATP and pH value, development of rigor, accumulation of octopine and increase in total viable counts were delayed for about two days, compared with that packed with air. During storage at 5 deg C the rigor occurred after 4 days without wrapping, after 5 days by paper towel and after 6 days by antibacterial sheet, respectively. In the adductor muscle wrapped in antibacterial sheet, it was observed that the decrease in ATP and pH value, and the increase in total viable counts were delayed, compared with control. From these results, the following procedures should be done in order to distribute the scallop adductor muscle of high quality. 1 . In order to wash scallop adductor muscle after harvest sterilized seawater or artificial seawater should be used. The washing treatment with fresh water is not suitable as the rigor was accelerated. 2 . Storage temperature at 5 deg C should be carried out. The rigor is developed at the temperature lower than 5 deg C . 3 . As the rigor occurs quickly during storage in the adductor muscle of scallop caught in summer, it is undesirable to cool scallop excessively. 4 . It is possible to retain the high quality by packaging with 02 gas or by covering with antibacterial sheet.