Taste component comparisons of single seed Pacific oysters collected in the first and the second harvest years in Nagasaki prefecture

Abstract

We compared the taste components of Pacific oysters (Crassostrea gigas) cultured using the single seed method (single seed oysters) off the coast of Konagai (Nagasaki Prefecture, Japan) that were cultured for different periods. Single seed oysters that had been farmed up to the first harvest year (first-year oysters), the procedure typical in this area, and those that had been kept for an additional summer and into the second harvest year (second-year oysters) were compared. We analyzed taste components including free amino acids, ATP and related compounds, and glycogen levels in the oysters that were obtained in the different harvest seasons. The experiments were repeated at 4 different times between February 2013 and February 2014 because of chemical constituent fluctuations under various environmental conditions. First, we used 2-way ANOVA to analyze all groups of the data collected in the experimental replicates and then we independently evaluated differences between the 2 groups, first- and second-year oysters, using t-tests. The second-year single seed oysters showed significantly higher values of whole body weights and soft-tissue weights than those of first-year oysters. However, the soft tissue ratios, meaning soft tissue per gram of the whole body weight including the shell, were significantly lower in second-year oysters than first-year oysters, which suggested that second-year oysters had less edible contents. Significantly higher glycine, alanine, and serine levels were observed in first-year oysters than in second-year oysters, indicating that first-year oysters might be more sweet-tasting. In contrast, no significant differences in AMP, IMP, and glycogen levels were observed between the 2 groups of single seed oysters. Moreover, in a taste evaluation test of the 2 oyster groups performed in January 2014, different culture periods had little or no effect on taste, except for their better shape and larger size.