Biology Reference
In-Depth Information
28.3 Results
Echogenicity of the central myomer increased in thawed subjects, and the mean and
median values of the gray levels were significantly different in the three US studies
of the first step (Table
28.1
). In the second step, QUS BUA, BMD, and QUI values
were significantly higher in thawed sea breams. No significant differences were
found between fish thawed once and fished thawed twice. SOS showed no statistical
differences among the three groups (Table
28.2
).
28.4 Discussion
In a previous study, gray-level analysis of the central epiaxial myomer demonstrated
to be a simple and useful method to assess fish freshness (Meomartino et al.
2006
). In
the present study, the method was simplified, and the modifications were more
reproducible. A marked increase in echogenicity with a more significant difference
among the fresh and thawed sea breams was evident. No common values were
observed between fresh and twice-thawed subjects, but
there were many
overlapping values between fresh and once-thawed fishes.
To verify whether the differences between fresh and thawed tissues
demonstrated by US images could be expressed numerically, comparisons among
fresh, once-thawed, and twice-thawed sea breams were made using QUS. This
method, with the exception of the SOS values, demonstrated a significant difference
between fresh and thawed fishes but not between once- and twice-thawed sea
breams. This lesser sensitivity of the QUS, compared to the US imaging, could
be explained by at least two reasons (a) the tissues studied were soft tissues in which
US progresses virtually at the same speed and (b) the device used in this study had
been designed for human bone density assessments, and its probe used a very low
frequency that was likely unable to detect the small differences in the SOS and
impedances present in the examined tissues.
The study demonstrated a direct correlation between echogenicity and hydration
status of fresh sea breams. Since thawing causes both sarcolemmal damage and
intracellular fluid loss, tissue stiffness is produced, which affects tissue density and
ultrasound speed. These changes cause an increase in tissue echogenicity, which
may be assessed subjectively but could also be translatable numerically. The
preliminary findings are promising and show that US studies could be valuable
tools to recognize thawed fish. US could be used for quality and safety controls
performed for official and private purposes. Dedicated devices and cutoff values for
several fish species and products are needed before US studies may be proposed and
routinely used.
