Over the last ten years, demand for fresh and frozen tuna to prepare delicatessen products such as sushi or sashimi has soared in
the Japanese market and worldwide. The ability to supply this fish
to distant markets makes the trade in frozen tuna popular. In the
frozen tuna industry, harvested tuna is typically kept in a deep-frozen state below À60 °C (Zhao et al., 1998) until transportation to
local markets or processing factories in order to preserve its quality
for prolonged periods of time (Santos-Yap, 1995).
To defrost frozen tuna, it may be thawed (temperature of the
coldest spot being just above the product’s freezing point) or tempered (temperature of the warmest spot being just below the product’s freezing point). For processing purposes, tempering is usually
performed for ease of handling. The typical target temperature
range in industrial-scale defrosting of meat is À2 to À5 °C (Farag
et al., 2009) because at these temperatures, meat products are
highly amenable to mechanical chopping (James and James,
2002). Safe and efficient technologies to temper or thaw frozen
blocks of tuna are under intensive development; the control of
temperature during these processes is critical.
The tuna industry is always interested in faster and more compact systems while maintaining the high quality demanded by
consumers.