Investigations into the Qualities of Farmed, Fresh Southern Bluefin Tuna, Air-Freighted from Port Lincoln, South Australia to Tokyo, Japan

Author: Alistair Ewan Douglas

Douglas, Alistair Ewan, 2009 Investigations into the Qualities of Farmed, Fresh Southern Bluefin Tuna, Air-Freighted from Port Lincoln, South Australia to Tokyo, Japan, Flinders University, School of Biological Sciences

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The establishment of the Aquafin CRC enabled Japan-based research into the qualities of farmed, fresh Southern bluefin tuna to be conducted. This occurred via industry collaboration in both Australia and Japan, and through the establishment of a memorandum of understanding between Flinders University of South Australia and the Tokyo University of Fisheries (now the Tokyo University of Marine Science and Technology), and an agreement between the Aquafin CRC and Nippon Suisan, the product was profiled, and instrumental and sensory investigations into the qualities of this valuable product were able to be developed and undertaken. Although the three major cuts of tuna white muscle, known as Akami, Chutoro, and Otoro, are compositionally different, they were shown to have similar patterns of change post-mortem for a selection of bio-chemical parameters commonly associated with 'quality', potentially allowing for the indirect assessment of the more valuable cut (Otoro) from the destructive sampling of the less valuable cut (Akami). Further, the establishment of a correlation between expert subjective assigned ranks of 'quality' and a ratio of derived red, green, and blue (RGB) values from digital images of the flesh, offers a new objective quality assessment technique that is both rapid and non-destructive. In addition, a balanced and statistically robust analytical protocol was developed for the sensory assessment of the whole carcass qualities of tuna flesh. The protocol allows for the affect of any on-farm or in-chain manipulations on the sensory properties of the flesh that are directly perceptible to consumers to be assessed. As the product has a reputation for short colour shelf-life on the market, the effects of using vitamin supplements as a counter measure (as per the industry practice) on the concentrations of vitamins in the flesh and on the colour shelf-life of the end product were investigated. Vitamin supplementation was categorically proven to aid in the colour retention of the flesh of farmed Southern bluefin tuna with low to medium levels of fat both in Australia and in Japan. Harvest stress is known to affect the qualities of fish flesh, and in this study the effects of a prevalent industry harvesting practice on a selection of sensory and biochemical quality related characteristics of tuna flesh were investigated. Although there were no significant differences in the majority of the sensory and biochemical indicators of quality between fish harvested at the beginning or at the end of a commercial tuna harvest, expert-calibrated RGB ratios and the sensory descriptors of transparency and brightness resulted in significant deleterious effects of harvest stress on the Akami and the valuable Otoro sections respectively. The time-temperature management of chilled tuna carcasses when air-freighted to Japan, as well as the effects of shipping on the day of harvest or the day after harvest on flesh quality were investigated. Within the cold chain, the most likely periods when temperature control could be violated were shown to be during the loading and off-loading of the tuna coffins at the airports. And, although there were no statistical significant differences between the sensory and biochemical parameters measured from fish shipped on the same day as harvest when compared to those shipped a day after harvest, averages favoured the latter where recorded carcass temperatures were lower and more stable. Finally this body of work demonstrated that collaborative market-based research can be undertaken in Japan, and that product quality needs to be measured in a way that is sympathetic to customer culture and expectations.

Keywords: southern bluefin tuna,quality,sensory,stress,cold-chain,vitamin

Subject: Biological sciences thesis

Thesis type: Doctor of Philosophy
Completed: 2009
School: School of Biological Sciences
Supervisor: Prof. H. Allan Bremner