Development of model cured fermented fish sausage from Albacore tuna
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This project was carried out to explore how to create an export opportunity for Tonga that would have a measure of geographical exclusivity. The product is a model cured fermented tuna sausage that could be produced in Tonga from the commercial species albacore tuna (Thunnus alalunga). The motive for this model is that certain features of Tonga, namely a hot climate, expensive electricity for alternative tuna preservation methods and long shipping times to foreign markets, can be turned from a disadvantage to an advantage. The fish meat sausage was, salted, nitrite cured and bacillus-fermented at 32°C with a Tongan carbohydrate source, taro to create a product stable that requires little or no refrigeration. The research was carried out in two phases. The first was to determine the effect of microwave cooking on the fermentable sugar formation in tubers (taro, potato, kumara), and having defined a useful hydrolysed source, the second phase was sausage production to define its physiochemical properties. Of the three potential cooked carbohydrate sources, kumara showed the highest glucose concentration followed by taro and then potato after hydrolysis. Taro, which is particularly important to Tonga as a staple food, generated potentially useful concentrations of glucose and was chosen for further work. The concentrations of taro used in this study were 0, 10, 20 and 30%, a likely range of concentrations to fulfill one criteria; a fermented tuna product but produced at minimal cost. Tuna is much more expensive than taro. After four days of fermentation at 32ºC, the pH of each treatment was between 4.1 and 3.9, very low by fermented meat standards. Hardness and springiness increased on Day 4 while cohesiveness and adhesiveness decreased. The product was increasingly hard, sticky and brittle, probably due to staling, more formally called retrogradation of taro starch. The colour changes showed an increase in L* (light reflectance) while the a* (redness) values decreased in relative to b* (yellowness) values confirming that a brown fermented fish mince (FFM) sausage was produced. Proteolysis in sausage containing 20% taro, measured colorimetrically by soluble peptide bonds, was greatest for uncured FFM (P < 0.001) sausage compared to cured FFM sausage. Lipid oxidation measured by thiobarbituric acid method was unvarying with curing and with time providing there is no important difference between curing and uncuring. Histamine being the sole biogenic amine decreased in concentration with a statistically significant but unimportant difference between cured and uncured FFM sausage. These values were lower than the maximum allowable limit of 200 ppm in New Zealand as well as those reported for fermented fish sausage in Southeast Asia. The results point to commercial opportunities and further research in which sensory analysis should be performed before the products can be tested in the market.