Small tuna - Potential raw material for high value-added food processing in Vietnam

Tuna belongs to the family of Scombridae and is the most important economic fish species of Vietnam’s waters. This kind of marine fish widely distributed in several seas of Vietnam includes many species divided into two main groups: ocean tuna and small tuna. Ocean tuna includes big tuna such as yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus), which are often used for export as frozen loins or whole fish. Small tuna is usually 20 - 70 cm in size and 0.5 - 4 kg in weight. Some popular small tuna species of our country as well as information related to distribution areas, seasons and methods of processing these fishes were shown in Table 1.

Table 1. Distribution area, seasons, fishing methods of some small tuna species in Vietnam

Small tuna production in Vietnam and in the world

Small tuna species is the group of pelagic fish having the highest reserves among seafood species with a total production of 760,000 tons. In which, skipjack tuna (Katsuwonus pelamis, Figure 1) has a dominant reserve with about 618,000 tons, accounting for more than 50% of the total large pelagic fish stocks (Vasep, 2019). The whole country currently has about 3,500 fishing boats, 14% of them are offshore boats, with about 35,000 fishermen engaged in tuna fishing in the far seas, with the ability to catch about 200,000 tons/year.

Figure 1. Skipjack tuna (Katsuwonus pelamis)

The central coast of our country has the richest resources of skipjack tuna (striped tuna) with estimated reserves ranging from 406,000 to 422,000 tons. The allowable exploitation capacity of this fish is 165,500-177,200 tons/year (Research Institute for Marine Fisheries, 2016).

There are two tuna catching seasons in Vietnam's waters: the main season starts from April to August and the secondary season from October to February of the next year. Tuna often gather in shoal and migrate. The shoal consists of several different species. Fish catching methods are mainly by using seine, hook,... “Nghề câu vàng” – a catch method introduced in the 1990s has quickly become an important tuna fishing way.

Within 5 years, from 2008 to 2013, our country's tuna export has increased sharply from 188 million to more than 520 million US dollars. In 2013, Vietnam's tuna was exported to 112 markets, reached more than 526 million US dollars, ranked the third among the main seafood exports (after pangasius and shrimp). In addition, the share of tuna in Vietnam's total seafood exports increased from 13% in 2009 to 22% in 2018. Main exported tuna species include yellowfin, bigeye, longfin, southern bluefin, and skipjack tuna...

In the world, skipjack is the most catched species in group of tuna. In 2018, according to the latest statistics published by the Western and Central Pacific Fisheries Commission (WCPFC), this kind of fish accounted for 66% (1,795,048 tons) of the total provisional production in this area. Furthermore, the total production of all commercial tuna species in the central and western Pacific regions contributes to 55% of the global tuna catch (Vasep, 2018).

Chemical composition and nutritional value of small tuna

Tuna is generally a food material with high nutritional value. The chemical composition of some small tuna species was shown in Table 2.

Table 2. Main chemical composition of some small tuna species

(Source: Mahaliyana et al., 2015; Rani et al., 2016)

As can be seen, in tuna, protein accounts for over 20% - much higher than the protein content in pork or chicken meat. In addition, mineral content is quite high, from 0.9-1.4%, while fat only accounts for about 0.4-1.0%.

Besides, according to Mahaliyana et al. (2015) and Sanchéz-Zapata et al. (2011), all essential amino acids were found in tuna meat and account for 49-52% of total amino acids. Polyunsaturated fatty acids accounts for 64% of total fatty acids, with a high proportion of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA). In terms of mineral content, skipjack tuna meat is rich in iron (240 mg/100g), copper (50 mg/100g) and zinc (68.9 mg/100g), in particular, tuna meat contains high levels of selenium, reaching about 50 µg/100g (Yoshida et al., 2002; Mahaliyan et al., 2015). All of these minerals are essential for human metabolism.

However, with outstanding advantages in terms of both production and nutritional value, this valuable small tuna has been only used as fresh fish or exported as raw material to China (Vasep, 2019). Currently, we do not have deep processing to increase the value of small tuna species and we have been not interested in the domestic market (Báo Thanh Niên, May 2017).

Tuna meat, when being a raw material for the food processing industry, has good technological properties such as high water and oil holding capacity beside its good emulsifying ability and stability. These properties make tuna meat suitable for emulsified and heat-processed products such as sausages. Furthermore, the gelatinization ability by heat and the elasticity and toughness change of proteins are related to the ability of developing structural properties for food product. Myosin in muscle forms non-reversible gels under the action of heat. These gels have high water holding capacity, have good elasticity and are not affected by heat.

Thus, small tuna can be a potential source of raw materials for the seafood processing industry of our country. Therefore, it is necessary to have researches on processing technology of high-value-added products to improve the value in use as well as economic value of these fishes. These new products from tuna will contribute to the diversification of seafood products to meet the tastes of consumers.

References

1.  Viện Nghiên cứu Hải sản (2016). Điều tra, đánh giá nguồn lợi sinh vật biển Việt Nam. Dự án điều tra cơ bản của Bộ Nông nghiệp và Phát triển nông thôn.

2.  Mahaliyana, A. S., Jinadasa, B. K. K. K., Liyanage, N. P. P., Jayasinghe, G. D. T. M., & Jayamanne, S. C. (2015). Nutritional composition of skipjack tuna (Katsuwonus pelamis) caught from the Oceanic Waters around Sri Lankae. American Journal of Food and Nutrition, 3(4), 106-111.

3.  Sánchez-Zapata E., Amensour M., Oliver R., Fuentes-Zaragoza E., Navarro C., Fernández-López J., Sendra E., Sayas E., Pérez-Alvarez J. A. Quality Characteristics of Dark Muscle from Yellowfin Tuna Thunnus albacares to Its Potential Application in the Food Industry, Food and Nutrition Sciences, 2011, 2, 22-30.

4.  Yoshida M., Abe M., Fukunaga K., Kikuchi K., 2002, Bioavailability of selenium in the defatted dark muscle of tuna, Food Additives & Contaminants, 19 (10), 990-995.

5.  FAO, 1995. Quality and quality changes in fresh fish

http://www.fao.org/3/v7180e/V7180E00.HTM#Contents, truy cập ngày 06/10/2020.

6.  Vasep, 2018. Giải pháp đưa nghề cá ngừ đại dương phát triển bền vững.

http://vasep.com.vn/Tin-Tuc/1210_53334/Giai-phap-dua-nghe-cau-ca-ngu-dai-duong-phat-trien-ben-vung.htm, ngày truy cập 27/09/2020.

7.  Vasep, 2019. Tổng quan ngành cá ngừ.

http://vasep.com.vn/Tin-Tuc/1019_56185/Tong-quan-nganh-ca-ngu.htm, truy cập ngày 27/09/2020.

8.  Tổng cục thủy sản, 2019. Diễn đàn hoạt động khai thác thủy sản trên biển Việt Nam và vai trò của nghiệp đoàn nghề cá.

https://tongcucthuysan.gov.vn/vi-vn/khai-th%C3%A1c-th%E1%BB%A7y-s%E1%BA%A3n/-khai-th%C3%A1c/doc-tin/013795/2019-10-31/dien-dan-hoat-dong-khai-thac-thuy-san-tren-bien-viet-nam-va-vai-tro-cua-nghiep-doan-nghe-ca, truy cập ngày 27/09/2020.

Trần Thị Thu Hằng, Nguyễn Thị Quyên

 Department of Food Processing Technology, Faculty of Food Science and Technology