Salt Penetration in Whole Raw Tuna Frozen Onboard Vessel by Brine Immersion: An Industrial Study

The commercial tuna industry is a global business. In 2016, the catch of commercial tunas was 4.9 million tons. Most of the tuna intended for canning is harvested at sea and needs to be chilled, or chilled and frozen at sea, and then processed into cans or other containers to preserve freshness and wholesomeness. Twothirds of this global catch of tuna are frozen in salt (sodium chloride) brine. The U.S. FDA offers recommended dietary allowances for many nutrients, including sodium, and encourages the consumer to lower their sodium intake. Depending on a host of factors, the direct contact between brine and the fish will result in some salt (sodium) uptake into the fish muscle. To better understand the impacts of these factors on sodium uptake, this paper describes a multiple regression study of salt penetration in tuna frozen in salt brine and offers suggestions to reduce the salt levels in the tuna delivered to the canneries. The following are best practices to produce excellent quality purse seine fish: 1) Always have enough cold refrigerated seawater (RSW) (-1°C or 30°F) or cold brine (-20°C or -4°F) to receive and chill the maximum expected catch. Do not catch the fish if it cannot be chilled immediately. 2) Quickly transfer the fish from the net to the wells with chilled RSW or cold brine. Brail fast. 3) Do not overpack the wells. This is a critical practice to achieve rapid chilling and freezing rates, greatly reduce physical damage, and facilitate easier and faster unloading. 4) Restrict the time the tuna spends in the The primary species in volume and value are skipjack tuna, Katsuwonus pelamis; yellowfin tuna, Thunnus albacares; bigeye tuna, Thunnus obesus; tonggol, Thunnus tonggol; and albacore, Thunnus alalunga. These tunas are primarily caught by purse seiners and longline vessels. Pole-and-line boats using live baitfish (baitboats) are also used to capture the tuna, depending on the species and availability of baitfish and of near-shore processing stations (Hamilton et al.2; ISSF3). Skipjack tuna (SKJ), yellowfin tuna (YFN), bigeye tuna (BET), and other species of tuna are schooling fish. They are caught in large numbers by purse seiners that encircle the fish to 2Hamilton, A., A. Lewis, M. A. McCoy, E. Havice, and L. Campling. 2011. Market and industry dynamics in the global tuna supply chain. Pac. Is. Forum Fish. Agency, 95 p. (avail. at https://www. ffa.int/node/567, accessed 5 May 2018). 3ISSF (International Seafood Sustainability Foundation). 2018. Interactive Stock Status Tool (avail. at https://iss-foundation.org/about-tuna/ status-of-the-stocks/interactive-stock-statustool/, accessed 5 May 2018). RSW. If the chilled tuna remains in RSW for a maximum of 5 days, brine the well. If the well is only partially filled, spray the brine over the fish. If the fish size is small (i.e., Auxis spp.), the amount of time stored in RSW before brining may need to be even less. 5) Freeze the fish completely to a minimum of -12°C (10.4°F) backbone or core temperature. 6) Dry the wells (remove the brine) after the fish have been completely frozen. 7) Unload the fish dry and frozen at -20°C(-4°F), if possible. The colder the better for the quality of the fish. The tuna fishing restrictions in 2019 include full retention of tunas so all usable fish need to be transported to markets for use, including the very small fish, which could have a very high salt content. capture them: schooling tuna are often seen at the ocean surface feeding on smaller fish (baitfish). Tunas and other schooling fish also often gather under floating objects in the ocean, such as logs, seaweed, dead whales, etc. (Castro et al., 2002). For many years fishermen have built small structures or Floating Aggregating Devices (FADs) to try to attract schools of tuna. In the late 1970’s, the use of FADs was proposed to reduce porpoise mortality in the Eastern Tropical Pacific (ETP) (DeBeer, 1980). FADs are so successful at attracting fish that currently, in 2018, there are periodic closures of fishing on FADs for resource management and sustainability reasons (ISSF4). In 2016, the catch of commercial tunas was 4.9 million tons (ISSF3). Most 4ISSF (International Seafood Sustainability Foundation). 2018. Mixed Results for Tuna Conservation, FAD Management and MCS Tools at IOTC (avail. at https://iss-foundation.org/mixedresults-for-tuna-conservation-fad-managementand-mcs-tools-at-iotc/, accessed 28 June 2018).