Factors Affecting Water Holding Capacity and Texture in Cooked Albacore Tuna (Thunnus alalunga)

Abstract

The goal of this research project was to determine if temperature during precooking and cooling process, initial quality of the fish, muscle location and initial meat pH promoted the activity of heat-stable endogenous proteases in albacore tuna. Proteolytic activity was measured as the rate of MHC degradation. Albacore tuna was exposed at cooking temperature range of 50-60ºC reported in prior studies as optimum for proteolytic enzyme activity and responsible for textural degradation of fish meat. Also, tuna samples were exposed to high temperature (70ºC) to minimize meat texture degradation by stopping or slowing down their activity. Meat texture degradation during the cooling process was also measured by placing precooked meat into isothermal cooling temperatures ranges that tuna would experience during this process. Meat textural degradation was tracked by measuring MHC by SDS-PAGE, texture quality by using the Kramer shear press and sensory analysis of texture.

Initial meat quality and postmortem pH of fresh muscle albacore did not affect the rate of proteolytic degradation. Rate of degradation of belly meat was higher than rate of degradation of tail and dorsal meat. Meat from all three body positions degrades the most when precooked at temperatures lower than 70ºC. However, precooking albacore tuna at 70ºC did not inactivate proteolytic enzymes, since MHC degraded even when the cooked meat was cooled at lower temperatures. Degradation of MHC observed in precooked albacore tuna was highly related to muscle texture properties. Belly and dorsal albacore tuna muscle precooked at 50C resulted the less strong in texture, as measured by Kramer press and sensory analysis, and with less moisture content than meat precooked at 70C, and also show evidence of larger grittiness and a more grainy mouthfeel. The softening of albacore tuna muscle may be explained by heat-stable protease activity, while the relative toughening of tuna muscle is probably due to decrease of proteases activity and only protein denaturation had significant effect on texture quality.

In the second study, meat textural degradation as consequence of autolysis during precooking was traced by measuring piece integrity by applying a methodology prior developed in our lab for skipjack tuna. Also can yield was measured as an additional a way to follow textural degradation, which could vary if the texture of meat causes it to decrease its ability to hold water. Drained and press weight data of canned albacore tuna allowed to determine albacore tuna can yield.

Dorsal and belly meat of albacore tuna, when precooked at 50ºC evidenced the highest rate of autolysis, giving as result a greater percentage of small flakes, plus lower yield after both precooking and canning.