Quality changes of Eastern little tuna (Euthynnus affinis) slices treated with caffeic or tannic acid (0.2 g kg−1) and the control during 15 days of refrigerated storage in air or under modified atmospheric packaging (MAP: 60% CO2, 35% N2, 5% O2) were studied. Tannic acid exhibited a greater preventive effect on metmyoglobin (metMb) formation and lipid oxidation than did caffeic acid (P < 0.05). Samples treated with tannic acid and kept under MAP (MT) had the lowest lipid oxidation (P < 0.05). After 12 days of storage, changes in unsaturated fatty acids, especially n-3 fatty acids, were lower in MT, compared with tuna slices stored in air. Based on microbiological acceptability, the shelf-life of tuna kept in air and MAP was estimated to be 6 and 12 days, respectively, irrespective of phenolic compounds treatment. Therefore, tannic acid exhibited a combined effect with MAP on inhibition of metMb formation, lipid oxidation and microbial growth, thereby improving the acceptance and increasing the shelf-life of tuna slices during refrigerated storage.
Antioxidants have been used to reduce lipid oxidation and off-odor development. Phenolic compounds, the secondary metabolites present typically in plants, have been reported for their antioxidative activity by donating electrons and chelating metals (Medina, Gallardo, González, Lois, & Hedges, 2007). Tang, Sheehan, Buckley, Morrissey, and Kerry (2001) reported the higher antioxidant effect of tea catechin in meat, poultry and fish than α-tocopherol at the same concentration (0.3 g kg−1) used. Corresponding to the ability of electron donating, caffeic acid showed the most preventive effect on lipid oxidation in minced horse mackerel, compared with other hydroxycinnamic acids and catechins (Medina et al., 2007).
Modified atmospheric packaging (MAP) has been proved to be an effective preservation method, in which the shelf-life extension and quality retention of fish and fish products can be achieved (Masniyom, Benjakul, & Visessanguan, 2002). Thiansilakul, Benjakul, and Richards (2011) found that high concentration of oxygen likely converted the purified oxymyoglobin (oxyMb) to metmyoglobin (metMb) and induced a higher discoloration of Eastern little tuna fillet, compared with vacuum condition. MAP under a high level of CO2 (40–100%) is used to inhibit bacterial growth and extend shelf-life of fish and fishery products (Sivertsvik, Jeksrud, & Rosnes, 2002). Fresh seabass (Lates calcarifer) slices stored under MAP enriched with CO2 (80–100%) exhibited better odor, flavor and acceptability score in comparison with fish slices kept in air (Masniyom et al., 2002). In addition, using MAP (60% CO2, 35% N2, 5% O2) in combination with tannic acid treatment (0.2 g kg−1) lowered lipid oxidation, heme protein changes and microbial growth as well as improved the sensory acceptance of refrigerated striped catfish slices (Maqsood & Benjakul, 2010).
Eastern little tuna (Euthynnus affinis) is a species available in the Gulf of Thailand and the Indian Ocean with the volume of 22,220 metric tons and a value of 18 million US dollars in 2008 which provide the high global economic value for canning and sashimi (Fisheries Foreign Affairs Division, 2008). To prolong the shelf-life of fish with minimized quality losses during storage, suppression of lipid oxidation and heme proteins changes are required. The objective of this investigation was to study the effect of phenolic compounds, caffeic acid or tannic acid, on quality changes of Eastern little tuna slices kept under different packaging atmospheres during refrigerated storage.
During refrigerated storage, tuna slices underwent discoloration, lipid oxidation and spoilage, leading to a lower acceptance. In the presence of phenolic compounds (200 ppm), metMb formation and lipid oxidation were lowered. The greater antioxidative activity was found in tannic acid, compared with caffeic acid. Tuna slices treated with tannic acid and kept under MAP (60% CO2, 35% N2, 5% O2) generally had the lower discoloration and lipid oxidation. Therefore, treatment of tuna slices with tannic acid in combination with MAP could maintain the quality of tuna slices resulting in a shelf-life of 12 days.
