Seaweeds extracts as antioxidants and antimicrobial agents and their effects on quality of tilapia Minced (Oreochromis niloticus)

The extraction of minced tilapia has emerged as an attractive process due to the possibility of greater recovery of the tissue after filleting. However, mechanical separation increases the surface exposure, leading to incorporation of oxygen and consequently to the \"off-flavor\" due to rancidity, making necessary the use of additives for its preservation. The tendency is to use natural products as alternatives to chemical additives. Among the natural products, seaweeds present in its composition secondary metabolites with high antioxidant and antimicrobial activities. This research aimed to evaluate the chemical composition and biological activities of four seaweeds varieties and their effects when applied to the tilapia Minced. Nori, Kombu, Hijiki and Wakame seaweeds were extracted by 2 and 7 days, at room temperature, with ethanol 60, 80 and 100%. The phenolic content, antioxidant and antimicrobial activities in vitro were determined. The antioxidant activity by accelerated methods, Oxipres and Rancimat, were also evaluated. Seaweeds bioactive profiles were elucidated by liquid and gas chromatography. These seaweeds were applied to the tilapia Minced, that was stored at -18 °C for 180 days. The Minced were analyzed as to their composition, freshness characteristics by pH, TBARS and TVB-N, instrumental color, color and rancidity aroma by sensory analysis, microbiological standards, and fatty acid composition, at 0, 60, 120 and 180 days of storage. It was observed that the extraction after two days, with 60% ethanol, was the most efficient way to extract the phenolic compounds. Hijiki and Nori showed the highest levels of these compounds and therefore higher antioxidant activity in vitro. The extracts showed no antimicrobial activity against Salmonella Enteritidis, Escherichia coli and Staphylococcus aureus. For Klebsiella pneumoniae and Listeria monocytogenes, more efficient extracts were extracted with ethanol 100%. Hijiki and Nori seaweeds were selected as the most bioactive and submitted to accelerated oxidation tests. When applied in soy oil in the Rancimat, and tilapia Minced, in the Oxipres, these seaweeds have demonstrated effective antioxidant activity. By chromatography, the most important compounds identified were, in Nori, chlorogenic, caffeic and vanillic acids, besides the amino acids alanine, glycine, proline and valine, glucose and sorbitol. In the Hijiki seaweed, it was detected chlorogenic, caffeic and cinnamic acids, alanine and proline, as well as, ribitol and xylitol, fructose, and linoleic acid. In the test of frozen Minced storage, for 180 days, the application of Nori and Hijiki extracts did not modify neither the composition nor the pH. Seaweeds were effective in controlling the TVB-N production, but, for TBARS, although they were within acceptable limits, the seaweeds showed pro-oxidant activities. As to the microbiological aspects, the minceds complied with legal requirements. Sensorially, the tasters detected no difference in the \"rancid aroma\", only small differences in the product color. It can be concluded that the Minced tilapia, seaweed added, remained within the standards of quality during frozen storage. It should be noted, moreover, the difference in the antioxidant response, according to the method used. (AU)