Atividade antioxidante dos polissacarídeos sulfatados da rodofícea Gracilaria birdiae em carne mecanicamente obtida de resíduos de filetagem de Tilápia-do-Nilo (Oreochromis niloticus)

Abstract

The fishery industry generates a large quantity of protein residues with high nutritional value. Nile tilapia (Oreochromis niloticus) is the most widely cultivated fish species in Brazil, with the greatest potential for waste recovery. However, residues used in the preparation of mechanically separated meat (MSM) are more susceptible to lipid oxidation, and the addition of antioxidants is necessary. The objective of this study was to evaluate the antioxidant potential of the total sulfated polysaccharide (TSP) of the red sea kelp Gracilaria birdiae in the Nile tilapia MSM as an alternative to the synthetic butylated hydroxytoluene (BHT) antioxidant. PST was obtained by refining aqueous extraction (1.5% w/v, 80°C, 4h) and determined its yield based on the dehydrated mass. The total sugars, sulfate and protein contents were determined, as well as the agarose gel electrophoresis load standard (0.5%), using glycosaminoglycans as standards. In the evaluation of the antioxidant potential of the TSP (0.125 - 4mg/mL), the in vitro evaluation of the free reducing potential of 1,1-Diphenyl-2-picrylhydrazyl (DPPH) free radical and the ferrous ion chelation effect was performed using BHT and Ethylenediamine tetraacetic acid (EDTA) as standards, respectively. The TSP obtained by RefAqE was applied to the MSM of unwashed Nile tilapia at different concentrations (0.01, 0.02 or 0.03 g/100g), the positive control received the antioxidant BHT (0.01 g/100g) and the control without additive. The treated CMS was stored at -22°C for 180 days and evaluated for moisture content, lipids, proteins and ash at the beginning and at the end of the experiment, as well as the potential of hydrogen (pH), the formation of total volatile bases and lipid oxidation. Initial microbiological analyzes were performed for thermotolerant coliforms at 45ºC, coagulase positive staphylococci and Salmonella sp. at time zero and performed the standard count for psychrotrophic bacteria during the experiment. The crude yield of TSPs from Gracilaria birdiae was 36.81±16.01% from the dehydrated raw material. The content of total sugars and free sulfate were 77.39% and 3.00%, respectively. No proteins were detected in the sample of the polymer examined. The electrophoretic profile revealed polydisperse TSP with similar mobility to mammalian dermatan sulfate. The antioxidant free radicals DPPH reduction and ferrous ion chelation showed concentration-dependent (0.125 - 4 mg/mL) and were both less effective than BHT and EDTA (p<0.05). The centesimal composition of CMS underwent few changes throughout the frozen storage, being more significant the reduction of humidity among the treatments (p<0.05). The MSM treated with PST showed growth of psychotrophic microorganisms and increase of the nitrogen of the total volatile bases during the frozen storage, but there was no growth of bacteria controlled by the legislation and the pH remained stable during the experiment. In addition, there was reduction in the formation of malonaldehyde content at concentrations of 0.01 and 0.02 g/100g (p<0.05). Therefore, the TSP of the red seaweed G. birdiae shows as an alternative to the synthetic antioxidant BHT, when applied in CMS of tilapia.