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Antioxidant and antimicrobial effects of stevia (Stevia rebaudiana Bert.) extracts during preservation of refrigerated salmon paste

Stevia (Stevia rebaudiana Bert.) is a relevant source of natural phenolic compounds with antioxidant and antimicrobial properties. The aim of this study was to evaluate the potential protective effect of crude stevia extracts on the quality and shelf-life of salmon (Salmo salar) paste. For this, polyphenol extracts obtained by water extraction, ethanol/water extraction and supercritical CO2 with ethanol extraction were evaluated in preserving salmon paste. Salmon paste was stored under refrigerated conditions (5°C)for 21 days, being primary, secondary, and total lipid oxidations monitored along storage by means of peroxide, p-anisidine, and TOTOX indices, respectively. In addition, v3/v6 ratio, polyene index, and a-tocopherol were monitored. Microbiological analysis comprised the investigation of aerobic mesophiles and psychrotrophes. Salmon paste samples treated with ethanol/water and supercriticalCO2-ethanol stevia extracts exhibited the highest (p < 0.05) v3/v6 ratio and a-tocopherol content.Besides, partial inhibition of both primary and secondary lipid oxidation events and aerobes and psychrotroph growth was also observed in both samples. These results correlated with the fact that ethanol/water and supercritical CO2-ethanol extracts provided the highest DPPH and FRAP values.These results open the way to the utilization of bioactive compounds from stevia leaves for the preservation of foods derived from salmon