Abstract

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 purpose, polyphenol extracts obtained by stevia extraction with water, ethanol/water or ethanol-supercritical CO2 were evaluated throughout the refrigerated storage (5 ºC for 21 days) of salmon paste. Primary, secondary and total lipid oxidation compounds were monitored along storage by means of peroxide, p-anisidine and TOTOX indices, respectively. In addition, ω3/ω6 fatty acids ratio, polyene index and α-tocopherol content were monitored. Additionally, microbial development was analysed by means of the evolution of the aerobic mesophiles and psychrotrophes counts. Salmon paste samples treated with ethanol/water and ethanol-supercritical CO2 stevia extracts exhibited the highest (p<0.05) ω3/ω6 ratio and α-tocopherol content. Besides, partial inhibition of both primary and secondary lipid oxidation events as well as aerobes and psychrotroph growth was also observed in both kinds of paste samples. These results agreed with the fact that ethanol/water and ethanol-supercritical CO2 extracts provided the highest DPPH and FRAP values. It is concluded that, on the basis of employing the present stevia extracts, it is possible to obtain a preservative effect on salmon paste throughout its refrigerated storage, as a result of inhibiting the two most important damage pathways (i.e., development of lipid oxidation and microbial activity). The results obtained in this research show the possibility of using stevia and/or its derivatives of the sweetener industry as an alternative source of natural antioxidants to be applied for the refrigerated storage of fatty fish pastes.