Inhibition of Shewanella spp. growth by Syzygium australe and Syzygium luehmannii extracts: natural methods for the prevention of fish spoilage.

Syzygium australe and Syzygium luehmannii fruit and leaf were investigated for their ability to inhibit Shewanella spp. growth. Extracts of both Syzygium spp. displayed potent growth inhibitory properties against all Shewanella spp. tested in disc diffusion and liquid diffusion assays. In general, S. australe extracts were more potent inhibitors of Shewanella spp. growth, and the fruit extracts were generally better than the corresponding leaf extracts. The methanolic S. australe fruit extract was a particularly potent inhibitor of all Shewanella spp. growth, with MIC values as low as 87 µg/mL. The aqueous and ethyl acetate S. australe fruit extracts were similarly potent inhibitors of Shewanella spp. growth, albeit with slightly higher MIC values. Several other Syzygium spp. extracts also were potent bacterial growth inhibitors, albeit with MIC values generally >1000 µg/mL. The most potent S. australe fruit extracts were nontoxic in the Artemia franciscana bioassay, with LC50 values substantially >1000 µg/mL. The potent bacterial growth inhibitory activity and lack of toxicity of the S. australe fruit extracts indicate their potential as natural fish and seafood preservatives.