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The present study was conducted to evaluate the antioxidant activity of medicinal plant Rhizophora mucronata (R. mucronata). Shade dried stem bark of R. mucronata was powdered and extracted with 95% ethanol and water by cold extraction method. The total phenolic and flavonoid contents of water and ethanol extract of air dried stem bark was estimated by using spectrometric method. Antioxidant activity of R. mucronata was determined by using different methods namely DPPH radical scavenging assay, ferric reducing assay, nitric oxide radical scavenging assay, superoxide radical scavenging assay and ABTS radical scavenging assay, and its IC50 values were found to be 110.85, 193.47, 109.06, 88.69 and 12.56 ìg/ml for aqueous extract and 59.63, 242.71, 103.21, 84.95 and 4.21 ìg/ml respectively. The extracts exhibited marked dose dependent in vitro antioxidant activity. Secondary metabolite isolation and characterization and in vivo evaluation of aqueous and ethanolic extracts were under progress.

Scombroid food poisoning is a food borne illness that results from eating spoiled (decayed) fish. Histamine is the causative agent of scombroid poisoning, a food borne chemical intoxication. Histamine is one of the main biogenic amines and it is heterocyclic and biologically active primary amine, formed post-mortem in the muscles of scombroid and non-scombroid fish. The present study was carried out to isolate histamine-producing bacteria from a local fish and to test antibacterial activity of mangrove isolates of Lactobacillus species against the histamine producing bacteria. Fresh tuna fish (Euthinus affinis) obtained from Parangipettai coast and they were divided in to three groups. One group of the fish samples were stored directly and another two group of the fish samples were dipped in cold distilled water containing bacteriocin of Lactobacillus sp. and partially purified bacteriocin (10 ml, 1% v/v) respectively. The fish samples, after treatment were stored at 5, 15, 20 and 25 0C for the period of 24, 48, 72 and 96 h, respectively. Histamine quantification was performed at an interval of 24 h for four days. According to the results obtained it was proved that mangrove isolates of Lactobacillus species having high antimicrobial activity against histamine-producing bacteria which is responsible for spoilage of sea foods.

In this work, in vitro biosynthesis of silver nanoparticles was achieved using AgNO3 as a substrate by L. plantrum isolated from mangrove rhizosphere region in South East Coast of India (Gulf of Mannar). The biosynthesis was faster within a minute of silver ion coming in contact with the cell filtrate. Presence of silver nanoparticles in the culture filtrate was confirmed by absorption peak at 430 nm. The biosynthesis of nanoparticles was the maximum when the culture filtrate was treated with 1.0mM AgNO3 and pH 6.0, incubated at 5 .C for 24 h and its nanoparticles was used for antimicrobial activity. The culture filtrate, precipitated with ammonium sulphate, was proved to have a single protein band with a molecular weight of 70 kDa using polyacrylamide gel electrophoresis. The present work highlighted the possibility of using the marine bacterial strain of L. plantrum to achieve a fast rate of nanoparticles synthesis and also used as antimicrobial agent.