Phenolic compounds from cashew (Anacardium occidentale L.) leaves were extracted using ethanol with the aid of ultrasonication. Three independent variables, including ultrasound amplitude, time, and ethanol concentration, were used for response surface methodology (RSM) along with the central composite design (CCD). Under the optimized condition (70% amplitude; 40 min; 80% ethanol), the extraction yield and total phenolic contents were 24.50% and 431.16 mg GAE/g dry extract, respectively. Cashew leaf extract (CLE) had the lower minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against Shewanella sp. than P. aeruginosa. The release of K+ and Mg2+ ions from damaged cell membranes with a coincidental decrease of TTC dehydrogenase activity were augmented when treated with CLE. In addition, scanning electron microscopic (SEM) image revealed deformations and perforation of cell walls of bacteria treated with CLE. The dominant compounds in CLE were amentoflavone, quercetin, and its glycosides. Based on microbial challenge test, the growth of P. aeruginosa and Shewanella sp. inoculated in tilapia slices were inhibited by CLE at 400 and 600 ppm within 15 days of refrigerated storage.

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Long pepper (LP), soursop (SS), green vein kratom (GK), and red vein kratom (RK) leaf ethanolic extracts were prepared using an ultrasonic device, followed by dechlorophyllization by the sedimentation process. Antioxidant and antimicrobial activities of the extracts were studied. Highest yield and total phenolic content were found in RK extract (P < 0.05). In general, RK extract showed the lowest minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) towards four bacteria (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Shewanella sp.), when compared with other extracts. Addition of GK extract at 600 mg kg À1 retarded chemical changes and lowered microbiological growth in Nile tilapia mince within 12 days at 4 °C. Lipid oxidation was also impeded with the aid of GK extract. Therefore, GK extract inhibited both spoilage and pathogenic bacteria, and prevented lipid oxidation, thus extending the shelf-life of tilapia mince.