Pacific whiteleg shrimp (Penaeus vannamei) is an economically important crustacean in Vietnam thanks to its high and increasing production.

Published in Vietnam Journal of Agricultural Sciences, the paper (full open access at:  https://doi.org/10.31817/vjas.2022.5.4.04 ) quantified the phenolic contents and the antioxidant capacities of leaf extract powders from three Myrtaceae plants, namely Cleistocalyx operculatus (Vietnamese name: Vối), Psidium guajava (Ổi), and Rhodomyrtus tomentosa (Sim), investigate their inhibitive activities on the growth of bacteria isolated from spoiled shrimps, and evaluate their values as preservative agents in the cold storage of Pacific whiteleg shrimps (Penaeus vannamei).

The extract leaf powders from R. tomentosa, C. operculatus, and P. guajava had high phenolic contents of 281.25, 282.36, and 349.51 mg gallic acid equivalent/g leaf extract, respectively. Among the three plants, the extract powders of R. tomentosa and P. guajava leaves had the highest antioxidant capacities (about 4 mmol Trolox equivalent (TE)/g) followed by the one of C. operculatus (2.85 mmol TE/g).

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Inhibition zones of the three Myrtaceae leaf extract powders against Aeromonas sp2 and Aeromonas sp3 isolated from cold-stored spoiled whiteleg shrimp (0: control, 1: 10 mg/mL, 2: 20 mg/mL, 3: 30 mg/mL, 4: 40 mg/mL, 5: 50 mg/mL, 6: 75 mg/mL)

These three extract powders showed significant antibacterial activities against the seven bacteria isolated from cold-stored spoiled whiteleg shrimps with the inhibition zones ranging from 0.33 to 19.67mm depending on the extract concentration. Among the three leaf extracts, the one from P. guajava leaves showed the highest inhibitive activity. Aeromonas sp2 was the most sensible to Myrtaceae leaf extracts while Aeromonas sp4 was the least affected strain.

All of the extracts showed high inhibitive activities against melanosis, volatile nitrogen-containing compounds formation, lipid oxidation, and microbial growth in stored shrimps, thereby prolonging the shelf-life of the shrimps. The results suggested the potential application of these three Myrtaceae plants as sources of antioxidant and antimicrobial agents in the cold storage of shrimps.