Abstract
This study aimed to increase the antibacterial activity of chitosan-polylactic acid (PLA) composite film by adding nisin and ethylenediaminetetraacetic acid (EDTA). We evaluated the mechanical, physicochemical, and antibacterial properties of various PLA composite films, as well as the enhancement effect of PLA composite films with EDTA + nisin on the preservation of grouper fillets. Films of PLA alone, PLA plus chitosan (C5), PLA plus nisin + EDTA (EN2), and PLA plus chitosan plus nisin + EDTA (C5EN1 and C5EN2) were prepared. The addition of EDTA + nisin to the chitosan-PLA matrix significantly improved the antibacterial activity of the PLA composite film, with C5EN1 and C5EN2 films showing the highest antibacterial activity among the five films. Compared with the fish samples covered by C5, the counts of several microbial categories (i.e., mesophilic bacteria, psychrotrophic bacteria, coliforms, Aeromonas, Pseudomonas, and Vibrio) and total volatile basic nitrogen content in fish were significantly reduced in the samples covered by C5EN1. In addition, the counts of samples covered by C5EN1 or C5 were significantly lower compared to the uncovered and PLA film-covered samples.
Highlights
Aquatic products are susceptible to microbial deterioration
Nisin alone (10–75 μg/mL), without 5 μg/mL chitosan, had almost no activity against E. coli, whereas chitosan alone at 5 μg/mL had some activity against E. coli
Compared with the survival (8 log CFU/mL) of the control in Figure 1A, the survival in the broth containing only 20 mM ethylenediaminetetraacetic acid (EDTA) in Figure 1B was reduced by approximately 0.9 log CFU/mL
Summary
Aquatic products are susceptible to microbial deterioration. Approximately 30 million tons of aquatic products are not properly preserved after being caught, leading to their deterioration [1]. Fish meat is more susceptible to spoilage than livestock meat owing to its higher content of water and free amino acid and lower content of connective tissue. Various biochemical and enzymatic changes are triggered in fish muscles immediately after death, especially at incorrect processing temperatures. Both these changes and microbial activity cause the degradation of fish muscle [2]. Various fish preservation techniques are used to prevent the fish quality from deterioration and extend its shelf-life; these include the use of preservatives, the management of water activity and pH, and the combination of packaging and cold-chain transportation systems. [3]
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