Abstract
The objective of this research was to explore the antimicrobial activity and mechanism of carvacrol against Vibrio Parahemolyticus, Shewanella putrefaciens, Staphylococcus aureus and Pseudomonas fluorescens and evaluate the effect of the addition of carvacrol/β-cyclodextrin emulsions to flaxseed gum (FSG)-sodium alginate (SA) edible films on the preservation of Chinese sea bass (Lateolabrax maculatus) fillets during refrigerated storage. The minimum inhibitory concentration (MIC) of carvacrol against V. parahemolyticus, S. putrefaciens, S. aureus and P. fluorescens were 0.5, 0.5, 0.125, and 0.5 mg/mL, respectively. Alkaline phosphatase activity assay, nucleotide and protein leakage, and scanning electron microscope demonstrated that carvacrol damaged the external structure of the tested bacterial cells causing leakage of cytoplasmic components. At the same time, when FSG-SA films containing carvacrol used as coating agents for Chinese sea bass fillets cold storage, FSG-SA films containing 1.0 or 2.0 mg/mL carvacrol could significantly reduce TVB-N content, K-value, the degree of microbial deterioration and maintain quality of sea bass fillets according to organoleptic evaluation results.
Highlights
Chinese sea bass (Lateolabrax maculatus) is recognized as one of the most important mariculture fish in China, and its high protein and low-fat content make it value-added seafood product with increasing demand [1]
It was obvious that the Alkaline Phosphatase (AKP) activities increased along with the increased carvacrol concentration from 0.5 × minimum inhibitory concentration (MIC) to 2 × MIC for all the tested bacterial strains, which indicated carvacrol damage the cell wall resulting the leakage of AKP from the cells
The usage of flaxseed gum (FSG)-Sodium alginate (SA) films containing carvacrol significantly retarded the K-values increase during storage, which had an analogous trend with the Total Volatile Base Nitrogen (TVB-N) values. These results indicated that FSG-SA coatings containing carvacrol could suppress the degradation of ATP resulting from spoilage organism and microbial enzymes and keep good quality of sea bass fillets samples during cold storage
Summary
Chinese sea bass (Lateolabrax maculatus) is recognized as one of the most important mariculture fish in China, and its high protein and low-fat content make it value-added seafood product with increasing demand [1]. Gutted sea bass is extremely susceptible to endogenous enzymes and exogenous spoilage microflora, leading to lipid oxidation, protein degradation, or decomposition [2]. The short shelf life of refrigerated sea bass is a hinderance to the sales of fresh sea bass, extending the gutted sea bass shelf life and keeping the freshness would benefit the sea bass farming. Active coating is an innovative concept that could extend the shelf-life of seafood products and provides microbial safety for consumers [3,4,5]. Materials available for active coating generally include polysaccharides, proteins and lipids. SA has Molecules 2019, 24, 3292; doi:10.3390/molecules24183292 www.mdpi.com/journal/molecules
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