Efeito do revestimento de quitosana associado ao óleo essencial de cravo na conservação de filés de tambaqui

Abstract

CAPÍTULO 1 = The objective of this work was to evaluate the effectiveness of the chitosan coating associated with clove essential oil in the conservation of tambaqui fillets. In the first stage of the experiment the antimicrobial activity of chitosan and clove essential oil (OEC) was evaluated with the application of chitosan coatings associated with OEC in fillets of tambaqui, intentionally contaminated with pathogenic microorganisms. The second step consisted of evaluating the shelf life of the treated tambaqui fillets (chitosan solution 2% - T1; chitosan solution 2% + OEC 1600 μg.mL-1 - T2; chitosan solution 0,5% + OEC 800 μg.mL-1 – T3; BHT 100 mg.mL-1 - T4 and sterile control distilled water), kept under freezing (-18ºC) by means of physico-chemical analyzes (pH, moisture, lipids and lipid oxidation) and microbiological of arable psychrotrophic bacteria. The sensorial analysis was performed through the characteristic profile test, multiple comparison and preference ordering, being applied to 40 untrained testers. Minimal Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were only observed for Listeria monocytogenes at 2% chitosan and Staphylococcus aureus at 0,25% and 0,5% chitosan, respectively. Pseudomonas aeruginosa presented a MIC of 3200 μg.mL-1, Salmonella Enteretidis, Escherichia coli and S. aureus of 1600 μg.mL-1 and L. monocytogenes of 800 μg.mL-1 for OEC. There was no CBM for the microorganisms tested, being the bacteriostatic oil. The chitosan coating showed inhibition of all pathogens tested on tambaqui fillets, however, synergism with OEC significantly potentiated the coating effect (p <0.05). The OEC-associated chitosan and chitosan coated treatments effectively retarded lipid oxidation, inhibited the growth of psychrotrophic arable bacteria, and reduced physico-chemical changes, such as pH and moisture, during freezing. The treated steaks were accepted by the tasters, with averages superior to 4. The most preferred of the tasters was by the fillets without addition of the OEC. The chitosan 14 coating associated with OEC is promising to be used as a natural preservative, aiming to control pathogens and increase the shelf life of tambaqui fillets.

CAPÍTULO 2 = The objective of this work was to evaluate the antimicrobial potential of the chitosan coating associated with clove essential oil (OEC) in tambaqui fillets. The inhibition rate of chitosan was determined by means of the agar diffusion test at concentrations of 0; 0,0625; 0,125; 0,5; 1 and 2%. The antimicrobial activity of clove essential oil, Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) was verified. The antimicrobial potential of the coating (chitosan 2%, chitosan 2% + OEC 1600 μg.mL-1 and chitosan 0,5% + OEC 800 μg.mL-1) was verified with the intentional contamination of fillets with Escherichia coli O157:H7 CDCEDL933, Listeria monocytogenes CERELA, Pseudomonas aeruginosa ATCC27853, Salmonella Enteretidis ATCC 13076 and Staphylococcus aureus ATCC43300 maintained under refrigeration at 4°C/72h. Inhibition of 100%, CIM and CBM was obtained for L. monocytogenes at 2% and S. aureus at 0,5% of chitosan. The other microorganisms were not inhibited. The OEC showed inhibition halos varying from 09,75 to 19,36 mm. Pseudomonas aeruginosa presented a MIC of 3200 μg.mL-1, S. Enteretidis, E. coli and S. aureus of 1600 μg.mL-1 and L. monocytogenes of 800 μg.mL-1. There was no CBM for the microorganisms tested, being the bacteriostatic oil. The chitosan coating showed inhibition of all pathogens tested in tambaqui fillets, however, synergism with OEC significantly potentiated the coating effect (p<0,05), being more effective in the inhibition of L. monocytogenes and S. aureus. The chitosan coatings associated to OEC showed a promising antimicrobial effect for the control of pathogens in tambaqui fillets, being more effective against Gram positive pathogens.

CAPÍTULO 3 = The objective of the work was evaluated in the framework of chitosan coating and its association with clove essential oil (OEC) in the preservation of tambaqui fillets kept under frozen storage at -18ºC. The fillets were separated into groups and submitted to the treatments: chitosan solution 2% (T1), chitosan solution 2% + OEC 1600 μg.mL-1 (T2), 0.5% chitosan solution + OEC 800 μg.mL-1 (T3), butylhydroxytoluene-BHT solution 100 mg.mL-1 (T4) and sterile distilled water (control). After the treatments, the steaks were individually packed in polyethylene plastic films and stored under freezing at -18 ° C ± 1 ° C for 120 days. The physico-chemical analyzes (pH, moisture, lipids and lipid oxidation) and microbiological (cultivable psychrotrophic bacteria) were performed on days 1, 30, 60, 90 and 120 days. The sensory analysis of the steaks was carried out by means of the evaluation of the profile of characteristics, multiple choice and order of preference, being applied to 40 untrained tasters. The results indicate that chitosan coating treatments and OEC-associated chitosan coating effectively retarded lipid oxidation, inhibited the growth of psychrotrophic arable bacteria, and reduced physico-chemical changes, such as pH and moisture, during freezing. The treated steaks were accepted by the tasters, with averages greater than 4. Chitosan coatings and their association with clove essential oil may be promising for use as natural preservatives, in order to extend the shelf life of tambaqui fillets during storage by freezing.