Conservação de queijo coalho por combinação de alta pressão hidrostática e embalagem ativa antimicrobiana

Abstract

This thesis aimed to evaluate the effects of high hydrostatic pressure (HHP) processing (200, 300 or 400 MPa/5 or 10 min) on the functional properties of cellulose acetate (CA) film, with or without incorporation oregano essential oil (OEO), as well as to evaluate the effects of HHP (300 MPa/5min or 400 MPa/10 min) and/or antimicrobial film (AF) on the texture, color parameters and inactivation of Staphylococcus aureus, Escherichia coli and Listeria monocytogenes in coalho cheese (CC) stored for 21 days/5oC. After processing with HHP, CA film without OEO showed a reduction in tensile strength (TS) and in Young's module (YM) and an increase in elongation at break (EB), luminosity, yellow/red color and opacity. The pressurized films showed reduced affinity for water, detected through the analysis of moisture absorption (MA), contact angle and water vapor transmission rate (WVTR). Delaminations caused by HHP processing were detected by scanning electron microscopy (SEM), except for films treated with 200 MPa/10 min and 300 MPa/10 min. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyzes showed predominance of amorphous structure for all films. In addition, treatment with HHP caused an increase in mechanical strength during sealing at 250 oC. For the CA film incorporated with OEO, processing with HHP caused optical changes, reduced TS, YM, WVTR, MA and increased EB and contact angle, in addition to delamination observed in SEM images. XRD curves detected a predominance of amorphous structure in all films, which may have prevented the detection of thermal parameters for most samples, in DSC analysis. The processing of AF with HHP did not affect the efficiency of the OEO evaluated in culture media (agar, BHI broth and micro-atmosphere), showing total inhibition of Staphylococcus aureus, Escherichia coli and Listeria monocytogenes, for all films. In the stored CC, the combination of AF and 400 MPa/10 min was the most efficient against the three bacteria studied, at zero time and throughout storage, while treatment only with HHP was not able to prevent the multiplication of bacteria in the samples of CC. Therefore, only the AF or the combination of AF and HHP were effective in controlling microbial growth in CC. As for color parameters, processing with HHP and/or packaging with AF caused an increase in brightness and yellow / red color in the CC samples at 21 days of storage under refrigeration (5 oC). For the texture parameters of CC, the presence of FA did not cause significant changes, while the treatment with 400 MPa / 10 min caused the greatest reductions in hardness and cohesiveness and an increase in gumminess and chewiness. The springiness of the CC was not affected by any of the conditions studied.