Morten Sivertsvik

Solubility and absorption rate of carbon dioxide into non-respiring foods: Part 1: Development and validation of experimental apparatus using a manometric method

Abstract An apparatus to determine the solubility and rate of absorption of CO 2 from pressure changes over time was built and validated against water. A high correlation ( r 2 >0.99) between the measured solubility and theoretical solubility was found. The solubility determinations using the manometric method were more accurate than using a CO 2 electrode. The solubility of CO 2 increased linearly with the partial pressure of CO 2 , and a quadratic response was observed for the gas volume/product volume ( g / p ) ratio. The temperature dependency of the solubility is according to the temperature dependency of Henry’s constant. The rate of absorption is primarily affected by the %-level of CO 2 in the atmosphere, and the effective diffusion constant is primarily affected by the %-level of CO 2 and the g / p -ratio. The time to reach 50% solubility was about 3 h and equilibrium was reached after 48 h.

Microflora Assessments Using PCR–Denaturing Gradient Gel Electrophoresis of Ozone-Treated and Modified-Atmosphere-Packaged Farmed Cod Fillets

Denaturing gradient gel electrophoresis (DGGE) of a PCR-amplified 16S rDNA sequence was used to characterize changes in the microbial flora caused by ozone (O3) treatment of farmed cod (Gadus morhua). Portions of cod were produced under controlled conditions, bathed in fresh water supplemented with 2 ppm of O3 for 30 min, and packaged in modified atmosphere (MA: 60% CO2 and 40% N2) before 4 degrees C storage. Control samples were packaged in MA or air, without prior O3 treatment. Samples were analyzed by PCR-DGGE to determine the predominant bacterial flora and to examine possible differences in the microbial community due to O3 treatment. The DGGE analysis during the storage period showed that the O3 treatment produced no significant difference in the microbial flora compared with the controls. Sequencing of 16S rDNA detected the specific spoilage bacteria Photobacterium phosphoreum, Pseudomonas spp., Shewanella baltica, and Shewanella putrefaciens as the predominant bacteria in all samples. PCR-DGGE results were supported by culture and sensory analyses used in predicting product shelf life. Aerobic plate count, H2S-producing bacteria, and psychrotrophic bacterial counts demonstrated no significant extension of the shelf life of MA-packaged, O3-treated cod fillets.

Comparative Analysis of the Composition and Active Property Evaluation of Certain Essential Oils to Assess their Potential Applications in Active Food Packaging

The antifungal, antibacterial, and antioxidant activity of four commercial essential oils (EOs) (thyme, clove, rosemary, and tea tree) from Romanian production were studied in order to assess them as bioactive compounds for active food packaging applications. The chemical composition of the oils was determined with the Folin–Ciocâlteu method and gas chromatography coupled with mass spectrometry and flame ionization detectors, and it was found that they respect the AFNOR/ISO standard limits. The EOs were tested against three food spoilage fungi—Fusarium graminearum, Penicillium corylophilum, and Aspergillus brasiliensis—and three potential pathogenic food bacteria—Staphylococcus aureus, Escherichia coli, and Listeria monocytogenes—using the disc diffusion method. It was found that the EOs of thyme, clove, and tea tree can be used as antimicrobial agents against the tested fungi and bacteria, thyme having the highest inhibitory effect. Concerning antioxidant activity determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2’-azino-bis 3-ethylbenzthiazoline-6-sulfonic acid (ABTS) methods, it has been established that the clove oil exhibits the highest activity because of its high phenolic content. Promising results were obtained by their incorporation into chitosan emulsions and films, which show potential for food packaging. Therefore, these essential oils could be suitable alternatives to chemical additives, satisfying the consumer demand for naturally preserved food products ensuring its safety.

Antioxidant/Antibacterial Electrospun Nanocoatings Applied onto PLA Films

Polylactic acid (PLA) films were coated by coaxial electrospinning with essential and vegetable oils (clove and argan oils) and encapsulated into chitosan, in order to combine the biodegradability and mechanical properties of PLA substrates with the antimicrobial and antioxidant properties of the chitosan–oil nanocoatings. It has been established that the morphology of the electrospun nanocoatings mainly depend on the average molecular weight (MW) of chitosan. Oil beads, encapsulated into the main chitosan nanofibers, were obtained using high-MW chitosan (Chit-H). Oil encapsulated in chitosan naoparticles resulted when low-MW chitosan (Chit-L) was used. The coating layer, with a thickness of 100 ± 20 nm, had greater roughness for the samples containing Chit-H compared with the samples containing Chit-L. The coated PLA films had higher antibacterial activity when the nanocoating contained clove oil rather than when argan oil was used, for both types of chitosan. Nanocoatings containing Chit-H had higher antibacterial activity compared with those containing Chit-L, for both types of oil tested, due to the larger surface area of the rougher nanoscaled morphology of the coating layer that contained Chit-L. The chitosan–clove oil combination had higher antioxidant activity compared to the simple chitosan nanocoating, which confirmed their synergistic activities. The low activity of systems containing argan oil was explained by big differences between their chemical composition and viscosity.