Juan I. Maté

Modelling effective moisture difusivity of rough rice (Lido cultivar) at low drying temperatures

The drying rate of Lido medium rough rice was determined at 35, 25, 12 and 5 °C at relative humidity varying from 30% to 70% and at two air velocities, 2.5 and 0.75 m/s. The experimental data were fitted to four models: single exponential model, biparametric exponential model, Page model and two term exponential model. The biparametric exponential model and the Page model provided the best fit. However the biparametric exponential model was preferred due to its simplicity of application.

Antimicrobial effectiveness of oregano and sage essential oils incorporated into whey protein films or cellulose-based filter paper.

BACKGROUND In this study the antimicrobial effectiveness of oregano and sage essential oils (EOs) incorporated into two different matrices, whey protein isolate (WPI) and cellulose-based filter paper, was analysed. RESULTS Antimicrobial properties of WPI-based films containing oregano and sage EOs were tested against Listeria innocua, Staphylococcus aureus and Salmonella enteritidis. Oregano EO showed antimicrobial activity against all three micro-organisms. The highest inhibition zones were against L. innocua. However, sage EO did not show antimicrobial activity against any of the micro-organisms. Antimicrobial activity was confirmed for both EOs using cellulose-based filter paper as supporting matrix, although it was significantly more intense for oregano EO. Inhibition surfaces were significantly greater when compared with those of the WPI films. This finding is likely due to the higher porosity and diffusivity of the active compounds in the filter paper. CONCLUSION The interactions between the EOs and the films have a critical effect on the diffusivity of the active compounds and therefore on the final antimicrobial activity. As a result, to obtain active edible films, it is necessary to find the equilibrium point between the nature and concentration of the active compounds in the EO and the formulation of the film.

Whey protein isolate edible films with essential oils incorporated to improve the microbial quality of poultry.

BACKGROUND Whey protein isolate edible films with oregano or clove essential oils (EOs) incorporated as natural antimicrobials have been developed, with the aim of enhancing the microbial quality of poultry. The effectiveness of the films was determined against both the whole and selected microbiota developed during different periods of cold storage on the surface of skinless chicken breast. Tests were conducted by using both turbidimetric and agar disc diffusion methods. RESULTS The antimicrobial edible films developed showed high effectiveness against the main spoilers developed on the surface of skinless chicken breasts cold-stored for 8 days. The films based on oregano EO showed greater effectiveness than those based on clove EO. Still, clove EO could be part of an effective antimicrobial edible film. Enterobacteriaceae was the most susceptible to the effect of the films when lower concentrations of EO were incorporated. The largest inhibition surfaces obtained were provoked by films with the highest concentration of oregano EO incorporated against lactic acid bacteria. CONCLUSION The antimicrobial edible films developed in this study inhibited the growth of the microbial populations that developed through storage of the chicken breast and caused its spoilage. The results of this research have direct application in the food industry to enhance the control of the development of spoilers such as Pseudomonas spp. or lactic acid bacteria.

Effect of Drying Conditions on the Mechanical and Barrier Properties of Films Based on Chitosan

Films plasticized with glycerine were prepared using chitosan with two different molecular weights (Mw), 780 and 430 kDa. Films were obtained by drying at 80 and 40°C at 20 and 40% relative humidity (RH) in a climatic chamber. Drying kinetics were established by the measurement of the evolution of the actual temperatures of the film forming solutions. Chitosan Mw did not show any significant influence on drying kinetics. Drying temperature affected drying kinetics in a more intense way than drying RH. Maximum tensile strength (86 MPa) and elongation at break (56.5%) were obtained with slow drying cycles (lower drying T) and when higher Mw chitosan was employed. Minimum water vapor permeability (0.59 g · mm/kPa · h · m) was achieved for films dried at faster drying cycles (higher drying T). Chitosan Mw was not a significant factor affecting water vapor permeability.

Improvement of the microbiological quality of ready-to-eat peeled shrimps (Penaeus vannamei) by the use of chitosan coatings

Chitosan coatings incorporated with 0.5% of oregano and thyme EO were applied onto ready-to-eat peeled shrimp tails and packed under MAP conditions. The growth of naturally present spoilage microorganisms was evaluated for 12days during chilled storage (4°C). Coatings containing thyme EO were more effective in inhibiting the microbial species studied, specially lactic acid and psychrotrophic bacteria. As carrier of EOs, chitosan was more effective in inhibiting the growth of bacteria present in peeled shrimps than the direct application of an oil-water (O/W) emulsion. Finally, results from sensory analysis showed that the sensorial quality was affected by the chitosan-thyme coatings despite characteristics like firmness and colour were kept. The present work demonstrates the effectiveness of chitosan enriched coatings, offering a promising alternative to control the growth of spoilage and pathogen microorganisms on peeled shrimps during refrigeration storage.

Effect of Antimicrobial Edible Coatings and Modified Atmosphere Packaging on the Microbiological Quality of Cold Stored Hake (Merluccius merluccius) Fillets

The effect of whey protein isolate (WPI) coatings incorporated with essential oils (EOs) and combined with modified atmosphere packaging (MAP) on the microbiological quality of fresh hake fillets was evaluated. Fresh hake fillets were coated with different formulations of WPI-EO coatings and packaged under air and MAP conditions (50% CO2/45% N2/5% O2). When WPI-enriched films were applied with or without the presence of MAP over hake fillets with a high initial microbial population, a limited but significant effect on the microbial growth was observed. This effect was more intense on Enterobacteriaceae and H2S-producing bacteria. When hake fillets with lower initial microbial counts were treated, a more intense antimicrobial effect was observed and a synergistic effect between WPI-EO coatings and MAP was detected. A significant extension of the lag phase and reduction, primarily, on the total viable counts and H2S-producing bacteria, was detected, doubling the shelf-life of hake fillets compared with control samples. The initial microbial load of the samples is a key factor influencing the effectiveness of the treatment. The obtained results demonstrated the effectiveness of this combined strategy as a promising alternative for enhancing the microbial quality of fish products during storage at refrigeration temperatures.