ABSTRACT
Salmonella Senftenberg is a pathogen agent causative of foodborne disease and it is considered the most heat-resistant serovar within this genus. Food industries use heat treatment and chemical antimicrobials in order to eliminate this microorganism in food, but consumers prefer natural antimicrobials as essential oils and their components. This study evaluates the combined effect of thermal treatments and different concentrations of D-limonene nanoemulsion on the inactivation of Salmonella (S.) Senftenberg. The results showed an important effect of the nanoemulsified D-limonene on the heat resistance of S. Senftenberg. The δ50 °C value was reduced by 85%, 96% and 98% when 0.1, 0.5 and 1 mM of nanoemulsified D-limonene was added to the heating medium. The effect was kept along all the heating temperatures researched and the shape of the survival curves did not change with the addition of the antimicrobial. The results obtained in this research could be very useful for food industries for optimizing or improving heat treatments applied to food.
ABSTRACT
The application of d-limonene in form of nanoemulsion has been proved to reduce dramatically the thermal resistance of Listeria monocytogenes in culture media. The present research shows very promising results on the application in food products. The thermal resistance of L. monocytogenes was reduced 90 times when 0.5 mM nanoemulsified d-limonene was added to apple juice. This is the biggest reduction in the heat resistance of a microorganism caused by an antimicrobial described ever. However, no effect was found in carrot juice. A carrot juice system was prepared in an attempt to unravel which juice constituents were responsible for the lack of effect. When fat and fibre were not included in the carrot juice system formulation, the thermal resistance of L. monocytogenes was, again, dramatically reduced in presence of nanoemulsified d-limonene, so these components were shown to interfere with the effect. Once this interaction with food constituents becomes solved, the addition of nanoemulsified antimicrobials would allow to reduce greatly the intensity of the thermal treatments currently applied in the food processing industry.
Subject(s)
Cyclohexenes/pharmacology , Dietary Fats , Dietary Fiber , Fruit and Vegetable Juices/microbiology , Hot Temperature , Listeria monocytogenes/drug effects , Terpenes/pharmacology , Colony Count, Microbial , Culture Media , Cyclohexenes/chemistry , Daucus carota/microbiology , Emulsions/pharmacology , Food Microbiology , Food-Processing Industry/methods , Fruit and Vegetable Juices/analysis , Limonene , Malus/anatomy & histology , Malus/microbiology , Terpenes/chemistryABSTRACT
The present work evaluated the antibacterial effect of nanoemulsions from natural compounds d-limonene and nisin against Listeria monocytogenes in tryptic soy broth growth medium, chicken broth, and vegetable cream. Experiments were performed by means of optical density growth curves and studies of viability in culture media and foods. Stability of nanoemulsions was evaluated by a Mastersizer 2000 equipment. Results showed greater effectiveness when applying D-limonene in form of nanoemulsion than when applying it directly, and when using both compounds together, both directly and in the form of nanoemulsion. Concentration of L. monocytogenes decreased at least in three log cycles in all the culture media and foods used within the first 90 min after the addition of the natural antimicrobials combined in form of nanoemulsion. Moreover, the growth of L. monocytogenes was inhibited with the combination of antimicrobials in the four weeks that the experiment lasted. Nanoemulsion technology would solve present problems of solubility and stability of oily antimicrobials in the food industry.
