Exploiting the synergism among physical and chemical processes for improving food safety

This article provides an overview of recent published information on the subject of synergistic lethal effects that emerge from the combination of physical and/or chemical processes applied to enhance food safety. Despite important recent advances in non-thermal technologies, the greatest synergistic lethal effects emerge from combining them with traditional, relatively mild heat treatments. The combined application of antimicrobials has shown that their main constituents interact effectively, and great synergistic effects have been described with the capacity of either inhibiting or inactivating pathogens. Moreover, natural antimicrobials are more effective when pathogens are previously damaged sublethally by the application of physical technologies. Such combinations allow for a considerable reduction of treatment intensity and costs, along with a noticeable improvement in food quality and safety

Deshojado precoz en Viura y Malvasía riojana

En este trabajo se ha estudiado la aplicación de deshojado precoz en las variedades blancas Viura y Malvasía riojana como herramienta para el control del rendimiento y la mejora de la sanidad de la uva, con el objetivo de incrementar la calidad de sus vinos. Estas variedades presentan una producción elevada y racimos de gran tamaño, muy compactos, por lo que son bastante sensibles a Botrytis cinerea. Los resultados obtenidos indican que esta práctica puede plantearse como un método eficaz para el control del rendimiento y la mejora del estado sanitario de la uva; asimismo, favorece una correcta evolución del proceso de maduración, mejorando la composición de la uva debido al incremento del contenido de sólidos solubles y de compuestos fenólicos. La disminución de la acidez total y el aumento de pH que se producen en la uva, debido a la modificación del microclima de los racimos y al control del rendimiento, podría considerarse un inconveniente a tener en cuenta, sobre todo en el caso de variedades blancas que se caracterizan por un déficit de acidez total.Peer Reviewe

Incubation with a complex orange essential oil leads to evolved mutants with increased resistance and tolerance

Emergence of strains with increased resistance/tolerance to natural antimicrobials was evidenced after cyclic exposure to carvacrol, citral, and (+)-limonene oxide. However, no previous studies have reported the development of resistance and tolerance to complex essential oils (EOs). This study seeks to evaluate the occurrence of Staphylococcus aureus strains resistant and tolerant to a complex orange essential oil (OEO) after prolonged cyclic treatments at low concentrations. Phenotypic characterization of evolved strains revealed an increase of minimum inhibitory and bactericidal concentration for OEO, a better growth fitness in presence of OEO, and an enhanced survival to lethal treatments, compared to wild-type strain. However, no significant differences (p > 0.05) in cross-resistance to antibiotics were observed. Mutations in hepT and accA in evolved strains highlight the important role of oxidative stress in the cell response to OEO, as well as the relevance of the cell membrane in the cell response to these natural antimicrobials. This study demonstrates the emergence of S. aureus strains that are resistant and tolerant to EO (Citrus sinensis). This phenomenon should be taken into account to assure the efficacy of natural antimicrobials in the design of food preservation strategies, in cleaning and disinfection protocols, and in clinical applications against resistant bacteria

Antimicrobial activity of suspensions and nanoemulsions of citral in combination with heat or pulsed electric fields

The application of essential oils in form of nanoemulsions has been proposed as a method to improve their solubility in aqueous solutions, and hence their antimicrobial activity. The objective of this study was to evaluate the antimicrobial activity of citral, applied directly or in combined treatments with heat or pulsed electric fields (PEF), as a function of the inoculation procedure assayed: (i) a simple, vigorous shaking method by vortex agitation (suspension of citral; s-citral) or (ii) the previous preparation of nanoemulsions by the emulsion phase inversion (EPI) method (nanoemulsion of citral; n-citral). n-Citral was more effective in either inhibiting or inactivating Escherichia coli O157:H7 Sakai than s-citral. However, when combined with heat, a greater synergistic effect was observed with s-citral rather than with n-citral, either in lab media (pH 7·0 and 4·0) or apple juice. For instance, while almost 5 log10 cell cycles were inactivated in apple juice after 15 min at 53°C in the presence of 0·1 µl ml-1 of s-citral, the use of n-citral required 30 min. The use of nanoemulsions did not modify the slight synergism observed when citral and mild PEF were combined (150 µs, 30 kV cm-1). Significance and Impact of the Study: The exploration of different delivery systems of antimicrobial compounds such as citral in aqueous food products aids in the establishment of successful combined treatments for food preservation. While at room temperature, citral in form of a nanoemulsion shows a higher antimicrobial activity; its combination with heat would imply a partial loss of the outstanding synergistic lethal effect achieved when added in suspension form. Therefore, the most suitable procedure to magnify the synergism between heat and citral when processing juices would merely require an intense homogenization step prior to the combined treatment

Modified cyclodextrin type and dehydration methods exert a significant effect on the antimicrobial activity of encapsulated carvacrol and thymol

BACKGROUND The antimicrobial activity of essential oils and their constituents has led to increasing interest in using them as natural preservative agents. However, their high sensitivity to light and oxygen, their volatility and their low aqueous solubility are all obstacles to their application in the food, cosmetic or pharmaceutical industries. Encapsulation in cyclodextrins (CDs) is a solution for the application of such essential oils. RESULTS The complexation of carvacrol and thymol with hydroxypropyl (HP)‐α‐, HP‐β‐ and HP‐γ‐CD, the behavior of the solid complexes prepared by freeze‐drying and spray‐drying methods and the antibacterial activity of solid complexes were studied. Kc values of HP‐α‐ and HP‐γ‐CD complexes with carvacrol (118.4 and 365.7 L mol−1) and thymol (112.5 and 239.7 L mol −1) were far lower than those observed for HP‐β‐CD complexes with carvacrol (2268.2 L mol −1) and thymol (881.6 L mol −1). The lower stability of HP‐α‐ and HP‐γ‐CD complexes increased the release of compounds, thereby affecting the antimicrobial activity of carvacrol and thymol to a lesser extent than complexation with HP‐β‐CD, normally used in the encapsulation of carvacrol and thymol. HP‐β‐CD encapsulation of carvacrol and thymol markedly reduced their antimicrobial activity. The freeze‐drying method barely affected the antimicrobial activity of carvacrol and thymol after encapsulation, while spray drying could be considered for the production of solid complexes in combination with the appropriate CD. CONCLUSIONS It was thus demonstrated that HP‐α‐ and HP‐γ‐CD are very suitable alternatives for the encapsulation of carvacrol and thymol with the purpose of preserving their bacteriostatic and bactericidal activities

A new hybrid taxon on genus Thymus L. collected in Aragón (Spain)

MXrEo SANZ, G.; MERcADAL FERRERUELA, N. E. & Písco GARCÍA, J. M. 1995. Sobre un hibrido nuevo del género Thymus L. detectado en Aragón. Bot. Complutensis 20: 69-73. Se comunica el hallazgo de un nuevo hibrido del género Thwnus L. (Labiatae) en la provincia de Teruel, el cual se describe con el nombre de Th. x henitoi Mateo, Mercadal & Pisco, nothosp. nswa, alquc se le supone la combinación parental Th. godayanus Rivas-Martínez et al. x Ni. pulegioides L.Málvo SANZ. G.; MERCADAI. FERRERtJELA, N. E. & Písco GARCÍA, J. M, 1995. A new hybrid taxon on genus Thymus L. collected in Aragón (Spain). BoL Coniplutensis 20: 69-73. A new nothospccics belonging to the genus Thvmus L. (Labiatae) coming from Teruel province (Aragon, NE Spain) is described. The new name proposed is Th. benitoi Mateo, Mercadal & Pisco, nothosp. nova. which its presumed parents are Ni. goda yanas Rivas-Martínez eraL and ib. pulegioides L