RESUMO
AIMS: The objective of this study was to determine the interactions between common spoilage yeast, Candida tropicalis, isolated from ultrafiltration membranes, and Escherichia coli O157:H7 and Salmonella sp. on stainless steel surfaces. METHODS AND RESULTS: Single and dual-species attachment assays were performed on stainless steel at 25°C using apple juice as culture medium. The growth of Salmonella sp. rose when it was co-cultivated with C. tropicalis in dual biofilms at 16 and 24 h; the same effect was observed for E. coli O157:H7 at 24 h. The colonization of C. tropicalis on stainless steel surfaces was reduced when it was co-cultivated with both pathogenic bacteria, reducing C. tropicalis population by at least 1.0 log unit. Visualization by SEM demonstrated that E. coli O157:H7 and Salmonella sp. adhere closely to hyphal elements using anchorage structures to attach to the surface and other cells. CONCLUSIONS: These results suggest a route for potential increased survival of pathogens in juice processing environments. These support the notion that the species involved interact in mixed yeast-bacteria communities favouring the development of bacteria over yeast. SIGNIFICANCE AND IMPACT OF THE STUDY: This study support the plausibility that pathogen interactions with strong biofilm forming members of spoilage microbiota, such as C. tropicalis, might play an important role for the survival and dissemination of E. coli O157:H7 and Salmonella sp. in food-processing environments.
Assuntos
Bebidas/microbiologia , Candida tropicalis/fisiologia , Escherichia coli O157/fisiologia , Malus , Salmonella/fisiologia , Aderência Bacteriana , Biofilmes , Candida tropicalis/isolamento & purificação , Candida tropicalis/ultraestrutura , Escherichia coli O157/crescimento & desenvolvimento , Escherichia coli O157/ultraestrutura , Microbiologia de Alimentos , Interações Microbianas , Salmonella/crescimento & desenvolvimento , Salmonella/ultraestrutura , Aço Inoxidável , UltrafiltraçãoRESUMO
Turbidity of freshly squeezed apple juice is produced by a polydisperse suspension of particles coming from the cellular tissue. After precipitation of coarse particles by gravity, only fine-colloidal particles remain in suspension. Aggregation of colloidal particles leads to the formation of fractal structures. The fractal dimension is a measure of the internal density of these aggregates and depends on their mechanism of aggregation. Digitized images of primary particles and aggregates of depectinized, diafiltered cloudy apple juice were obtained by scanning electron microscopy (SEM). Average radius of the primary particles was found to be a = 40 ± 11 nm. Maximum radius of the aggregates, R(L), ranged between 250 and 7750 nm. Fractal dimension of the aggregates was determined by analyzing SEM images with the variogram method, obtaining an average value of D(f) = 2.3 ± 0.1. This value is typical of aggregates formed by rapid flocculation or diffusion limited aggregation. Diafiltration process was found to reduce the average size and polydispersity of the aggregates, determined by photon correlation spectroscopy. Average gyration radius of the aggregates before juice diafiltration was found to be R(g) = 629 ± 87 nm. Average number of primary particles per aggregate was calculated to be N = 1174.
Assuntos
Bebidas , Fractais , Malus/química , Filtração , Floculação , Microscopia Eletrônica de Varredura , Modelos Teóricos , Tamanho da PartículaRESUMO
Rheological data on a food together with data on its composition and structure or microstructure should lead to understanding the interrelationships between them. A number of foods are dispersions of solids in liquids, liquids in liquids, or gas in liquids. The dispersed particles may be colloidal in nature with dimensions < 10 mum, or larger noncolloidal particles (> 10 mum). For both colloidal and noncolloidal dispersions (either in dilute or concentrated regimes), several theoretical equations exist that provide insights into the role of key rheological parameters, such as particle volume fraction and size, interparticle forces, and fractal dimension on their viscosity, yield stress, and modulus. When theoretical models cannot be easily applied to foods with complex structures, structural analysis and structure-based models provide insight into the role of solids loading and interparticle bonding on rheological behavior. In this review, recent studies on colloidal and noncolloidal food dispersions in which theoretical models as well as structural analysis were employed are discussed.