In situ microstructure and rheological behavior of yeast biofilms from the juice processing industries

The factors affecting the mechanical properties of biofilms formed by yeast species (Rhodotorula mucilaginosa, Candida krusei, C. kefyr and C. tropicalis) isolated from the juice processing industries have been investigated. Variables studied were: the food matrix (apple/pear juice), the sugar concentration (6/12 °Bx) and the hydrodynamic conditions (static/turbulent flow). A range of environmental cues were included as the mechanical properties of biofilms are complex. Yeast counts were significantly higher in turbulent flow compared with under static conditions. The thickness of the biofilm ranged from 38 to 148 μm, from static to turbulent flow. Yeast biofilms grown under turbulent flow conditions were viscoelastic with a predominant solid-like behavior and were structurally stronger than those grown under static conditions, indicating gel-type structures. Only the type of flow had a significant effect on [Formula: see text] and G*. Flow velocity and nutrient status modulated the biofilm thickness, the biomass and the mechanical properties. A better knowledge of the factors controlling biofilm formation will help in the development of control strategies.

Dual-species relations between Candida tropicalis isolated from apple juice ultrafiltration membranes, with Escherichia coli O157:H7 and Salmonella sp

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.

In situ rheology of yeast biofilms

The aim of the present work was to investigate the in situ rheological behavior of yeast biofilms growing on stainless steel under static and turbulent flow. The species used (Rhodototula mucilaginosa, Candida krusei, Candida kefyr and Candida tropicalis) were isolated from a clarified apple juice industry. The flow conditions impacted biofilm composition over time, with a predominance of C. krusei under static and turbulent flow. Likewise, structural variations occurred, with a tighter appearance under dynamic flow. Under turbulent flow there was an increase of 112 μm in biofilm thickness at 11 weeks (p < 0.001) and cell morphology was governed by hyphal structures and rounded cells. Using the in situ growth method introduced here, yeast biofilms were determined to be viscoelastic materials with a predominantly solid-like behavior, and neither this nor the G'0 values were significantly affected by the flow conditions or the growth time, and at large deformations their weak structure collapsed beyond a critical strain of about 1.5-5%. The present work could represent a starting point for developing in situ measurements of yeast rheology and contribute to a thin body of knowledge about fungal biofilm formation.

Calculation of the Effective Diffusion Coefficients in Drying of Chemical and Mechanical Pretreated Rosehip Fruits (Rosa eglanteria L.) with Selected Mass Transfer Models

The aim of this work was to select models of mass transfer to estimate effective mass diffusion coefficients during the dehydration of Rosa eglanteria fruits with air at 70°C. Fruits were pretreated chemically and mechanically (dipping it in NaOH and ethyl oleate solutions and cutting or perforating the fruit cuticle). Selected models were those of Becker and Fick’s second law, considering fruit shrinkage during drying. Both models satisfactorily predict the fruit drying, and the different pretreatments, to total or partially remove this waxen cuticle, noticeably improved water diffusion, reducing the time of processing from 28% (NaOH) to 52% (oleate and mechanical pretreatments). Mechanical pretreatments were the more effective, because oleate presents quality problems.

Pectin extraction from quince (Cydonia oblonga) pomace applying alternative methods: effect of process variables and preliminary optimization

The objectives of this study were to introduce alternative methods in the process of pectin extraction from quince pomace, to determine the effect of selected process variables (factors) on the obtained pectin, and to perform a preliminary optimization of the process. A fractional factorial experimental design was applied, where the factors considered were six: quince pomace pretreatment (washing vs blanching), drying method (hot air vs LPSSD), acid extraction conditions (pH, temperature, and time), and pectin extract concentration method (vacuum evaporation vs ultrafiltration). The effects of these factors and their interactions on pectin yield (Y: 0.2-34.2 mg/g), GalA content (44.5-76.2%), and DM (47.5-90.9%), were determined. For these three responses, extraction pH was the main effect, but it was involved in two and three factors interactions. Regarding alternative methods, LPSSD was required for maximum Y and GalA, and ultrafiltration for maximum GalA and DM. Response models were used to predict optimum process conditions (quince blanching, pomace drying by LPSSD, acid extraction at pH 2.20, 80 , 3 h, and concentration under vacuum) to simultaneously maximize Y (25.2 mg/g), GalA (66.3%), and DM (66.4%).

Influence of the extraction-purification conditions on final properties of alginates obtained from brown algae (Macrocystis pyrifera)

In this work, three methods (ethanol, HCl, and CaCl(2) routes) of sodium alginate extraction-purification from brown seaweeds (Macrocystis pyrifera) were used in order to study the influence of process conditions on final properties of the polymer. In the CaCl(2) route, was found that the precipitation step in presence of calcium ions followed by proton-exchange in acid medium clearly gives alginates with the lowest molecular weight and poor mechanical properties. It is well known that the acid treatment degrade the ether bonds on the polymeric chain. Ethanol route displayed the best performance, where the highest yield and rheological properties were attained with the lowest number of steps. Although the polymer I.1 showed a molar mass and polydispersity index (M(w)/M(n)) similar to those of commercial sample, its mechanical properties were lower. This performance is related to the higher content of guluronic acid in the commercial alginate, which promotes a more successful calcium chelation. Moreover, the employment of pH 4 in the acid pre-treatment improved the yield of the ethanol route, avoiding the ether linkage hydrolysis. Therefore, samples I.2 and I.3 displayed a higher M(w) and a narrower distribution of molecular weights than commercial sample, which gave a higher viscosity and better viscoelastic properties.

Early heart rate variations during head-up tilt table testing as a predictor of outcome of the test

Head-up tilt table testing (HUTT) is a useful tool for the diagnosis of unknown origin of syncope. A setback is its duration. This study tries to establish a specific parameter that, according to the heart rate elevation in the test's initial phase, allows a reliable prediction of its outcome. In a prospective study, every patient being under unknown syncope workup was included. A two-phase 20-minute tilt table test was performed. The initial phase was passive, and the second required pharmacological stimulation with isoproterenol. The basal and 5- and 10-minute heart rate values of the passive phase were measured and compared within the group and against negative tests. During a 1-year period, 115 HUTT were performed: 88 were positive and 27 negative. The negative HUTT patients had an increase in HR of 5.05 (+/- 13.5) beats/min at 5 minutes, and 5.79 (+/- 12.9) beats/min at 10 minutes (P = 0.2). Those with a positive HUTT had an increase of 9.05 (+/- 14.5) beats/min at 5 minutes, and of 10 (+/- 13.4) beats/min at 10 minutes (P < 0.001). There were no significant changes in HR when comparing positive to negative HUTT. There is no specific number that allows predication of outcome early in HUTT. Within the group, variations are important. Only a group tendency can be established, which strongly correlates with the results obtained during the test.

Iatrogenic renal vascular injury

Bilateral arteriovenous fistulas secondary to percutaneous needle biopsy of each kidney developed in a patient with malignant hypertension and chronic failure. The fistulas with aneurysmal formation and hematuria were of such magnitude that bilateral nephrectomy was required for control. The patient is now normotensive and is maintained on hemodialysis. The advisability of renal needle biopsy in uncontrolled hypertension is questioned. Cases of intrarenal arteriovenous fistulas resulting from percutaneous needle biopsy of the kidney are being reported with increasing frequency. The exact incidence of fistula formation after kidney biopsy is unknown, but several series based on arteriographic studies show an incidence as high as 18 per cent. Although many of these fistulas disappear spontaneously, approximately 4 per cent persist. A review of the literature failed to reveal the incidence of aneurysmal formation. Our case was complicated by formation of bilateral renal arteriovenous fistulas secondary to repeat bilateral percutaneous needle biopsy and right open renal biopsy. Subsequent gross hematuria from the right ureteral orifice also resulted which was proved by cystoscopy and required replacement with several units of blood. The likelihood of rupture led to bilateral nephrectomy.