Microbiome of free-living amoebae isolated from drinking water

Free-living amoebae (FLA) are protozoa that can be found in water networks where they prey on bacteria within biofilms. Most bacteria are digested rapidly by phagocytosis, however some are able to survive within amoebae and some are even able to multiply, as it is the case for Legionella pneumophila. These resisting bacteria are a potential health problem as they could also resist to macrophage phagocytosis. Several publications already reported intra-amoebal bacteria but the methods of identification did not allow metagenomic analysis and are partly based on co-culture with one selected amoebal strain. The aim of our study was to conduct a rRNA-targeted metagenomic analysis on amoebae and intra-amoebal bacteria found in drinking water network, to provide the first FLA microbiome in environmental strains. Three sites of a water network were sampled during four months. Culturable FLA were isolated and total DNA was prepared, allowing purification of both amoebal and bacterial DNA. Metagenomic studies were then conducted through 18S or 16S amplicons sequencing. Hartmannella was by far the most represented genus of FLA. Regarding intra-amoebal bacteria, 54 genera were identified, among which 21 were newly described intra-amoebal bacteria, underlying the power of our approach. There were high differences in bacterial diversity between the three sites. Several genera were highly represented and/or found at least in two sites, underlying that these bacteria could be able to multiply within FLA. Our method is therefore useful to identify FLA microbiome and could be applied to other networks to have a more comprehensive view of intra-amoebal diversity.     

The effect of different porous media on moisture loss and oil absorption profiles during frying using glass micromodels

Microstructure plays a key role in oil absorption during frying. The aim of this work was to improve our understanding of the relationship between microstructure and oil absorption, through the use of glass micromodels to obtain evidence of transport phenomena in three porous networks. Micromodels were saturated with water and partially immersed in oil at 190°C. Moisture and oil profiles were imaged to get water and oil saturation maps. Image and fractal analyses were performed to describe the morphology of the evaporation and oil fronts. Results showed that higher porosity facilitated the moisture removal and promoted greater oil absorption during cooling. The fractal dimension showed that microstructures with a relatively high number of fine capillaries were less stable and propitiated fingering during the advance of the evaporation front. In all matrices, the disruption of the surface oil film due to air penetration was a critical factor to stop oil imbibition. © 2015 American Institute of Chemical Engineers AIChE J, 62: 629–638, 2016     

Evidence for widespread Wolbachia infection in isopod crustaceans: molecular identification and host feminization

Wolbachia are maternally inherited, intracellular, alpha proteobacteria that infect a wide range of arthropods. They cause three kinds of reproductive alterations in their hosts: cytoplasmic incompatibility, parthenogenesis and feminization. There have been many studies of the distribution of Wolbachia in arthropods, but very few crustacean species are known to be infected. We investigated the prevalence of Wolbachia in 85 species from five crustacean orders. Twenty-two isopod species were found to carry these bacteria. The bacteria were found mainly in terrestrial species, suggesting that Wolbachia came from a continental environment. The evolutionary relationships between these Wolbachia strains were determined by sequencing bacterial genes and by interspecific transfers. All the bacteria associated with isopods belonged to the Wolbachia B group, based on 16S rDNA sequence data. All the terrestrial isopod symbionts in this group except one formed an independent clade. The results of interspecific transfers show evidence of specialization of Wolbachia symbionts to their isopod hosts. They also suggest that host species plays a more important role than bacterial phylogeny in determining the phenotype induced by Wolbachia infection.     

Vacuum frying reduces oil uptake and improves the quality parameters of carrot crisps

Recent consumer trends towards healthier and low fat products have had a significant impact on the snack industry. The objective of this study was to examine the most important quality parameters of vacuum and atmospheric fried carrot slices in order to identify the specific advantages of vacuum technology. Said parameters include oil uptake, colour changes, and trans α and β-carotene degradation. Equivalent thermal driving forces were used (ΔT = 60 °C and 80 °C) to compare the processes, maintaining a constant difference in temperature between the oil and the boiling point of water at the working pressure. The results showed that vacuum frying can reduce oil content by nearly 50% (d.b.) and preserve approximately 90% of trans α-carotene and 86% of trans β-carotene. This process also allowed for the raw carrot colour to be preserved, which was reflected by good correlations between a∗ and trans β-carotene content, b∗ and trans α-carotene content, and hue and total carotenoid content.     

Comparison between atmospheric and vacuum frying of apple slices

Vacuum deep-fat frying is a new technology that can be used to improve quality attributes of fried food because of the low temperatures employed and minimal exposure to oxygen. In this paper atmospheric and vacuum frying of apple slices were compared, in terms of oil uptake, moisture loss and color development. In addition, some apple slices were pre-dried (up to 64% w.b.) before vacuum frying to determine the overall effect. To carry out appropriate comparisons between both technologies equivalent thermal driving forces were used in both processes (ΔT = 40, 50, 60 °C), keeping a constant difference between the oil temperature and the boiling point of water at the working pressure. Vacuum frying was shown to be a promising technique that can be used to reduce oil content in fried apple slices while preserving the color of the product. Particularly, drying prior to vacuum frying was shown to give the best results. For instance, when using a driving force of ΔT = 60 °C, pre-dried vacuum fried slices absorbed less than 50% of the oil absorbed by atmospheric fried ones. Interestingly, a strong relationship between water loss and oil content was observed in both technologies, allowing the extension of observations that have been made for atmospheric frying.     

Microstructural characterization of deep-fat fried formulated products using confocal scanning laser microscopy and a non-invasive double staining procedure

The aim of this work was to characterize the inner microstructure of different fried formulated products to understand its relationship to oil absorption. Two product categories, which were either based on potato-flakes or wheat gluten, were analyzed. A non-invasive double staining procedure to perform a two channel observation using confocal scanning laser microscopy was set-up. The dough was directly stained during preparation with fluorescein-5-isothiocyanate (FITC), laminated and fried in oil stained with Nile Red. Thereafter, samples were observed without further intrusion. Pore size, porosity and oil were quantified using image analysis. A direct relationship between porosity and oil absorption was found in gluten-based products, but, no relationship was detected in potato-flakes-based ones. Further, gluten-based products were less porous but retained, in general, more oil. Parameters such as pore tortuosity and/or connectivity, as well as oil wettability, might explain such differences. In addition, the developed microscopy technique developed herein may be used in other food systems.     

Understanding the Effect of Vacuum Level in Structure Development and Oil Absorption in Vacuum-Fried Wheat Starch and Gluten-Based Snacks

Vacuum frying has gained a significant strategic importance for future fried food manufacturing since, due to the low-temperature processing, significant benefits such as the improvement of fried product safety and quality can be obtained. So far, all studies have focused on agricultural products, such as potatoes, which are already structured by nature, but none of them has included fabricated products. This imposes a challenge since minimum conditions must be ensured to form structure during processing. The objective of this work was to understand the role of water boiling point (T _bp) and processing temperature (T _oil) in structure formation, oil absorption, and most important quality attributes of starch-based products during vacuum frying. Fabricated products were made of a reconstituted blend of gluten (12 % d.b.) and wheat starch (88 % d.b.) in order to accurately control ingredients proportion. Samples were fried varying the T _bp from 38 to 71 °C while keeping a thermal driving force of 70 °C (i.e., T _oil???T _bp?=?70 °C). Another set of samples was fried varying the thermal driving force from 37 to 70 °C while maintaining a T _bp of 71 °C. Results showed that a higher T _bp favored the capacity of the matrix to form structure due to starch gelatinization in the presence of water and temperature, reducing the oil content of the fried products. This was confirmed by scanning electron microphotographs. Results were consistent with textural measurements that showed a higher breaking force as the processing pressure increased (i.e., T _bp), which was inversely related to oil absorption (R ²?=?0.92). In accordance, this study allows understanding the effect of vacuum level in structure development and oil absorption in vacuum-fried products when different food building blocks (gluten and wheat starch) are combined.     

A Dirichlet–Neumann cost functional approach for the Bernoulli problem

The Bernoulli problem is rephrased into a shape optimization problem. In particular, the cost function, which turns out to be a constitutive law gap functional, is borrowed from inverse problem formulations. The shape derivative of the cost functional is explicitly determined. The gradient information is combined with the level set method in a steepest descent algorithm to solve the shape optimization problem. The efficiency of this approach is illustrated by numerical results for both interior and exterior Bernoulli problems.