Carbon dioxide local heat transfer coefficients during flow boiling in a horizontal circular smooth tube

Carbon dioxide is gaining renewed interest as an environmentally safe refrigerant. In order to improve the energy efficiency of R744 systems, an accurate knowledge of heat transfer coefficients is fundamental.In this paper experimental heat transfer coefficients during flow boiling of R744 in a smooth, horizontal, circular, 6.00 mm inner diameter tube are presented. We obtained 217 experimental points in 18 operating conditions commonly encountered in dry-expansion evaporators investigating the effect of the mass flux within the range from 200 to 349 kg/m² s, the saturation temperature within the range from ?7.8 to 5.8 °C, the heat flux within the range from 10.0 to 20.6 kW/m² and the vapor quality within the range from 0.02 to 0.98.An interpretation of the experimental trends based on the local circumferential distribution of heat transfer coefficients, the flow regimes and the thermophysical properties is proposed.Besides the measured data are compared with those predicted by the Cheng et al. [L. Cheng, G. Ribatski, J.R. Thome, New prediction methods for CO₂ evaporation inside tubes: Part II – An updated general flow boiling heat transfer model based on flow patterns, International Journal of Heat and Mass Transfer 51 (2008) 125–135] and Yoon et al. [R. Yun, Y. Kim, M.S. Kim, Y. Choi, Boiling heat transfer and dryout phenomenon of CO₂ in a horizontal smooth tube, International Journal of Heat and Mass Transfer 46 (2003) 2353–2361] correlations to determine the best predictive method for the tested operating conditions.     

Monitoring of perfluorinated compounds in edible fish from the Mediterranean Sea

Perfluorooctanoic acid (PFOA) and perfluorooctane sulphonate (PFOS) are environmental contaminants belonging to a chemical group known as perfluorinated compounds (PCFs). The United States Environmental Protection Agency (US EPA) considers both compounds to be carcinogenic. The goal of the present study was to evaluate the contamination levels of PFOS and PFOA in edible fish of the Mediterranean Sea. Twenty six fish muscles, 17 fish livers, five series of cephalopods (each composed of ten specimens) and thirteen series of bivalves (each composed of about 50 specimens) were used for the investigation. A fast sample treatment, followed by an LC–ESI–MS/MS method is described for the identification, and quantification of PFOA and PFOS in fish. The method was in-house-validated through the determination of precision, accuracy, specificity, calibration curve, decision limit (CCα), and detection capability (CCβ). The results showed PFOA and PFOS levels in fishes and molluscs lower than those reported for analogue matrices in different geographic areas. Therefore, our biomonitoring results did not show that the Mediterranean Sea had any particularly alarming pollution by PFCs, although it is located in a semi-closed basin with scarce water change. Nonetheless, a worrying element is that a few fish showed extremely high contamination by PFOA and PFOS. This finding needs further clarification in order to assess whether such unusual contamination is linked to “dot-like” pollutant release, which could explain the anomaly.     

A new platform for Real-Time PCR detection of Salmonella spp., Listeria monocytogenes and Escherichia coli O157 in milk

Intoxications and infections caused by food-borne pathogens represent an increasing public health problem, and diagnostic tests in multiplex format are needed for the rapid identification of food contaminations caused by more than one microbial species. We have developed a multiple PCR-based platform for the simultaneous detection of the widespread milk-associated pathogens Salmonella spp., Listeria monocytogenes and Escherichia coli O157. The assay combines an enrichment step in a medium properly formulated for the simultaneous growth of target pathogens, a DNA isolation method, and a multiplex Real-Time PCR detection system based either on dual-labelled probes (mRT-PCR), or on melting curve analysis (mHRM). The second, producing a distinct peak for each amplification product, allows the qualitative assessment of pathogen presence. Moreover, the internal amplification control (IAC) included in the reaction, ensuring the reliability of results, complies with quality management programmes. Inclusivity and exclusivity were 100% each, with a detection limit of 1 CFU for each pathogen in a total of five 25 ml-aliquots of raw milk, and a duration of two working days.The assay represents an alternative approach for the qualitative detection of the cited bacterial species, suitable for a relatively inexpensive screening of several milk samples, reducing the turnaround time and the workload.     

In Vitro Starch Digestibility of Commercial Gluten‐Free Pasta: The Role of Ingredients and Origin

Gluten replacement in gluten‐free (GF) products presents major challenges for the food industry in terms of sensorial, technological and nutritional characteristics. The absence of gluten reportedly affects starch digestibility, thus increasing the postprandial glycaemic response. However, the role of ingredients and processing conditions has been addressed only seldom. We investigated the in vitro starch digestibility of 9 commercial GF products (5 Italian pasta and 4 Oriental noodles) differing in formulation and processing conditions. Content of rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) were assessed and combined with information on starch pasting properties and on the overall protein organization. Oriental noodles presented higher relative levels of RS and RDS than Western‐style pasta, that often had SDS levels compatible with low rates of starch digestion. As regard formulation, presence of multiple ingredients seems to likely increase the RDS level, as did the different protein organization in the various samples.     

Nuclear DNA barcodes for cod identification in mildly-treated and processed food products

Gadoids are a group of fish with historical importance in the fishing industry. The high demand for cod is one of the reasons why cod products are often mislabelled, and numerous observations have been made on the replacement of Atlantic cod (Gadus morhua) by cheaper species or its illegal capture in contravention of fish quotas. Fish species identification is traditionally based on morphological features, but this may be difficult in case of heat-treated or processed products, or where the species look similar, as in the Gadoid group. DNA-based approaches (using either nuclear or mitochondrial DNA) are most commonly used in this case, due to their high specificity and to the high resilience of the target molecules to food processing techniques. In this article, we identified, using an automated screening approach, novel barcode regions and their associated primers in the nuclear genome, to be used for the efficient identification of Gadoids. The barcode regions were tested on official and commercial samples, raw or mildly treated products, like frozen, or salted, as well as pre-cooked complex mixtures and processed samples, using next-generation sequencing (NGS) technique. The method proposed could complement existing fish identification strategies in establishing an efficient framework to detect and prevent frauds along the food chain.     

Assessing the Potential Content of Ethyl Carbamate in White,Red, and Rosé Wines as a Key Factor for Pursuing Urea Degradation by Purified Acid Urease

The ethyl carbamate (EC) content of a wine after a given temperature‐time storage was theoretically predicted from the potential concentration of ethyl carbamate (PEC), as determined via an accelerated EC formation test. Such information was used to decide whether an enzymatic treatment was needed to reduce the wine urea level before bottling/aging. To this end, 6 white, red, and rosé wines, manufactured in Italy as such or enriched with urea, were tested for their PEC content either before or after enzymatic treatment using a purified acid urease preparation derived from Lactobacillus fermentum. The treatment was severely affected by the total phenolic content (TP) of the wine, the estimated pseudo‐first‐order kinetic rate constant for NH₃ formation reducing by a factor of approximately 2000 as the TP increased from 0 to 1.64 g L^‐1. Such a sensitivity to TP was by far greater than that pertaining to a killed cell‐based enzyme preparation used previously. Urea hydrolysis was successful at reducing EC concentration in wines with low levels of TP and other EC precursors.     

Beer Clarification by Novel Ceramic Hollow‐Fiber Membranes: Effect of Pore Size on Product Quality

In this work, the crossflow microfiltration performance of rough beer samples was assessed using ceramic hollow‐fiber (HF) membrane modules with a nominal pore size ranging from 0.2 to 1.4 μm. Under constant operating conditions (that is, transmembrane pressure difference, TMP = 2.35 bar; feed superficial velocity, v_S = 2.5 m/s; temperature, T = 10 °C), quite small steady‐state permeation fluxes (J^*) of 32 or 37 L/m²/h were achieved using the 0.2‐ or 0.5‐μm symmetric membrane modules. Both permeates exhibited turbidity <1 EBC unit, but a significant reduction in density, viscosity, color, extract, and foam half‐life with respect to their corresponding retentates. The 0.8‐μm asymmetric membrane module might be selected, its corresponding permeate having quite a good turbidity and medium reduction in the aforementioned beer quality parameters. Moreover, it exhibited J^* values of the same order of magnitude of those claimed for the polyethersulfone HF membrane modules currently commercialized. The 1.4‐μm asymmetric membrane module yielded quite a high steady‐state permeation flux (196 ± 38 L/m²/h), and a minimum decline in permeate quality parameters, except for the high levels of turbidity at room temperature and chill haze. In the circumstances, such a membrane module might be regarded as a real valid alternative to conventional powder filters on condition that the resulting permeate were submitted to a final finishing step using 0.45‐ or 0.65‐μm microbially rated membrane cartridges prior to aseptic bottling. A novel combined beer clarification process was thus outlined.     

Novel Procedure for Lager Beer Clarification and Stabilization Using Sequential Enzymatic,Centrifugal, Regenerable PVPP and Crossflow Microfiltration Processing

In this work, the crossflow microfiltration (CFMF) performance of different lots of lager beer, produced in a pilot scale at the Italian Brewing Research Centre (CERB, Perugia, Italy), was assessed in a bench-top plant, equipped with a 0.8-μm ceramic tubular membrane module, under constant crossflow velocity of 6 m s^?1, transmembrane pressure difference of 3.74 bar, temperature of ~10 °C, and periodic CO₂ backflushing. By feeding different beer samples (i.e., as such, precentrifuged (C), or pretreated with a commercial enzyme preparation to degrade the original arabinoxylans and β-glucans and then centrifuged (EC) to minimize the fouling contribution of yeast cells, aggregates, and polysaccharides), it was possible to increase the average permeation flux (expressed as mean value?±?standard deviation) from 112?±?13 to 199?±?17 or 330?±?22 L m^?2 h^?1, respectively. Only when using the EC-pretreated beer specimens, the permeate turbidity at 20 °C approached the limiting one (<0.6 EBC unit) recommended by the European Brewery Convention standards. As expected, the permeate chill haze at 0 °C was generally higher than the above haze target. By submitting EC-pretreated beer seeded with 0.5 g L^?1 of regenerable polyvinylpolypyrrolidone (PVPP) to CFMF, it was possible to reduce the initial total polyphenol content by 30 % and permeate chill haze to 0.60?±?0.01 EBC unit, but the average permeation flux fell to 84?±?4 L m^?2 h^?1. By performing sequentially EC pretreatments, PVPP stabilization, cartridge filtration, and CFMF, it was possible not only to re-enhance the average permeation flux at about 230 L m^?2 h^?1 near to those achievable with DE filters, but also to obtain a chill haze-free permeate ready for aseptic packaging.