Lactobacilli isolated from kefir grains: evidence of the presence of S-layer proteins

In the present study we report for the first time the presence of S-layer proteins in Lactobacillus kefir and Lactobacillus parakefir isolated from kefir grains. Soluble whole-cell protein profile obtained either by mechanical disruption (X-press) or by a combined treatment with lysozyme and SDS on whole cells, showed a significant band of apparent molecular mass of 66-71 kDa as measured by SDS-PAGE. The intensity of this band was considerably reduced when cells were treated with 5 M-LiCl. The above mentioned proteins were recovered in the LiCl extracts. After dialysis and concentration, the proteins extracted were able to reassemble in a regular array. Negative staining of these protein preparations were analysed by transmission electron microscopy and a paracrystalline arrangement was seen. Thin sections of bacteria analysed by transmission electron micrographs showed an outermost layer over the bacterial cell wall, that was lost after the LiCl treatment. The production of this surface structure under different culture conditions was also evaluated. Finally, the relationship between the presence of S-layer proteins and surface properties (e.g. adhesion to Caco-2 cells, autoaggregation, and hemagglutination) was investigated.     

Escherichia coli of poultry food origin as reservoir of sulphonamide resistance genes and integrons

The antimicrobial resistance phenotype and genotype, the flanking regions of sulphonamide resistance genes and the integrons were analyzed in 166 Escherichia coli isolates recovered from poultry meat in Tunisia. High percentages of resistance were detected to ampicillin, streptomycin, nalidixic acid, sulphonamide and tetracycline (66-95%), and lower percentages to gentamicin, amoxicillin-clavulanic acid and cefoxitin (1-4%). The bla_TEM, tet(A)/tet(B), aph(3′)-Ia, aac(6′)-Ib-cr, aac(3)-II and cmlA genes were identified in 92, 82, 29, 2, 2 and 7 isolates, respectively. Class 1 and/or class 2 integrons were detected in 52% of E. coli isolates and five different gene cassette arrangements were identified in the variable regions of class 1 integrons, which included antimicrobial resistance determinants. Sixty-eight isolates contained the sul1 gene and 37 of them presented this gene into a class 1 integron structure. The sul3 gene was detected associated with non-classic class 1 integrons in 4 out of 46 sul3-positive isolates. The sul2 gene was detected in 66 isolates, 51 of them were linked to strA/B genes in seven different genetic structures. Seventy-three-per-cent of integron-positive isolates presented resistance to at least five different antimicrobial families versus 38.7% of integron-negative isolates. Our study highlights the role of commensal E. coli isolates from poultry meat as an important reservoir for sulphonamide resistance genes and integrons carrying antimicrobial resistance genes.     

Influence of whey protein aggregation on the residence time distribution in a tubular heat exchanger and a helical holding tube during heat treatment process

The residence time distribution (RTD) of a whey protein (WP) suspension flowing through a heat treatment system was studied. The experimental system is the tubular heat exchanger and the helical holding section of a laboratory scale thermal process. RTD was measured in isothermal conditions at 60 °C, a temperature involving no WP aggregation, and at 87 °C, temperature at which WP aggregates. Two flow rates (20 L/h and 49 L/h) were tested with two different lengths of holding tube in order to maintain the same order of magnitude of the holding time. Methylene blue was used as tracer and spectrophotometer analysis were performed to determine the outlet concentration. These investigations yielded to great differences between the RTD in aggregation and no aggregation conditions. The minimum residence time is shorter when WP aggregation occurs due to the modification of the velocity field inside the tubular devices with the local enhancement of the viscosity. Fitting the experimental results with a new compartment model based on the generalized convection model give very good agreement contrary to the more classical RTD models. This RTD model could be used in combination with a population balance model in order to predict the WP aggregates size dispersion.     

On ‘Discussion on Barkhausen and Nyquist stability criteria’

The present article is related to the recently published paper given in Singh (Analog Integr Circuits Signal Process, 62, 327–332, 2010), which depicts the failure of Barkhausen criterion concerning the determination of condition of oscillation for startup of sinusoidal oscillation. In particular, the sinusoidal oscillator circuit considered in this article is one of the possible four alternatives of the Wien-bridge oscillator (WBO). In other previous articles by the same aforementioned author (Singh, Analog Integr Circuits Signal Process 48, 251–255, 2006; Singh, Analog Integr Circuits Signal Process 50, 127–132, 2007), some examples are provided with the objective of sustaining this hypothesis. In this article, however, the study of RC oscillator circuits based on the Barkhausen criterion is reconsidered. This point of view involves to consider the classical structure of a sinusoidal oscillator as a system consisting of a positive feedback loop composed of a general amplifier block (with its corresponding local negative feedback that stabilizes the gain) plus a general passive network. Taking into account this point of view, it is shown that Barkhausen criterion (specifically, the practical form of this criterion) allows to predict properly the startup of oscillations of the circuit considered in the article (Singh 2010).     

Onion (<Emphasis Type="Italic">Allium cepa</Emphasis> L.) by-products as source of dietary fiber: physicochemical properties and effect on serum lipid levels in high-fat fed rats

The effect of industrial processes used to obtain onion by-products was evaluated. Fiber composition and physicochemical properties were assessed in order to choose the best process to obtain high-fiber ingredients. Moreover, the effect of the inclusion of the dietary fiber-rich onion by-products in a high-fat diet on serum lipids of rats was also evaluated. Bagasse was the best by-product since it showed the highest fiber content with a balanced soluble-to-insoluble fiber ratio and the best physicochemical properties. This fact is related to its high fiber content and also due to its composition, rich in uronic acids and polysaccharides, which explains its high cation exchange capacity, water-holding capacity and swelling capacity. In addition, the inclusion of Bagasse in a high-fat diet produced a reduction in the serum lipid and total cholesterol increases induced by high-fat diet. This effect could be related to the high cation exchange and swelling capacities that Bagasse showed, since these properties can create a concerted effect in reducing the number of intact micelles available, the transit time, and consequently the total time available for cholesterol and lipid absorption in the small intestine.     

Phenolic profiles,antioxidant activity and in vitro antiviral properties of apple pomace

Methanolic and acetonic extracts of apple pomace were evaluated for phenolic profiles, antioxidant properties and antiviral effect against herpes simplex virus type 1 (HSV-1) and 2 (HSV-2). Acetone extraction yielded the higher amounts of phenolic compounds. The extraction method influenced the phenolic composition although antioxidant activity correlated weakly with phenols concentration. Among the polyphenols analysed, quercetin glycosides were the most important family, followed by dihydrochalcones. Apple pomace extracts were able to inhibit both HSV-1 and HSV-2 replication in Vero cells by more than 50%, at non-cytotoxic concentrations. Selectivity indexes (SI) ranged from 9.5 to 12.2.     

Calcium and protein intake and bone markers in premenopausic and posmenopausic women with normal bone mineral density from Comodoro Rivadavia (Argentina)

Healthy premenopausal women (Pre n=28) and posmenopausal (Pos n=22), living in Comodoro Rivadavia (Argentina), with normal femoral neck and lumbar spine bone mineral density (BMD) were studied. Usual daily calcium intake (CaI) and protein intake (PrI) were calculated according to an special questionaire and the National Food Composition Tables. Fasting blood samples and 24 h urine were collected. Laboratory measurements were: in urine (U): calcium (Ca), creatinine (Crea) and deoxypiridinoline (Dpyr); in serum: Bone Alkaline Phosphatase (BAPh). The results presented the following media +/- SD (minimum - maximum) in Pre and Pos, respectively: CaI (mg/d): 694 +/- 411 (190 - 2,117); 918 +/- 304 (471 - 1740) (p < 0.01); PrI (g/d): 64.6 +/- 25.4 (33.5 - 136); 63.7 +/- 17.6 (41.5 - 95.2); daily UCa (mg/d): 123 +/- 85 (20 +/- 369); 114 +/- 66 (17 - 252); Ca/crea (mg/mg): 0.124 +/- 0.086 (0.014 - 0.372); 0.131 +/- 0.077 (0.020 - 0.338); Dpyr/crea (nM/mM): 5.5 +/- 1.5 (3.4 - 10.3); 7.1 +/- 2.3 (3.9 - 14.5) (p < 0.01); BAPh (UI/l): 58 +/- 12 (28 - 94); 70 +/- 20 (32 - 99) (p < 0.01). CaI was lower than the Adequate Dietary calcium intake in 86% and 82% of the Pre and Pos women, respectively. There was no correlation between CaI, PrI and the biochemical indicators. Conclusions: in these healthy women, without bone mass loss and with wide range of CaI, although usually low, markers of bone turnover, would be a balance between the increase of bone formation and resorption.     

Recycling of high impact polystyrene in coextruded sheet: Influence of the number of processing cycles on the microstructure and macroscopic properties

High impact polystyrene(HIPS) was repeatedly coextruded at 220°C, maintaining a constant composition of 70 wt% of virgin HIPS and 30 wt% of recycled HIPS. The gel content (GC), grafting degree (GD), swell index (SI), morphology of the rubber phase, and average molecular weight of the polystyrene (PS) matrix ( _w) were characterized after each processing cycle. The effect of these parameters on the melt flow index (MFI), the shear viscosity (η), the power law index (n), the Izod impact, and the stress at break were evaluated. The results demonstrated that the rheological properties changed with the number of processing cycles, e.g. the MFI decreased in the first cycle from 2.8 to 1.7 g/10 min, while from the second to the sixth cycle increased to 3.4 ± 0.2 g/10 min. The power law index increased from n = 0.29, after the first processing cycle, to n = 0.34 in the sixth cycle. The changes in MFI and n were attributed to changes in the physical structure of the rubber phase and to chain scissions in the PS matrix, caused by the recycling. Finally, the impact strength decreased with the increasing number of processing cycles, while the tensile stress at break remained constant. POLYM. ENG. SCI., 46:1698–1705, 2006. © 2006 Society of Plastics Engineers     

Protease (PrA and PrB) and prolyl and arginyl aminopeptidase activities from Debaryomyces hansenii as a function of growth phase and nutrient sources

The effects of nutrient sources and growth phase of Debaryomyces hansenii on the protease (PrA and PrB) and aminopeptidase (prolyl-[PAP] and arginyl-[AAP] aminopeptidases) activities were investigated. These activities were also monitored during growth on a whole sarcoplasmic muscle protein extract (WSPE) and on an equivalent medium but free of compounds under 10 kDa (SPE>10 kDa). The levels of specific protease and aminopeptidase activities were higher when cells were grown in urea and dipeptides than when grown in either ammonium or free amino acids as nitrogen sources. The level of each aminopeptidase (PAP or AAP) activity was preferentially induced by its own substrate (ProLeu or LysAla), suggesting a role in the utilization of exogenous peptides. Higher specific activities for all proteolytic enzymes were detected when using acetate as carbon source. The time course experiments carried out on urea or sarcoplasmic protein-containing media revealed an increase in all activities during transition and advanced stages of stationary phase of growth. In muscle protein extracts, the absence of low molecular mass nutrients (SPE>10 kDa) initially induced the production of PrA, PrB, and AAP activities, possibly involved in the breakdown of muscle oligopeptides.     

A contribution to solve the problem of coating properties extraction in quartz crystal microbalance applications

The problem of coating properties extraction in quartz crystal resonator (QCR) applications is one of the challenging tasks of QCR applications, not completely solved even in theoretical conditions. The present work demonstrates that the problem is determined only for a set of three parameters of the coating, which concentrate the four coating properties. The following parameters are chosen: the surface mass density m8 = p1h1, the loss tangent tan delta1 = G'1/G'1, and the magnitude of the characteristic impedance /Z1(c)/ = (p1/G1/)(1/2). An algorithm is proposed that permits, in ideal conditions, an unambiguous extraction of these parameters, starting only from the admittance spectrum of a three-layer compound resonator, obtained from the one-dimensional transmission-line model (TLM) around the resonance. The algorithm introduces three additional improvements in relation to other routines: the calculation time is drastically reduced, the problem of erroneous solutions related to relative minima in typical fitting routines is eliminated, and a systematic error analysis in the extraction of the coating properties in real practice can be carried out. The use of the proposed algorithm as a tool for studying the effects of different phenomena such as slipping or surface roughness is introduced.