A transcultural study on stirred strawberry yogurt: consumer acceptability versus sensory quality with trained panel

The present work was designed in order to obtain the cut off point, to be used in a shelf life study on whole stirred strawberry yogurt. The study was simultaneously carried out in Argentina, Chile and Costa Rica, assaying the same kind of product, elaborated in each one of the countries. The sensory quality parameters obtained from trained panelists and the consumers acceptability, were correlated by using the cut off point methodology through a quality evaluation by the Karlsruhe scale. According to preliminary studies, the storage at 42 degrees C produced considerable damage on parameters such as pH, acidity (volumetric assay), viscosity and sensory quality. For each sample, the cut off point was determined. This value corresponds to the threshold score for the sensory quality, where the consumer starts to perceive negative changes in the product, when comparing with the fresh product. The rejection percentage was also calculated according to the cut off point. The cut off points and the percentage of rejection obtained by the three participating countries were similar. Data obtained from Costa Rica showed changes in color, acidity and rancidity. Argentinean yogurts developed acidity that had a negative effect on texture, appearance and residual flavors. Chilean samples presented a sensory quality that remains almost without change through the studied time. The differences of the deterioration pattern amongst the three countries, demonstrates that the products are different in formulation and elaboration process, in spite of been the same kind of yogurt. This could be explained by differences specified in the regulation of each country.     

New hydroxyproline based methacrylic polybetaines: Synthesis, pH sensitivity and catalytic activity

The synthesis of two new types of methacrylic polybetaines bearing trans-4-hydroxy-l-proline connected via its hydroxyl group is described, one with an aliphatic spacer of 6 carbon atoms and the other without any spacer. The pH sensitivity in aqueous media and the catalytic activity of the products in asymmetric aldol additions have been studied. The two polyzwitterions show an isoelectric point (IEP) close to 3. Swelling of networks prepared with the two monomers exhibit reversible pH sensitivity; the largest the pH distance from the IEP, the higher the net charge (positive or negative) and the higher the swelling. At basic pH and an ionic strength of 0.15, maximum swelling degrees of around 11 and 24 (g water/g polymer) have been found for the systems with and without spacer respectively. The polymers have been shown to be efficient catalysts for aldol reactions under homogeneous conditions in DMF but not in water.     

Synthesis and Characterization of Nanostructured Cerium Dioxide Thin Films Deposited by Ultrasonic Spray Pyrolysis

Nanostructured thin films of cerium dioxide have been prepared on single-crystalline silicon substrates by ultrasonic spray pyrolysis using cerium acetylacetonate as a metal–organic precursor dissolved in anhydrous methanol and acetic acid as an additive. The morphology, structure, optical index, and electrical properties were studied by X-ray diffraction, scanning electron microscopy, atomic force microscopy, ellipsometry, and impedance spectroscopy. The use of additives is very important to obtain crack-free films. The substrate temperature and flow rate was optimized for obtaining smooth ( R _a<0.4 nm), dense ( n >2), and homogeneous nanocrystalline films with grain sizes as small as 10 nm. The influence of thermal annealing on the structural properties of films was studied. The low activation energy calculated for total conductivity (0.133 eV) is attributed to the nanometric size of the grains.     

Quality Changes and Tocopherols and γ-Orizanol Concentrations in Rice Bran Oil During the Refining Process

The quality changes and the concentrations of tocopherols and γ-oryzanol, during successive steps of rice bran oil refining (RBO), were studied. For this purpose, samples of crude, degummed, neutralized, bleached, dewaxed and deodorized RBO were taken from an industrial plant and analyzed. The moisture, pH, acidity, peroxide value and unsaponifiable matter, were determined. The fatty acid composition was evaluated by GC, and the concentrations of tocopherols and γ-oryzanol were determined using HPLC with fluorescence and UV–Vis detection, respectively. To identify γ-oryzanol components, fractions of the HPLC eluant were collected and analyzed using mass spectrometry. Oil refining reduced the peroxide value and acidity to 1 and 3% of the values obtained in crude RBO, respectively. The fatty acid composition were not significantly altered during refining. The concentrations of the tocopherols in RBO followed the order α > (β + γ) > δ. The total concentration of tocopherols was 26 mg/100 g, and remained practically unaltered during refining. Up to nine components were distinguished in γ-oryzanol. After collecting the elution fractions, up to six components were identified by electrospray mass spectrometry. Refining reduced the total concentration of γ-oryzanol to 2% of its initial value.     

Analysis of bacterial community during the fermentation of pulque, a traditional Mexican alcoholic beverage, using a polyphasic approach

In this study, the characterization of the bacterial community present during the fermentation of pulque, a traditional Mexican alcoholic beverage from maguey (Agave), was determined for the first time by a polyphasic approach in which both culture and non-culture dependent methods were utilized. The work included the isolation of lactic acid bacteria (LAB), aerobic mesophiles, and 16S rDNA clone libraries from total DNA extracted from the maguey sap (aguamiel) used as substrate, after inoculation with a sample of previously produced pulque and followed by 6-h fermentation. Microbiological diversity results were correlated with fermentation process parameters such as sucrose, glucose, fructose and fermentation product concentrations. In addition, medium rheological behavior analysis and scanning electron microscopy in aguamiel and during pulque fermentation were also performed. Our results showed that both culture and non-culture dependent approaches allowed the detection of several new and previously reported species within the alpha-, gamma-Proteobacteria and Firmicutes. Bacteria diversity in aguamiel was composed by the heterofermentative Leuconostoc citreum, L. mesenteroides, L. kimchi, the gamma-Proteobacteria Erwinia rhapontici, Enterobacter spp. and Acinetobacter radioresistens. Inoculation with previously fermented pulque incorporated to the system microbiota, homofermentative lactobacilli related to Lactobacillus acidophilus, several alpha-Proteobacteria such as Zymomonas mobilis and Acetobacter malorum, other gamma-Proteobacteria and an important amount of yeasts, creating a starting metabolic diversity composed by homofermentative and heterofermentative LAB, acetic and ethanol producing microorganisms. At the end of the fermentation process, the bacterial diversity was mainly composed by the homofermentative Lactobacillus acidophilus, the heterofermentative L. mesenteroides, Lactococcus lactis subsp. lactis and the alpha-Proteobacteria A. malorum. After a 6-h fermentation, 83.27% of total sugars detected after inoculation were consumed (228.4 mM hexose equivalents) and a carbon (C) recovery of 66.18% in fermentation products was estimated. They were produced 284.4 mM C as ethanol, 71.5 mM C as acetic acid and 19 mM C as lactic acid, demonstrating the presence of homo- and heterofermentative, acetic and alcoholic metabolisms in the final product. It was also found, after hydrolysis, that the exopolysaccharide produced during the fermentation was mainly composed by fructose residues, probably inulin or levan.     

Short-term maternal psychological stress in the post-conception period in ewes affects fetal growth and gestation length

Fetal development can be influenced by maternal environment in the peri-conceptional period. This study investigated the effect of maternal feed intake and psychological stress within the first 6 days after conception on embryo development and fetal growth. Superovulated ewes (n=40) were artificially inseminated with semen from one ram. Ewes were then divided into four groups (n=10): group 1 (control) was fed at maintenance level, group 2 (high) at 2x maintenance, and group 3 (low) at 0.5x maintenance on days 2-6 after conception. Group 4 (stress) was fed at maintenance level and then an intense physical and psychological stress challenge was applied for 1 h only on days 2 and 3 after conception. Embryos were recovered at day 6. A total of 113 transferable grade embryos were transferred singly into synchronized untreated recipients, while the remaining embryos (n=165) were fixed and stained for cell counts. Post-conception maternal stress or feed intake did not alter the cell count or grade of day 6 embryos. Fetuses from the stress group had longer crown-rump lengths at day 30 and longer femur length at day 58. Fetuses from the stressed and high feed groups had greater abdominal circumferences at day 85. Subsequent birth weights were not significantly different. Ewes carrying lambs from the stress treatment had shorter gestation lengths. These results show that short-term perturbations of the post-conception maternal environment have measurable effects on fetal development and gestation length.     

Minimization of entropy generation by asymmetric convective cooling

The uniform internal heating of a solid slab and the viscous flow between two parallel walls, are used to illustrate the possibility of minimizing the global entropy generation rate by cooling the external surfaces convectively in an asymmetric way. The known analytic expressions for the temperature field, in the first case, and the velocity and temperature fields, in the second case, are used to calculate the global entropy generation rate explicitly. In dimensionless terms, this function depends on the dimensionless ambient temperature and convective heat transfer coefficients (Biot numbers) of each surface which, in general, are not assumed to be the same. When the Biot numbers for each surface are equal, the entropy generation rate shows a monotonic increase. However, when the Biot numbers are different this function displays a minimum for specific cooling conditions.     

Optimized reduction of spur tones in fractional frequency synthesizers

In this article the contribution of the digital \Upsigma\Updelta\Upsigma\Updelta modulator in fractional frequency synthesizers is explored. Due to the circuit’s non linear behavior, the spur tones generated by the digital \Upsigma\Updelta\Upsigma\Updelta modulation degrade the synthesizer’s phase noise even in regions where the charge pump noise is dominant. A new method to dither digital MASH \Upsigma\Updelta\Upsigma\Updelta modulators for fractional frequency synthesizers is proposed. The method barely increases the circuit complexity and has the same performance as more cumbersome architectures. Also, a new design consideration to linearize the voltage control oscillator is proposed. Experimental results are obtained in an on-chip fractional synthesizer manufactured in CMOS technology.     

Pesticide residue analysis by RPLC–GC in lycopene and other carotenoids obtained from tomatoes by supercritical fluid extraction

In the present work supercritical fluid extraction (SFE) is used to obtain carotenoids from tomatoes which were previously treated with pesticides. A procedure to determine pesticides in the extracts by RPLC–GC using the TOTAD interface is proposed. Tomatoes growing in an experimental plot were treated with different pesticides, and after picking, pesticide residues in the tomatoes were analysed and the tomatoes were used to obtain carotenoids by SFE. The carotenoid extracts were analysed using the above mentioned method. The data obtained indicated that trace amounts of the pesticides were extracted together with the carotenoids by SFE. The concentration of pesticide obtained in the second separation vessel was higher than that obtained in the first separation vessel. We conclude that only pesticide-free tomatoes should be used to extract carotenoids for applications as a nutritional supplement or in the cosmetic and pharmaceutical industries.