Mechanical spectra and calorimetric evaluation of gelatin–xanthan gum systems with high levels of co-solutes in the glassy state

Mechanical properties of gelatin–xanthan gum (XG) mixtures with high levels of co-solutes were examined by dynamic mechanical analysis (DMA). The mechanical spectra of the samples were modeled according to the Williams–Landel–Ferry (WLF) equation/free-volume theory, which requires an entropic lightly cross-linked network. For the α dispersion, E′ and E′′ superposed with the horizontal shift factor a_T, which was temperature-dependent according to the WLF equation; no other secondary dispersion mechanism was detected. The addition of XG to gelatin networks with high levels of co-solutes changed the glass transition temperature (T_g) and kinetics of glass transition and glassy states. In the glassy state, the WLF equation was unable to follow progress in the mechanical properties, which were better described by the Andrade equation. The calorimetric measurements of the gelatin–XG systems were made using a modulated temperature differential scanning calorimetry (MTDSC) to improve the determination of T_g. The samples were exposed to two cooling and heating cycles to provide a controlled recent thermal history in the temperature range of 40 °C to −70 °C. The T_g values of the samples were determined from the second heating cycle in the reversing heat signal. The calorimetric T_g values increased with increasing glucose syrup:sucrose ratio due to increased crosslinking, whereas mechanical T_g decreased with increased XG content due to network formation.     

Rheological evaluation of gelatin–xanthan gum system with high levels of co-solutes in the rubber-to-glass transition region

Effects of moisture content, xanthan gum (XG) addition, and glucose syrup (GS):sucrose ratio on the gelation of gelatin-XG systems with high levels of co-solutes were investigated in the rubbery and the glass transition regions. Frequency sweep tests were performed between 0.1 and 100 rad and the storage (G′) and loss (G″) moduli of the system were measured in the temperature range of 60 to −15 °C. The onset of glass transition region increased with decreasing moisture content. The time–temperature superposition yielded master curves of G′ and G″ as a function of timescale of measurement. G″ and G″ were superimposed with the horizontal shift factor a_T, which was temperature dependent according to the Williams–Landel–Ferry (WLF) equation. Glass transition temperature (T_g) of the samples were determined by dynamic mechanical analysis (DMA) from the peak of tan δ. T_g decreased with XG addition. The energy of vitrification of samples with XG increased compared to samples containing only gelatin. Relaxation spectra of the samples were calculated from rheological measurements using the first and second approximations. The Rouse theory was more closely followed with the second approximation.     

Temperature rises during tooth bleaching with different light-curing units

The aim of this study was to evaluate the influence of three different light-curing units on the temperature rise induced in the pulpal cavity, when bleached with 35% hydrogen peroxide (HP). Forty extracted maxillary central incisors were randomly divided into four groups according to photoactivation procedure (n = 10). Whiteness HP (WHP) bleaching agent which contains 35% HP bleach was placed on the facial tooth surface and no photoactivation device was used (control); an blue light-emitting diode (LED, 40 s), a diode laser (4 W, Continous mode, 20 s), and Nd:YAG laser (4 W, 60 Hz frequency, 20 s). Temperature rise in the pulpal chamber was measured with a J-type thermocouple wire that was connected to a data logger before and immediately after each 20–40 s application. One tooth of each group was selected for scanning electron microscope analysis. Data were analyzed using one-way ANOVA followed by the Games Howell post hoc test at a preset α of 0.05. One-way ANOVA revealed that there was a significant difference among the light-curing units (p < 0.05) and between control group and light-curing units (p < 0.05). The Nd:YAG induced significantly, which resulted in higher temperature increase than other light-curing units (10.7 °C). The LED unit produced the lowest temperature changes (3.2 °C) among the light-curing units. The presence of the bleaching gel did not cause a temperature increase in control group (0 °C). The results suggested that using light-curing units caused temperature changes in the intrapulpal cavity during tooth bleaching. The use of LED will be more safer for pulpal health when assisted with WHP bleaching gel.     

Hydrogenation of olefins catalyzed by Pd(II) complexes containing a perfluoroalkylated S,O-chelating ligand in supercritical CO2 and organic solvents

Pd(II) complexes with the tridentate ligands heptadecafluorodecyl-thiophene-2-carboxylate (L₁ = SOSR_f1, R_f1 = (CH₂)₂(CF₂)₇CF₃) and heptadecafluorononil thiophene-2-carboxylate (L₂ = SOOR_f2, R_f2 = (CH₂)(CF₂)₇CF₃) have been synthesized, and their catalytic activities for the homogeneous hydrogenation of olefins have been studied with molecular hydrogen in scCO₂ and organic solvents. Both perfluoroalkylated-heterocycle ligands potentially have three donor atom sets (SOO/SOS). Depending on the soft-hard interaction between palladium and the donor atoms of the ligands, different activities for the Pd(II) complexes were observed. The nature of the solvent had an effect upon the hydrogenation of olefins. The effects of temperature and H₂ pressure on the hydrogenation of styrene were also investigated.     

Antioxidant activity and total phenolic,organic acid and sugar content in commercial pomegranate juices

Pomegranate fruit and pomegranate juices (PJs) have taken great attention for their health benefits in the last years. The purpose of this study is to analyse the antioxidant activities, along with the organic acid and sugar contents of pomegranate juices sold in the Turkish markets. In the present study, we evaluated total phenolics (TPs), free radical scavenging capacity by 2,2-diphenyl-1-picrylhydrazyl (DPPH), and ferric reducing capacity of seven commercial PJs. Organic acid and sugar contents of juices were determined by capillary zone electrophoresis. The results showed that commercial pomegranate juices had markedly high total phenolic contents and antioxidant capacity. Fructose (F) and glucose (G) were found as the major sugars. The major acids were citric and malic. From the F/G ratio, organic acid profiles, TPs, and antioxidant capacity values, a possible adulteration was detected in one of the juices.     

Effects of using combined essential oils on quality parameters of bio‐yogurt

Present study aims to develop a new type of probiotic yogurt with ginger and chamomile essential oils (EOs) at therapeutic levels (0.2 and 0.4%) by evaluating its some physical, chemical, microbiological and sensory characteristics. Probiotic types of yogurt samples and those with 0.4% ginger EO gave the largest counts of viable probiotic bacteria in the rates of 8.32 cfu/g and 8.01 cfu/g, respectively. It gave larger syneresis rate (8.64 mL/25 g) on the first day than the rest of the samples while C1 (only probiotic strain with direct vat set starter culture) sample represented the lowest rate (5.9 mL/25 g) on day 21. Among the samples with various contents, C2 (inoculated probiotic strain with 0.2% essential oil ginger) and C3 (inoculated probiotic strain with 0.4% essential oil ginger) were found to be organoleptically the most acceptable with close scores to that of control.

Practical applications

Antibacterial and antioxidant activities of essential oils have received considerable attention in food preservation. During bio‐yogurt storage, the edible film incorporating ginger and chamomile essential oils showed reducing effect on the microbial growth and extended the shelf‐life of samples.     

A review on traditional Turkish fermented non-alcoholic beverages: Microbiota,fermentation process and quality characteristics

Shalgam juice, hardaliye, boza, ayran (yoghurt drink) and kefir are the most known traditional Turkish fermented non-alcoholic beverages. The first three are obtained from vegetables, fruits and cereals, and the last two ones are made of milk. Shalgam juice, hardaliye and ayran are produced by lactic acid fermentation. Their microbiota is mainly composed of lactic acid bacteria (LAB). Lactobacillus plantarum, Lactobacillus brevis and Lactobacillus paracasei subsp. paracasei in shalgam fermentation and L. paracasei subsp. paracasei and Lactobacillus casei subsp. pseudoplantarum in hardaliye fermentation are predominant. Ayran is traditionally prepared by mixing yoghurt with water and salt. Yoghurt starter cultures are used in industrial ayran production. On the other hand, both alcohol and lactic acid fermentation occur in boza and kefir. Boza is prepared by using a mixture of maize, wheat and rice or their flours and water. Generally previously produced boza or sourdough/yoghurt are used as starter culture which is rich in Lactobacillus spp. and yeasts. Kefir is prepared by inoculation of raw milk with kefir grains which consists of different species of yeasts, LAB, acetic acid bacteria in a protein and polysaccharide matrix. The microbiota of boza and kefir is affected from raw materials, the origin and the production methods.     

Performance characterization of a microwave transistor subject to the noise and matching requirements

In this paper, the gain G_T of a microwave transistor is expressed analytically in terms of the mismatchings (V_in ≥ 1, V_out ≥ 1) at the ports, noise figure F ≥ F_min and the [z]‐parameter and noise parameters. Firstly, because the input termination Z_S determines the noise F ≥ F_min, thus the input termination Z_S is pre‐determined to lie on the tangent constant noise and available gain circles so that the maximum power delivery is ensured for the given noise. Then, a design configuration is constructed in the input impedance Z_in‐ plane covering the gain and the required input and output mismatch circles within the Unconditionally Stable Working Area for the predetermined input termination Z_S. Finally, the compatible (F ≥ F_min, G_T, V_in ≥ 1, V_out ≥ 1) quadrates for either required or optimum (V_in ≥ 1, V_out ≥ 1) couples are obtained with their (Z_S, Z_L) couples from the analysis of the design configuration. Furthermore, a case study is also presented for the full flexible performance characterization of a selected microwave transistor. It can be concluded that the near future microwave transistor is expected to be identified by performance data base built by its compatible (F ≥ F_min, G_T, V_in ≥ 1, V_out ≥ 1) quadrates and the (Z_S, Z_L) terminations within the device operation domain to overview all the possible low‐noise amplifier designs using the full device capacity. Copyright © 2015 John Wiley & Sons, Ltd.