Vibration-induced particle formation during yogurt fermentation—Effect of frequency and amplitude

Machinery such as pumps used for the commercial production of fermented milk products cause vibrations that can spread to the fermentation tanks. During fermentation, such vibrations can disturb the gelation of milk proteins by causing texture defects including lumpiness and syneresis. To study the effect of vibrations on yogurt structure systematically, an experimental setup was developed consisting of a vibration exciter to generate defined vibrational states and accelerometers for monitoring. During the fermentation of skim milk, vibrations (frequency sweep: 25 to 1,005 Hz) were introduced at different pH (5.7 to 5.1, step width 0.1 units) for 200 s. Physical properties of set gels (syneresis, firmness) and resultant stirred yogurts (visible particles, rheology, laser diffraction) were analyzed. Vibrational treatments at pH 5.5 to 5.2 increased syneresis, gel firmness, and the number of large particles (d > 0.9 mm); hence, this period was considered critical. The particle number increased from 34 ± 5 to 242 ± 16 particles per 100 g of yogurt due to vibrations at pH 5.4. In further experiments, yogurts were excited with fixed frequencies (30, 300, and 1,000 Hz). All treatments increased syneresis, firmness, and particle formation. As the strongest effect was observed by applying 30 Hz, the amplitude was set to vibration accelerations of a = 5, 10, 15, 20, and 25 m/s² in the final experiments. The number of large particles was increased due to each treatment and a positive correlation with the amplitude was found. We concluded that vibrations during gelation increase the collision probability of aggregating milk proteins, resulting in a compressed set gel with syneresis. Resultant stirred yogurts exhibit large particles with a compact structure leading to a reduced water-holding capacity and product viscosity.     

Environmental factors for phage-induced fermentation problems: replication and adsorption of the Lactococcus lactis phage P008 as influenced by temperature and pH

The lactococcal phage P008 was investigated for its growth characteristics under certain environmental conditions. Phage growth was characterized by the latency period, the average burst size (determined in one-step growth experiments) and by the percentage of adsorption to the host cells after 1, 5, 10 and 15 min (determined in modified one-step growth experiments). The incubation conditions studied were temperatures from 20 to 40 degrees C and pH values of 4.8 and 6.4. The growth medium was ultrafiltration permeate of skim milk, which forms the water phase of milk. Both, the temperature and the pH influenced the growth parameters: Increased temperature as well as low pH led to a faster latency along with a higher average burst size. The percentage of adsorption was at maximum when the standard conditions of 30 degrees C and pH 6.4 were applied. Below pH 5, adsorption was reduced to below 10%. A decrease of temperature slightly reduced phage multiplication. Data were incorporated into a model to simulate phage multiplication under certain conditions, taking the percentage adsorption into account. The cell destruction of the host culture was calculated accordingly. The simulation (extrapolation) was validated by experimental growth curves of phages and phage-infected host cultures.     

Production of cloned horse foals using roscovitine-treated donor cells and activation with sperm extract and/or ionomycin

We evaluated the effect of different activation treatments on the production of blastocysts and foals by nuclear transfer. Donor cells were prepared using roscovitine treatment, which has previously been associated with increased production of viable offspring. All activation treatments were followed by culture in 6-dimethylaminopurine (6-DMAP) for 4 h. In experiment 1, blastocyst production after activation by injection of sperm extract followed by treatment with ionomycin was significantly higher than that for activation with a serial treatment of ionomycin, 6-DMAP, and ionomycin (12.5 vs 2.8%; P < 0.05) and tended to be higher than that for injection of sperm extract alone (3.4%; P = 0.07). In experiment 2, there were no significant differences in blastocyst development among treatments with ionomycin once or twice, sperm extract then ionomycin, or ionomycin then sperm extract (range 4.6-7.3%). Overall, transfer of 26 blastocysts resulted in 16 pregnancies (62%) and 9 live foals (35% of transferred embryos). Treatment with sperm extract followed by ionomycin produced a live foal rate per embryo transferred of 5/10 (50%). One foal died of pneumonia 48 h post partum and one foal died at 1 week of age after complications during induction of anesthesia; the remaining seven foals are currently 10-14 months of age.     

Influence of the suspension media on the thermal treatment of mesophilic lactococcal bacteriophages

The thermal resistances of the Lactococcus lactis phages P008 (a heat-sensitive wide-spread phage) and P680 (a heat-resistant phage) suspended in milk and in solutions supplemented with milk components were studied to elucidate the protective role of milk on phage inactivation. For both phages a decrease of inactivation was observed in casein solution. Furthermore, the inactivation kinetics of the phages in whey, in whey cream (3.5%, 20%, 30% fat) and in whey protein concentrate (0.7%, 5%, 10% protein) were tested. The inactivation experiments in whey cream and in whey protein concentrate having different concentrations of fat and protein revealed that fat had no influence on the inactivation, while, in contrast, the presence of protein had a protective effect.     

The attitudes of research chemists.

Principal component analysis of questionnaire data from roughly ? of the nation's PhD graduates in chemistry in 1960-1961 isolated 3 basic attitude patterns: (a) attitudes valuing freedom and "pure science"; (b) materialistic attitudes accepting business values, possibly at the expense of science values; and (c) attitudes which see little conflict between industry and science values. New PhD's with high pure science attitudes tended to enter academic employment; others to enter industry. For an independent sample of 286 industrial chemists, both the orientation to "applied science" and the materialistic orientation were stronger for chemists with high number of years experience than for recent hires. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sorption of benzenesulfonates by weak base anion exchange resins

Weak base phenol formaldehyde anion exchange resins were found to have an excellent capacity for removing the anionic organic species benzenesulfonate (BS), p-toluenesulfonate (PTS) and dodecylbenzenesulfonate (DBS) from pH 2 and 4 solutions. The capacity for DBS was generally greater than that of activated carbon and significantly greater than that of a polystyrene-divinylbenzene resin with no ion exchange functional groups. The maximum capacity of the weak base resins appeared to be limited by the exchange capacity of the resin. The mechanism of removal was strongly indicated as being either ion exchange at the amine functional groups in the acid form, or uptake of a proton by the amine groups in the free base form with the organic anion as the associated counter ion. Increasing concentrations of Cl⁻ decreased the amount of organic anion that could be sorbed.The swelling of one of the resins, Duolite A-7, also had a marked effect on its sorption capacity. The pores of the acid chloride or acid organic anion form of the resin were apparently larger than those of the free base form; thus, as conversion of the resin to the acid form took place, a greater amount of uptake was observed. The effect of swelling on the capacity of Duolite S-37 was much less, apparently owing to its larger pore structure, but its capacity for DBS at low pH was lower than that for A-7 because of its lower nitrogen content. Also, BS and DBS were easily removed from the weak base resins by washing them with NaOH. Four bed volumes of 1 m NaOH gave essentially complete regeneration of BS saturated A-7.     

Protonation patterns in tetracycline:tet repressor recognition: simulations and experiments

Resistance to the antibiotic tetracycline (Tc) is regulated by its binding as a Tc:Mg2+ complex to the Tet Repressor protein (TetR). Tc:TetR recognition is a complex problem, with the protein and ligand each having several possible conformations and protonation states, which are difficult to elucidate by experiment alone. We used a combination of free-energy simulations and crystallographic analysis to investigate the electrostatic interactions between protein and ligand and the possible role of induced fit in Tc binding. Tc in solution was described quantum mechanically, while Tc:TetR interactions were described by a recent, high-quality molecular-mechanics model. The orientations of the amide and imidazole groups were determined experimentally by a careful analysis of Debye-Waller factors in alternate crystallographic models. The agreement with experiment for these orientations suggested that the simulations and their more detailed, thermodynamic predictions were reliable. We found that the ligand prefers an extended, zwitterionic state both in solution and in complexation with the protein. Tc is thus preorganized for binding, while the protein combines lock-and-key behavior for regions close to the ligand's amide, enolate, and ammonium groups, with an induced fit for regions close to the Mg2+ ion. These insights and the modeling techniques employed should be of interest for engineering improved TetR ligands and improved TetR proteins for gene regulation, as well as for drug design.     

Sterilization of heparinized Cuprophan hemodialysis membranes

The effects of sterilization of dry heparinized Cuprophan hemodialysis membranes by means of ethylene oxide (EtO) exposure, gamma irradiation, or steam on the anticoagulant activity and chemical characteristics of immobilized heparin and the permeability of the membrane were investigated. Sterilization did not result in a release of heparin or heparin fragments from heparinized Cuprophan. Sterilization of heparinized Cuprophan by means of EtO exposure and gamma irradiation induced a slight, insignificant decrease of the anticoagulant activity. In contrast, steam-sterilized heparinized Cuprophan showed a higher anticoagulant activity than unsterilized heparinized Cuprophan, which was most likely caused by cleavage of some of the covalent bonds between heparin and Cupropha. The effects of sterilization on the permeability of unmodified Cuprophan and heparinized Cuprophan were compared. The permeability of unmodified Cuprophan for vitamin B₁₂ (Vit B₁₂) and sulfobromophthalein (SBP) was reduced by 20–35% after EtO exposure and gamma irradiation and was reduced by 90–95% after steam sterilization. The water permeability of unmodified Cuprophan remained the same after EtO exposure and gamma irradiation but also dramatically reduced after steam sterilization. These reductions were ascribed to the collapse of pores of the membrane. The permeability of heparinized Cuprophan was not affected by EtO exposure and gamma irradiation but dramatically reduced after steam sterilization, although to a lesser extent than in the case of unmodified Cuprophan. Apparently, the presence of immobilized heparin (partially) prevented the collapse of pores during sterilization. Gamma irradiation was recommended as the preferred method of sterilization for heparinized Cuprophan.     

Invasive pulmonary aspergillosis due to Aspergillus terreus: 12-year experience and review of the literature

A 12-year retrospective analysis was done to identify and evaluate in detail cases of invasive pulmonary aspergillosis (IPA) caused by Aspergillus terreus. We identified 13 A. terreus infections among 133 total cases of confirmed invasive aspergillosis; 11 were IPA and 2 were primary peritoneal infections. Of the 11 patients with IPA, 7 developed neutropenia during hospitalization, and the remaining four were receiving immunosuppressive agents. Ten patients with IPA died; one liver transplantation patient without neutropenia survived after treatment with amphotericin B, itraconazole, and a pulmonary lobectomy. Six patients developed disseminated disease, with the heart the most common extrapulmonary site identified (four patients). These cases demonstrate that IPA caused by A. terreus rapidly progresses in immunocompromised patients receiving amphotericin B and illustrate the need for sensitive diagnostic tests and more effective antifungal agents.