Heat-sensitive Substances Research Articles

Use of microcalorimetry in monitoring stability studies. Example: vitamin A esters.

Vitamin A is very sensitive to chemical degradation caused by oxygen, light, heat, and other stress factors. If light and oxygen are excluded, the dominant degradation reaction for vitamin A derivatives is heat-induced formation of kitols, that is, dimers or higher oligomers. In this study vitamin A esters were used as model systems to evaluate microcalorimetry as a tool for monitoring the stability of heat sensitive substances. To obtain more knowledge about the model reaction, analytical investigations (supercritical fluid chromatography) were also performed. Because analytical and microcalorimetry data were consistent, a quantitative description of the kinetics and thermodynamics of the kitol formation reaction could be obtained. Aside from the academic motivation, this is important for practical purposes such as shelf life stability of vitamin A in feed, food, and pharmaceutical products. The vitamin A stability of a given sample can easily be predicted from the initial heat flow in a simple microcalorimetry experiment. Compared to conventional stability tests, this offers savings of money and time.

A novel, endogenous inhibitor of 7-ethoxyresorufin- O-deethylase activity isolated from liver cytosolic fractions of bream ( Abramis brama L.)

The cytosolic supernatant of bream ( Abramis brama L.) liver homogenates inhibits the 7-ethoxyresorufin- O-deethylase (EROD) activity of pike ( Esox lucius) microsomal fractions. The inhibitor shows no activity against 7-ethoxycoumarin- O-deethylase and benzo( a)pyrene hydroxylase indicating a high isoenzyme specificity. The inhibiting component is a heat-sensitive substance (56°C for 5′) which is not self regenerating after subsequent cooling. It can be isolated from the cytosolic fraction using two combined steps of ion exchange chromatography. The purification factor is 500-fold with a recovery rate of 70%. SDS–PAGE of the purified fractions indicate that electrophoretic purity was not achieved. However, a prominent band at about 97 kDa was present in all fractions in a close intensity–activity relationship. The molecular weight of the native form of the purified protein was determined to be 175±35 kDa using gel filtration on a Sephacryl S 300 HR column. So far the inhibitor can be characterized as a protein. It shows strong tendencies to aggregate due to lipophilic interactions. These interactions can be repressed by the addition of 1% sodium cholate. The inhibitor has an optimum activity at 25°C and pH 8.0. The inhibitor does not correspond to any of the known cytosolic, endogenous inhibitors of EROD activities in fish, including proteases, cytosolic phosphatases, kinases and resorufin reductase (e.g. DT-diaphorase), although a non-dicoumarol (10 μM)-inhibited menadione oxidoreductase activity of up to 46.7±0.4 nmol/min per mg inhibitory protein was measured. Kinetic studies using Michaelis–Menten kinetics with purified inhibitor fractions prove a non-competitive mode of inhibition. As this kind of inhibitor is not described yet it is named CERODIP (cytosolic, EROD-inhibiting protein).

Evaporator with wiped film as the reboiler of the vacuum rectifying column

Abstract Vacuum distillation and rectification of heat-sensitive substances is usually accompanied by some thermal decomposition, which can be minimized by decreasing the operating temperature and by reducing the contact time of the distilled mixture with heated surfaces. A considerable reduction of the residence time can be acheived in reboilers of the evaporator type with liquid film, which produce vapours for the vacuum rectifying column. This paper describes such a reboiler–evaporator with wiped liquid film with two evaporating surfaces. On one of them, the evaporation of the original feed takes place, on the second, the evaporation of the reflux from the column occurs. The experimental results of separation efficiency of the vacuum rectifying column with a reboiler of the type described in the laboratory scale, are presented with dependence on feed, reflux and temperature conditions in the rebolier. With suitable heating of the reflux surface it is possible to control the vapour and liquid flows in the column.

Aqueous nanodispersions prepared by a salting-out process

Cellulose acetate phthalate nanodispersions were prepared in the form of a redispersible powder by a new preparation technique based on the salting-out process between two miscible solvents. This method involved the selection of salts producing the salting-out of acetone from water. Poly(vinyl alcohol) was used as protective colloid during the particle formation step and in the finished product. For a pharmaceutical use, the advantage of this new technique is that the process does not require any surfactant or increase in temperature and thus may be useful for biopolymers or heat-sensitive substances. These nanodispersions may also be dried by lyophilization and the particles subsequently redispersed in an aqueous medium before use.

Measurement of vapor-liquid equilibria at elevated temperatures and pressures using a flow type apparatus

Vapor-liquid equilibrium data were obtained for CO 2-n-heptane, CO 2-n-decane, CO 2-trans-decalin, CO 2-tetralin, CO 2-quinoline, benzene-tetralin and benzene-quinoline systems in the temperature range from 340 to 710 K at several pressures up to 25 MPa. A flow-type apparatus was developed and used for vapor-liquid equilibrium measurements in order to reduce the residence time of heat sensitive substances at high temperatures. The operation of the present apparatus was easy and improved by employing an overflow type self-control system equipped with a back pressure regulator. The reliability of this experimental apparatus and procedure was proven since the vapor-liquid equilibrium data for the CO 2-n-heptane system were in good agreement with literature data and the vapor and liquid phase compositions were independent of the sample flow rate within the range of flow rate employed. Measured data were correlated using equations of state and mixing rules based on the corresponding state principle.

Measurement of vapor-liquid equilibria at elevated temperatures and pressures using a flow type apparatus.

A new flow-type apparatus was developed using an overflow-type liquid level self-control system and a back pressure regulator. The present apparatus makes possible vapor-liquid equilibrium measurements at high temperatures by minimizing the residence time of heat-sensitive substances. It was shown that the resulting vapor-and liquid-phase compositions were independent of the sample flow rate within the range of flow rates employed. Vapor-liquid equilibrium data were measured with this apparatus for the systems CO2-n-heptane, CO2-n-decane, CO2-teans-decalin, CO2-tetralin, CO2-quinoline, benzene-tetralin and benzene-quinoline in the temperature range from 340 to 710 K at several pressures up to 23 MPa.

Distillation of heat-sensitive substances

A new method is suggested for the quantitative determination of distillation process requirements. In this method two simultaneously occurring processes, the distillation process and the chemical reaction initiated by the heat sensitivity of one of the compounds contained in the material to be processed, are considered. The equipment is classified in relation to the thermal hazard imposed by the distillation of heat-sensitive substances. Some formulae are proposed which permit the design of the distillation process for heat-sensitive materials. Model characteristics are carried out for both flash and differential distillations.

Methylene-bis-Propionate Preservation of High-Moisture Corn

Methylene-bis-propionate (MBP) was compared to a 15% formaldehyde solution (FOR) and propionic acid (PA) as a preservative for high-moisture corn (HMC). In a field trial, MBP, FOR and PA at concentrations of .78%, 1.00% and .80% (wt preservative/wt corn), respectively, were applied to 70.4 M3 (2,000 bu) lots of freshly harvested yellow dent corn (20 to 26%) moisture). Microbiological changes were evaluated throughout 240 days of storage in concrete silos, and the performance of 25 feedlot heifers was determined on corn treated with each of the preservatives. MBP exhibited superior antifungal and antibacterial properties throughout storage, whereas FOR controlled fungi and bacteria less than 20 days. PA controlled microbial activity during most of storage but was less effective than MBP. Average daily gain (kg) and feed-to-gain ratio for the respective (MBP, FOR and PA) rations were: 1.00 and 6.78, .97 and 6.85 and 1.10 and 6.04. Laboratory experiments were conducted to determine the fat of MBP on HMC. MBP broke down to PA and formaldehyde within 9 hr after contacting the wet grain. This breakdown appears to be a hydrolytic process which is catalyzed by a heat-sensitive substance. Minimum levels of MBP preserved high-moisture corn in laboratory tests longer than mixtures of PA and FOR.

Heat sensitive factor necessary for mitosis onset in Physarum polycephalum (temperature shift/heat shock/cycloheximide/ts mutant)

Physarum synchronous plasmodia were submitted to temperature shifts during the cell cycle and the onset of mitosis was followed at both temperatures. After 22 to 31 or 32° shifts, delays in mitosis onset, dependent upon protein synthesis, were observed at 32° and found to increase as the time separating the shift from the control mitosis decreases. The modification of a general metabolic process or the inactivation of a catalytic heat sensitive substance cannot account for such a result. The proposed model postulates a substance acting in a stoichiometric way, which can occur under three structural forms: two active forms synthesized at low and high temperatures respectively and an inactive one which comes from the transformation of the low temperature active form placed at high temperature. The constant delays observed after some shifts (29 to 32°) suggest that this substance is acting through a polymeric structure which would be necessary for the mitotic process and the initiation of the following DNA synthesis.

Decomposition of cellulose in soils.

1. Cellulose decomposition in forest and orchard soils was investigated by studying the breakdown of boiled and washed cellophane in the soils and in vitro. Decomposition occurred from quick to slow in the order: orchard on clay soil, forest on clay soil, forest on sandy loam, and in the latter in the order: calcareous mull, acid mull and mor. 2. In the different forest soils which were investigated the rate of decomposition was parallel to their water capacity. It slowed down considerably when the water content of the soil decreased, especially after the wilting point was reached. 3. Of the fungi isolated from these soils, those from orchard soil — 5% to 50%Fusarium spp. — were among the fastest decomposers of cellulose. This agrees with, and may explain the high rate of decomposition in orchard soil. 4. Decomposition in pure culture is quicker than in soil. As filtersterilized soil extract checked the decomposition in pure culture, but heat-sterilized soil extract did not, an extractable but heat-sensitive substance may be one retarding factor.