Microwaves and heat in aldehyde fixation: model experiments with bovine serum albumin

Effect of Temperature and Pressure on the Stability of Protein Microbubbles

Protein microbubbles are air bubbles with a network of interacting proteins at the air-water interface. Protein microbubbles are commonly used in medical diagnostic and therapeutic research. They have also recently gained interest in the research area of food as they can be used as structural elements to control texture, allowing for the manufacture of healthier foods with increased consumer perception. For the application of microbubbles in the food industry, it is important to gain insights into their stability under food processing conditions. In this study, we tested the stability of protein microbubbles against heating and pressurization. Microbubbles could be heated to 50 °C for 2 min or pressurized to 100 kPa overpressure for 15 s without significantly affecting their stability. At higher pressures and temperatures, the microbubbles became unstable and buckled. Buckling was observed above a critical pressure and was influenced by the shell modulus. The addition of cross-linkers like glutaraldehyde and tannic acid resulted in microbubbles that were stable against all tested temperatures and overpressures, more specifically, up to 120 °C and 470 kPa, respectively. We found a relation between the storage temperatures of microbubble dispersions (4, 10, 15, and 21 °C) and a decrease in the number of microbubbles with the highest decrease at the highest storage temperature. The average rupture time of microbubbles stored at different storage temperatures followed an Arrhenius relation with an activation energy for rupture of the shell of approximately 27 kT. This strength ensures applicability of microbubbles in food processes only at moderate temperatures and storage for a moderate period of time. After the proteins in the shell are cross-linked, the microbubbles can withstand pressures and temperatures that are representative of food processes.

Microwave-treated gelatin microspheres as drug delivery system

The crosslinking process of natural macromolecules with microwave energy should have the potentiality to overcome the problems due to the toxicity of the residuals of chemical crosslinking agents and moreover of the "in vivo" biodegradation products of the chemical crosslinked macromolecule. To evaluate the effective crosslinking of the gelatin forming the microspheres, the water-soluble fraction at 37 degrees C, the water absorption capability, the free amino and free carboxylic acid groups of the gelatin were determined. The structural change in the gelatin microspheres has been detected by the porosity studies. Moreover, both the "in vitro" biodegradability and the biocompatibility of the gelatin microspheres microwave-treated after a subcutaneous injection into female albino guinea pigs were tested. As the results suggest only the gelatin microspheres microwave-treated for 10 min at an inlet temperature of 250 degrees C could have been modified by the crosslink formation among the macromolecular chains. The gelatin microspheres treated with the microwave energy were very well biodegraded as indicated both by the "in vitro" enzymatic degradation studies and mainly by the histopathological examination. This latter study has also demonstrated the biocompatibility of the gelatin microspheres crosslinked with the microwave energy. In order to evaluate the feasibility of the microwave crosslinking process for pharmaceutical applications, both the drug loading and the drug release processes were evaluated using diclofenac as drug model, either as acidic form or as sodium salt. The microspheres were swollen in aqueous solution of diclofenac sodium salt, followed by a washing procedure with cool water to maintain the sodium salt into the microspheres or with pH 1.5 HCl to induce the diclofenac precipitation. To increase the amount of diclofenac acid form in the microspheres, the procedure was repeated three times washing with pH 1.5 HCl after each swelling process. Both the X-ray diffractometry and thermal analysis investigations showed a different physical state of the two drug forms in the microspheres, i.e. the amorphous state of the sodium salt and the crystalline state of the acidic form. According to the experimental results, the drug is released from gelatin microspheres according to the drug loading and the drug solubility.

Modeling formalin fixation and antigen retrieval with bovine pancreatic RNase A II. Interrelationship of cross-linking, immunoreactivity, and heat treatment

In this study, gel electrophoresis and capture enzyme-linked immunosorbent assay were used to assess the effect of formaldehyde treatment on the structural and immunological properties of bovine pancreatic ribonuclease A (RNase A). Prolonged incubation of RNase A in a 10% formalin solution leads to the formation of extensive intra- and intermolecular cross-links. However, these formaldehyde cross-links do not completely eliminate the recognition of RNase A by a polyclonal antibody. Comparative immunotitration of monomers, dimers, and oligomers greater than pentamers isolated from formalin-treated RNase A demonstrated that reduction of immunoreactivity due to intramolecular modifications prevails over the excluded volume effect of intermolecular cross-links. The latter only becomes important for intermolecular cross-links involving four or more molecules. The restoration of RNase A immunoreactivity during heating correlates with the reversal of formaldehyde cross-links if the incubation temperature does not exceed the denaturation temperature of the formalin-treated RNase A preparation. We conclude that formaldehyde cross-links stabilize antigens against the denaturing effects of high temperature, but the reversal of these cross-links is necessary for the restoration of immunoreactivity.

Freeze-drying allows double nonradioactive ISH and antigenic labeling

Because tissue freeze-drying is an excellent way to preserve antigenic conformation, we have tested the feasibility of this technique to reveal nonradioactive in situ hybridization (ISH) of tissue mRNA. We have compared mRNA detection after different methods of tissue preservation, freeze-drying, cryosectioning, and formaldehyde or methanol fixation. Our results show that nonradioactive ISH is more sensitive for tissues preserved by freeze-drying than for other tissue preparations. We have demonstrated that freeze-drying allows combination of ISH and immunohistochemistry for simultaneous detection of mRNA and antigen because with this technique of tissue preservation ISH does not affect the sensitivity or the amount of the detected antigens. This work underscores the fact that tissue freeze-drying is an easy, convenient, and reliable technique for both ISH and immunohistochemistry and achieves excellent structural conditions for nonradioactive detection.