Impact of vacuum-induced surface freezing on inter- and intra-vial heterogeneity

This paper aims to study the impact of freezing on both within-batch (inter-vial) and within- product (intra-vial) heterogeneity. This analysis has been carried out using two freezing protocols, the conventional shelf-ramped method and the Vacuum Induced Surface Freezing, and placebo formulations containing both crystallizing (mannitol) and amorphous (lactose and sucrose) excipients. The freezing conditions (i.e., the temperature of freezing, the temperature and time of the equilibration phase, and the filling volume) were found to have a dramatic impact on both the within-batch and the within-product homogeneity. Overall, we observed that the control of freezing can effectively minimize the variability in product characteristics, and moisture content, within the same batch. In addition to more uniform production, the control of freezing was found to be fundamental to achieve a more uniform product than that produced by the shelf-ramped freezing method. The influence of the freezing protocol on the crystallization process of mannitol was also investigated, showing that the temperature of freezing plays a key role in the formation of the mannitol polymorphs

A comparison of freezing-damage during isochoric and isobaric freezing of the potato.

BACKGROUND:Freezing is commonly used for food preservation. It is usually done under constant atmospheric pressure (isobaric). While extending the life of the produce, isobaric freezing has detrimental effects. It causes loss of food weight and changes in food quality. Using thermodynamic analysis, we have developed a theoretical model of the process of freezing in a constant volume system (isochoric). The mathematical model suggests that the detrimental effects associated with isobaric freezing may be reduced in an isochoric freezing system. To explore this hypothesis, we performed a preliminary study on the isochoric freezing of a produce with which our group has experience, the potato. METHOD:Experiments were performed in an isochoric freezing device we designed. The device is robust and has no moving parts. For comparison, we used a geometrically identical isobaric freezing device. Following freezing and thawing, the samples were weighed, examined with colorimetry, and examined with microscopy. RESULTS:It was found that potatoes frozen to -5 °C in an isochoric system experienced no weight loss and limited enzymatic browning. In contrast the -5 °C isobaric frozen potato experienced substantial weight loss and substantial enzymatic browning. Microscopic analysis shows that the structural integrity of the potato is maintained after freezing in the isochoric system and impaired after freezing in the isobaric system. DISCUSSION:Tissue damage during isobaric freezing is caused by the increase in extracellular osmolality and the mechanical damage by ice crystals. Our thermodynamic analysis predicts that during isochoric freezing the intracellular osmolality remains comparable to the extracellular osmolality and that isochoric systems can be designed to eliminate the mechanical damage by ice. The results of this preliminary study seem to confirm the theoretical predictions. CONCLUSION:This is a preliminary exploratory study on isochoric freezing of food. We have shown that the quality of a food product preserved by isochoric freezing is better than the quality of food preserved to the same temperature in isobaric conditions. Obviously, more extensive research remains to be done to extend this study to lower freezing temperatures and other food items

Effects of Freezing on Soil Temperature, Freezing Front Propagation and Moisture Redistribution in Peat: Laboratory Investigations

There are not many studies that report water movement in freezing peat. Soil column studies under controlled laboratory settings can help isolate and understand the effects of different factors controlling freezing of the active layer in organic covered permafrost terrain. In this study, four peat Mesocosms were subjected to temperature gradients by bringing the Mesocosm tops in contact with subzero air temperature while maintaining a continuously frozen layer at the bottom (proxy permafrost). Soil water movement towards the freezing front (from warmer to colder regions) was inferred from soil freezing curves, liquid water content time series and from the total water content of frozen core samples collected at the end of freezing cycle. A substantial amount of water, enough to raise the upper surface of frozen saturated soil within 15 cm of the soil surface at the end of freezing period appeared to have moved upwards during freezing. Diffusion under moisture gradients and effects of temperature on soil matric potential, at least in the initial period, appear to drive such movement as seen from analysis of freezing curves. Freezing front (separation front between soil zones containing and free of ice) propagation is controlled by latent heat for a long time during freezing. A simple conceptual model describing freezing of an organic active layer initially resembling a variable moisture landscape is proposed based upon the results of this study. The results of this study will help in understanding, and ultimately forecasting, the hydrologic response of wetland-dominated terrain underlain by discontinuous permafrost

The Study of Thermal Reversibility of the Freezing-defrost Process of Browned Onion

The features and dynamics of the freezing-defrost processes of the studied sample of browned onion were established and studied. At the research it was revealed, that at freezing temperature –20 °С the value of maximal freezing speed does not change.The process of defrost of browned onion was carried out using calorimeter with the reverse connection on temperature and PID-regulator, on the temperature curve of its freezing. It was determined, that the process of defrost of the studied sample needs more heat that is educed at freezing. The modes of stepped defrost that testify to the possibility of thermal reversibility of freezing process were experimentally established.The direct dependence of educed and consumed heat quantity on the mode of thermal processing of studied sample was revealed. The more moisture was eliminated from the food product, the less heat must be consumed for defrost. The analogous dependence is typical also for the freezing process.The received data can be used for determination of the rational modes of freezing and defrost of the browned onion

To freeze or not to: Quantum correlations under local decoherence

We provide necessary and sufficient conditions for freezing of quantum correlations as measured by quantum discord and quantum work deficit in the case of bipartite as well as multipartite states subjected to local noisy channels. We recognize that inhomogeneity of the magnetizations of the shared quantum states plays an important role in the freezing phenomena. We show that the frozen value of the quantum correlation and the time interval for freezing follow a complementarity relation. For states which do not exhibit "exact" freezing, but can be frozen "effectively", by having a very slow decay rate with suitable tuning of the state parameters, we introduce an index -- the freezing index -- to quantify the goodness of freezing. We find that the freezing index can be used to detect quantum phase transitions and discuss the corresponding scaling behavior.Comment: 14 pages, 9 figures, close to published version, title changed by Phys. Rev. A. to 'Freezing of quantum correlations under local decoherence

Cascade Freezing of Supercooled Water Droplet Collectives

Surface icing affects the safety and performance of numerous processes in technology. Previous studies mostly investigated freezing of individual droplets. The interaction among multiple droplets during freezing is investigated less, especially on nanotextured icephobic surfaces, despite its practical importance as water droplets never appear in isolation, but in groups. Here we show that freezing of a supercooled droplet leads to spontaneous self-heating and induces strong vaporization. The resulting, rapidly propagating vapor front causes immediate cascading freezing of neighboring supercooled droplets upon reaching them. We put forth the explanation that, as the vapor approaches cold neighboring droplets, it can lead to local supersaturation and formation of airborne microscopic ice crystals, which act as freezing nucleation sites. The sequential triggering and propagation of this mechanism results in the rapid freezing of an entire droplet ensemble resulting in ice coverage of the nanotextured surface. Although cascade freezing is observed in a low-pressure environment, it introduces an unexpected pathway of freezing propagation that can be crucial for the performance of rationally designed icephobic surfaces