Inactivation mechanisms of lactic acid starter cultures preserved by drying processes

The preservation of lactic acid starter cultures by drying are of increased interest. A further improvement of cell viability is, however, still needed, and the insight into inactivation mechanisms of the cells is a prerequisite. In this present work, we review the inactivation mechanisms of lactic acid starter cultures during drying which are not yet completely understood. Inactivation is not only induced by dehydration inactivation but also by thermal- and cryo-injuries depending on the drying processes employed. The cell membrane has been reported as a major site of damage during drying or rehydration where transitions of membrane phases occur. Some drying processes, such as freeze drying or spray drying, involve subzero or very high temperatures. These physical conditions pose additional stresses to cells during the drying processes. Injuries of cells subjected to freezing temperatures may be due to the high electrolyte concentration (solution effect) or intracellular ice formation, depending on the cooling rate. High temperatures affect most essential cellular components. It is difficult to identify a critical component, although ribosomal functionality is speculated as the primary reason. The activation during storage is mainly due to membrane lipid oxidation, while the storage conditions such as temperature moisture content of the dried starter cultures are important factors.     

Corticular photosynthesis drives bark water uptake to refill embolized vessels in dehydrated branches of Salix matsudana

It is well known that xylem embolism can be repaired by bark water uptake and that the sugar required for embolism refilling can be provided by corticular photosynthesis. However, the relationship between corticular photosynthesis and embolism repair by bark water uptake is still poorly understood. In this study, the role of corticular photosynthesis in embolism repair was assessed using Salix matsudana branch segments dehydrated to ?1.9 MPa (P₅₀, water potential at 50% loss of conductivity). The results indicated that corticular photosynthesis significantly promoted water uptake and nonstructural carbohydrate (NSC) accumulation in the bark and xylem during soaking, thereby effectively enhancing the refilling of the embolized vessels and the recovery of hydraulic conductivity. Furthermore, the influence of the extent of dehydration on the embolism refilling enhanced by corticular photosynthesis was investigated. The enhanced refilling effects were much higher in the mildly dehydrated (?1.5 MPa) and moderately dehydrated (?1.9 MPa) branch segments than in the severely dehydrated (?2.2 MPa) branch segments. This study provides evidence that corticular photosynthesis plays a crucial role in xylem embolism repair by bark water uptake for mildly and moderately dehydrated branches.     

Broadband spectral verification of optical clearing reversibility in lung tissue

The increase of tissue transparency through sequential optical immersion clearing treatments and treatment reversibility have high interest for clinical applications. To evaluate the clearing reversibility in a broad spectral range and the magnitude of the transparency created by a second treatment, the present study consisted on measuring the spectral collimated transmittance of lung tissues during a sequence of two treatments with electronic cigarette (e-cig) fluid, which was intercalated with an immersion in saline. The saline immersion clearly reverted the clearing effect in the lung tissue in the spectral range between 220 and 1000 nm. By a later application of a second treatment with the e-cig fluid, the magnitude of the optical clearing effect was observed to be about the double as the one observed in the first treatment, showing that the molecules of the optical clearing agent might have converted some bound water into mobile water during the first treatment.     

A Membrane Filter-Giemsa Procedure for Yeast Microcolonies

Yeast mlcrocolonies grown on 5 × 10 nun rectangles of membrane (Millipore) filter are treated through the membrane pores with 0.5% sodium azide for 2-3 hr, 10% perchloric acid for 4 days, and Giemsa stain for 1 day. After dehydration in air, they are permanently mounted. Similar preparations can be made with cells from sporularion cultures.     

Changes in the content of individual lipid classes of a lichen <Emphasis Type="Italic">Peltigera aphthosa</Emphasis> during dehydration and subsequent rehydration

A lichen Peltigera aphthosa (L.) Willd. was subjected to a short-term (7 days) or a long-term (180 and 540 days) dehydration followed by rehydration. Then the composition and content of lipids, as well as the rate of their metabolism (the rate of sodium 2-¹⁴C-acetate incorporation) were investigated. The long-term dehydration resulted in a dramatic decrease in the content (per dry wt) of major extrachloroplastic phospholipids, mainly phosphatidylcholines and phosphatidylethanolamines. The rehydration of lichen thalli after a short-term and long-term dehydration also resulted in an enhanced breakdown of these lipid molecules; however, it was accompanied by their rather intense in vivo synthesis, which was decreased after long-term dehydration. In contrast to phospholipids, the betaine lipids, diacylglyceroltrimethylhomoserines (DGTSs), were involved in metabolic processes to a far lesser extent. In the course of rehydration, their content was virtually unchanged and decreased only after 540 days of dehydration. The rate of incorporation of sodium 2-¹⁴C-acetate into the DGTS molecules was moderate and did not change even after long-term dehydration. Glycolipids were characterized by a fair tolerance to hydrolytic processes and by an increase in the rate of their synthesis after 540 days of the lichen dehydration. Responses of neutral lipids to dehydration turned out to be different. The long-term dehydration (for 540 days) was accompanied by a decrease in the contents of free sterols and sterol esters, whereas the contents of di- and triacylglycerols remained unchanged. Rehydration resulted in a decrease in diacylglycerol and sterol ester contents. All neutral lipids were characterized by a dramatic decrease in the rate of de novo synthesis after long-term dehydration. It was suggested that the tolerance of lichen to long-term dehydration was appreciably determined by the tolerance of its phycobiont, in this case, a green alga Coccomyxa sp.; the bulk of its lipids was characterized by a minimum rate of breakdown and, at the same time, by a stable synthesis.Translated from Fiziologiya Rastenii, Vol. 52, No. 1, 2005, pp. 43–50.Original Russian Text Copyright © 2005 by Kotlova, Sinyutina.     

Reduced water intake: Implications for rodent developmental and reproductive toxicity studies

In developmental and reproductive toxicity studies, drinking water is a common means of delivering the test agent. Reduced consumption of toxicant-containing water raises questions about indirect effects of reduced maternal fluid consumption resulting from unpalatability, versus direct effects of the test compound. Issues to consider include: objective assessment of dehydration and thirst, the relative contributions of innate and learned behaviors to drinking behavior and flavor preference, and the objective assessment of physiologic stress. Not only do lab animals under ad lib conditions consume more water than the minimum required to maintain fluid balance, animals faced with water restriction have substantial physiologic capacity for protection of metabolic processes. Measures of blood biochemistry can provide quantifiable, objective indications of fluid balance, but changes in these parameters could result from other causes such as effects of a test toxicant. Consummatory behaviors in response to perceived need are highly influenced by learning. Hence, the drinking behavior, water intake, and flavor acceptance/preference of animals used in toxicology experiments could be subject to learning experiences with the test compound. Physiological symptoms of stress produced by water deprivation may be distinguishable from the symptoms associated with other generalized stressors, such as food deprivation, but doing so may be beyond the scope of most developmental or reproductive toxicity studies. Use of concurrent controls, paired to test groups for water consumption, could help distinguish between the direct effects of a test toxicant as opposed to effects of reduced water consumption alone. Birth Defects Res (Part B), 86:157–175, 2009. ©2009 Wiley-Liss, Inc.