Emerging techniques for cell disruption and extraction of valuable bio-molecules of microalgae Nannochloropsis sp.

Bioprocess and Biosystems Engineering - Microalgae of Nannochloropsis sp. present valuable source of bio-molecules (pigments, lipids, proteins) that have nutritional potential for the...     

Sin3 histone deacetylase controls level of spontaneous and UV-induced mutagenesis in yeast Saccharomyces cerevisiae

SIN3 gene product operates as a repressor for a huge amount of genes in Saccharomyces cerevisiae. Sin3 protein with a mass of about 175 kDa is a member of the RPD3 protein complex with an assessed mass of greater than 2 million Da. It was previously shown that RPD3 gene mutations influence recombination and repair processes in S. cerevisiae yeasts. We studied the impacts of the sin3 mutation on UV-light sensitivity and UV-induced mutagenesis in budding yeast cells. The deletion of the SIN3 gene causes weak UV-sensitivity of mutant budding cells as compared to the wild-type strain. These results show that the sin3 mutation decreases both spontaneous and UV-induced levels of levels. This fact is hypothetically related to the malfunction of ribonucleotide reductase activity regulation, which leads to a decrease in the dNTP pool and the inaccurate error-prone damage bypass postreplication repair pathway, which in turn provokes a reduction in the incidence of mutations.     

Effect of a Pulsed Electric Field and Osmotic Treatment on Freezing of Potato Tissue

This work discusses the effects of pulsed electric field (PEF) and osmotic pre-treatments on potato tissue structure and on the freezing and freeze-drying behaviour of this tissue. Potato samples (26-mm diameter, 10-mm height) were treated by PEF (400 V/cm) to high level of disintegration (conductivity disintegration index Z was ≈0.95) and were subjected to osmotic treatment in an aqueous solution of NaCl. The samples were either frozen in an air-blast freezer at air temperature of −80 °C and velocity of 2 m/s or freeze-dried at 0 °C and 0.04-mbar pressure. The scanning electron microscope (SEM) images evidenced similarity in structure of the cell walls and area and morphology of starch granules for untreated and PEF-treated potato tissues. However, sequential (PEF + osmotic) pre-treatment of potato tissue resulted in starch granules with rougher surface. The profiles of freezing curves were strongly dependent on pre-treatment. The longest effective freezing time t _f was observed for untreated tissue, and the values of t _f were decreasing in the following sequence: untreated > PEF pre-treated > PEF + osmotically pre-treated. The faster freezing and freeze drying and visually better quality of the dried samples were observed for PEF or sequential PEF + osmotic pre-treatments. The SEM analysis revealed also a noticeable disorder of starch granule surface morphology inside the cells of the freeze-dried potatoes after sequential PEF + osmotic pre-treatment.     

Effect of a Pulsed Electric Field Treatment on Expression Behavior and Juice Quality of Chardonnay Grape

This work discusses the effects of pulsed electric field (PEF) application on low-pressure mechanical expression (the pressure maximum was 1 bar) and characteristics of juice produced from Chardonnay white grape. The experiments were carried out using a texture analyzer equipped with a PEF-treatment compression chamber operated at moderate electric field strength E = 400 V/cm. Two regimes of extraction were compared: expression at constant pressure (0.5 or 1 bar) and expression at progressive pressure increase (from 0 to 1 bar). This last one was chosen for the scale-down modeling of industrial grape pressing process. It was shown that PEF treatment at the electric field E = 400 V/cm and the total time of treatment t _PEF ≈ 0.1 s allowed reaching of a high level of cell disintegration, Z ≈ 0.8. The energy consumption of PEF treatment corresponding to this level of disintegration was rather low and equal to W ≈ 15 kJ/kg. The PEF pretreatment resulted in juice yield increase from 67% to 75% (1 h of pressing at constant pressure of 1.0 bar). PEF treatment accelerated development of grape deformation. Decrease of difference between deformations of untreated and PEF-treated samples at high pressure and long-pressing time was observed. Statistical analysis showed no significant effect of PEF treatment on turbidity and content of polyphenols for the constant pressure regime. However, PEF treatment application resulted in elevation of the content of polyphenols (more than 15%) for the progressive pressure-increase regime.