Green extraction of polyphenols from grapefruit peels using high voltage electrical discharges, deep eutectic solvents and aqueous glycerol.

Deep eutectic solvents (DES) and aqueous glycerol were proposed as green alternatives to conventional solvents for the extraction of polyphenols from grapefruit peels. In order to increase the extraction kinetics and yields of polyphenols, high voltage electrical discharges (HVED) were used as a pre-treatment technology (energy varied between 7.27 and 218 kJ/kg). Results showed that the HVED energy input can be reduced, when the subsequent solid-liquid extraction was performed in 20% (w/v) aqueous glycerol or in DES (lactic acid: glucose) instead of water. The addition of glycerol has reduced the energy of the pre-treatment by 6 times. The same diffusivity of polyphenols (4 × 10-11 m2/s) was obtained in water from HVED pre-treated peels at 218 kJ/kg and in aqueous glycerol from pre-treated peels at 36 kJ/kg. The solubility of naringin, the main flavonoid compound of grapefruit peels in the solvents, was investigated through a theoretical modelling of its Hansen solubility parameters.

Comparative analysis of trehalose production by Debaryomyces hansenii and Saccharomyces cerevisiae under saline stress.

The comparative analysis of growth, intracellular content of Na+ and K+, and the production of trehalose in the halophilic Debaryomyces hansenii and Saccharomyces cerevisiae were determined under saline stress. The yeast species were studied based on their ability to grow in the absence or presence of 0.6 or 1.0 M NaCl and KCl. D. hansenii strains grew better and accumulated more Na+ than S. cerevisiae under saline stress (0.6 and 1.0 M of NaCl), compared to S. cerevisiae strains under similar conditions. By two methods, we found that D. hansenii showed a higher production of trehalose, compared to S. cerevisiae; S. cerevisiae active dry yeast contained more trehalose than a regular commercial strain (S. cerevisiae La Azteca) under all conditions, except when the cells were grown in the presence of 1.0 M NaCl. In our experiments, it was found that D. hansenii accumulates more glycerol than trehalose under saline stress (2.0 and 3.0 M salts). However, under moderate NaCl stress, the cells accumulated more trehalose than glycerol. We suggest that the elevated production of trehalose in D. hansenii plays a role as reserve carbohydrate, as reported for other microorganisms.