Green and efficient removal of heavy metals from Porphyra haitanensis using natural deep eutectic solvents.

BACKGROUND: Porphyra haitanensis now faces serious heavy metal pollution problems. Natural deep eutectic solvents (NADESs) have been recognized as a novel class of sustainable solvents, which can be used for heavy metal removal. In this study, 28 kinds of NADESs were prepared and investigated as eluent in the removal of lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As), and copper (Cu) from P. haitanensis for the first time, and the adsorption mechanism of NADESs was also studied. RESULTS: The removals were greatly improved by NADESs compared with control where the removal rates of Pb, Cd, Cr, As and Cu were 17.4-87.54%, 57.54-100%, 9.8-48.59%, 21.32-78.24% and 11.68-79.73%, respectively. The optimal condition was 10% water content and solid-liquid ratio of 1:20. Moreover, the addition of 20% natural surfactant arabic gum can further increase the heavy metals removal rates of NADESs. The adsorption mechanism experiments showed that the pseudo second-order model and the Freundlich adsorption model can better explain the adsorption mechanism of NADESs on heavy metals removal. CONCLUSION: Taken together, a green and efficient method for removing heavy metals from P. haitanensis was established. © 2020 Society of Chemical Industry.

Carrier-Free Immobilization of Rutin Degrading Enzyme Extracted From Fusarium spp.

In this study, a strain with rutin degrading enzyme (RDE) activity was screened from moldy tartary buckwheat and subsequently identified as Fusarium spp. The structure and enzyme characteristics of CLEA-RDE formed by immobilization via cross-linking were then investigated. Further, the optimal catalysis conditions of CLEA-RDE in natural deep eutectic solvents (NADESs) serving as hydrolysis solvents were also investigated. The results of SEM and spectrum indicated that CLEA-RDE became more stable than free-RDE due to the cross-linking. Interestingly, CLEA-RDE showed a wider range of pH adaptation and higher tolerance to low temperatures (20 - 30°C) and hydrophobic environments. The results of orthogonal experiments revealed that the optimal condition for rutin hydrolysis was under pH 5.0 and 40oC with the degradation rate of 10.65 mg min-1 L-1. The preparation of CLEA-RDE without a carrier-based immobilization method reduces the loss of enzyme activity, improves the stability of the enzyme and can be applied to the investigation of immobilization of various enzymes, thus providing a referred idea for the improvement of catalysts in industrial production.

Effects of natural deep eutectic solvents on lactic acid bacteria viability during cryopreservation.

In this study, a new method of cryopreservation of lactic acid bacteria (LAB) using natural deep eutectic solvents (NADESs) was developed. Survival rates of LAB during 24-h short-term and 180-day long-term cryostorage at - 20 °C were investigated. The results revealed that survival of Streptococcus thermophilus (S. thermophilus) in NADESs after 24 h of cryostorage was superior to survival of two other tested LAB. Moreover, survival was higher at a ratio of NADESs to S. thermophilus of 1:1 (v/v) than observed using a 4:1 (v/v) ratio. Representative freezing characteristics of five NADESs were elucidated, including thermodynamic properties and hydrogen bonding interactions after addition of water. In order to identify the protective mechanism of NADESs on cell structure and vital metabolic enzymes of S. thermophilus during cryostorage, transmission electron microscopy (TEM) and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) were employed and enzyme activities of both lactate dehydrogenase (LDH) and ß-galactosidase were determined. Subsequently, NADES GlyP prepared from glycerol and L-proline was demonstrated to maintain cell membrane structural integrity and significantly (p < 0.05) maintain activities of both intracellular enzymes of S. thermophilus. Moreover, NADESs could efficiently penetrate S. thermophilus cells and intracellular ß-galactosidase activity could be used to demonstrate NADESs effectiveness in maintaining S. thermophilus survival after long-term cryostorage. These results demonstrate that NADESs can be used as green cryoprotective chemical agents (CPAs) that can efficiently increase LAB viability during cryostorage. These results should have great value in the food production and probiotics industries.