Instability of natural deep eutectic solvents (NADESs) induced by Amadori rearrangement and its effects on cryopreservation of yeast cells
Hu Rui, Da‐Wen Sun, You Tian, Liang Xu, Libin Sun
Abstract
Natural deep eutectic solvents (NADESs) showing higher cryoprotective effects are attracting concerns, because during the storage, system browning always occurs in aldose/amino acid-based NADESs, which generated brown substances remarkably weaken the cryoprotective effects. In this study, proline/glucose-based (PG) and proline/sorbitol-based (PS) NADESs were prepared, of which storage stability, browning profile, brown substance, and cryoprotective effects were investigated. Results showed that PG at molar ratios of 1:1, 2:1, and 3:1, as well as PS at 1:1, and 2:1 can form NADESs, among which only the PG-based ones could get browning after storage. The predominant brown substance was identified as 1-deoxy-1-L-proline- d -fructose (C 11 H 19 O 7 N, 278 m / z ), which was subsequently verified to show cytotoxicity and decrease Saccharomyces cerevisiae cells viability after cryopreservation, suggesting that the brown substance could take a negative effect on cryopreservation. This study may help to attract more concerns to the storage and cryopreservation stabilities of the NADESs in food-related applications. • The colour of aldose/amino acid-based NADESs deepened with storage time. • The brown substance was mainly Amadori rearrangement products (ARPs). • The predominant brown substance was 1-deoxy-1-L-proline- d -fructose (C 11 H 19 O 7 N). • The browned NADESs were much less cryoprotective than the freshly prepared ones. • The post-thaw cell viability was found to decrease as the browning index increased.