Optimization of Regioselective α-Glucosylation of Hesperetin Catalyzed by Cyclodextrin Glucanotransferase.

The regioselective α-glucosylation of hesperetin was achieved by a transglycosylation reaction catalyzed by cyclodextrin glucanotransferase (CGTase) from Thermoanaerobacter sp. using soluble starch as glucosyl donor. By combining mass spectrometry (ESI-TOF) and 2D-NMR analysis, the main monoglucosylated derivative was fully characterized (hesperetin 7-O-α-d-glucopyranoside). In order to increase the yield of monoglucoside, several reaction parameters were optimized: Nature and percentage of cosolvent, composition of the aqueous phase, glucosyl donor, temperature, and the concentrations of hesperetin and soluble starch. Under the optimal conditions, which included the presence of 30% of bis(2-methoxyethyl) ether as cosolvent, the maximum concentration of monoglucoside was approximately 2 mM, obtained after 24 h of reaction. To our knowledge, this is the first report of direct glucosylation of hesperetin employing free enzymes instead of whole cells.

Efficient α-Glucosylation of Epigallocatechin Gallate Catalyzed by Cyclodextrin Glucanotransferase from Thermoanaerobacter Species.

The glycosylation of plant polyphenols may modulate their solubility and bioavailability and protect these molecules from oxygen, light degradation, and during gastrointestinal transit. In this work, the synthesis of various α-glucosyl derivatives of (-)-epigallocatechin gallate, the predominant catechin in green tea, was performed in water at 50 °C by a transglycosylation reaction catalyzed by cyclodextrin glycosyltransferase from Thermoanaerobacter sp. The molecular weight of reaction products was determined by high-performance liquid chromatography coupled to mass spectrometry. Using hydrolyzed potato starch as a glucosyl donor, two main monoglucosides were obtained with conversion yields of 58 and 13%, respectively. The products were isolated and chemically characterized by combining two-dimensional nuclear magnetic resonance methods. The major derivative was epigallocatechin gallate 3'- O-α-d-glucopyranoside (1), and the minor derivative was epigallocatechin gallate 7- O-α-d-glucopyranoside (2).

The Impact of a Teaching or Singing Career on the Female Vocal Quality at the Mean Age of 67 Years: A Pilot Study.

OBJECTIVES: The purpose of this study was to measure the objective and subjective vocal quality in women aged between 60 and 75 years. Secondly, the impact of a teaching or singing career on the vocal quality was investigated by comparing the vocal quality of retired women with different careers. STUDY DESIGN: This is a case-control study. METHODS: Seventy-three retired women between 60 and 75 years (mean age: 67 years, standard deviation: 4.49) participated in the study and were divided into three groups: women with a teaching career (n = 21), choir singers with a singing career (n = 12), and women with a non-vocal career (n = 40). All subjects underwent the same assessment protocol consisting of objective (aerodynamic, maximum performance, vocal range, acoustic measurements, and the Dysphonia Severity Index) and subjective (the Voice Handicap Index, auditory-perceptual evaluations by three listeners) voice measurements. RESULTS: In all three groups, objective and perceptual voice analysis showed a mild dysphonia. No differences in the Dysphonia Severity Index were found between the three groups. The voices of choir singers with a singing career were perceived significantly less rough than voices of the women with a non-vocal career. Additionally, the lowest frequency of the frequency range was significantly lower in the retired teachers and choir singers than in the controls. CONCLUSION: The results of this study prudently suggest that a singing or a teaching career compared with a non-vocal career has a positive impact on the vocal frequency range, and that singing has a positive impact on the perceptual vocal quality of the older female voice.