Anti-tyrosinase kinetics and antibacterial process of caffeic acid N-nonyl ester in Chinese Olive (Canarium album) postharvest.

Enzymatic browning and bacterial putrefaction are mainly responsible for quality losses of Chinese Olive (Canarium album) postharvest and lead to very short shelf life on average. Screening anti-browning and anti-bacterial agents is important for preservation of Chinese Olive. Caffeic acid N-nonyl ester (C-9) and caffeic acid N- Heptyl ester (C-7) was synthesized as inhibitors of tyrosinase, which is a key enzyme in browning process. The compound of C-9 could inhibit the activity of tyrosinase strongly and its IC50 value was determined to be 37.5µM, while the compound of C-7 had no inhibitory ability. Kinetic analyses showed that compound of C-9 has been a reversible inhibitory mechanism below 50µM and been irreversible mechanisms above 50µM. For the reversible inhibitory mechanism, the values of inhibitory constants (KI and KIS) were determined to be 24.6 and 37.4µM, respectively. The results of Chinese Olive fruit postharvest showed that the compound of C-9 could effectively anti-browning and anti-bacterial putrefaction. In addition, this compound had strong antibacterial activities against Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Salmonella. Therefore, C-9 could be a potential anti-browning and anti-bacterial reagent.

Heat inactivation kinetics of Hypocrea orientalis ß-glucosidase with enhanced thermal stability by glucose.

Thermal inactivation kinetics of Hypocrea orientalis ß-glucosidase and effect of glucose on thermostability of the enzyme have been determined in this paper. Kinetic studies showed that the thermal inactivation was irreversible and first-order reaction. The microscopic rate constants for inactivation of free enzyme and substrate-enzyme complex were both determined, which suggested that substrates can protect ß-glucosidase against thermal deactivation effectively. On the other hand, glucose was found to protect ß-glucosidase from heat inactivation to remain almost whole activity below 70°C at 20mM concentration, whereas the apparent inactivation rate of BG decreased to be 0.3×10(-3)s(-1) in the presence of 5mM glucose, smaller than that of sugar-free enzyme (1.91×10(-3)s(-1)). The intrinsic fluorescence spectra results showed that glucose also had stabilizing effect on the conformation of BG against thermal denaturation. Docking simulation depicted the interaction mode between glucose and active residues of the enzyme to produce stabilizing effect.