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.

Alpha-substituted derivatives of cinnamaldehyde as tyrosinase inhibitors: inhibitory mechanism and molecular analysis.

Alpha-substituted derivatives of cinnamaldehyde (alpha-bromocinnamaldehyde, alpha-chlorocinnamaldehyde, and alpha-methylcinnamaldehyde) were used as inhibitors on mushroom tyrosinase. The result showed that three compounds can reduce both monophenolase and diphenolase activity on tyrosinase, and the inhibition was reversible. The IC50 values of alpha-bromocinnamaldehyde, alpha-chlorocinnamaldehyde, and alpha-methylcinnamaldehyde were 0.075, 0.140, and 0.440 mM on monophenolase and 0.049, 0.110, and 0.450 mM on diphenolase, respectively. The inhibition types and constants on diphenolase for these inhibitors were further studied. The molecular inhibition mechanisms of tyrosinase by the derivatives were investigated by UV-scanning study, fluorescence quenching, and molecular docking. These assays demonstrated that the derivatives could decrease the formation of o-quinones, and all derivatives were static quenchers of mushroom tyrosinase. Docking results implied that they could not form metal interactions with the copper ions of the enzyme, whereas they could interact with the amino acid residues of active site center. This research on alpha-substituted derivatives of cinnamaldehyde as tyrosinase inhibitors would lead to advances in the field of antityrosinase.

Enzymatic saccharification of cassava residues and glucose inhibitory kinetics on ß-glucosidase from Hypocrea orientalis.

Cassava residues are byproducts of the starch industry containing abundant cellulose for bioproduction of green fuel. To obtain maximum sugar yields from cassava residues, the optimal conditions for hydrolyzing the residues were determined using cellulase prepared from a novel Hypocrea orientalis strain. The optimal pH value and optimal temperature for the cellulase hydrolysis were 5.0 and 50 °C, respectively. The concentration of NaOH was determined to be 1% for pretreatment of cassava residues to gain enough soluble sugars suitably. The yield of released sugars was 10 mg/mL in the optimal conditions after 24 h of reaction, which was similar to that of bagasse and wheat grass. Inhibition kinetics of H. orientalis ß-glucosidase (BG) by glucose was first studied using the progress-of-substrate-reaction method as described by Tsou (Tsou, C. L. Adv. Enzymol. Related Areas Mol. Biol. 1988, 61, 381-436), and the microscopic inhibition rate constants of glucose were determined. The results showed that glucose could inhibit BG reversibly and competitively. The rate constants of forward (k(+0)) and reverse (k(-0)) reaction were measured to be 4.88 × 10(-4) (mM·s)(-1) and 2.7 × 10(-4) s(-1), respectively. Meanwhile, the inhibition was more significant than that of L-glucose, D-mannose, D-galactose, D-aminoglucose, acetyl-D-glucose, and D-fructose. This work reveals how to increase sugar yields and reduce product inhibition during enzymatic saccharification of cellulose.