Gui-Li Huang,Tian-Tian Liu,Jia-Jia Ma,Ling-Xiang Sun,Si-Yao Sui,Xin-Yao Quan,Yu-Ning Wang
The harvested loquat fruits are prone to browning, leading to a decline in fruit quality. Inhibiting activity of polyphenol oxidase (PPO) is an important way to prevent browning. In this study, we evaluated the inhibitory impact of oligomeric procyanidins (OPC) on hydroxylation of monophenol and oxidation of o-diphenol catalyzed by PPO and effect of OPC on loquat fruits storage . The obtained results revealed that OPC could attenuate the activity of monophenolase and diphenolase. For monophenolase activity, the inhibition rate was observed to be dose-dependent with an IC 50 of 11.6 ± 3.4 μg/mL for the steady-state rate. For diphenolase activity, OPC inhibited PPO activity ( IC 50 = 15.75 ± 2.1 μg/mL) with a reversible and competitive mechanism and quenched fluorescence of PPO by forming OPC-PPO complex with one binding site in a static procedure. In addition, the data obtained from storage assays revealed that OPC could enhance the quality of harvested loquat fruits by attenuating the PPO activity, augmenting the content of total phenolics and flavonoids , and simultaneously delaying the browning of loquats. In this research, we identified a potent PPO inhibitor and expanded its potential as a food preservative.
This study aimed to investigate the structural features, antioxidant activity, tyrosinase inhibitory effect, and mechanism of proanthocyanidins from leaf and fruit of Leucaena leucocephala. MALDI-TOF-MS, thiolysis coupled with HPLC-ESI-MS, and 13C-NMR confirmed that these proanthocyanidins were complex mixtures of propelargonidins, procyanidins, and prodelphinidins. (Epi)catechin, (epi)gallocatechin, (epi)catechin gallate, and (epi)gallocatechin gallate were the main constitutive units. The findings obtained from enzyme analysis revealed that the proanthocyanidins had inhibitory effects on both monophenolase and diphenolase of tyrosinase. The IC50 values of leaf and fruit proanthocyanidins were 73.5 ± 2.7 and 52.3 ± 3.5 µg/mL for monophenolase activity, and 27.2 ± 1.4 and 16.1 ± 1.1 µg/mL for diphenolase activity, respectively. The inhibition of diphenolase by proanthocyanidins were proved to be reversible and mixed type. In addition, it was also found from various antioxidant methods that the proanthocyanidins in leaf and fruit possessed potent DPPH radical scavenging activity with IC50 values of 103.4 ± 0.8 and 87.8 ± 1.1 µg/mL, ABTS radical scavenging activity with IC50 values of 72.9 ± 0.4 and 65.7 ± 0.9 µg/mL, and ferric reducing antioxidant power with FRAP values of 3.74 ± 0.03 and 4.02 ± 0.15 mmol AAE/g, respectively. The results obtained suggested that the proanthocyanidins from leaf and fruit of L. leucocephala might have the potential to be exploited as natural tyrosinase inhibitors and antioxidants.
危险品化学品经营许可证（带存储）