Isolation, Characterization, Antioxidant Activity, Metal-Chelating Activity, and Protein-Precipitating Capacity of Condensed Tannins from Plum (<i>Prunus salicina</i>) Fruit

• Main Authors: Liangliang Zhang (Author), He Zhang (Author), Lihua Tang (Author), Xinyu Hu (Author), Man Xu (Author)
• Format: Book
• Published: MDPI AG, 2022-04-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.
• Notes: 10.3390/antiox11040714; 2076-3921
• Keywords: <i>Prunus salicina</i>; condensed tannins; antioxidant activity; MALDI-TOF MS; metal ions; protein-precipitating capacity; Therapeutics. Pharmacology; RM1-950
• Source: Antioxidants, Vol 11, Iss 4, p 714 (2022)

The type of polymeric condensed tannins from plum fruit (<i>Prunus salicina</i>) (PCT), the degree of polymerization and the distribution of polymers were characterized by MALDI-TOF MS and NMR spectroscopy. The metal-binding capacity of PCT with five metal ions (Cu²⁺, Zn²⁺, Al³⁺, Fe²⁺, and Fe³⁺) was characterized by a fluorescence quenching method. The results demonstrated the following: epicatechin was the basic unit occurring in PCT, and A-type and B-type linkages were the most common between the structural units of the polymers. The PCT have a strong antioxidant activity, which is comparable with that of the synthetic antioxidant BHA. The quenching mechanism of the PCT's fluorescence intensity by Zn²⁺, Cu²⁺, and Al³⁺ was different from that of Fe³⁺ and Fe²⁺. Fe³⁺, Al³⁺ and Fe²⁺ had much higher affinities for the PCT than Zn²⁺ and Cu²⁺. A simple UV-Vis spectra method was developed to determine the protein-precipitating capacity of tannins. Bovine serum albumin (BSA) was effectively precipitated by tannins isolated from plum fruits, Chinese gallnut, sorghum grain, and <i>Platycarya strobilacea</i> at pH values between 4.5 and 5.0. A statistically significant linear relationship (<i>p</i> < 0.0001 or <i>p</i> < 0.0003) existed between the amount of tannin-protein complex formed and the amount of tannins added to the reaction mixture. The slopes of these lines indicated the protein-precipitating capacity of tannins.