Polymerization of proanthocyanidins catalyzed by polyphenol oxidase from lotus seedpod

Extraction Methods, Properties, Functions, and Interactions with Other Nutrients of Lotus Procyanidins: A Review

Lotus procyanidins, natural polyphenolic compounds isolated from the lotus plant family, are widely recognized as potent antioxidants that scavenge free radicals in the human body and exhibit various pharmacological effects, such as anti-inflammatory, anticancer, antiobesity, and hypoglycemic. With promising applications in food and healthcare, lotus procyanidins have attracted extensive attention in recent years. This review provides a comprehensive summary of current research on lotus procyanidins, including extraction methods, properties, functions, and interactions with other nutrient components. Furthermore, this review offers an outlook on future research directions, providing ideas and references for the exploitation and utilization of lotus.

Purification and Characterization of a Dark Red Skin Related Dimeric Polyphenol Oxidase from Huaniu Apples

The distinct dark-red skin of Huaniu apples renders them attractive to customers. However, the mechanism that leads to the development of the color of the fruit is unclear. In this study, we found that compared with red Fuji (a bright-red apple cultivar), Huaniu apples had higher contents of (−)-epicatechin (EC), (−)-epigallocatechin (EGC), (−)-gallocatechin gallate (GCG), and procyanidins (PCs) B2 and C1 in the peel, which implies that the polymerization of the flavanols and PCs may be correlated with the dark-red skin of the fruit. Using EC as a substrate, we purified an enzyme from Huaniu peel. We performed protein sequencing and discovered that the enzyme was a polyphenol oxidase (PPO). The molecular weight of the enzyme was approximately 140 kDa, which we estimated by native-PAGE and SDS-PAGE, while it was 61 kDa by urea-SDS-PAGE, from which we discovered that the PPO was a dimer. We observed the lowest K_m value for catechol (0.60 mM), and the best substrate was 4-methylcatechol, with a V_max of 526.32 U mg⁻¹ protein. EC is a suitable natural substrate, with a K_m value of 1.17 mM, and 55.27% of the V_max/K_m of 4-methylcatechol. When we used EC as a substrate, the optimum temperature and pH of the PPO were 25 °C and 5.0, respectively. In summary, we purified a dimeric PPO from Huaniu apples that showed high activity to EC, which might catalyze the polymerization of flavanols and PCs and lead to the dark-red color development of the fruit.

Two Kaempferol Glycosides Separated from Camellia Oleifera Meal by High-Speed Countercurrent Chromatography and Their Possible Application for Antioxidation

Recently, kaempferol and its glycosides have attracted considerable attention owing to their potentially health-benefitting properties including protection against chronic diseases. Here, a microwave-assisted extraction (MAE) method was developed for the extraction of total flavonoid glycosides (FG) from Camellia oleifera meal, a major agrifood waste largely generated as a byproduct from the Camellia oil processing industry. Compared with traditional extraction methods, MAE enables more efficient extraction of FG. High-speed countercurrent chromatography was then applied to separate FG from MAE extract, and two major compounds were successfully separated with purities above 90.0% as determined by HPLC. These two compounds were further identified by UV, FT-IR, ESI-MS, ¹ H-NMR, and ¹³ C-NMR as kaempferol 3-O-[α-L-rhamnopyranosyl-(1→6)-β-D-glucopyranosyl]-7-O-β-D-glucopyranoside and kaempferol 3-O-[β-D-glucopyranosyl-(1→4)-α-L-rhamnopyranosyl]-7-O-α-L-rhamnopyranoside, which were for the first time separated from C. oleifera meal. The results of antioxidant activity assay demonstrated that both compounds had excellent scavenging activity for DPPH radical, and exhibited protective effects against H₂ O₂ -induced oxidative damage of vascular endothelial cells. The findings of this work suggest the possibility of employing C. oleifera meal as an attractive source of health-promoting compounds, and at the same time facilitate its high-value reuse and reduction of environmental burden.

Microwave Pretreatment and Enzymolysis Optimization of the Lotus Seed Protein

Pretreatment with a microwave was conducted before enzymolysis and shown to enhance the enzymolysis, which changed the secondary structure of the lotus seed protein. Under high-power microwave irradiation, sub bonds of the protein were broken, causing disaggregation and unfolding of the secondary structure, namely a decrease in the intermolecular aggregate structure and increase in the random coil structure, making the protein bonds susceptible to papain in the enzymolysis. On the other hand, a response surface methodology (RSM) was launched to investigate the influence of the enzymolysis process variables on the DH (degree of hydrolysis). The statistical analysis revealed that the optimized conditions were a protein substrate concentration of 15 g/L, pH of 5.5, enzymolysis temperature of 57 °C, papain amount of 0.5 g/L, and enzymolysis time of 45 min, for which the predicted value of the DH was 35.64%. The results indicated that a microwave also had better potential for applications in the enzymolysis of foods.

Protein and polyphenols involved in sediment formation in cloudy litchi juice

Sedimentation is a major issue in juice production. This paper aims to study the mechanisms of precipitate formation during the storage of cloudy litchi juice. The sediment concentration, relative turbidity, and ζ potential were analyzed. The supernatant and sediment were separated to determine the contents of proteins and phenolics. The results showed that the amount of sediment increased during the storage. In addition, the total protein and total phenolic content in the supernatant decreased, whereas the glutelin and total phenolic contents in the sediment increased significantly (p < 0.05). Moreover, our results showed that the amounts of procyanidin B₂ and quercetin-3-O-rutinose-7-O-rhamnoside in the supernatant decreased noticeably. However, these two substances could not be detected in the sediment. In summary, the formation of sediment from litchi juice is mainly caused by the slow denaturation of proteins and the oxidation of procyanidin B₂ and quercetin-3-O-rutinose-7-O-rhamnoside.

Chemical Compositions, Antiobesity, and Antioxidant Effects of Proanthocyanidins from Lotus Seed Epicarp and Lotus Seed Pot

Lotus seed epicarp (LSE) and lotus seed pot (LSP) were characterized, and a total of 5 and 7 proanthocyanidins (PAs) were identified in purified LSE and LSP extract, respectively. Purified LSE and LSP PAs significantly suppressed the body weight and weight gain of white adipose tissue (WAT) and decreased the WAT cell size in high-fat diet-induced obese mice regardless of the daily food intake. LSE or LSP administration significantly lowered the serum leptin level and improved the serum and liver lipid profiles (including total cholesterol (TC), triglycerides (TG), high-density lipoprotein-cholesterol (HDL-C), and low-density lipoprotein-cholesterol (LDL-C) levels), increased activities of antioxidant enzymes (superoxide dismutase (SOD) and glutathione transferase (GST)) and reduced glutathione (GSH) concentration, and suppressed lipid peroxidation in hepatic tissue. LSP PAs were generally more effective than LSE PAs. Both extracts ameliorated obesity, insulin resistance, and oxidative damage in obese mice, suggesting they are good candidates for value-added functional food and nutraceutical ingredients.