Phenolic compounds and antioxidant activity in sweet potato after heat treatment.

BACKGROUND: The ability of heat treatment with a soaking solvent to increase soluble phenolic compounds due to the liberation or breakdown of the cell matrix has been investigated in various plants. This study investigated the changes in phenolic compounds and antioxidant activities of 12 sweet potato cultivars after heat treatment with distilled water or prethanol A. RESULTS: The highest total polyphenol content (134.67 mg gallic acid equivalents/g extract residue) and flavonoid content (65.43 mg catechin equivalents/g extract residue) was observed in the 'Jami' (JM) cultivar after heat treatment with prethanol A. Higher polyphenol and flavonoid content was generally observed in the purple sweet potato cultivars. Salicylic acid was the major phenolic acid, followed by protocatechuic acid or chlorogenic acid in almost all untreated sweet potato cultivars. The salicylic acid, vanillic acid, gallic acid, and caffeic acid content of the sweet potatoes increased after the heat treatment, whereas the protocatechuic acid and chlorogenic acid content decreased. The highest 1,1-Diphenyl-2-picrylhydrazyl (DPPH) and 2,2-azinobis(3-ethyl benzothiazoline)-6-sulfonic acid (ABTS) radical scavenging activity levels were observed in the JM cultivar subjected to heat treatment with prethanol A (48.15 and 80.00 mg TE/g extract residue, respectively). CONCLUSION: These results suggest that heat treatment with a soaking solvent is an efficient method to enhance the antioxidant characteristics of Korean sweet potato cultivars. © 2019 Society of Chemical Industry.

Oat germination and ultrafiltration process improves the polyphenol and avenanthramide contents with protective effect in oxidative-damaged HepG2 cells.

Oat is the nutritious crop containing various compounds with antioxidant properties, such as polyphenols. In this study, we investigated the effect of germination and ultrafiltration process on polyphenol and avenanthramide contents in oat as well as their cytoprotective effect. Germination of oat for 48 hr significantly increased avenanthramide (5.5 to 11.3 mg/g) and polyphenol (115 to 155 mg GAE/g) contents. The compounds were more concentrated after ultrafiltration using 10 kDa membranes (polyphenol, 206 GAE/g; avenanthramide, 18 mg/g). In addition, oat extracts significantly reduced the cellular ROS level against tert-butyl hydroperoxide (t-BHP) stimulation in HepG2 cells. In the mechanistic study, oat extracts induced Nrf2 translocation to the nucleus by inhibition of Keap1 expression, resulting into upregulation of γ-GCS and NQO1. In conclusion, oat germination and ultrafiltration processes increased the polyphenol content, including that of avenanthramide. These extracts protected cells from t-BHP by radical scavenging activities and induced Nrf2 pathway activation. PRACTICAL APPLICATIONS: This study presents the method for avenanthramide-concentrated extract which is unique bioactive compounds in oat. In addition, antioxidant activity and their mechanisms of the avenanthramide-enriched extracts were evaluated. The polyphenol compounds including avenanthramide were found to increase after germination and ultrafiltration, thereby improving the radical scavenging ability. These results can be utilized as data for the development of health-promoting materials using oats.