Effects of pH on antioxidant and prooxidant properties of common medicinal herbs

Abstract

Background: We studied in vitro and vivo antioxidant and prooxidant abilities of aqueous extracts from Rosa canina L., Rhodiola rosea L., Hypericum perforatum L., and Gentiana lutea L. Methodology: Total antioxidant capacity was measured by four assays (phosphomolybdate method, Fe3+-reducing activity, ABTS•+ scavenging, H2O2 scavenging). Prooxidant activity was estimated by H2O2 production. Yeast viability in the presence of H2O2 and/or plant extracts was determined by plating or by counting live cells’ number. Results: Plant extracts differed in the total phenolic content (R. canina > R. rosea > H. perforatum > G. lutea) which clearly correlated with their ABTS•+ scavenging activity (R2 = 0.963). H2O2 scavenging activity was not clearly associated with plant phenol levels and was significantly higher in acidic, than in alkaline medium. In line with this, plant extracts effectively protected yeast S. cereviasiae against H2O2 and stimulated reproductive ability of yeast cells at acidic but not at alkaline pH. At alkaline pH, plant extracts produced certain amounts of H2O2 which were related to their phenolic content. Conclusion: The antioxidant activity of plant extracts is decreased at alkaline pH with an increase in the prooxidant activity. It reduces protective capacity of plant extracts against oxidative and other stresses in vivo.

Effect of acidified turmeric and/or black pepper on growth performance and meat quality of broiler chickens

“…Data on the antioxidant activities and total phenolics of the herbs are presented in Table 1. This finding was different from Bayliak et al [10] reporting the increased antioxidant capacities of medicinal herbs in acidic pH solvent. The difference in pH values of media (to dissolve the herbs) seemed to be responsible for the discrepancy results above.…”

“…Studies showed that the nutritional and functional properties of plant-derived products may be improved through acidification. Sarr and Tsai [9] formerly reported that acidification resulted in higher nutritional factors and antioxidant capacities of tomato juice, while Bayliak et al [10] found the increased antioxidant capacities in medicinal herbs with acidic treatment. In accordance, the solubility and stability of curcumin increased in the acid solution [11,12].…”

Ethanolic extract of Betel ( Piper betle L.) and Chaphlu ( Piper sarmentosum Roxb.) dechlorophyllized using sedimentation process: Production, characteristics, and antioxidant activities

“…It was noted that TPC and antioxidant activities were higher ( p < .05) in acidic medium than in the alkaline medium. Decreased antioxidant activity in alkaline medium was attributed to the instability of some phenolic compounds (Bayliak et al., 2016), change in pH or a certain pH may lead to conformational changes of some phenolic constituents in the plant extracts, thus, affecting TPC and antioxidant activities (Friedman & Jürgens, 2000). Results of DPPH‐RSA and FRAP showed parallel trend to that of TPC, in which TPC and antioxidant activities were highest at pH 5 ( p < .05).…”

Influence of Abiotic Stress Factors on the Antioxidant Properties and Polyphenols Profile Composition of Green Barley (Hordeum vulgare L.)

“…Nowadays, food is intended not only for nutrition, but also for the prevention of chronic and nutrition-related diseases, as well as for improving people's general well-being. In connection with the growing knowledge of consumers about functional food products, new, functional raw materials are being required that contain appropriate phytochemical compounds that help fight diseases or oxidative stress [3][4][5]. One of these raw materials is green barley.…”