Screening the antioxidant activity of thermal or non-thermally treated fruit juices by in vitro and in vivo assays

The health benefits of fruit juices have been associated with their high content of antioxidant compounds. Commercial juice has been traditionally heat-processed to destroy microorganisms and enzymes. However, high temperatures induce undesirable changes in the nutritional value of the juice. High-intensity pulsed electric fields (HIPEF) are being studied as an alternative to heat treatments. In addition, in vitro and in vivo methods have been recommended to determine the antioxidant potential of juices in a complementary manner. Thus, the antioxidant activity of untreated, high-intensity pulsed electric fields (HIPEF) or heat-treated fruit juices (tomato, apple, pineapple and orange) was studied using in vitro (TEAC, DPPH, FRAP and Folin-Ciocalteu) and in vivo assays (Saccharomyces cerevisiae). Vitamin C and total phenolic compounds in these juices were determined. The highest antioxidant activities (12.01 mmol of Trolox/L) were obtained through the Folin-Ciocalteu assay in orange juices. The lowest values (0.119 mmol of Trolox/L) were found in apple juice analysed by the FRAP assay. Vitamin C content varied from 10 mg/L (orange juice) to 344 mg/L (orange juice). The highest concentration of total phenolic compounds was determined in orange juice (1238 mg/L), whereas the lowest value was found in tomato juices (149 mg/L). The effect of HIPEF and thermal processing on the antioxidant potential of juices depended on the fruits used to prepare the juices and the antioxidant activity assay conducted. Vitamin C concentration was directly related to the antioxidant activity analysed by Folin-Ciocalteu and FRAP methods and the S. cerevisiae growth rate. S. cerevisiae yeast can be used as a feasible in vivo assay to further determine the antioxidant activity of fruit juices.This study has been carried out with financial support from Universitat de Lleida through a joint Agrotecnio/IRBLleida grant. This work was also supported by the Ministerio de Economia y Competividad (Spain) through the Project BFU2010-17656 and by the Generalitat de Catalunya (2014SGR/1000). Judit Puigpinos thanks University of Lleida for the predoctoral grant

Cth2 protein mediates early adaptation of yeast cells to oxidative stress conditions

Cth2 is an mRNA-binding protein that participates in remodeling yeast cell metabolism in iron starvation conditions by promoting decay of the targeted molecules, in order to avoid excess iron consumption. This study shows that in the absence of Cth2 immediate upregulation of expression of several of the iron regulon genes (involved in high affinity iron uptake and intracellular iron redistribution) upon oxidative stress by hydroperoxide is more intense than in wild type conditions where Cth2 is present. The oxidative stress provokes a temporary increase in the levels of Cth2 (itself a member of the iron regulon). In such conditions Cth2 molecules accumulate at P bodies-like structures when the constitutive mRNA decay machinery is compromised. In addition, a null Δcth2 mutant shows defects, in comparison to CTH2 wild type cells, in exit from α factor-induced arrest at the G1 stage of the cell cycle when hydroperoxide treatment is applied. The cell cycle defects are rescued in conditions that compromise uptake of external iron into the cytosol. The observations support a role of Cth2 in modulating expression of diverse iron regulon genes, excluding those specifically involved in the reductive branch of the high-affinity transport. This would result in immediate adaptation of the yeast cells to an oxidative stress, by controlling uptake of oxidant-promoting iron cations.This study was supported by grant BFU2010-17656 from Spanish Ministerio de Economía y Competitividad (www.mineco.gob.es)