Storage stability of an antioxidant tea prepared from purple corn (Zea mays L.) cob and stevia (Stevia rebaudiana Bert.) and its effects on biomarkers of oxidative stress in healthy humans

Tea is consumed worldwide, and it is highly appreciated by consumers as a functional, healthy, and natural drink. The objectives of this research were to evaluate (1) the storage stability and (2) the consumption effect on biomarkers of oxidative stress of an antioxidant tea prepared from purple corn cob and stevia (AOxTea). The AOxTea bags were subjected to storage environments of 75 or 85 % of relative humidity at 30, 40 and 50 °C for up to 19 days. During this time, total polyphenols (TP), total monomeric anthocyanin, TEAC, ORAC_PGR, and color were monitored. Biomarkers TEAC, ORAC_PGR, antioxidant enzymes activities, protein carbonyls, and OXY-SCORE index were analyzed on healthy volunteers (n = 18, both genders, BMI = 19–25.5 kg/m², age = 18–45 years, divided into a control group and an AOxTea consumption group) on time 0, after 2- and 4- weeks of twice daily consumption. During storage, TP and color did not significantly change, while anthocyanins and antioxidant capacity decreased significantly to up 22 and 43 % of their initial values, respectively, in the most severe conditions. Evaluation of the effect of AOxTea on humans showed a significant decrease in ORAC_PGR and in protein carbonyls after 4 and 2 weeks, respectively, in the consumption group, however, OXY-SCORE values in both groups did not vary significantly. Results indicate that AOxTea has a considerable stability until reaching the typical maximum legal moisture for teas (10 %) and no significant effect of consumption in OXY-SCORE index was found.