Decline in antioxidant capacity of Indian herbal teas during storage and its relation to phenolic content

Abstract

The changes in the stability of antioxidant capacity with time and its relation to the phenolic content were evaluated in eight Indian herbal teas. These herbal teas are claimed to be antistress, immunomodulator, anti-aging, anti-inflammatory, appetizer, stimulant, blood purifier, energizer, antidepressant, antidiabetic, rejuvenative, analgesic, antiviral, nervine, diuretic, antihypertensive and memory enhancer. Antioxidant capacity was determined over a period of 15 months from the date of their procurement using assays for SOD mimetic activity, LPO inhibitory capacity and total thiol content, which decreased positively with time. Total phenolic content was determined spectrometrically according to the Folin-Ciocalteu method and calculated as gallic acid equivalents (GAE). Herbal teas with higher phenolic content showed a comparatively less decline in antioxidant capacity. The SOD mimetic activity values in control samples (at the time of procurement) were seen to be in the range of 54.63–93.64 units/min/mg of extract which after 15 months of storage decreased upto 7.4-folds in some samples. LPO inhibitory capacity was observed upto 96.75% in herbal tea E at the time of procurement which dropped to 63.85% inhibition of MDA formation/5μl of extract after 15 months. In case of total thiol, the values were seen in the range of 0.55–1.71 mg/g and after 15 months it was from 0.12 to 0.21 mg/g. In all these cases high antioxidant activity was seen in the samples with higher phenolic content which also showed comparatively less decline in antioxidant capacity after considerable storage time. The results have significance, as most of the herbal teas available in the local markets in India do not carry any information regarding the period of use without decline in its beneficial effects.