Comparative evaluation of the effects of pretreatments on the nutritional and chemical properties of ginger leaf-based herbal tea

Abstract

There is increasing awareness and acceptance of herbal teas because of their contribution to nutrition and health. The use of ginger (Zingiber officinale) leaves as tea in some communities has been reported. While many research efforts have focused on ginger rhizomes, there is a limited report on ginger leaves’ nutritional, antioxidant properties and also what effect application of different heat pretreatments will have on the final product. The present study sought to develop a ginger leaf-based herbal tea and examine the effects of postharvest pretreatments such as steam blanching before drying, hot water blanching before drying and directly drying on the nutritional and chemical properties of the tea. Fresh green leaves were sorted, washed and drained. A batch of the leaves was evenly steam blanched at 1000C for 5 minutes before drying, another set was dipped in boiling water at 1000C for 3 minutes and the last batch was dried directly at 550C under standard conditions. The dried leaves were milled, packed in tea bags and a sample each was evaluated for its proximate, mineral, vitamin C, phytochemicals and antioxidant properties following standard procedures. The results showed that steam blanching significantly (p<0.05) increased the protein, fat, sodium, potassium, saponin and the antioxidant potential (ferric reducing antioxidant power) compared to those that were hot water-blanched before drying and those dried directly. However, vitamin C, tannin, phytate, oxalate and zinc contents decreased significantly when compared with the fresh leaves. The free radical scavenging activity examined using DPPH activity, phenols and flavonoids did not vary significantly between the steam blanched and fresh leaves. These findings showed that steam blanching of ginger leaves before drying for consumption as a functional beverage is beneficial in terms of nutrient and antinutrient properties compared to hot water blanching before drying and direct drying. Therefore, this method of processing could be adapted for improved nutrition.