Effect of brewing time and temperature on antioxidant capacity and phenols of white tea: Relationship with sensory properties

Highlights

• Teas brewed at 98 °C for 7 min had high antioxidant capacity and phenols content.

• Such conditions were preferred by sensory panels compared to mild infusion.

• Green teas are more antioxidant than white teas under the same brewing conditions.

• One cup of white tea contributes to a 22% of the daily antioxidant intake in Spain.

Abstract

White tea is highly consumed due to its sensory properties and health benefits, although most scientific reports don’t include the analysis of both properties. Therefore, the objective of the present study was to unravel the best brewing conditions for optimal extraction of the bioactive compounds and antioxidant capacity, while realising the best sensory properties. Infusions of eighty commercial teas (sold in bags or leaves) were obtained at different time–temperature ratios, studying bioactive compounds (caffeine and individual catechins), antioxidant capacity and sensory analysis. Brewing at 98 °C for 7 min was the best condition to obtain a high content of antioxidant polyphenols and pleasant sensory properties. Those teas sold in bags give rise to tea brews with almost double antioxidant capacity. In conclusion, it is very important to link sensory and chemical data to obtain optimal sensorial quality and the highest healthy properties in white tea infusions.

Introduction

Green tea is one of the most consumed beverages around the world due to its sensory attributes and socio-cultural factors, especially in Asia (Hilal & Engelhardt, 2007). However, white tea (an unfermented tea made from the new growth buds and young leaves of the plant) is well recognized by its higher sensorial quality and health properties (Cabrera, Artacho, & Giménez, 2006). Thus, tea has been related to beneficial effects on several diseases such as neurodegenerative and cardiovascular diseases, diabetes, obesity and basically, to every pathology involving oxidative stress (Higdon & Frei, 2003). Such protection is most probably due to a wide range of bioactive compounds in tea beverage such as flavonoids, other polyphenols, caffeine or theanine (Vuong, 2014). Flavan-3-ols, commonly called catechins, can account for up to 30% of the dry weight of white and green tea leaves, being epigallocatechin-gallate (EGCG) the major component (Cabrera et al., 2006, Jain et al., 2013). Consumption of 200–300 mg of EGCG (5–6 tea cups/day) has beneficial effects on cardiovascular health (da Silva Pinto, 2013) since EGCG and other catechins are very effective scavengers of radical oxygen species (ROS) and radical nitrogen species (RNS) both in vitro and in vivo.

The presence of these bioactive molecules depends on several factors. On one hand, the industrial process to obtain the commercial product from fresh leaves affects the amount of these compounds (Gorjanović et al., 2012). Thus, white and green teas suffer several drying steps, being less aggressive in white tea (Cabrera et al., 2003, Pastoriza et al., 2017a). On the contrary, black and red tea suffer an oxidation process where phenolics and other substances are oxidized (Vuong, 2014). On the other hand, preparing the beverage by infusion becomes another critical point since this process allows the extraction of bioactive compounds from tea (Damiani, Bacchetti, Padella, Tiano, & Carloni, 2014). The extraction of catechins depends on time and temperature, so monitoring these parameters while making the infusion is of great importance to get all the benefits from tea (Komes, Horžić, Belščak, Ganić, & Vulić, 2010). This extraction process affects not only the antioxidant capacity of the tea beverage but also its organoleptic characteristics, since the extracted molecules also play a role in taste (Pastoriza, Pérez-Burillo, & Rufián-Henares, 2017b). Finally, the physical state of tea leaves also play a role on sensory properties. In this sense, Castiglioni, Damiani, Astolfi, and Carloni (2015) found that milled leaves (usually sold in bags) have a more astringent taste than those obtained from whole leaves (those found in high-quality teas).

Different researchers have studied the extraction kinetics of catechins from white tea, based on water temperature and extraction time (Dai et al., 2017, Lin et al., 2017, Tan et al., 2017) but they usually lack the study of sensory analysis. On the other hand, there are scientific reports that centered on the effect of water temperature and extraction time on sensory properties (Castiglioni et al., 2015, Lantano et al., 2015, Lin et al., 2014) or even antioxidant capacity, but lacked analysis of the extraction of bioactive compounds. Therefore, the aim of this research was to perform a deep study on the effect of the extraction time and temperature on the release of healthy molecules and antioxidant capacity of white tea (Chinese Pai Mu Tan) infusion, in relation to their sensory attributes. After deciding the best time–temperature binomial for optimal sensory properties, the antioxidant capacity and bioactive compounds content of white and green teas commercialized in Spain were then measured. In addition to these studies, the influence of commercial presentation of teas (whole leaves vs. bagged teas) was also assessed.