Traditionally, bush tea has been used for the treatment of various ailments such as boils, acne, infected wounds, cuts, headaches, colds, loss of voice and throat infection (Mudau et al., 2006; Nchabeleng et al., 2013), hypertension, heart disease, and diabetes (Nchabeleng et al., 2013). The extracts from soaked roots and leaves are reportedly used as an anthelminthic by the VhaVenda people (Mbambezeli, 2005). It is also used for cleansing or purifying blood (Joubert et al., 2008; Roberts, 1990). Bush tea contains 5-hydroxy-6,7,8,3′,4′,5′-hexamethoxy-flavan-3-ol (Mashimbye et al., 2006), 3-0-demethyldigicitrin, 5,6,7,8,3′,4′-hexamethoxyflavone and quercetin, polyphenols (Mudau et al., 2007a), tannins (Mudau et al., 2007b), and antioxidants (Mogotlane et al., 2007). Tea flush has been known to be followed by carbohydrate accumulation reserves, which are channeled toward polyphenol production (Roberts, 1990). During tea flush, total polyphenols range from 20% to 35%. The clone being examined, soil type, leaf age, agronomic practices, and climatic conditions determine the chemical composition of the tea leaves (Hartmann et al., 1996).
Antioxidant content is associated with those compounds which are able to protect biological systems against the harmful effects of reactions of extreme oxidation, which involve nitrogen and oxygen species reaction (Mogotlane et al., 2007). Thus, to an extent, altering chemical compositions will also have an impact on compounds that facilitate the scavenging ability of reactive oxygen species.
Generally, microelements such as Zn, aluminium (Al), Cu, and B are key components in many biological compounds, and play a significant role in increasing photosynthesis of the crop (Ibrahim et al., 2011) and the production of secondary metabolites (Ibrahim and Hawa, 2013). Previous studies showed that agronomic practices such as the application of macroelements such as nitrogen (N), phosphorus (P), and potassium (K) (Mudau et al., 2007a), pruning, and drying methods are cultural practices which influence the quality of bush tea.
Herbal tea quality is measured by metabolites such as tea polyphenols. Polyphenol-rich diets have been linked with prevention of several chronic and degenerative diseases (Neilson and Ferruzzi, 2011), including cancer (Neuhouser, 2004), cardiovascular disorders (Ding et al., 2006), obesity, and diabetes (Nagao et al., 2009; Thielecke and Boschmann, 2009), including neurodegenerative disorders (Mandel et al., 2005). Polyphenols are extensively altered during first-pass metabolism such that, the resulting metabolites are conjugates (e.g., sulfates and glucuronates) of the parent aglycone or conjugates of methylated parent aglycones (Barbosa, 2007). Tannins on the other hand are also involved in the formation of polyphenols and their astringent nature impacts on the taste of tea (Arbenz and Avérous, 2016), while the flavonoids indirectly influence antioxidant activity (Tan et al., 2016) However, micronutrients are involved in the metabolism by way of precursors from both the shikimate and the acetate-malonate pathways (Crozier et al., 2000; Urquiaga, and Leighton, 2000). In this study, the indirect effect of micronutrient foliar application on polyphenols, tannins, flavonoids, and antioxidants is that linked to tea quality. However, data that describe the effect of microelements on growth, productivity, and chemical composition of bush tea are lacking. Therefore, the aim of the study was to determine the effect of selected microelements (B, Fe, Zn, and Cu) on the quality of bush tea. The study was intended to provide the baseline for the foliar spray application of micronutrients to enhance quality of bush tea.
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