## 1 Introduction  
Tea is known to have both preventive and therapeutic disease ameliorating abilities. It is rich in phytochemicals that have significant therapeutic effects [1]. The tea plant has two major varieties: the small-leaved China plant (_Camelia sinensis sinensis_) and the large-leaved Assam plant (_Camelia sinensis assamica_). Commercially available teas can be categorized into three types based on their processing method and degree of fermentation: black tea (maximally fermented), oolong tea (partially fermented), and green tea (unfermented), all of which come from the same plant, _C. sinensis_[2, 3, 4]. Black tea is one of the most popular refreshing drinks consumed worldwide. It is obtained from the maximally oxidized leaves of _C. sinensis_ var. _assamia_[5, 6]. It is rich in theaflavins and thearubugins, which are responsible for the distinct red-brown colour, stronger flavour, and astringent taste [7; 8]. Both of these phytochemicals are known to have antioxidant, antidiabetic, antidyslipidemic, antihyperglycemic, cardioprotective, and cancer preventive effects and are associated with augmenting beneficial gut microbiota [9; 10].  
Black tea has health-promoting effects, such as anti-inflammatory, antioxidant, antiviral, antiallergic, and anticarcinogenic effects [11; 12]. To enhance the medicinal properties and flavour of black tea. It can be supplemented with ginger, tulsi leaves, green cardamom, and other medicinal herbs.  
Earlier studies reported that herbs have various bioactive compounds with antioxidant properties [13; 14]. When these compounds are combined, they may show a higher scavenging effect than a single compound. There can be three types of possible interactions (synergistic, additive, or antagonistic) between phytoconstituents that may modulate their biological properties [15; 16]. Some studies have reported that the ratio of phytochemicals or plant extracts in the mixture can influence the antioxidant potential of the whole extract [17; 18]. The concentration and ratio of the antioxidants in the mixtures influence the interactive effect. Numerous antioxidant interactions (antagonistic, additive, and synergistic) have been identified over the last decades from combinations of diverse bioactive compounds, such as purified compounds (vitamins and phytochemicals), synthesized antioxidants, crude extracts, and enzymes. A study conducted on five different ratios of green tea (GT) and _O. gratissimum_ (OG) revealed that the GT+OG combination at 1:1 demonstrated the highest antioxidant potency with maximum synergism [19]. _Ocimum_ spp., commonly known as tulsi in India, is used as an additive in black tea preparation. _O. gratissimum_ is a herbaceous plant commonly known to have immense therapeutic, chemopre, and free radical scavenging abilities [20; 21]. Eugenol is one of the important active compounds of _O. gratissimum_ and has demonstrated analgesic, antioxidant, and anti-inflammatory effects. It also exhibited ameliorating effects against type 2 diabetes, cancer, and metabolic syndrome [22]. A previous study in our laboratory illustrated that BT combined with OG showed high antioxidant activity compared to other _Ocimum_ spp. (_O. sanctum_ and _O. canum_) [23]. Black tea bags mainly contain black tea granules, and the tea bags or unbagged tea (black tea granules) are commonly used for black tea preparation in comparison to whole leaf black tea. The current study was undertaken to evaluate the effect of altering the ratios of black tea granules and _O. gratissimum_ on the antioxidant potential of the binary mixture.