Tea additions

The processes involved in the production of black tea results in a tea with a bitter taste, which is often the reason for black tea being consumed with milk (Langley-Evans, 2001:75) and sugar (Sharma et al., 2008:124). A study investigated the effect of added sugar and milk on the antioxidant status of black tea. Black tea with only sugar added, black tea with only milk added, black tea with milk and sugar added and plain black tea were prepared for the analysis. The results indicated that the antioxidant activity of black tea is enhanced and stabilised with sugar or milk added (Sharma et al., 2008:124). A different study conducted by van Het Hof et al.

(1998:356) assessed blood catechin levels after black or green tea consumption and the influence of adding skim milk to black tea. The study findings indicated that black and green tea catechins are quickly absorbed and that milk does not weaken the bioavailability of these flavonoid compounds.

Hollman et al. (2001:297) performed a study that evaluated the influence of milk addition to tea on flavonol absorption from tea in 18 healthy subjects. Each subject consumed only two of the following four beverages for a period of three days: black tea without additions (plain black tea), black tea with added milk, plain green tea and water. One cup of the beverage was consumed every two hours resulting in an intake of eight cups daily. The black tea (135 mL) itself was consumed with 15 mL milk to represent the black tea with added milk sample. The findings indicated that the flavonols from tea are absorbed and that milk addition does not influence the bioavailability. Studies done by van Het Hof et al. (1998:356), Leenen et al. (2000:87) and Catterall et al. (2003:3863) additionally confirmed that milk addition to tea does not reduce the bioavailability of the antioxidants present in tea.

Ryan and Petit (2010:14) also evaluated the influence of added skim, semi-skim and whole milk in various amounts on the antioxidant capacity of prepared black tea samples from five brands.

The results found were in contrast to that of the above studies with regards to milk addition to tea. The TAC of all the black tea brands evaluated decreased when 10 mL, 15 mL and 20 mL of bovine milk (skim, semi-skim and whole milk) were added to a 200 mL tea infusion. For all the brands of black teas that were compared, the addition of the skim milk significantly (p < 0.05)

reduced the TAC in comparison to the tea with the same volume of water added (Ryan & Petit, 2010:14). The study concluded that the effect of milk on the in vitro TAC may be related to the fat content of the milk. A number of fat-soluble antioxidants are present in milk (tocopherols, retinols and carotenoids). Therefore, the antioxidant potential of milk is decreased when its fat content is decreased which is due to the reduction in the fat soluble antioxidant components present (Ryan & Petit, 2010:17). A study was also undertaken by Ryan and Sutherland (2011:3115) to determine whether the addition of different types of soya milk or semi-skim bovine milk decreased the TAC of black tea. Soya milk addition to black tea was found to be a valuable substitute to using the semi-skim form of bovine milk for persons who wish to uphold the total antioxidant potential of a cup of tea.

In a study performed by Dubeau et al. (2010:539), the influence of milk addition on the antioxidant capacity of green, Darjeerling and English breakfast tea was investigated. The mean antioxidant capacity of the teas with milk addition was significantly (p < 0.05) lower than those with no milk (the plain teas). The researchers stated that milk decreased the electron donation ability of tea polyphenols at the electrode surface. The different teas were not equally affected by the addition of milk. It was suggested that some of the polyphenol compounds present in the teas might interact more readily with milk than others (Dubeau et al., 2010:542). Savage et al.

(2003:415) also confirmed the antioxidant reducing effect associated with milk addition to tea.

The study confirmed that regular tea consumption with added milk will result in the absorption of only a small amount of oxalate from the tea.

Langley-Evans (2000:309) performed a study with nine healthy adults for three days. The objective of the research was to evaluate the contribution of black tea flavonoids to the plasma TAC using the FRAP assay. On the first day of the study the participants consumed no tea. On the second and third day they consumed either black tea with or without milk at hourly interims from 09:00 to 14:00. Subjects who consumed no tea showed an unchanged plasma FRAP through the evaluation period. Those consuming black tea with milk showed no significant changes in the plasma FRAP between 09:00 and 12:00 and a 50% higher plasma FRAP between 12:00 and 15:00 which was not statistically significant. Considering those participants who consumed plain black tea, the plasma FRAP was significantly higher (65%; p = 0.02) between 09:00 and 12:00 and at 15:00 it was still higher than at 09:00 (76%; p = 0.002). This research also established that milk addition to black tea negatively influenced the antioxidant content.

Honey is also sometimes added to tea as a natural sweetener. Substances present in honey, such as vitamins, minerals, proteins and antioxidants are of nutritional value (Ajibola et al., 2012:61). Toydemir et al. (2015:127) determined the effects of honey addition on the antioxidant properties of different herbal teas. Two types of honey (flower and pine honey) were added to nine different herbal teas (melissa, ginger, fennel, green tea, rosehip, linden, daily, sage and echinacea) at different temperatures. The total phenolic content and the TAC of the tea samples with added honey were higher (up to 57% for both the honey types) than the samples without honey addition (Toydemir et al., 2015:127).

Campanella et al. (2003:734) conducted tests to determine the TAC of tea with different additions, for example a normal cup of tea, with or without lemon or herbal flavours added or milk added. Tea flavoured with camomile had the lowest TAC, while green tea and tea with lemon added had the highest TAC. Bottled tea with lemon added had a higher TAC than bottled tea with peach added (Campanella et al., 2003:734). Hot tea with added lemon or milk respectively resulted in an increased and a decreased antioxidant capacity, in comparison to a normal tea infusion. The increased antioxidant capacity of the lemon infused tea was said to be due to the ascorbic acid present in lemon (Campanella et al., 2003:733). Majchrzak et al.

(2004:447) through in vitro experimentation compared the antioxidant activity of several types of tea and evaluated the effect of the addition of lemon juice on the TAC. The researchers found that the tea samples with added lemon or lemon juice had a higher TAC than those without lemon juice added (Majchrzak et al., 2004:450). The same results were reported by Komes et al.

(2010:175). These researchers found that the addition of lemon juice resulted in an increased antioxidant capacity of all the green teas studied. Commercially flavoured teas are popular in European countries because of its flavour and therapeutic properties. Dried fruit aromas or natural aromas are added to these teas as a last step before the packaging (Pekal et al., 2011:681).