Assessing the antioxidant potential of soft beverages in the Turkish market: a comprehensive study

ABSTRACT

Soft beverages are an important part of fluid intake; however, it should be the main target to choose the right beverages according to healthy nutrition. This study aimed to determine, evaluate, and create a database of the total antioxidant capacity (TAC) contents of widely consumed soft beverages in local markets in Turkey. A total of 394 beverages, including 60 carbonated, 100 non-carbonated, 136 tea (teabags for cups and teapots and, shredded tea leaves), 75 coffee (instant and brewed), and 23 fermented beverages, with expiration dates at most half their shelf life, were analyzed. Shredded tea leaves and brewed coffees were prepared with different brewing techniques. TAC was analyzed on the MINDRAY-BS400 device using commercial kit ABTS (2,2’-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) and results are presented as mmol Trolox Equivalent(TE)/L. Statistical analyses were performed using SPSS 26. The mean TAC of all beverages was 3.7 ± 1.4 mmolTE/L (.120–5.535 mmolTE/L), with the highest content of tea and coffee (4.3 ± .6 mmol TE/L) and the lowest carbonated beverages (1.4 ± 1.5 mmolTE/L) (p < .05). The overall results showed that all soft beverages have antioxidant activity; however, the right choice of soft beverages might contribute to the dietary TAC and increase fluid intake.

KEYWORDS:

• Total antioxidant capacity
• polyphenol
• soft drinks
• beverages

Introduction

Water, taking part in almost all of the functions of the human body, is essential for the continuation of life.^[1,2] Losing only 1–2% of body water can impair consciousness and exercise capacity. Insufficient total fluid intake can cause health problems associated with the formation of kidney stones, deterioration of renal functions, hyperglycemia, and some components of metabolic syndrome; therefore, it is crucial to ensure adequate hydration.^[3] Most fluid consumption in the diet is provided by drinking water and soft beverages (tea, coffee, fruit juice, carbonated drinks, energy drinks, etc.).^[2,4] The most preferred beverages worldwide after drinking water are hot drinks (tea and coffee) and sugary drinks, although they vary culturally. Drinking water (1.04 L/day) constitutes almost half of the fluid intake, followed by hot drinks (.51 L/day), sugary drinks (.20 L/day), and fruit juices (.12 L/day) in Turkey.^[5]

Although beverages contribute to hydration status, the preferred type of beverage can have a beneficial or harmful effect on health.^[4,6] It is known that beverages containing sugar and low in nutrients (non-100% fruit juices, fruit drinks, carbonated drinks, energy drinks) increase the risk of chronic diseases such as type 2 diabetes mellitus, obesity, and coronary heart disease by causing weight gain.^[6–9] Furthermore, the overconsumption of sugary drinks is associated with hypocalcemia and osteoporosis.^[6,10] On the other hand, there are also types of beverages rich in phytochemicals, such as phenolic acids and flavonoids, and some nutrients. 100% fruit juices contain vitamins A, C, E, K, and B₆, thiamine, niacin, folate, choline, potassium, iron, manganese, fiber, flavonoids, and carotenoids.^[11] Moreover, tea and coffee are rich in bioactive compounds, many of which have antioxidant properties, such as caffeine, catechins, flavonols, and diterpenes.^[12,13] Soft beverages can also be produced from leaf or seed extracts and fruit juices/puree, apart from tea and coffee.^[4] Therefore, beverages containing herbal ingredients can reduce the risk of developing many diseases related to oxidative stress owing to antioxidants and bioactive elements in their composition.^[14–19]

Oxidative stress is defined as an imbalance between the pro-oxidants produced by endogenous (immune cell activation, inflammation, ischemia, infection, cancer, excessive exercise, mental stress, aging) and exogenous sources (environmental pollutants, heavy metals, some drugs, smoking, alcohol consumption, radiation) and the capacity of the organism to counter these radicals by the antioxidative system.^[20–22] Oxidative stress damage cells and cause serious health problems such as neurodegenerative diseases, inflammatory diseases, immune dysfunction, cardiovascular diseases, diabetes, allergies, cancer, and aging.^[23–25] Antioxidants reduce the risk of oxidative damage by acting as radical scavenging, hydrogen and electron donors, peroxide decomposers, singlet oxygen quenchers, enzyme inhibitors, synergists, and metal chelating agents.^[24] Many studies have proven the role of individual dietary antioxidants in improving redox status and health interactions.^[26–30] However, antioxidants do not act alone in vivo by showing synergistic, antagonistic, and additive interactions with each other.^[31] Thus, the concept of “Total Antioxidant Capacity,” a more comprehensive concept that investigates the cumulative effect of antioxidants by accepting that antioxidants interact with each other, has emerged.^[32] To date, various TAC methods have appeared, including competitive methods that react with stable free radicals in the environment, using reference components as probes, and methods based on the principle of reduction of metal ions.^[33] One of the most widely used colorimetric methods is those based on 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonate) (ABTS radical dot+). Reduced ABTS is colorless and turns into its characteristic blue-green color when oxidized. When mixed with any oxidizable substance, colored ABTS+ converts into its original colorless form by reducing.^[34] Soft beverages are an integral part of the human diet and a significant contributor to dietary total antioxidant capacity.^[35–37]

Soft beverages are an important part of fluid intake; however, it should be the main target to choose the right beverages according to contents in healthy nutrition. This study aimed to determine, evaluate, and create a database of the TAC contents of widely consumed soft beverages in local markets in Turkey.

Materials and methods

Collection and preparation of samples

The raw data from the 2017 National Nutrition and Health Survey, representing the general consumption patterns in Turkey, underwent thorough examination. Subsequently, beverage selection was carried out by considering the beverages commonly consumed by individuals, as indicated in the survey data.^[38] For this study, a total of 394 nonalcoholic beverages, including 60 carbonated beverages, 100 non-carbonated beverages, 211 tea & coffee, and 23 fermented beverages, were purchased from local chain markets in Ankara/Turkey, with expiration dates at most half their shelf life. The samples were stored at room temperature or 4°C following the storage advice on the product package and analyzed within two days after they were purchased.

Non-carbonated beverages, fermented beverages, and cold tea & coffee samples were shaken before opening the package. The ready-to-drink hot chocolate was heated over low heat with continuous stirring until it reached 100°C and then analyzed. Ready-to-drink hot chocolate, hot chocolate prepared with powder mixture, and smoothy were diluted 1:1 before analysis. Samples requiring preparation (tea, coffee, and powdered beverages) were prepared just before the analysis following the preparation instructions on the package and analyzed without waiting. All samples were centrifuged at 5000 rpm for 10 minutes before analysis and worked in duplicate.

Preparation of tea samples

Within the scope of the study, tea bags (for cups and teapots) and shredded tea leaves of distinct brands were analyzed. A total of 76 different teabags for cups, including black tea (n = 13), green tea (n = 20), white tea (n = 4), and herbal and fruit teas (n = 39), were chosen for the study. Tea bags for cups are prepared with boiling/boiled-and-waited (70–100°C) tap water and brewed for 3–10 minutes following the preparation instructions of the packages. Tea bags were moved up and down in the cup at least five times before removal (Table 1).

Table 1. Preparation of tea and coffee samples*.

	n	Water Temperature (^0C)	Waiting/Brewing Time (min)	Amount
Teas
Teabags for cups
Black Tea	13	100	3–4	1 teabag/200–250 mL water
Green Tea	17	80–90	3–5
Green Tea	3	100	3–6
White Tea	4	70–85	3–10
Herbal and Fruit Tea	36	100	3–6
Fruit Tea with Vitamins	3	80	5
Brewed Teas (In steel teapot)				-
Instant black tea	2	100	2	1 sachet/100 mL water
Shredded tea leaves	19	100	15	2,5 g tea/100 mL water
Shredded tea leaves	4	100	30 and 60	2,5 g tea/100 mL water
Shredded tea leaves	2	20	15	2,5 g tea/100 mL water
Shredded tea leaves ^§	2	100	15	2,5 g tea/100 mL water
Shredded tea leaves	2	100	15 min brewing −24 h waited and heated	2,5 g tea/100 mL water
Teabag black tea for teapot	4	100	15 and 30	1 teabag/200 mL water
Shredded green tea leaves	3	100	5 and 15	2,5 g tea/200 mL water
Teabag green tea for teapot	1	100	10	1 teabag/300 mL water
Herbal and Fruit Tea	3	80	4–5	5g tea/200 mL water
Mate-Mago Mixed Herbal Tea	1	100	4–5	5g tea/200 mL water
Coffees
Instant Coffees
Soluble Granulated Coffee	7	80–85	-	2 g coffee/200 mL water
Soluble Granulated Coffee Blend	20	80–85	-	1 sachet coffee/150–200 mL water
Instant Turkish Coffee	2	100	-	1 sachet coffee/70 mL water
Brewed Coffees
Filter Coffee (In coffee machine)	4	20	3–4	7g coffee/180 mL water
Filter Coffee (In french press)	4	80	5	7g coffee/180 mL water
Practical Filter Coffee	2	80	3–4	1 packet coffee/120–200 mL water
Practical Filter Coffee	1	95	3	1 packet coffee/300 mL water
Turkish Coffee	3	20	4–5	6 g coffee/65 mL water
Dibek Coffee	1	20	4–5	14,5 g coffeee/70 mL water

*Tap water was used in the preparation of all samples.

§ Brewed in a porcelain teapot.

A total of 41 shredded tea leaves, including black tea (n = 33), green tea (n = 4), and herbal and fruit tea (n = 4), were analyzed. Shredded black teas were prepared by brewing 2.5 g of black tea/100 mL of boiled tap water for 15, 30, and 60 minutes in a steel teapot, traditionally the most preferred method. Two shredded black tea leaves were brewed in a porcelain teapot for 15 minutes to distinguish whether the brewing material contributed to the analysis results in the method used. Two shredded black tea leaves were brewed for 15 minutes using the traditional and less preferred cold-water brewing method to observe the effect of the temperature of the brewing water. In addition, reheating and consuming pre-brewed tea at home is a frequently preferred method in our country. Therefore, two black tea samples were brewed with the traditionally preferred method, kept for 24 hours, and then heated until the water temperature reached 100°C (Table 1). On the other hand, teabags for teapot black teas were prepared by brewing for 15 and 30 minutes in a steel teapot, using 200 mL of boiled tap water for one teapot bag. Shredded green teas were prepared by brewing for 5 and 15 minutes using 2.5 g tea/with 200 mL boiled tap water. The green teabag tea for the teapot was brewed with a tea bag/300 mL of boiled tap water for 10 minutes. Shredded herbal and fruit teas were prepared by brewing 5 g tea/with 200 mL boiling/boiled-and-waited tap water at 80–100°C for 4–5 minutes (Table 1). Two samples, defined as “fast brewing tea/instant tea” containing finely ground tea leaves, were prepared with a pack/with 100 mL of boiled tap water and then left for 2 minutes (Table 1).

Preparation of coffee samples

In the scope of the study, instant (soluble granulated coffee) and brewed coffee samples of several brands were analyzed. Forty-four various coffees were selected, including instant coffee and coffee blends (n = 29), filter coffee (n = 8), practical filter coffee (n = 3), and Turkish coffee varieties (n = 4). Instant coffee and coffee blends were prepared by mixing 2 g or a sachet of coffee/with 150–200 mL of boiled-and-waited tap water (80–100°C), following the package instructions. Instant Turkish coffee was prepared by mixing one sachet of coffee/with 70 ml of boiled tap water (Table 1).

Filter coffee samples were brewed in the machine or French press using 7 g of coffee/with 180 mL of water. Practical filter coffees were brewed for 3–4 minutes using a pack of coffee/with 120–300 mL of boiled-and-waited tap water (80–95°C), following the package instructions. Turkish coffee varieties were cooked on low heat for 4–5 minutes using 6–14.5 g of coffee/with 65–70 mL of cold tap water (Table 1). The coffee grounds at the bottom of the cups were not included, and only the liquid part was taken into the tube.

Preparation of powder drink samples

Within the scope of the study, six powdered drinks were analyzed, including salep, chocolate milk, flavored drink powder, and spiced milk tea drink powder. Salep and hot chocolate milk drink powders were prepared by adding 150–180 mL of boiling milk to a packet (17 and 18.5, respectively. Chocolate drink powder with vitamins was prepared by adding 200 mL of cold milk (4°C) for 13.5 g of powder drink. Flavored drink powders were prepared by adding 250 mL of cold water (4°C) for a 20 g powder drink. A spiced milk tea drink was prepared by adding 180 mL of boiling tap water to a packet (19 g).

Analysis of Total Antioxidant Capacity (TAC) (mmol/L)

The ABTS method was selected due to its rapidity, cost-effectiveness, reproducibility, ease of handling, and versatility. This method provides the advantage of being able to measure both lipophilic and hydrophilic antioxidants, performing effectively across a wide range of pH levels, and exhibiting reactivity with both synthetic and natural antioxidants. Total antioxidant capacity (TAC) levels were analyzed fully automatically on the MINDRAY-BS400 instrument with a commercially available kit (Catalog number: RL0017, Relassay-Turkey). In this method, the characteristic color (dark blue-green) of the more stable ABTS (2,2’-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)) radical cation is bleached by antioxidants. The change in absorbance at 660 nm is related to the antioxidant level in the sample.

The experimental procedure involved dispensing 300 µl of reagent 1, consisting of acetate buffer with a concentration of .4 mol/l at pH 5.8, along with 18 µl of the sample using an automatic device. These volumes were then combined in a cuvette, thoroughly mixed, and the initial reading was taken at 660 nm exactly 30 seconds after the mixing process. Following the initial reading, 45 µl of reagent 2, comprising a prochromogen solution with ABTS at a concentration of 30 mmol/l, was measured and combined. The mixture was then incubated at 37°C for 5 minutes. Subsequently, the second reading was taken at 660 nm. The test assay has a sensitivity of less than 3%. The assay is calibrated with a standard antioxidant solution conventionally called Trolox Equivalent (vitamin E analog), and results are expressed in mmol Trolox Equivalent (TE)/L (Relassay, Turkey).^[34]

Statistical analysis

All the statistical analyses were performed using Statistical Packages for Social Sciences (SPSS 26, SPSS Inc. Chicago, IL; USA). Visual tests (histograms, probability plots) and the Kolmogorov-Smirnov test were used to determine whether or not outcome variables were normally distributed. As the results were not normally distributed, a two-step approach for transforming continuous variables to normal by Templeton G. (2011) was used to perform parametric tests.^[39] The Levene test was used to assess the homogeneity of the variances. The One-way ANOVA test was used to compare the mean values of homogeneous subgroups. Welch Test was used to compare the mean values of non-homogeneous subgroups. When an overall significance was observed, pairwise post hoc tests were performed using Tukey and Tamhanes T₂ for homogeneous and non-homogeneous variances, respectively. The p-value <.05 (two-sided) was considered statistical significance.

Results and discussion

This study’s samples comprised 15.2% carbonated beverages, 25.4% non-carbonated beverages, 53.6% tea&coffee and 5.8% fermented beverages. All the beverages examined showed antioxidant properties, and the antioxidant capacity differs according to the fruit juice, plant extracts, and added antioxidant content. The mean TAC value of the analyzed beverages was 3.7 ± 1.4 mmol TE/L, ranging from .120 to 5.535 mmol TE/L. When all soft beverage groups were evaluated, tea and coffee (4.3 ± .6 mmol TE/L) had the highest TAC and carbonated beverages had the lowest TAC (.648 ± .865 mmol TE/L); however, carbonated beverages with added antioxidant/vitamin was 2.4 ± 1.5 mmol/L TE (p < .05). The TAC value of non-carbonated beverages was 3.8 ± 1.3 mmol TE/L, and that of fermented beverages was 3.6 ± 1.1 mmol TE/L (Figure 1).

Figure 1. Total Antioxidant Capacity of Beverage Groups.

P<.05 Welch Test, Tamhane T_{2 .} There is a statistically significant difference between different letters. Error bars represent the 95% confidence interval.

Carbonated soft beverages

The mean TAC value of all carbonated beverages (n = 60) examined within the scope of the study was 1.4 ± 1.5 mmol/L TE. In this category, it is seen that the TAC values of carbonated beverages containing fruit juice and plant extracts and containing vitamin C/antioxidant are higher than the others (Suppl 1). The mean TAC values of carbonated drinks were sorted as flavored natural mineral water with added vitamin C, fruit soda, detox juice, fruit-concentrated sparkling natural mineral water, flavored soda, energy drink, cola, flavored or unflavored sparkling natural mineral water, and tonic, in descending order (Figure 2) (p < .05). The mean TAC value of flavored sparkling natural mineral water with added vitamin C (4.3 ± .6 mmol TE/L) was significantly higher than other carbonated drinks, as expected (p < .05). Flavored vinegar carbonated drinks, available in the markets as detox water, one of today’s popular drinks, had the highest TAC value (1.6 ± .9 mmol TE/L) in the third rank. The deionized apple juice concentrate and apple cider vinegar in these beverages are thought to be responsible for their antioxidant capacity. As shown in the study by Budak (2021), apple cider vinegar contains gallic acid and chlorogenic acid in particular, as well as catechin, epicatechin, and p-coumaric acid.^[40]

Figure 2. Total Antioxidant Capacity of Carbonated Beverages.

SNMW: Sparkling Natural Mineral Water. Welch Test, post-hoc Tamhane T₂ test p<.05. There is a statistically significant difference between different letters. Error bars represent the 95% confidence interval.

It was determined that cola drinks, natural mineral waters, and tonics had the lowest TAC value among carbonated beverages (p < .05)(Figure-2). Similar to this study, Hong et al.. (2016) also reported that carbonated beverages such as energy drinks and cola have the lowest TAC values compared to other beverages.^[41] Brenna et al. found the TAC value of cola drinks in the range of .170 to .328 mmol TE/L with different methods, including Ferric Reducing Antioxidant Power (FRAP) and 2,2-diphenyl-1picryl-hydrazyl-hydrate (DPPH).^[42] There are relatively few studies on the TAC value of carbonated beverages in the literature. Although there is also limited literature on the phenolic composition of carbonated beverages such as cola and cola drinks since they do not contain phenolic components that may contribute to their antioxidant activities, minimal amounts of natural extracts and some chemical components added as colorants are thought to be responsible for their antioxidant activities.^[4,42] Caramel is used as a colorant in cola and fruit soda drinks. Caramel contains components with reducing activity consisting of 5-(hydroxymethyl)-2-furfural (HMF) and a mixture of sugar and amino ingredients. Furthermore, caffeine is thought to contribute to the TAC value of these beverages owing to its -OH scavenging activity.^[4] Quinine in the composition of tonic waters and herbal extracts in the composition of energy drinks provide the antioxidant activity of these drinks.^[43,44]

Non-carbonated soft beverages

The mean TAC value of the non-carbonated soft beverages (n = 100) analyzed within the scope of the study was 3.8 ± 1.3 mmol TE/L. The flavored chocolate and cocoa milk drink had the highest TAC value (5.145 mmol/L) among the non-carbonated beverages (Suppl Table 2). Cocoa beans and chocolate are rich in polyphenols (epicatechin, gallocatechin, epigallocatechin, phenolics, procyanins, anthocyanins, flavone, and flavonol glycosides) and have high TAC value.^[45–47] One study reported that cocoa products have a higher antioxidant capacity and contain more flavonoids per serving than tea and red wine.^[48] Therefore, unsurprisingly, it had the highest TAC level among non-carbonated beverages. The chocolate and cocoa milk drink was followed by soft beverages containing mixed fruit juice and puree (with added antioxidants) (5.07 ± .01 mmol TE/L) and 100% orange-carrot and apple juice (5.070 mmol TE/L)(Suppl Table-2). Besides the addition of antioxidants, it was reported that some fruits in mixed fruit juices show higher antioxidant activity by creating a synergetic effect. As Liu et al.^[49] revealed, combining fruits such as oranges, grapes, apples, and blueberries produced a synergetic effect on antioxidant activity in vitro. In contrast, each fruit’s median effective dose (EC₅₀) was five times greater than in the combination.^[50]

When non-carbonated soft beverages were divided into categories, the average TAC values were ranked from largest to smallest as 100% fruit juices, detox juices, milk drinks, fruit nectars, fruit-flavored drinks, fruit drinks, and powder drinks (Figure-3). According to the findings, the mean TAC values of 100% fruit juices (4.6 ± .7 mmol TE/L) and fruit nectars (4.0 ± 1.0 mmol TE/L) were significantly higher than fruit drinks (2.9 ± 1.6 mmol TE/L), and fruit flavored beverages (3.4 ± 1.0 mmol TE/L)(p < .05) (Figure 3). Although the amount of fruit content in these drinks differs from country to country, according to the Turkish Food Codex (Turkish Food Codex Communiqué on Non-Alcoholic Drinks-2007/26), fruit nectars should contain at least 25–50% fruit juice and/or puree, and fruit drinks should have at least 10% fruit juice and/or puree. Today, detox drinks are often part of popular weight-loss diet practices.^[51] According to the label information, these beverages examined within the scope of the study consist of vegetable and/or fruit juices/purees and added antioxidants. Therefore, it is unsurprising that these beverages’ average TAC value (4.1 ± 1.0 mmol TE/L) is close to 100% fruit juice.

Figure 3. Total Antioxidant Capacity of Non-Carbonated Beverages.

One-way ANOVA test, p<.05, post hoc Tukey test. There is a statistically significant difference between different letters. Error bars represent the 95% confidence interval.

In this study, the average TAC values of 100% fruit juice varieties are sorted from largest to smallest as orange-carrot-apple, orange-peach apple-cherry pomegranate, mixed fruit/vegetable, red grape, white grape, black mulberry, tomato, and apple juices (p > .05) (Suppl Table 2). As it is known, flavones (chrysin) are in the skins of fruits; flavanones (naringin, naringenin, taxifolin, eriodictyol, hesperidin, isosacuranetin) are in citrus fruits; among flavonols, kaempferol is in grapefruit, quercetin is in fruits such as tomatoes, apples, cranberries, strawberries, and raspberries, rutin is in citrus; among flavononols, engeleteinn and astilbine are in white grape skin; among anthocyanidins, cyanidin is in cherries, sour cherries, raspberries, strawberries, and grapes, while delphinium and pelargonidin are in dark colored fruits.^[19] In a review comparing fruit and fruit juices by Wootton Beard and Ryan, it was reported that pomegranate (19400 µmol/kg) and pomegranate juice (8557–10232 µmol/L) had the highest antioxidant capacity. Beet (8355–9500 µmol/L) and grapefruit (7268–7668 µmol/L) juices pursued pomegranate.^[18] In different studies, it has been shown that pomegranate juice had the highest TAC value among fruit juices.^[41,52] It is thought that pomegranate juices contribute significantly to their high antioxidant capacity since the outer skin and arils containing punicalagin, which is known to have high antioxidant value, are not removed in commercially sold pomegranate juices.^[18] In the study of Wern et al., in which freshly squeezed pomegranate juice and commercial pomegranate juices were compared, it was reported that commercial pomegranate juice had a higher antioxidant capacity.^[52] In this study, pomegranate juice (5.007 mmol TE/L) ranked high among 100% fruit juices in terms of TAC value (Suppl Table 2). When the 100% fruit juices in the literature are compared, it is seen that there are different results.^{[18,41,45,52–55]} The TAC values of fruit juice and juice/puree/extract-containing beverages vary depending on the type of fruit, the fruit ratio it contains, caramel color, and whether antioxidant/vitamin C is added. In addition, the geographical region of the fruits used, the fruit juice extraction technique, preservatives, the ripeness of the fruits, the parts of the fruits, and the packaging material may cause differences in antioxidant capacity.^[4,54–56]

Tea and coffee

Tea and coffee are popular beverages that are consumed almost every day around the world and are considered indispensable parts of diets. Many studies have shown that tea and coffee significantly contribute to the total antioxidant capacity of the diet.^[36,57–61] The mean TAC value of the teas examined in the study (n = 136) was 4.2 ± .6 mmol TE/L. Also, for the teas analyzed, the mean TAC value of the teabags (for cups) of flavored green teas (4.656 ± .005 mmol TE/L) was the highest and followed by teabags (for cups) of green tea blends (4.650 mmol TE/L), white tea (4.650 mmol TE/L), green tea (4.647 mmol TE/L) and flavored black tea (4.638 ± .006 mmol TE/L)(Suppl Table 3). Teas predominantly contain flavonoids known for their antioxidant properties.^[13] The majority of the polyphenol content of teas is due to catechins ((+)-catechin, (+)-Gallocatechin, (−)-Epicatechin, (−)-Epigallocatechin, (−)-Epicatechin gallate, (−)-Epigallocatechin gallate).^[19] The production of tea is a multi-step process. The top bud and the two leaves next to it are known as the most valuable part of the tea,^[62] and these teas are sold as may tea or first-harvest tea in Turkey. The first harvest teas of three different brands were analyzed in this study and showed similar TAC values with other brewed teas (p > .05)(data not shown). After the tea leaves are collected, they are left to wither and are then plucked or cut. In white tea, the leaves are immediately left to dry after they are collected. Different machines and technologies are used in the plucking, cutting, and fermentation stages.^[62] Polyphenol oxidase and peroxidase enzymes that occur naturally during the fermentation of fresh tea leaves oxidize catechin monomers, and thus some catechins combine to form complex compounds such as theaflavin, theacinensin, and thearubigin.^{[13,19,45,63]} Black tea is produced due to the complete fermentation of the tea leaves. Green and white tea, on the other hand, preserve their polyphenol contents because they do not undergo fermentation.^[45,63] Hence, green and white tea are expected to have the highest TAC value. The TAC values of teabags of all green tea blends (excluding green tea-turmeric-echinacea), black teas (with probiotic, plain, flavored), white tea, linden, chai spiced/fruit/vitamin mixed herbal teas, mixed fruit tea, rosehip tea, and quick-brew black teas were significantly higher than other teas (p < .05). TAC values of different brands of brewed tea in the market were fairly close (4.131 ± .002 mmol TE/L)(Suppl Table 3). When teas were grouped, the TAC values were listed from largest to smallest, white tea teabag, green tea teabag, instant black tea, black tea teabag, mixed herbal tea with fruit (with vitamins) teabag, brewed green tea, brewed black tea, brewed mixed herbal tea, mixed herbal and fruit tea teabag and ice tea (Figure 4). Instant black tea (4.627 ± .004 mmol TE/L), teabags of black tea (4.6 ± .3 mmol TE/L), green tea (4.646 ± .013 mmol TE/L), white tea (4.648 ± .008 mmol TE/L) and mixed herb tea (with vitamins) (4.5 ± .2 mmol TE/L) revealed significantly higher TAC than brewed teas (p < .05)(Figure 4). Similarly, a study by Nickiniaz et al. showed that black tea teabags produced higher antioxidant activity and polyphenols in the same period than loosely packed tea containing larger particles.^[64] Teas used in producing tea bags contain smaller particles than brewed teas. The type of tea sold as quick-brew tea/instant tea is similar to teabags and contains much finer particles than brewed tea. Thus, different tea components can be extracted more quickly. It should also be noted that the material from which the teabag is made can also affect the composition of the tea infusion.

Figure 4. Total Antioxidant Capacity of Teas.

*Added vitamins

Welch Test, Tamhane T2 p<.05. There is a statistically significant difference between different letters. Error bars represent the 95% confidence interval.

One of the most critical factors affecting the TAC values of teas is brewing time. Adequate infusion time is required for the dry plant to absorb the water sufficiently into its matrix and then for the phytochemicals to pass into the water. It has been reported that more phenolic components were infused in water in the first 5 minutes but did not increase after 8 and 10 minutes.^[65] The study by Cleverdon et al. also showed that ~ 80–90% of polyphenols in teas other than green tea were released in the first five minutes.^[66] Therefore, not only does brewing tea for a long time not reveal more phenolic compounds, but also negatively affects the taste and quality of tea.^[65] In this study, the effect of different brewing times on the TAC value was also investigated, and there was no significant difference between 15, 30, 60 min brewing times. Likewise, the brewing method, temperature, and material were also examined within the scope of the study; however, it was found that the brewing method, the brewing temperature, and the type of teapot used did not significantly affect the TAC value (Suppl Table 3). In summary, the TAC value of teas can be affected by many factors, such as the type of tea, the brand, the geographical region and season when the tea is collected, the quality of the leaves collected, the age of the plant, the processing method and technique, the fermentation time, the technology used and the teabag material.^[62,64–66]

The mean TAC value of the coffees examined in this study (n = 75) was 4.5 ± .6 mmol TE/L (Suppl Table 4). Cold (ice) coffee (5.0 ± .4 mmol TE/L) had the highest TAC value and was followed by Turkish coffee (4.615 ± .017 mmol TE/L), instant coffee (4.3 ± .6 mmol TE/L), practical filter coffee (4.2 ± .5 mmol TE/L), filter coffee (4.116 ± .005 mmol TE/L) and coffee-milk beverage (3.7 ± .4 mmol TE/L) (p < .05)(Figure 5). Coffee is a beverage that contains more than 1000 different bioactive components besides caffeine. Methylxanthines (caffeine, theobromine, theophylline), diterpene alcohols (cafestol, kahweol), chlorogenic acids (caffeoylquinic acids, feruloyl quinic acids, p-coumaroylquinic acids), flavonoids (catechins, anthocyanins), hydroxycinnamic acids, (ferulic acids, caffeic acid, p-coumaric acid), tocopherols and melanoidins are among the bioactive components found in coffee.^[12,67] During the roasting process, some components such as 5- caffeoylquinic acids (CQA), 3,4-diCQA, 3,5-diCQA, phenolic acid, trigonelline, polyphenolic content, cafestol, and kahweol decrease, while components such as melanoidins, chlorogenic lactones, gallic acid, nicotinic acid, caffeic acid, flavonoids, N-methyl pyridinium increase in green coffee beans.^[12]

Figure 5. Total Antioxidant Capacity of Coffees.

Welch Test, posthoc- Tamhane T₂ , p<.05. There is a statistically significant difference between different letters. Error bars represent the 95% confidence interval.

Instant coffees (soluble granulated coffee) investigated in this study revealed higher TAC values than brewing filter coffees (p < .05). Similarly, the studies of Brazova et al. and Zujko and Witkowska reported that the TAC value of instant coffees was 3.5 times higher than brewing coffees.^[45,68] In the production stage of instant coffees, the procedures required for the water-dissolving coffee beans may also cause the transition of bioactive components into water.^[69] It was also thought that the concentration at the extraction phase might also cause this difference.^[57] It is seen that the results of the studies on the effect of different methods (Turkish, instant, filter) on the TAC value of coffee were different.^[69–73]

Coffees undergo processes such as fermentation, roasting, grinding, and brewing, significantly changing the final product’s polyphenol content. The composition of coffee is affected by many factors, such as characteristics of raw materials (species, origin, and genetic), agricultural practices (traditional or organic), techniques applied post-harvest (dry or age), storage time and conditions, degree of roasting (light, medium, intensive), type of roasting process (standard or torrefacto), type of commercial coffee (roasted or soluble), grinding and brewing method (boiling, filter or espresso).^[57,67] Mejia et al. claimed that even two cups of coffee, drunk in a row, would never have the same composition.^[67]

Fermented beverages

The mean TAC value of fermented beverages (n = 23) analyzed in this study was 3.6 ± 1.1 mmol TE/L(Suppl Table 5). Although there was no significant difference between fermented beverages regarding TAC values, beet juice (4.625 mmol TE/L) had the highest TAC value, followed by fermented green tea (kombucha) (4.1 ± .3 mmol TE/L) (p > .05) (Figure 6). Beet juice contains phenolic components, ascorbic acid, carotenoids, and betalains.^[74] Shalgam, also known as fermented black carrot juice, is a traditional red beverage constituted as a result of lactic acid fermentation of sourdough, bulgur flour, turnip, and water, and contains cyanidin-3-glycoside.^[75] Kombucha tea is formed due to the fermentation of sugary tea with symbiotic bacteria and yeast cultures. As a result of bacteria and yeast fermentation, the catechin components are thought to increase antioxidant power by degradation. Both bioactive components and vitamins and minerals in the tea composition contribute to the TAC value of Kombucha.^[76,77] Malt is defined as a dry and roasted form of other cereal used in beer production, especially barley, after germination under controlled conditions (Turkish Food Codex Beer Communiqué 2006/33). Malt beverage is a drink that does not contain alcohol made of barley and has more nutritious properties than beer. Malt drinks have dominantly (+)-catechins followed by gallic acid, syringic acid, ferulic acid, and protocatechuic acid. As well as polyphenols, products that occurred due to the Maillard reaction are responsible for the antioxidant activity of malt drinks.^[78] Boza is a traditional fermented beverage formed from yeast and lactic acid fermentation of grains such as millet, corn, wheat, and rice. Phenolic compounds and flavonoids released as a result of the fermentation of grains in their content may be responsible for the antioxidant capacity of this beverage.^[79]

Figure 6. Total Antioxidant Capacity of Fermented Drinks.

p>.05, ANOVA. *with fruits and prebiotics. Error bars represent the 95% confidence interval.

The strength of this study was to reach as many samples as possible by choosing different brands to represent all soft beverages consumed in Turkey within the scope of the project’s financial possibilities. In addition, it took considering different preparation, and cooking methods, which are thought to affect the TAC value. The most important limitation of this study was the evaluation of the TAC value of beverages solely with the ABTS method. Analysis results might be compared with each other by using different methods such as Ferric Reducing Antioxidant Power (FRAP), Total Radical Trapping Antioxidant Parameter (TRAP), and Oxygen Radical Absorption Capacity (ORAC). Besides the TAC, analyses might be made on which polyphenol components the beverages contained, and their correlations with antioxidant capacity might be explored.

Conclusion

Beverages contribute significantly to the individual’s fluid intake. In this context, with the right choice of nonalcoholic beverages, fluid intake can also contribute to the total antioxidant capacity of the diet. In this study, the means TAC values of different soft beverage categories were 4.3 ± .6 mmol TE/L for tea and coffee, 3.8 ± 1.3 mmol TE/L for non-carbonated drinks, 3.6 ± 1.1 mmol TE/L for fermented drinks and 1.4 ± 1.5 mmol TE/L for carbonated beverages. According to these results, tea and coffee, non-carbonated and fermented beverages, can be a good contributor to the dietary TAC. Among non-carbonated beverages, 100% fruit juices should be one of the first choices, as they contain both fruit and no added sugar. Fermented beverages are also an appropriate alternative because they contribute to the prebiotic and probiotic content of the diet and contain less sugar than other beverages.

Authors’ contribution statements

Conceptualization: [Rümeysa Yeniçağ and Neslişah Rakıcıoğlu]; Methodology[Rümeysa Yeniçağ and Neslişah Rakıcıoğlu]; Formal Analysis: [Rümeysa Yeniçağ]; Investigation: [Rümeysa Yeniçağ]; Resources: [Rümeysa Yeniçağ]; Writing-original draft: [Rümeysa Yeniçağ]; Writing-review & editing: [Neslişah Rakıcıoğlu]; Visualization: [Rümeysa Yeniçağ]; Supervision: [Neslişah Rakıcıoğlu]; Project administration: [Rümeysa Yeniçağ and Neslişah Rakıcıoğlu].

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/10942912.2024.2322160

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All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest or non-financial interest in the subject matter or materials discussed in this manuscript.