Suggested mechanism for the effect of sweeteners on radical scavenging activity of phenolic compounds in black and green tea

Figures & data

Table 1. Antioxidant activity of different tea extracts against DPPH and ABTS radicals.

	Against DPPH radical		Against ABTS radical
Sample no.	50 µg/ml	100 µg/ml	50 µg/ml	100 µg/ml
Green tea only	73.6 ± 0.95	93.8 ± 1.52	75.0 ± 4.1	95.8 ± 1.5
Green tea + sucrose 0.5%	73.0 ± 1.52	92.2 ± 2.1	75.6 ± 2.3	94.3 ± 1.6
Green tea + sucrose 1.0%	75.2 ± 1.6	94.08 ± 3.4	73.6 ± 1.05	92.1 ± 3.6
Green tea + sucrose 2.0%	70.8 ± 2.3	90.6 ± 2.3	71.8 ± 1.0	90.2 ± 2.1
Green tea + sucrose 4.0%	70.2 ± 1.5	90.9 ± 2.0	70.88 ± 1.63	90.6 ± 0.78
Black tea only	68.5 ± 3.6	86.8 ± 0.8	70.0 ± 2.5	87.0 ± 1.5
Black tea + sucrose 0.5%	71.5 ± 2.4	90.4 ± 1.4	73.04 ± 0.7	91.3 ± 0.32
Black tea + sucrose 1.0%	71.6 ± 1.3	89.6 ± 1.95	72.2 ± 1.4	90.2 ± 1.6
Black tea + sucrose 2.0%	71.4 ± 2.5	89.3 ± 0.74	73.3 ± 2.3	91.6 ± 3.85
Black tea + sucrose 4.0%	73.5 ± 1.6	92.1 ± 0.98	74.8 ± 1.05	91.9 ± 4.6
Green tea + 0.1% aspartame	71.12 ± 3.0	88.9 ± 1.2	74.2 ± 1.0	92.3 ± 0.9
Green tea + 0.2% aspartame	72.1 ± 1.5	89.1 ± 1.6	72.9 ± 3.4	92.5 ± 1.30
Green tea + 0.4% aspartame	70.48 ± 2.1	88.1 ± 1.1	70.9 ± 0.75	88.6 ± 2.4
Black tea + 0.1% aspartame	71.9 ± 2.3	89.4 ± 1.15	71.68 ± 1.3	89.6 ± 3.6
Black tea + 0.2% aspartame	72.53 ± 1.4	90.66 ± 0.55	72.8 ± 2.8	90.1 ± 1.8
Black tea + 0.4% aspartame	70.9 ± 1.31	88.6 ± 2.6	74.8 ± 0.9	92.0 ± 1.97
Sucrose	10.52 ±  1.3	14.8 ± 1.7	10.87 ± 1.9	15.9 ± 0.8
BHA	77.8 ± 1.15	92.5 ± 3.8	79.8 ± 2.3	95.3 ± 0.55
LSD 0.01	2.410	3.530	3.296	3.241

Note: Each value is presented as mean of triplet treatments, LSD: least different significantly at p ≤ .01 according to Duncan’s multiple range.

Table 2. Total phenolic compounds and flavonoids content (g/100g) in different tea extracts.

Sample no.	Phenolic	Flavonoids
Green tea only	0.40 ± 0.05	0.29 ± 0.0
Green tea + sucrose 0.5%	0.31 ± 0.1	0.25 ± 0.02
Green tea + sucrose 1.0%	0.31 ± 0.03	0.25 ± 0.0
Green tea + sucrose 2.0%	0.23 ± 0.0	0.20 ± 0.0
Green tea + sucrose 4.0%	0.27 ± 0.01	0.23 ± 0.05
Black tea only	0.17 ± 0.02	0.16 ± 0.01
Black tea + sucrose 0.5%	0.21 ± 0.03	0.14 ± 0.0
Black tea + sucrose 1.0%	0.19 ± 0.0	0.14 ± 0.0
Black tea + sucrose 2.0%	0.22 ± 0.04	0.11 ± 0.0
Black tea + sucrose 4.0%	0.11 ± 0.01	0.02 ± 0.0
Green tea + 0.1% aspartame	0.32 ± 0.0	0.23 ± 0.01
Green tea + 0.2% aspartame	0.34 ± 0.02	0.20 ± 0.0
Green tea + 0.4% aspartame	0.19 ± 0.03	0.15 ± 0.0
Black tea + 0.1% aspartame	0.21 ± 0.01	0.12 ± 0.0
Black tea + 0.2% aspartame	0.59 ± 0.10	0.31 ± 0.03
Black tea + 0.4% aspartame	0.66 ± 0.16	0.13 ± 0.0
LSD 0.01	0.0214	0.0199

Note: Each value is presented as mean of triplet treatments, LSD: least different significantly at p ≤ .01 according to Duncan’s multiple range test.

Figure 1. The dose–response curve of promising sample (green and black tea) compared with standard compound (BHA).

Figure 2. HPLC chromatogram obtained by the separation of green tea with aspartame extract.

Table 3. Phenolic compounds and caffeine content (µg/100g) in different tea extracts.

	Tea samples
Phenolic compounds	Green tea only	Green tea +  sucrose 1%	Green tea +  aspartame 0.1%	Black tea only	Black tea +  sucrose 1%	Black tea +  aspartame 0.1%
Syringic	136.56	434.67	438.72	148.75	281.1	110.91
Gallic acid	75.65	92.28	2600.79	2.76	130.62	12762
Pyrogallol	201.38	722.27	146.53	29.81	411.12	2060.45
4-amino-benzoic acid	2.68	13.75	4.55	0.522	7.157	0.01
Protocatchuic	131.58	774.31	85.55	25.91	113.47	3.39
Catechin	44.20	209.60	107.43	48.40	87.78	1.34
Chlorogenic	98.88	244.55	115.02	43.15	48.03	0.64
Catechol	134.71	150.89	64.14	15.81	58.98	170.88
Epicatechin	84.26	306.22	162.78	3.19	0.0	1.63
Caffeine	6081.86	8772.19	7530.139	6474.31	3755.30	7.82
p-OH-benzoic acid	0.0	342.32	0.0	0.0	258.95	1.55
Caffeic acid	9.57	33.64	33.75	2.12	50.74	0.29
Vanillic acid	46.44	111.27	21.145	8.94	32.33	10.35
Ferulic acid	10.33	15.27	24.34	0.14	6.93	0.02
Iso-ferulic acid	0.87	43.15	11.71	0.01	5.94	0.24
2-Vanilic acid	1.90	170.33	55.69	0.38	952.28	0.86
Ellagic acid	27.03	63.69	67.48	0.76	10.24	0.73
Alpha-coumaric acid	3.29	3.70	16.88	0.18	13.12	0.13
Benzoic acid	2.26	864.72	145.41	6.86	31.29	0.55
Salycilic acid	0.36	76.61	75.50	0.23	8.84	0.0
3,4,5 Methoxy cinnamic acid	0.08	7.61	1.27	0.11	0.79	0.13
Coumarine	0.19	3.61	26.36	0.21	0.78	0.22
p-coumaric acid	0.29	12.25	27.76	0.14	0.55	0.01
Cinnamic acid	0.21	0.25	1.12	0.19	0.18	0.17
Total phenolic compounds	1012.72	4696.96	4233.925	338.572	2511.217	15126.5

Figure 3. FTIR of tea extracts where, 1. green tea only, 2. green tea with sucrose, and 3. black tea only, 4. black tea with sucrose, 5. green tea with aspartame, and 6. black tea with aspartame.

Table 4. FTIR data of different tea extracts.

			Differences in green tea			Differences in Black tea
Bond	Functional group	Wave numbers (cm^−1) of green tea only	With sucrose	With aspartame	Wave numbers (cm^−1) of black tea only	With sucrose	With aspartame
O–H	Alcohol and phenols, amide	3439	−3.0	−5.0	3462	−27.0	−27.0
H–C–H	Alkyl chain	n.b.	ND	2926	n.b.	ND	2926
–C=C–	Alkene	1632	+9.0	−3.0	1637	−5.0	−6.0
Aromatic–C=C–	Aromatic alkene	1502	+8.0	−6.0	1445	−13.0	−16.0

Note: n.b.: new band.

Figure 4. The suggested reaction between sugar and phenols in green tea.

Figure 5. The suggested reaction between sugar and oxidized phenols (quinones) in black tea and possibility for scavenging of DPPH radical.

Table 5. The nature of interaction between sugar and tea.

	Green tea		Black tea
Samples	IC50	CI	IC50	CI	The nature of interaction
Tea only	33.9	–	36.76	–
Tea + sucrose	34.2	1.093	35.2	1.037	Additive
Sucrose	406	–	406	–

Note: IC₅₀ is calculated in µg/ml.

Table 6. Correlation matrix of tea compounds and antioxidant activities against DPPH and ABTS radicals.

Parameters	Flavonoids	Phenolic	ABTS	DPPH
DPPH	0.310	0.245	0.659
ABTS	0.381	0.398
Phenolic	0.514
Flavonoid