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Black goji berry (Lycium ruthenicum) tea has higher phytochemical contents and in vitro antioxidant properties than red goji berry (Lycium barbarum) tea

Black goji berry (Lycium ruthenicum) tea has higher phytochemical contents and in vitro... Goji berry tea, a traditional herbal tea, is the main ate mode of goji berry in Asia, yet few studies in comparison with red goji berry tea and black goji berry tea are carried out. This study investigated the effects of water temperature and soak time on the colour, phytochemicals, and the antioxidant capacity [2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), and the ferric-reducing antioxidant power (FRAP)] of two goji berry tea. A comparison of the bioactive compounds and antioxidant activities between black and red goji berry tea was conducted. Results showed that both red and black goji berry tea were rich in phytochemicals, giving high antioxidant ability. The levels of bioactive compounds and the antioxidant activity of the two goji berry tea increased as the increases in soak temperature and time. Black goji berry tea had higher phytochemicals and antioxidant property than those of red goji berry tea. Infused at 100° water for the same time, the levels of total polysaccharides (150  mg/100  ml), total polyphenols (238  mg/ml), and antioxidant capacity (550 μmol/100  ml) of black goji berry tea were 3.5, 2, and 5 times higher, respectively, in comparison with red goji berry tea. The results of this study demonstrate that hot drink of goji berry in China is a good habit and black goji berry tea may be a better choice. Key words: red goji berry (L. barbarum); black goji berry (L. ruthenicum); goji tea; phytochemicals; antioxidant activity. Red goji berry occupied approximately 90% of all commercially Introduction available goji berries (Wang et  al., 2018), and it has been planted Lycium plants (goji berries or wolfberries) are prevailing in China and in Northwest China for about 600  years (Chen et  al., 2013). Red other Asian areas (Seeram and Navindra, 2008). There are around goji berry has high economic significance as Traditional Chinese 80 species of Lycium L. (Solanaceae) in the world (Hitchcock, 1932; Medicine and nutritional purposes (Chang and So, 2008; Ruiz- Miller, 2002; Levin and Miller, 2005), with only seven species have Salinas, et al., 2020). been reported in China (Yisilam et al., 2018). However, only three spe- Recently, wild black goji berry (L.  ruthenicum) inhabiting in the cies (Lycium barbarum, Lycium chinense, and Lycium ruthenicum) are Qinghai-Tibet Plateau is attracting attentions of consumers (Han et al., consumed as medicine and food in China. Recently, goji berry has been 2014). Health care products containing Lycium ruthenicum Murray marketed as food and dietary supplement in various retail outlets in (LR) have also been sold in Chinese markets. Currently, the price of the world. Of particular, consumers from Europe and America show black goji berry is expensive, which is 10 times of red goji berry. The increasing interests in wolfberries due to their potential health benefits (Amagase and Farnsworth, 2011; Pedro et al., 2019; Sa et al., 2019). high price of black goji mainly is due to the scarcity of wild black goji © The Author(s) 2020. Published by Oxford University Press on behalf of Zhejiang University Press. 193 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 194 B. Liu et al., 2020, Vol. 4, No. 4 berry and higher functional value (Ni et  al., 2013; Islam et  al., 2017; Determination of total phenolics content (TPC) Abuduaibifu and Tamer, 2019). Islam et  al. (2017) found that black Black or red goji berry tea (0.2 ml) was added to a 10 ml colourimetric goji berry has higher polyphenols and antioxidant than red goji berry. cylinder which contained Folin–Ciocalteu reagent (0.5  ml), shaken Ni et al. (2013) found that black goji berry has higher polysaccharide thoroughly, and kept for 1  min. Then Na CO [1.5  ml, 20% (w/v)] 2 3 content than red goji berry. However, given that goji berry tea is the was added, and the solution was vortex mixed and made to 10  ml main ate form of goji berry (Sun et al., 2017), the phytochemicals and with distilled water. After 10 min, A761 was measured by a UV-752N bioactive activity of black goji berry were evaluated using the extracts of ultraviolet spectrophotometer (Yidian Analytical Instrument Co, Ltd, organic solvents (e.g. acetone and ethanol) in the existing studies which Shanghai, China) using distilled water as a blank. A calibration curve may not reflect the real values in daily consume form—goji berry tea. was prepared using a standard solution of gallic acid and the results Therefore, the aim of this study was to analyse and compare for TPC were expressed as mg gallic acid equivalents per 100 ml of tea the phytochemicals and antioxidant abilities of red goji berry and (Sun et al., 2017). black goji berry tea at different soak conditions, to provide scien- tific knowledge on traditional red and black goji berry tea for con- Colourimetric analysis of goji berry tea sumers’ daily life. The colour of the goji berry tea was monitored with colourimeter (Sun et  al., 2017). The infusion of red goji berry and black goji berry was added to cuvettes, and then subjected to a colourimeter Materials and Methods (ColorQuest XE, Hunter Associates Laboratory Inc., Reston, VA, Chemicals USA) for assessing L*, a*, b* with a D65 light source and an aper- Folin–Ciocalteu phenol reagent, 2, 2-diphenyl-1-picrylhydrazyl rad- ture size of 9.5 mm. ical (DPPH), 2,4,6-Tri-2-pyridyl-s-triazin (TPTZ), 2,2-azinobis-(3- ethylbenzothiazoline-6-sulfonic acid) (ABTS), and other reagents Total polysaccharides content (TPOC) analysis were analytical grade acquired from Aladdin Reagent Database Inc. Total polysaccharides were determined by the phenol-sulfuric acid (Shanghai, China). The following chemicals and compounds were method using glucose as the standard reported by Sun et al. (2017) purchased from Sigma–Aldrich (St. Louis, MO, USA): chlorogenic with slight modifications. acid, Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic Filtered black or red goji berry tea (1 ml) was placed into a acid), gallic acid, and rutin. 10 ml volumetric flask, made to 10 ml with distilled water, and mixed well. The diluted solution (1 ml) was used and A490 was Materials determined according to the method of the standard curve using Dried red goji berries (L.  barbarum L.) and black goji berries distilled water as the blank. The concentration and content of (L.  ruthenicum) were purchased from Golmud Yilin Goji berry glucose in the goji berry polysaccharide tea were calculated ac- Technology Development Co., Ltd, Golmud City, Qinghai Province cording to the regression equation. The conversion factor was (Figure  1). The moisture content was 6.20% and 10.45% (w/w), calculated as follows: respectively. Polysaccharide = CD M × 100%, f (1) Preparation of black goji berry tea and red goji berry tea where C is the glucose concentration in the sample, D is the dilution, Dried black or red goji berries were added to a flask, then purified f is the conversion factor, and M is the mass of dried goji berry. water (100 ml) was added to the flask, and the samples were infused a different number of times for different times at different temper- Evaluation of antioxidant activity atures. The tea was filtered by passage through a 45  µm pore  size Antioxidant activity (AA) of goji berry tea was determined by 2, polytetrafluoroethylene (PTFE) disposable syringe filter and kept at 29-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) 2, a constant volume of 100 ml. Figure 1. Dried red goji berries (a) and black goji berries (b) Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 Comparison between black goji berry and red goji berry, 2020, Vol. 4, No. 4 195 2-diphenyl-1-picrylhydrazyl radical (DPPH), and the ferric-reducing water and 0.1M acetate buffer (pH 3.6) (ratio 1:1:10, by vol.) (Xu antioxidant power (FRAP) assays. et al., 2008). Black or red goji berry tea (0.2 ml) was added to FRAP reagent (5.0 ml). After 10 min, A593 was measured by a UV-752N ultraviolet spectrophotometer and Trolox solution was used to make ABTS free radical-scavenging assay the calibration curves. The results are expressed as Trolox equivalent Potassium persulfate was dissolved in distilled water (140  mM, antioxidant capacity (TEAC) mg/g sample dry weight (DW). 440  μl), ABTS was dissolved by H O (7  mM); then potassium 2 2 persulfate solution was added to 25 ml ABTS solution and was kept in darkness at 25 °C for 12–16 h, and then diluted with ethanol to Statistical analysis A734 of 0.70 ± 0.02 (Xu et al., 2007). ABTS cation solution (7 mM, Experiments were repeated three times. Data were expressed as the 3.9  ml) was added to black or red goji berry tea (0.1  ml), mixed mean ± standard deviation. Statistical analyses were carried out using thoroughly, and then kept at 25 °C for 10 min. A734 was determined SPSS software, version 17.0 (SPSS Inc.). Data were compared with by a UV-752N ultraviolet spectrophotometer. A control (0.1 ml of ANOVA. Statistically significant differences were set at P < 0.05. methanol, 3.9 ml of ABTS solution) was prepared, and a calibration curve was constructed for the absorbance reduction and concentra- tion of the Trolox standard. The ABTS radical-scavenging ability is Results and Discussion expressed as TEAC mg/g DW. Variation of colour of red goji berry tea and black DPPH free radical-scavenging assay goji berry tea with soak temperature and time DPPH was dissolved in ethanol (0.1 mM), and then a black or red The colour of black and red goji berry tea is visually shown in goji berry tea (0.2 ml) was added to 3.9 ml DPPH solution and then Figure 2 and precisely quantified by L*, a*, and b* (Figure 3). It was kept in darkness for 30 min at 25 °C (Xu et  al., 2008). A517 was found that red goji berry tea and black goji berry tea presented light determined by a UV-752N ultraviolet spectrophotometer. The trolox yellow and purple, respectively, and the colour of both teas grad- solution was used to make the calibration curves and the results are ually changed to darker with the increase of time and temperature expressed as TEAC mg/g DW. (Figure 2). The L* value (representing the lightness) of black and red goji FRAP assay berry tea significantly decreased with the increasing soak tempera- Fresh FRAP reagent was prepared by mixing 10  mM TPTZ dis- ture and time (P < 0.05) (Figure 3a and 3b). Generally, the L* value solved in 40M HCL and 20 mM ferric chloride dissolved in distilled of black goji berry tea was lower than that of red goji berry tea. Figure 2. Red (a and b) and black (c and d) goji berry tea prepared at 25 and 100 °C for 5, 10, 15, 30, 60, and 100 min. Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 196 B. Liu et al., 2020, Vol. 4, No. 4 Black goji berry tea(a) Redgoji berry tea (b) Black goji berry tea (c)Red goji berry tea (d) Blackgoji berry tea (e)Red goji berry tea (f) Figure 3. The L*, a*, b* value of black and red goji berry tea prepared at different temperatures for different lengths of time (a–f) (significant differences were set at P < 0.05). The a* value (presenting its position between red and green) of The a* value of black go berry tea was higher than red goji berry tea black goji berry tea significantly increased with the increase of soak (P < 0.05) (Figure 3c and 3d). temperature time when soak time was 5  min, and the a* value of The b* value (meaning its yellow value) of red goji berry tea black goji berry firstly increased with the increase of temperature significantly increased with soak temperature varied from 0 to and then decreased with the increase of temperature when soak time 100 °C and time ranging from 5 to 100 min (P < 0.05) (Figure 3f). varied from 10 to 60 min (P < 0.05), whereas the a* value of red goji However, the b* value of black goji tea significantly decreased with berry tea was not significantly different at different soak conditions. the increasing soak temperature and time a (P < 0.05) (Figure  3e). Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 Comparison between black goji berry and red goji berry, 2020, Vol. 4, No. 4 197 The b* value of red goji berry tea was higher than that of black goji Effects of soak temperature, time, and times on the berry tea. total polysaccharides content (TPOC) of black and The variations of L*, a*, b* of red goji berry tea were connected red goji berry tea with the contents of soluble solid, polyphenols, and carotenoids at Polysaccharides are one of the water-soluble phytochemicals in goji different tea conditions, and the hue of red goji berry tea was deter- berry, which are focused on by many researchers. Total polysacchar- mined by the soluble carotenoids. The variations of L*, a*, b* of ides contents of black and red goji berry tea both significantly varied black goji berry tea were connected with the contents of soluble solid with soak temperature, time, and times (P < 0.05). Total polysac- and anthocyanins at different soak conditions, and the hue of black charides contents significantly increased with the increase of soak temperature and time (P < 0.05) (Figure 4a and 4b). TPOC of black goji berry tea was determined by the soluble anthocyanins. Blackgoji berry tea(a) Redgoji berry tea (b) Blackgoji berrytea(c)Red goji berry tea (d) Blackgoji berry tea (e)Red goji berry tea (f) Figure 4. Polysaccharides content of black and red goji berry tea at different temperatures for different time (a and b), and for different soak times (c and d) (significant differences were set at P < 0.05). Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 198 B. Liu et al., 2020, Vol. 4, No. 4 and red goji berry tea at 100  °C, 60  min was significantly higher of the red goji fruits’ skin (Lv, 2012); and thirdly, maybe due to the compared with the tea in other conditions (P < 0.05), indicating that higher contents in raw black goji dried fruits (Ni et al., 2013) and the polysaccharides are stable and high temperature and long time is lower molecular weight of polysaccharide in black goji berry (Lv, good for its diffusion. The TPOC value in black goji berry at 100 °C, 2012). 60  min was about 30 times of TPOC at 40  °C, 60  min, and simi- larly the contents of TPOC at 100 °C, 60 min was about 14 times Effects of soak temperature, time, and times on the of TPOC at 100 °C, 5 min. The TPOC significantly decreased with total phenolics content (TPC) of black and red goji increased times (P < 0.05) (Figure 4c and 4d). From Figure 4a and berry tea 4b, it was found that TPOC of black goji berry tea was far higher than red goji berry. Take 100 °C as an example, the TPOC of black Flavonoids and phenolic acids are the main polyphenols in red goji goji berry tea was 3.5 times of red goji berry. Figure 4c and 4d sug- berry, and anthocyanins are the main polyphenols in black goji berry. gested that the polysaccharides in black goji berry could be released Figure 5 shows the variation of TPC of black and red goji berry tea into water easier than red goji berry, and most of the polysaccharides with soak temperature, time, and times. TPC in both goji berry tea were released in the water during the first time, but red goji berry significantly increased with temperature ranging from 0 to 100  °C needed two times tea. The difference between two goji berry tea may and time ranging from 5 to 60 min, but the difference of TPC in goji be the following reasons: firstly, because of the differences in the berry tea between 80 and 100 °C was not significant (P  < 0.05); it surface-to-volume ratios, black goji berry are much smaller than red could contribute to the unstable condition of polyphenols at higher goji berry, which means much faster rates in heat and mass transfer; temperature, and the results are in agreement with the in tea colour secondly, maybe due to the higher in the thickness and compactness of Figure  2. The contents of TPC in black goji berry at 100  °C, Figure 5. Total phenolics contents of black and red goji berry tea at different temperatures for different time (a and b) and for different soak times (c and d) (significant differences were set at P < 0.05). Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 Comparison between black goji berry and red goji berry, 2020, Vol. 4, No. 4 199 Blackgoji berry tea(a) Redgoji berry tea (b) Blackgoji berrytea(c)Red goji berry tea (d) Blackgoji berry tea (e)Red goji berry tea (f) Figure 6. 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), and the ferric-reducing antioxidant power (FRAP) of black and red goji berry tea at different temperatures for different time (a, b, e, f, i, and j) and for different soak times (c, d, g, h, k, and l) (significant differences were set at P < 0.05). 60 min were about 2 times of TPC at 40 °C, 60 min, and similarly, Effects of soak temperature, time, and times on the the contents of TPC at 100 °C, 60 min were about 5 times of TPC antioxidant abilities of black and red goji berry tea at 100  °C, 5min. Comparing Figure  5a and 5b, TPC of black goji The antioxidant abilities of goji berry tea were determined using berry tea (243.4 mg/100 ml) was far higher than red goji berry tea FRAP, ABTS, and DPPH assays (Figure  6). The antioxidant abil- (108.90 mg/100 ml) at 100 °C, which is about 2 folds, and the results ities of black and red goji berry tea significantly increased with soak can be explained by that black goji berry has abundant anthocyanins temperature and time and significantly decreased with soak times while red goji berry does not (Wang et al., 2018). Different from poly- (P < 0.05), which was similar to variation trend of the polysacchar- saccharides, the difference of the TPC of goji berry between the first ides and polyphenols in goji berry tea. The antioxidant ability in tea time and the second tea time was not significantly different, so black goji berry at 100  °C, 60  min was about 3 times of those at the second tea was important for more polyphenols can be dissolved 40  °C, 60  min and the contents of antioxidant ability at 100  °C, (P < 0.05). 60 min were about 4 times of those at 100 °C, 5 min. The antioxidant Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 200 B. Liu et al., 2020, Vol. 4, No. 4 Black goji berry tea (g)Red goji berrytea (h) Black goji berry tea (i)Red goji berry tea (j) Black goji berry tea (k)Red goji berrytea (l) Figure 6. Continued. ability of black goji berry tea was far higher than red goji berry, and red goji berry and black goji berry tea are rich in phytochemicals and the AA of black goji berry tea was about two 2 to 5 folds of red goji show high antioxidant capacities. The contents of phytochemicals berry tea. The antioxidant ability of goji berry tea was related to the and the antioxidant capacity of a goji berry tea rised with soak tem- soluble polyphenols in tea. perature and time, Soaking using the cold or warm water, even at long time, will waste most of the phytochemicals and antioxidant activity. Black goji berry tea has far higher phytochemicals, antioxi- Conclusions dant property, and more desirable colours than red goji berry tea. In the present study, the effects of making tea with water on the colour, The results of this study suggest that high temperature and long soak and the content of phytochemicals and antioxidant ability of black time can be used to make a healthy goji berry tea, hot drink of goji and red goji berry tea were investigated and compared, which will berry is a good habit, and black goji berry may be a better choice, directly provide a scientific basis for daily diet. It is found that both but we need to change the habit of short tea time. Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 Comparison between black goji berry and red goji berry, 2020, Vol. 4, No. 4 201 Lv,  X.  P. (2012). Studies on Purification and Structural Characterization of Funding the Polysaccharide from Lycium ruthenium Murr. Master dissertation, This work was financially supported by National Natural Science Foundation Xi’an:Northwest University, Kirkland, Washington. 44–47. of China (31771982 and 31401474). Miller,  J.  S. (2002). Phylogenetic relationships and the evolution of gender dimorphism in Lycium (Solanaceae).Systematic Botany, 27: 416–428. Ni, W. H., Gao, T. T., Wang, H. L. et al. (2013). Anti-fatigue activity of poly- Conflict of Interest saccharides from the fruits of four Tibetan plateau indigenous medicinal The authors declare no conflicts of interest. plants. Journal of Ethnopharmacology, 150(2): 529–535. Pedro, A. C., Sánchez-Mata, M., Pérez-Rodríguez, M. L., et al. (2019). Quali- tative and nutritional comparison of goji berry fruits produced in organic and conventional systems. Scientia Horticulturae, 257: 108660. References Ruíz-Salinas, A. K., Vázquez-Roque, R. A., Díaz, A., et al. (2020). The treat- Abuduaibifu,  A., Tamer,  C.  E. (2019). Evaluation of physicochemical and ment of Goji berry (Lycium barbarum) improves the neuroplasticity of the bioaccessibility properties of goji berry kombucha. Journal of Food prefrontal cortex and hippocampus in aged rats. The Journal of Nutri- Processing and Preservation, 43(9): e14077. tional Biochemistry, 83: 108416. Amagase,  H. Farnsworth,  N.  R. (2011). A review of botanical characteris- Sa, R. R., Caldas, J. D., Santana, D. D., et al. (2019). Multielementar/centes- tics, phytochemistry, clinical relevance in efficacy and safety of Lycium imal composition and determination of bioactive phenolics in dried fruits barbarum fruit (Goji). 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A., Miller, J. S. (2005). Relationships within tribe Lycieae (Solanaceae): Yisilam, G., Mamut, R., Li, J., et al. (2018). Characterization of the complete paraphyly of Lycium and multiple origins of gender dimorphism American chloroplast genome of Lycium ruthenicum (Solanaceae). Mitochondrial Journal of Botany, 92(12): 2044–2053. DNA Part B, 3(1): 361–362. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Food Quality and Safety Oxford University Press

Black goji berry (Lycium ruthenicum) tea has higher phytochemical contents and in vitro antioxidant properties than red goji berry (Lycium barbarum) tea

Food Quality and Safety , Volume 4 (4) – Dec 18, 2020

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Oxford University Press
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© The Author(s) 2020. Published by Oxford University Press on behalf of Zhejiang University Press.
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2399-1399
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2399-1402
DOI
10.1093/fqsafe/fyaa022
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Abstract

Goji berry tea, a traditional herbal tea, is the main ate mode of goji berry in Asia, yet few studies in comparison with red goji berry tea and black goji berry tea are carried out. This study investigated the effects of water temperature and soak time on the colour, phytochemicals, and the antioxidant capacity [2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), and the ferric-reducing antioxidant power (FRAP)] of two goji berry tea. A comparison of the bioactive compounds and antioxidant activities between black and red goji berry tea was conducted. Results showed that both red and black goji berry tea were rich in phytochemicals, giving high antioxidant ability. The levels of bioactive compounds and the antioxidant activity of the two goji berry tea increased as the increases in soak temperature and time. Black goji berry tea had higher phytochemicals and antioxidant property than those of red goji berry tea. Infused at 100° water for the same time, the levels of total polysaccharides (150  mg/100  ml), total polyphenols (238  mg/ml), and antioxidant capacity (550 μmol/100  ml) of black goji berry tea were 3.5, 2, and 5 times higher, respectively, in comparison with red goji berry tea. The results of this study demonstrate that hot drink of goji berry in China is a good habit and black goji berry tea may be a better choice. Key words: red goji berry (L. barbarum); black goji berry (L. ruthenicum); goji tea; phytochemicals; antioxidant activity. Red goji berry occupied approximately 90% of all commercially Introduction available goji berries (Wang et  al., 2018), and it has been planted Lycium plants (goji berries or wolfberries) are prevailing in China and in Northwest China for about 600  years (Chen et  al., 2013). Red other Asian areas (Seeram and Navindra, 2008). There are around goji berry has high economic significance as Traditional Chinese 80 species of Lycium L. (Solanaceae) in the world (Hitchcock, 1932; Medicine and nutritional purposes (Chang and So, 2008; Ruiz- Miller, 2002; Levin and Miller, 2005), with only seven species have Salinas, et al., 2020). been reported in China (Yisilam et al., 2018). However, only three spe- Recently, wild black goji berry (L.  ruthenicum) inhabiting in the cies (Lycium barbarum, Lycium chinense, and Lycium ruthenicum) are Qinghai-Tibet Plateau is attracting attentions of consumers (Han et al., consumed as medicine and food in China. Recently, goji berry has been 2014). Health care products containing Lycium ruthenicum Murray marketed as food and dietary supplement in various retail outlets in (LR) have also been sold in Chinese markets. Currently, the price of the world. Of particular, consumers from Europe and America show black goji berry is expensive, which is 10 times of red goji berry. The increasing interests in wolfberries due to their potential health benefits (Amagase and Farnsworth, 2011; Pedro et al., 2019; Sa et al., 2019). high price of black goji mainly is due to the scarcity of wild black goji © The Author(s) 2020. Published by Oxford University Press on behalf of Zhejiang University Press. 193 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/ by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 194 B. Liu et al., 2020, Vol. 4, No. 4 berry and higher functional value (Ni et  al., 2013; Islam et  al., 2017; Determination of total phenolics content (TPC) Abuduaibifu and Tamer, 2019). Islam et  al. (2017) found that black Black or red goji berry tea (0.2 ml) was added to a 10 ml colourimetric goji berry has higher polyphenols and antioxidant than red goji berry. cylinder which contained Folin–Ciocalteu reagent (0.5  ml), shaken Ni et al. (2013) found that black goji berry has higher polysaccharide thoroughly, and kept for 1  min. Then Na CO [1.5  ml, 20% (w/v)] 2 3 content than red goji berry. However, given that goji berry tea is the was added, and the solution was vortex mixed and made to 10  ml main ate form of goji berry (Sun et al., 2017), the phytochemicals and with distilled water. After 10 min, A761 was measured by a UV-752N bioactive activity of black goji berry were evaluated using the extracts of ultraviolet spectrophotometer (Yidian Analytical Instrument Co, Ltd, organic solvents (e.g. acetone and ethanol) in the existing studies which Shanghai, China) using distilled water as a blank. A calibration curve may not reflect the real values in daily consume form—goji berry tea. was prepared using a standard solution of gallic acid and the results Therefore, the aim of this study was to analyse and compare for TPC were expressed as mg gallic acid equivalents per 100 ml of tea the phytochemicals and antioxidant abilities of red goji berry and (Sun et al., 2017). black goji berry tea at different soak conditions, to provide scien- tific knowledge on traditional red and black goji berry tea for con- Colourimetric analysis of goji berry tea sumers’ daily life. The colour of the goji berry tea was monitored with colourimeter (Sun et  al., 2017). The infusion of red goji berry and black goji berry was added to cuvettes, and then subjected to a colourimeter Materials and Methods (ColorQuest XE, Hunter Associates Laboratory Inc., Reston, VA, Chemicals USA) for assessing L*, a*, b* with a D65 light source and an aper- Folin–Ciocalteu phenol reagent, 2, 2-diphenyl-1-picrylhydrazyl rad- ture size of 9.5 mm. ical (DPPH), 2,4,6-Tri-2-pyridyl-s-triazin (TPTZ), 2,2-azinobis-(3- ethylbenzothiazoline-6-sulfonic acid) (ABTS), and other reagents Total polysaccharides content (TPOC) analysis were analytical grade acquired from Aladdin Reagent Database Inc. Total polysaccharides were determined by the phenol-sulfuric acid (Shanghai, China). The following chemicals and compounds were method using glucose as the standard reported by Sun et al. (2017) purchased from Sigma–Aldrich (St. Louis, MO, USA): chlorogenic with slight modifications. acid, Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic Filtered black or red goji berry tea (1 ml) was placed into a acid), gallic acid, and rutin. 10 ml volumetric flask, made to 10 ml with distilled water, and mixed well. The diluted solution (1 ml) was used and A490 was Materials determined according to the method of the standard curve using Dried red goji berries (L.  barbarum L.) and black goji berries distilled water as the blank. The concentration and content of (L.  ruthenicum) were purchased from Golmud Yilin Goji berry glucose in the goji berry polysaccharide tea were calculated ac- Technology Development Co., Ltd, Golmud City, Qinghai Province cording to the regression equation. The conversion factor was (Figure  1). The moisture content was 6.20% and 10.45% (w/w), calculated as follows: respectively. Polysaccharide = CD M × 100%, f (1) Preparation of black goji berry tea and red goji berry tea where C is the glucose concentration in the sample, D is the dilution, Dried black or red goji berries were added to a flask, then purified f is the conversion factor, and M is the mass of dried goji berry. water (100 ml) was added to the flask, and the samples were infused a different number of times for different times at different temper- Evaluation of antioxidant activity atures. The tea was filtered by passage through a 45  µm pore  size Antioxidant activity (AA) of goji berry tea was determined by 2, polytetrafluoroethylene (PTFE) disposable syringe filter and kept at 29-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) 2, a constant volume of 100 ml. Figure 1. Dried red goji berries (a) and black goji berries (b) Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 Comparison between black goji berry and red goji berry, 2020, Vol. 4, No. 4 195 2-diphenyl-1-picrylhydrazyl radical (DPPH), and the ferric-reducing water and 0.1M acetate buffer (pH 3.6) (ratio 1:1:10, by vol.) (Xu antioxidant power (FRAP) assays. et al., 2008). Black or red goji berry tea (0.2 ml) was added to FRAP reagent (5.0 ml). After 10 min, A593 was measured by a UV-752N ultraviolet spectrophotometer and Trolox solution was used to make ABTS free radical-scavenging assay the calibration curves. The results are expressed as Trolox equivalent Potassium persulfate was dissolved in distilled water (140  mM, antioxidant capacity (TEAC) mg/g sample dry weight (DW). 440  μl), ABTS was dissolved by H O (7  mM); then potassium 2 2 persulfate solution was added to 25 ml ABTS solution and was kept in darkness at 25 °C for 12–16 h, and then diluted with ethanol to Statistical analysis A734 of 0.70 ± 0.02 (Xu et al., 2007). ABTS cation solution (7 mM, Experiments were repeated three times. Data were expressed as the 3.9  ml) was added to black or red goji berry tea (0.1  ml), mixed mean ± standard deviation. Statistical analyses were carried out using thoroughly, and then kept at 25 °C for 10 min. A734 was determined SPSS software, version 17.0 (SPSS Inc.). Data were compared with by a UV-752N ultraviolet spectrophotometer. A control (0.1 ml of ANOVA. Statistically significant differences were set at P < 0.05. methanol, 3.9 ml of ABTS solution) was prepared, and a calibration curve was constructed for the absorbance reduction and concentra- tion of the Trolox standard. The ABTS radical-scavenging ability is Results and Discussion expressed as TEAC mg/g DW. Variation of colour of red goji berry tea and black DPPH free radical-scavenging assay goji berry tea with soak temperature and time DPPH was dissolved in ethanol (0.1 mM), and then a black or red The colour of black and red goji berry tea is visually shown in goji berry tea (0.2 ml) was added to 3.9 ml DPPH solution and then Figure 2 and precisely quantified by L*, a*, and b* (Figure 3). It was kept in darkness for 30 min at 25 °C (Xu et  al., 2008). A517 was found that red goji berry tea and black goji berry tea presented light determined by a UV-752N ultraviolet spectrophotometer. The trolox yellow and purple, respectively, and the colour of both teas grad- solution was used to make the calibration curves and the results are ually changed to darker with the increase of time and temperature expressed as TEAC mg/g DW. (Figure 2). The L* value (representing the lightness) of black and red goji FRAP assay berry tea significantly decreased with the increasing soak tempera- Fresh FRAP reagent was prepared by mixing 10  mM TPTZ dis- ture and time (P < 0.05) (Figure 3a and 3b). Generally, the L* value solved in 40M HCL and 20 mM ferric chloride dissolved in distilled of black goji berry tea was lower than that of red goji berry tea. Figure 2. Red (a and b) and black (c and d) goji berry tea prepared at 25 and 100 °C for 5, 10, 15, 30, 60, and 100 min. Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 196 B. Liu et al., 2020, Vol. 4, No. 4 Black goji berry tea(a) Redgoji berry tea (b) Black goji berry tea (c)Red goji berry tea (d) Blackgoji berry tea (e)Red goji berry tea (f) Figure 3. The L*, a*, b* value of black and red goji berry tea prepared at different temperatures for different lengths of time (a–f) (significant differences were set at P < 0.05). The a* value (presenting its position between red and green) of The a* value of black go berry tea was higher than red goji berry tea black goji berry tea significantly increased with the increase of soak (P < 0.05) (Figure 3c and 3d). temperature time when soak time was 5  min, and the a* value of The b* value (meaning its yellow value) of red goji berry tea black goji berry firstly increased with the increase of temperature significantly increased with soak temperature varied from 0 to and then decreased with the increase of temperature when soak time 100 °C and time ranging from 5 to 100 min (P < 0.05) (Figure 3f). varied from 10 to 60 min (P < 0.05), whereas the a* value of red goji However, the b* value of black goji tea significantly decreased with berry tea was not significantly different at different soak conditions. the increasing soak temperature and time a (P < 0.05) (Figure  3e). Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 Comparison between black goji berry and red goji berry, 2020, Vol. 4, No. 4 197 The b* value of red goji berry tea was higher than that of black goji Effects of soak temperature, time, and times on the berry tea. total polysaccharides content (TPOC) of black and The variations of L*, a*, b* of red goji berry tea were connected red goji berry tea with the contents of soluble solid, polyphenols, and carotenoids at Polysaccharides are one of the water-soluble phytochemicals in goji different tea conditions, and the hue of red goji berry tea was deter- berry, which are focused on by many researchers. Total polysacchar- mined by the soluble carotenoids. The variations of L*, a*, b* of ides contents of black and red goji berry tea both significantly varied black goji berry tea were connected with the contents of soluble solid with soak temperature, time, and times (P < 0.05). Total polysac- and anthocyanins at different soak conditions, and the hue of black charides contents significantly increased with the increase of soak temperature and time (P < 0.05) (Figure 4a and 4b). TPOC of black goji berry tea was determined by the soluble anthocyanins. Blackgoji berry tea(a) Redgoji berry tea (b) Blackgoji berrytea(c)Red goji berry tea (d) Blackgoji berry tea (e)Red goji berry tea (f) Figure 4. Polysaccharides content of black and red goji berry tea at different temperatures for different time (a and b), and for different soak times (c and d) (significant differences were set at P < 0.05). Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 198 B. Liu et al., 2020, Vol. 4, No. 4 and red goji berry tea at 100  °C, 60  min was significantly higher of the red goji fruits’ skin (Lv, 2012); and thirdly, maybe due to the compared with the tea in other conditions (P < 0.05), indicating that higher contents in raw black goji dried fruits (Ni et al., 2013) and the polysaccharides are stable and high temperature and long time is lower molecular weight of polysaccharide in black goji berry (Lv, good for its diffusion. The TPOC value in black goji berry at 100 °C, 2012). 60  min was about 30 times of TPOC at 40  °C, 60  min, and simi- larly the contents of TPOC at 100 °C, 60 min was about 14 times Effects of soak temperature, time, and times on the of TPOC at 100 °C, 5 min. The TPOC significantly decreased with total phenolics content (TPC) of black and red goji increased times (P < 0.05) (Figure 4c and 4d). From Figure 4a and berry tea 4b, it was found that TPOC of black goji berry tea was far higher than red goji berry. Take 100 °C as an example, the TPOC of black Flavonoids and phenolic acids are the main polyphenols in red goji goji berry tea was 3.5 times of red goji berry. Figure 4c and 4d sug- berry, and anthocyanins are the main polyphenols in black goji berry. gested that the polysaccharides in black goji berry could be released Figure 5 shows the variation of TPC of black and red goji berry tea into water easier than red goji berry, and most of the polysaccharides with soak temperature, time, and times. TPC in both goji berry tea were released in the water during the first time, but red goji berry significantly increased with temperature ranging from 0 to 100  °C needed two times tea. The difference between two goji berry tea may and time ranging from 5 to 60 min, but the difference of TPC in goji be the following reasons: firstly, because of the differences in the berry tea between 80 and 100 °C was not significant (P  < 0.05); it surface-to-volume ratios, black goji berry are much smaller than red could contribute to the unstable condition of polyphenols at higher goji berry, which means much faster rates in heat and mass transfer; temperature, and the results are in agreement with the in tea colour secondly, maybe due to the higher in the thickness and compactness of Figure  2. The contents of TPC in black goji berry at 100  °C, Figure 5. Total phenolics contents of black and red goji berry tea at different temperatures for different time (a and b) and for different soak times (c and d) (significant differences were set at P < 0.05). Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 Comparison between black goji berry and red goji berry, 2020, Vol. 4, No. 4 199 Blackgoji berry tea(a) Redgoji berry tea (b) Blackgoji berrytea(c)Red goji berry tea (d) Blackgoji berry tea (e)Red goji berry tea (f) Figure 6. 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl radical (DPPH), and the ferric-reducing antioxidant power (FRAP) of black and red goji berry tea at different temperatures for different time (a, b, e, f, i, and j) and for different soak times (c, d, g, h, k, and l) (significant differences were set at P < 0.05). 60 min were about 2 times of TPC at 40 °C, 60 min, and similarly, Effects of soak temperature, time, and times on the the contents of TPC at 100 °C, 60 min were about 5 times of TPC antioxidant abilities of black and red goji berry tea at 100  °C, 5min. Comparing Figure  5a and 5b, TPC of black goji The antioxidant abilities of goji berry tea were determined using berry tea (243.4 mg/100 ml) was far higher than red goji berry tea FRAP, ABTS, and DPPH assays (Figure  6). The antioxidant abil- (108.90 mg/100 ml) at 100 °C, which is about 2 folds, and the results ities of black and red goji berry tea significantly increased with soak can be explained by that black goji berry has abundant anthocyanins temperature and time and significantly decreased with soak times while red goji berry does not (Wang et al., 2018). Different from poly- (P < 0.05), which was similar to variation trend of the polysacchar- saccharides, the difference of the TPC of goji berry between the first ides and polyphenols in goji berry tea. The antioxidant ability in tea time and the second tea time was not significantly different, so black goji berry at 100  °C, 60  min was about 3 times of those at the second tea was important for more polyphenols can be dissolved 40  °C, 60  min and the contents of antioxidant ability at 100  °C, (P < 0.05). 60 min were about 4 times of those at 100 °C, 5 min. The antioxidant Downloaded from https://academic.oup.com/fqs/article/4/4/193/5893636 by DeepDyve user on 22 December 2020 200 B. Liu et al., 2020, Vol. 4, No. 4 Black goji berry tea (g)Red goji berrytea (h) Black goji berry tea (i)Red goji berry tea (j) Black goji berry tea (k)Red goji berrytea (l) Figure 6. Continued. ability of black goji berry tea was far higher than red goji berry, and red goji berry and black goji berry tea are rich in phytochemicals and the AA of black goji berry tea was about two 2 to 5 folds of red goji show high antioxidant capacities. The contents of phytochemicals berry tea. The antioxidant ability of goji berry tea was related to the and the antioxidant capacity of a goji berry tea rised with soak tem- soluble polyphenols in tea. perature and time, Soaking using the cold or warm water, even at long time, will waste most of the phytochemicals and antioxidant activity. Black goji berry tea has far higher phytochemicals, antioxi- Conclusions dant property, and more desirable colours than red goji berry tea. In the present study, the effects of making tea with water on the colour, The results of this study suggest that high temperature and long soak and the content of phytochemicals and antioxidant ability of black time can be used to make a healthy goji berry tea, hot drink of goji and red goji berry tea were investigated and compared, which will berry is a good habit, and black goji berry may be a better choice, directly provide a scientific basis for daily diet. It is found that both but we need to change the habit of short tea time. 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