Elsevier

Food Chemistry

Volume 133, Issue 3, 1 August 2012, Pages 953-959
Food Chemistry

Antioxidant and anti-glycation properties of Thai herbal teas in comparison with conventional teas

https://doi.org/10.1016/j.foodchem.2012.02.012Get rights and content

Abstract

Fifteen Thai herbal teas in comparison with teas of Camellia sinensis, were studied for their antioxidants and anti-glycation properties in correlation with their total phenolics, flavonoids, and non-flavonoids contents. Significant differences were observed among the tea infusions. Only stevia and sappan herbal teas had primary antioxidants and anti-glycation capacities comparable to C. sinensis. However, purple velvet, mulberry and false mallow herbal teas were exceptionally stronger in metal chelating capacity than the C. sinensis teas. Principal component analysis showed that total phenolics, particularly flavonoids highly correlated with primary antioxidants and anti-glycation. Cluster analysis showed that the properties of stevia and sappan herbal teas were similar to green, black and oolong teas. Some common, but rarely mentioned, Thai herbal teas could be choices of interest for healthy beverages and could be new dietary sources for bioactive compounds.

Highlights

► Thai herbal teas had antioxidants and anti-glycation capacities. ► Significance differences were observed among 18 teas studied. ► Only stevia, sappan primary antioxidants, anti-glycation comparable to Camellia sinensis. ► Purple velvet, mulberry, false mallow metal chelations higher than C. sinensis. ► Cluster analysis showed stevia, sappan properties similarly to C. sinensis.

Introduction

Free radicals are generated in the human body from endogenous (e.g. respiratory chain, oxidative enzymes) and exogenous (e.g. air pollution, smoking) sources. The occurrence of such free radicals is balanced by endogenous defense systems such as antioxidative enzymes and metal binding proteins (Young & Woodside, 2001). Overproduction of such free radicals leads to oxidative stress that damage cell matrices such as lipids, proteins and nucleic acids, resulting in the development of various diseases, e.g. cancers, diabetes, cardiovascular diseases and Alzheimer’s diseases (Barnham et al., 2004, Rahimi et al., 2005, Young and Woodside, 2001). Hence, the normal biological system can be maintained by exclusion of excessive amounts of free radicals by antioxidants.

Oxidative stress also plays a role in glycation. The glycation process starts with chemical reaction between available amino groups of amino acid residues in proteins and reducing sugars, resulting in the formation of Amadori products. Over time, these products are transformed through glycoxidative process and further modifications, and result in the formation of advanced glycation end products (AGEs) (Rojas and Morales, 2004, Wu and Yen, 2005). The glycation process occurs to higher extent under ageing and hyperglycemia such as diabetics in comparison to healthy persons (Baral et al., 2000). AGEs formation is also enhanced with oxidative stress (Parija et al., 2005, Selvaraj et al., 2002, Wu and Yen, 2005). In terms of pathogenesis, accumulation of AGEs is toxic to cells and can accelerate diabetic complications including retinopathy, neuropathy, cataract and atherosclerosis (Ahmed, 2005). The investigation of food with both antioxidative and anti-AGEs formation properties offers a potential prevention of such illness.

Teas brewed from Camellia sinensis and herbal tea brewed from the leaves, flowers, seeds, fruits and roots of plant species other than C. sinensis are some of the most consumed beverages worldwide. Beside the attractive flavours, their popularities come from their primary and secondary antioxidant properties (Aoshima et al., 2007, Horžić et al., 2009, Kome et al., 2010). Primary antioxidants directly scavenge free radicals, while secondary antioxidants indirectly prevent the formation of free radicals through Fenton’s reaction (Chan, Lim, Chong, Tan, & Wong, 2010). Teas of C. sinensis generally exhibit both primary and secondary antioxidant capacities higher than herbal teas such as lemon grass (Cymbopogon citratus), chamomile (Matricaria recutita) and rosemary (Rosmarinus officinalis). Herbal tea of mint (Mentha spicata) and peppermint (Mentha spicata) have exceptionally higher secondary antioxidant capacities than all teas of C. sinensis (Chan et al., 2010). Recent studies have shown that some teas possess not only antioxidant capacity but also anti-AGEs formation properties (Ho et al., 2010, Lunceford and Gugliucci, 2005). Black tea, balm (Melissa officinalis), sage (Salvia officinalis), mate (Ilex paraguariensis) and common verbena (Verbena officinalis) herbal teas exhibited anti-AGEs formation properties comparable to green tea (Ho et al., 2010, Lunceford and Gugliucci, 2005).

Hence, tea and herbal tea beverages are potential dietary sources for both antioxidant and anti-AGEs formation properties. However, the role of anti-AGEs formation capacity of various herbal teas is still not well investigated. Among those herbals, various Thai herbs such as mulberry (Morus alba), safflower (Carthamus tinctorius) are often consumed as herbal tea and are commercially available. However their health promoting properties, especially antioxidant and anti-AGEs formation properties have rarely been studied. The objective of this work was to study the antioxidants and anti-AGEs formation properties in correlation with phenolic, flavonoid and non-flavonoid contents of 15 Thai herbal teas comparing to conventional green, black and oolong teas for the first time.

Section snippets

Chemicals

Folin–Ciocalteu’s phenol reagent and gallic acid monohydrate were purchased from Sigma–Aldrich Chemie (Steinheim, Germany). l-Ascorbic acid was purchased from Riedel-deHaën®. Ferric chloride hexahydrate, ferric sulphate, d-glucose, sodium azide, potassium persulfate were obtained from Ajax Finechem (New South Wales, Australia). 2,4,6-Tri-(2-pyridil)-S-triazine (TPTZ), ferrozine (3-(2-pyridyl)-5,6-diphenyl-1,2,4-triazine), 2,2′-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid diammonium salt

Total phenolic, flavonoid and non-flavonoid contents

Total phenolic (TPC), flavonoid (TFC) and non-flavonoid (TNFC) contents were found in the tea infusions as shown in Fig. 1. Comparing to teas of C. sinensis, Thai herbal teas generally had lower TPC and TFC. Exceptions were stevia (SV) and sappan (S) herbal teas with total phenolic and flavonoid contents higher than oolong tea (OT). Among 18 infusions studied, green tea (GT) was recognized as the richest source of both total phenols and flavonoids, 132 and 125 mg GAE/100 ml respectively. Most of

Conclusion

We investigated antioxidants and anti-glycation capacities of 15 Thai herbal teas in comparison with green, black and oolong tea for the first time. Thai herbal teas generally had lower antioxidants and anti-glycation activities than teas of C. sinensis. Stevia and sappan herbal teas were the exceptions for their primary antioxidants and anti-glycation capacities. Among the properties tested, metal ion chelating efficiency of mulberry, purple velvet and false mallow herbal teas were outstanding

Acknowledgements

This work was financed from the Mahidol University research grant. The authors thank to the instrument center of Mahidol University Kanchanaburi Campus. Dr. Duangkamol Poltem, Division of Science and Liberal Arts, Mahidol University Kanchanaburi campus, is gratefully acknowledged for the statistical analysis technique.

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