Polyphenols are the important contributors of health protection and preventing various diseases including type 2 diabetes (T2D). Hence an investigation was made to determine the polyphenols  of selected Indian medicinal herbs  of Ocimum (T2) Gymnema (T3) ; Senna auriculata and cinnamon bark extracts (T4)  and Senna auriculata and ginger extracts (T5) by Fourier Transform Infrared (FTIR) spectroscopy. The results were compared with the leaves of Cameilla sinensis (T1-Green tea). Infra red absorption spectra of T4 revealed new peaks in the regions 4623 cm-1 and 4337.91 cm-1 were related directly to the presence of more functional groups such as polyphenols. This showed active constituents in herbal polyphenols of the T4 with mixed formulation of Senna auriculata  and Cinnamum zeylanicum. In all infusions the IR spectral peak values are absent between region 2220-2250 cm-1. This indicates  the absence of cyanide groups. From this it was confirmed that due to the absence of toxic substances in the selected medicinal plants are suitable for consumption. Hence the leaves of Ocimum sanctum and Gymnema sylvestre, flowers of Senna auriculata, bark of Cinnamum zeylanicum (cinnamon) and  rhizome of Zingiber officinale (ginger) are  recommended for herbal tea  formulations.

Herbal tea, FTIR study, Functional groups, Polyphenols.

Polyphenols are the important contributors of health protection and preventing various diseases. Unhealthy eating habits and sedentary lifestyles associated with urbanisation are common risk factors in developing type2 diabetes (T2D). Consuming functional food and beverages can help to overcome T2D. Polyphenols are the heterogeneous phytochemical group containing phenol rings. Plant-based and fruit-based foods are the main sources of polyphenols (Alma et al., 2003; Rusak et al., 2008; Anesini et al., 2008 ; Alothman and Bhat 2009).

Dietary polyphenols  could reduce starch digestion by the inhibition of α-amylase and α-glucosidase (Khokhar   and  Magnusdottir 2002; Kwon et al., 2008; Liang et al., 2007; Jianbo et al., 2011). Herbal tea consumed everyday as functional beverage influence the activities of α-amylase (Bailey, 2001; Cheng et al., 2012; Manousi et al., 2019; Raman et al., 2019). With the goodness of antidiabetic potentiality various  herbal formulations were experimented for their phytochemical constituents by conventional methods which are time consuming and non-reliable in the research field.

FTIR is one of the most widely used methods to identify the chemical constituents and determine the functional group and the chemical structure of the constituents. Earlier studies from the literature with reference to determination of functional groups and the chemical constituents profiling by FTIR had a remarkable role in medicinal plant study (Muruganantham et al., 2009; Qin  et al., 2010 ;  Baseri and  Baker (2011) ; Ragavendran et al., 2011).

Screening of phytochemical constituents of the medicinal herbs  by the conventional methods may not be reliable and a challegeable task in the field of research. Hence in the present study pure and mixed form of five medicinal herbs viz., Ocimum sanctum, Gymnema sylvestre, flowers of Senna auriculata, bark of  Cinnamum zeylanicum (cinnamon) and  rhizome of Zingiber officinale (ginger)  were selected to determine  the phytoconstituents  and functional groups by FTIR. IR spectra of the selected medicinal plants were analysed according to the peak/wave numbers.

Preparation of plant materials. Five medicinal plants leaves of Ocimum sanctum, Gymnema sylvestre, flowers of Senna auriculata , bark of  Cinnamum zeylanicum (cinnamon) and  rhizome of Zingiber officinale (ginger) were collected from  the herbal garden of  Madha Engineering College (MEC) of Chennai, India.  Healthy plants were selected from MEC herbal garden and the leaves, bark and flowers of the selected Indian medicinal plants for the study were dried at 50ºC in an oven. The powdered samples were stored in air tight bottles at room temperature for further analysis.

FTIR Study. The FTIR analysis was conducted on leaf powder samples of Ocimum (T2), Gymnema (T3), Senna auriculata and cinnamon bark extracts (T4) and Senna auriculata and ginger extracts (T5).  Fine powder of oven-dried (50ºC) leaves of selected medicinal herbs were taken. 1 mg of the sample was mixed with 50 mg KBr (FTIR-grade) and experiments were performed with an IR Prestige-21 (Shimadzu). One drop of the diluted extract was then mixed with 50 mg KBr. The scanning absorption range was 500 to 5000 cm−1. The peak values of FTIR were recorded for T1, T2, T3, T4 and T5. Each and every analysis was repeated twice to confirm the spectrum. 

FTIR spectrum was used to identify the functional group of the active components based on the peak value in the region of infra red radiation (Sohrabi et al., 2005; Schulz and Baranska 2007). The results  with reference to pure and mixed medicinal herbal formulations  in terms of peaks and  wave numbers  were explored. The IR spectra of  illustrated in the Fig. 1-5.

Fig. 1. FTIR profile of green tea extract (T1).

Fig. 2. FTIR profile of  Ocimum sanctum  (T2).

Fig. 3. FTIR profile of Gymnema sylvestre (T3).

Fig. 4. FTIR profile of  Senna auriculata &  Cinnamum zeylanicum (T4).

Fig. 5. FTIR profile of Senna auriculata  and  Zingiber officinale (T5).

The FTIR spectra  of pure and mixed tea formulations of Ocimum (T2) Gymnema (T3) ; Senna auriculata + cinnamon bark extracts (T4)  and Senna auriculata +  ginger extracts (T5) were illustrated in Fig. 2-5. The FTIR spectra of Green tea (Camellia sinensis) in T1 (Fig. 1) was used for comparison.

It is possible to directly relate the intensities of absorption bands to the concentration of the corresponding functional groups present in the  Ocimum sanctum, Gymnema sylvestre, Senna auriculata,  Cinnamum zeylanicum  and  Zingiber officinale. 

Similar kind of study  made by many researchers (Demiray et al., 2009; Konwar et al., 2011; Helal et al., 2014) for the rapid analysis and confirmation of phytoconstituent structures. At present Infra red absorption spectroscopy  revealed new peaks  in the regions 4623 cm-1 and 4337.91 cm-1 were related directly to the presence of more functional groups such as polyphenols. This showed the presence of active constituents in herbal polyphenols of  the T4 with the combination of Senna auriculata  and Cinnamum zeylanicum.

The results of Fourier Transform Infra red absorption  spectroscopy revealed the peak values  are illustrated in the Fig. 1-5. FTIR spectrum confirmed the presence of alcohol, phenol, alkanes, alkyl halide, amino acids , carboxylic acid, aromatic, amines in the rhizome, bark, flowers and leaves of the selected medicinal plants.

FTIR spectroscopy measurements are faster and accurate. The absorption radiations in FTIR for the green tea (T1) in the region 1626 cm-1 exhibits  C=C stretching vibration which can be conjugated with C=O. The intensities of absrorption bands between 2002.11 cm-1 and 2352 cm-1 illustrates the  free amino acids and amino related functional groups. Variable stretching vibrations of T4 spectra are found in the region 4623 cm-1 to 4337 cm-1. Most organic and inorganic compounds were identified  within this region (Fig. 6).

Fig. 6. Analysis of FTIR Spectral functional groups of herbal teas.

The more intense band occurring at 4623.37 cm-1 to 4337.91 cm-1; 3205.69 to 3186.40; 2358.94 to 2355.08; 2268.29 to 2002.11 and 1978.97  to 1625.99 cm-1 corresponding to O-H/N-H/ C-H/C=O stretching, bending, vibrations respectively indicate the presence of alcohol, amines, amides, amino acids and amino related compounds in Senna auriculata, Ocimum sanctum,  Gymnema sylvestre,  Cinnamum zeylanicum  and Zingiber officinale. Peak values are absent  between region 2220-2250 cm-1 which indicates  the absence of cyanide groups. From this it was confirmed that the absence of toxic substances in the selected medicinal plants. Hence all the selected medicinal plants are suitable for consumption and recommended for herbal tea formulations. Many researchers determined and confirmed the phytochemical constituents of various medicinal plants because of faster and accurate results obtained in FTIR (Saxena and Saxena 2012; Helal  et al., 2014; Gorgulu et al., 2007; Kumar and  Prasad 2011).

It is evident from the results of FTIR  indicated that herbal tea formulation  of T4 and T5  had contained higher amount of total phenols than green tea (T1) where as T2 and T3  showed similar peaks corresponding to T1 (Fig. 6).

FTIR  measurements were made for accuracy and direct identification of functional groups in the selected medicinal herbs.  It is evident from the results of FTIR  indicated that herbal tea in T4 (Senna auriculata  and Cinnamum zeylanicum) T5 (Senna auriculata and  Zingiber officinale) formulation also contained higher amount of total phenols than green tea  and more peaks in the spectrum next to T4. Whereas T2 (Ocimum sanctum) and T3 (Gymnema sylvestre) were recorded similar peaks in the FTIR spectrum corresponding to T1 (green tea). In summary all the selected medicinal plants are suitable for consumption and recommended for herbal tea formulations.

FTIR profiling of selected medicinal plants can be further studied with reference to the quality checking and characterization of new compounds/functional groups in the formulations for the pharmaceutical research and food science/technology.

Yasodha T., Vijayalakshmi M.S. and Pooja V.  (2024). FTIR Profiling of Herbal Teas prepared from Medicinal Plants. Biological Forum – An International Journal, 16(4): 08-11.