Ocimum Sanctum (Tulsi) Leaves and Herbal Syrup: A Review of Pharmacognostic And Phytochemical Evaluation and Formulation

Herbal medicines are therapeutic products obtained from plants, and they form the basis of traditional systems such as Ayurveda. They are widely used because they are easily available, relatively inexpensive and generally well tolerated. Plant drugs are given in many forms, and for liquid oral use the common forms are decoctions (kwatha), infusions, syrups and fermented preparations. A syrup is a concentrated aqueous solution of sugar, usually sucrose, to which the extract of the drug and suitable additives are added. [1] Tulsi (Ocimum sanctum L., family Lamiaceae; also called holy basil) is a sacred and widely used medicinal herb of India. Its leaves, seeds and roots are used in Ayurvedic medicine, and the leaves are traditionally given for cough, bronchitis, fever and other conditions; eugenol and ursolic acid are among its best-known constituents, and antioxidant, anti-inflammatory, antimicrobial and antidiabetic activities have been reported.[2] Because the quality of a herbal syrup depends first of all on the quality of the leaf from which it is made, the leaves must be authenticated and standardised before they are used.[3,4] Herbal syrups are popular for cough and respiratory complaints, and several tulsi-containing syrups have been formulated and evaluated. [5,6,7] The common forms of liquid oral herbal preparations are compared below.

Table: Liquid Oral Herbal Dosage Forms [1,3,8]

Herbal materials are natural products, so their composition changes with the species, the part used, the place and time of collection, drying and storage. Adulteration with other Ocimum species or other leaves, microbial contamination and pesticide residues can also affect the quality. For this reason the WHO has published methods for the quality control of herbal materials, and the Indian Pharmacopoeia and the Ayurvedic Formulary give standards and methods of preparation. [4,8,9]

Ocimum sanctum (Tulsi) Leaves

The leaves of Ocimum sanctum are the drug used for pharmacognostic and phytochemical evaluation and as the active ingredient of herbal syrups. Its botanical details and main constituents are given below.

Table: Profile of Ocimum sanctum Leaves [2,10]

A phytochemical and GC-MS study of the hydro-ethanolic leaf extract of Ocimum sanctum detected flavonoids, alkaloids and terpenoids and identified 40 compounds, with eugenol among the major ones.[10] The leaf has also been standardised for moisture content, total ash, water-soluble and acid-insoluble ash values, and the standardisation is considered useful for authenticating the genuine drug.[3]

Herbal Syrup as a Dosage Form

A syrup is a pleasant, viscous liquid dosage form that contains the extract of the drug dissolved in a concentrated sugar solution. Sucrose gives the sweetness and the viscosity and also helps to preserve the product, while the other additives (glycerin, a preservative and an acid) improve the stability and the taste.[1] A good herbal syrup should be clear and uniform, have a pleasant taste and odour, have a pH and a specific gravity within the usual limits, show no crystallisation or sedimentation, be free of microbial growth, and remain stable on storage.[1,6,7]

Table: Components of a Herbal Syrup [1,6]

Syrups can be prepared by the methods below. Preparation of a decoction followed by dissolving the sucrose in the hot filtrate follows the traditional method of preparing a kwatha and uses common laboratory equipment. The quality of the syrup depends on the strength of the extract, on the concentration of sucrose (a very high concentration crystallises on storage and a low one allows microbial growth), on the pH and on the preservative system. [1]

Table: Methods of Preparing Syrups [1]

Advantages and Limitations

Table: Advantages and Limitations of Herbal Syrup [1,3,6]

Applications

• Relief of cough, cold and bronchitis, as in the traditional use of tulsi.[2,5]
• General immunity booster and antioxidant supplement. [2]
• Base for polyherbal syrups, for example with ginger, turmeric, giloy or honey. [6,7]
• Pleasant vehicle for other herbal extracts in paediatric use.

Traditional and Standardised Tulsi Preparations

Many herbal syrups in the market are not standardised: the quantity of the herb, the extraction method and the quality of the leaf are often not stated. Pharmacopoeial standards for the raw drug and for herbal syrups are limited, so the leaf and the syrup have to be standardised separately. [3,4,9] The two kinds of preparation are compared below.

Table: Comparison of Traditional or Marketed Preparation and Standardised Syrup [3,4,9,11]

LITERATURE REVIEW

The studies below deal with the standardisation of tulsi and with the formulation and evaluation of herbal syrups.

Standardisation and Phytochemistry of Tulsi

Debbarma et al. standardised Ocimum sanctum, a herb used for bronchitis, malaria and skin illnesses. The raw drug was evaluated for moisture content, total ash, water-soluble ash and acid-insoluble ash, and an in-house mother tincture was standardised for total solids, pH, TLC, UV-visible spectra, weight per volume and alcohol content. The authors concluded that such standardisation is useful for authenticating the genuine drug. [3]

Joshi reviewed the phytoconstituents and the traditional, medicinal and bioactive uses of tulsi. The review notes that the chemical composition of tulsi is complex, that eugenol and ursolic acid are among the best-known compounds, and that standardisation has been difficult. Antioxidant, anti-inflammatory, antimicrobial, antidiabetic and antimalarial effects are described, and Ayurvedic practitioners use tulsi for anxiety, chronic cough, bronchitis and fever. [2]

Srivastava et al. prepared a 70% ethanol extract from the dried leaves of Ocimum sanctum and screened it for phytochemicals, and then analysed the extract by GC-MS. Flavonoids, alkaloids and terpenoids were detected, and GC-MS identified 40 compounds, with eugenol among the major ones. [10]

Herbal Syrups Containing Tulsi

Devkar et al. developed a herbal cough syrup using pudina, tulsi or cinnamon as the main ingredient with honey. The syrup was prepared at laboratory scale and evaluated for pH, viscosity, density and stability, and the authors reported that it was stable and that its antitussive activity at the lowest tested dose was better than that of the standard drug. [5]

Kumar and Anamika developed a polyherbal syrup for respiratory health from six indigenous plants, prepared as aqueous decoctions and combined with a sucrose-based simple syrup. The syrup was clear and dark brown with a pleasant aroma, its pH, specific gravity and viscosity were within the pharmacopoeial ranges, and alkaloids, flavonoids, tannins, saponins, phenolics, glycosides and essential oils were detected. The syrup was reported to be homogeneous and stable under the test conditions, and further in-vitro, stability, animal and clinical studies were recommended. [6]

Shendage et al. formulated a cough syrup with Tinospora cordifolia as the main ingredient together with tulsi, ginger, turmeric and honey, using methyl paraben as the preservative and water as the vehicle. The syrup was evaluated for appearance, colour, odour, taste, pH, viscosity, density, specific gravity, clarity, sedimentation and stability. It showed acceptable sensory properties, suitable pH and viscosity, good clarity and satisfactory physical stability, and the authors stated that pharmacological and clinical studies are needed. [7]

Table: Summary of the Studies Reviewed [2,3,5,6,7,10]

Observations from the Literature

Three points follow from the studies. First, tulsi leaf is standardised by its moisture content, ash values and phytochemical profile, and eugenol and flavonoids are its reported constituents. [2,3,10] Second, herbal syrups containing tulsi are evaluated by organoleptic properties, pH, density or specific gravity, viscosity, clarity, sedimentation and stability. [5,6,7] Third, the syrups reported so far are polyherbal or cough-specific, and the raw drug and the syrup are not usually evaluated together.

Table: Parameters Used in the Studies Reviewed [3,5,6,7,10]

Gap in the Literature

The reported studies either standardise the tulsi drug or its tincture, or formulate polyherbal syrups in which tulsi is one of several ingredients, but they do not evaluate the pharmacognostic and phytochemical quality of the tulsi leaf and then use the same leaf to prepare a syrup, study the effect of the extract strength on the quality of the syrup, and compare it with a marketed syrup.

Pharmacognostic Evaluation of Tulsi Leaves

Collection and Authentication

Fresh, mature leaves of tulsi are collected from healthy plants, preferably in the morning, and the identity of the plant is confirmed by a qualified botanist or the Department of Pharmacognosy. The identity is confirmed by the macroscopic characters of the leaf (shape, size, margin, venation, colour, odour and taste) and by powder microscopy, and a voucher specimen is kept. The leaf of Ocimum sanctum is aromatic and ovate to elliptical with a petiole, and as a member of the Lamiaceae it shows stomata and glandular and non-glandular trichomes in microscopy. [2,3] Leaves that are yellow, diseased, insect-infested or mixed with other Ocimum species or foreign matter are rejected.

Drying, Size Reduction and Sieving

The leaves are washed with water to remove dust, dried in shade (or in a hot air oven at not more than 50 °C so that the volatile oil is not lost), and powdered in an electric grinder using short intervals. The powder is passed through sieve no. 85[8] and stored in airtight containers away from light and moisture. For the preparation of the decoction, a coarse powder may be used instead of the fine powder.

Pharmacognostic and Physicochemical Standardisation

Table: Standardisation Parameters of the Leaf [3,4,9,12]

These tests are carried out on the leaf before it is used for the syrup, so that only material that complies with the limits of the Indian Pharmacopoeia and the WHO guidelines is accepted. [4,9]

Phytochemical Screening and TLC

Table: Preliminary Phytochemical Tests [10,12]

For TLC fingerprinting, a methanolic extract of the leaf is spotted on silica gel G plates, developed in toluene: ethyl acetate (93: 7), sprayed with vanillin–sulphuric acid reagent and heated, and the Rf values of the spots are noted.[3,12]

Formulation of Herbal Syrup

Materials Used

Table: Materials Commonly Used for a Tulsi Syrup [1,6,7]

Formulation

A typical formulation for a batch of 100 mL, with the decoction made at three leaf strengths, is shown below; the proportions are indicative and are adjusted after preliminary trials. [1,5]

Table: Typical Formulation of Tulsi Syrup (per 100 mL) [1,5]

Method of Preparation

1. The weighed quantity of the tulsi leaf (coarse powder) is boiled with water for about 15 minutes in a covered vessel and cooled.
2. The decoction is strained and filtered through a muslin cloth and then through filter paper, and the volume is adjusted with hot water.
3. Sucrose is dissolved in the hot filtrate by gentle heating and stirring, and the solution is cooled.
4. Glycerin, sodium benzoate (dissolved in a little water) and citric acid are added with stirring, and the volume is made up to 100 mL with purified water.
5. The syrup is filled into clean, dry, amber coloured bottles, sealed and labelled with the batch number and date.

Evaluation of Herbal Syrup

Herbal syrups are evaluated for their physical, phytochemical and microbial quality and for stability. The usual tests and their methods are given below. [5,6,7,9]

Table: Evaluation Parameters of Herbal Syrup [5,6,7,9,11]

Calculations

Table: Formulae Used in the Evaluation [4,9]

Quality Expected of a Herbal Syrup

Table: Observations Reported for Tulsi-containing Syrups [5,6,7]