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Several environmental, agricultural, urban and industrial factors, coupled with inadequate harvesting, storage and processing techniques, cause contamination in crude drugs, leading to a compromise in quality and efficacy of the products (Kneifel et al. 2002; Street et al. 2008). Many ayurvedic herbs are collected from wastelands and agricultural fields. Therefore, they may be contaminated with chemical pollutants, pesticide residues, bacteria and fungi. Contaminating micro-organisms and their toxins may lead to diseases, making the herbs hazardous for consumption (Govender et al. 2006; Van Vuuren et al. 2014). Major contributing factors to the growth of microbes are elevated temperatures and moisture (Hell and Mutegi 2011).
Contamination with Heavy Metals
Accumulation of heavy metals in medicinal herbs has been reported. Such contamination occurs when herbs grow' in heavily polluted soil. Some plants accumulate heavy metals like cadmium, from regular soil (Ernst and Coon 2001; Blagojevic et al. 2009; Gasser et al. 2009; Wenzig and Bauer 2009; Kabelitz 1998; Chizzola et al. 2003). However, ayurvedic herbs are relatively free from heavy metal contamination. Rao et al. (2011) examined the heavy metal content of Emblica officinalis fruits, Terminalia chebula fruits, Terminalia belerica fruits and Withania somnifera roots. Arsenic, cadmium, lead and mercury were found below' detection limits in all the samples.
Sebastian et al. (2015) reported an extensive investigation of the heavy metal content of ayurvedic herbs. They procured samples of 34 ayurvedic herbs from various suppliers in the country. These herbs were collected from four agro-climatic zones. The heavy metal content of the dried and powdered herbs was analyzed using an Agilent 7700X inductively coupled mass spectrometer (ICP-MS) (Agilent Technologies, U.S.A.). Heavy metals were not detected in many of the samples, and the others contained the contaminants well below the limits set by the Government of India (Lohar 2008).
Contamination with Micro-Organisms
Harvested ayurvedic crude herbs may inadvertently contain micro-organisms. Herbs tend to have higher microbial contamination than chemically defined active substances, and the microbial population present may differ qualitatively and quantitatively. Therefore, attention should be paid to the microbiological quality of ayurvedic medicines. Some micro-organisms can alter the physicochemical characteristics of the product, affecting the product’s quality. Constituents of the crude herb may be metabolized by the micro-organisms, leading to undesirable chemical changes. Microorganisms may also cause changes in appearance, smell or taste and pH of the medicine. If the pH changes significantly in an ayurvedic kvdtha containing a chemically ionizable preservative the efficacy of which is pH-dependent, like benzoic acid and sorbic acid, then the efficacy of the preservative may be diminished (Anonymous 2015).
During growth on herbal substrates, some molds produce mycotoxins. Some of these substances like aflatoxins and ochratoxin A can be secondary metabolites, while others like fumonisins may be hydrophilic. Mycotoxins can be formed during cultivation or wild growth of the plant or during the storage of the harvested crude herb. Some ayurvedic herbs like licorice root may be contaminated by ochratoxin A. This toxin is produced by Aspergillus ochraceus, Penicillium verrucosum and several other species of Aspergillus and Penicillium. Ochratoxin A is nephrotoxic and carcinogenic (Anonymous 2015).
Microbial contamination originates during the harvesting of the plant material or by the handling of the plant material or during human intervention, equipment, buildings, air ventilation systems and contamination during transportation. Minimizing contamination with micro-organisms and microbial toxins should be ensured ideally by monitoring and limiting these steps rather than by the use of decontamination methods (Anonymous 2015).
Contamination with Pesticides
During the different stages of collection or cultivation, storage, transport, distribution and processing of the herbs, pesticides and often fumigating agents are used against pests and unwanted deterioration. Thus, contaminants arising from pesticides or illegal use of unapproved pesticides during cultivation can also pose a threat to health (Yau et al. 2015). In a study that examined 36 crude Chinese herbs procured from large wholesale herb markets in South Korea, many were found to be contaminated with eight pesticides like benzene hexachloride, procymidone and endosulfan (Oh 2007). In another study, harvested wild plants were found to contain significantly higher levels of pesticides than cultivated samples, suggesting that local sources of industrial or agricultural pollution could be important factors contributing to contamination of herbs (Harris et al. 2011).
Rao et al. (2011) investigated the content of pesticide residues in fruits of Emblica officinalis, Terminalia chebula and Terminalia belerica and roots of Withania somnifera. Pesticide residues were found below detection limits in all the samples. However, somewhat contradictory results were reported by Rai et al. (2008). They estimated the levels of organochlorine pesticide residues like isoforms of H.C.H., D.D.T., D.D.D., D.D.E. and a-endosulfan, in constituent plants of the famous ayurvedic formula DasamUla (Aegle marmelos, Desmodium gangeticum, Gmelina arbo- rea, Oroxylum indicum, Premna latifolia, Solanum indicum, Solanum surratense, Stereospermum chelonoides, Tribulus terrestris and Uraria picta). The organochlorine pesticide residues viz., different metabolites of D.D.T., D.D.E., isomers of H.C.H. and a-endosulfan were checked in a total of 40 samples of single crude drugs. Although a-H.C.H. and y-H.C.H. were present in almost all the samples, other pesticides were not detected in them. D.D.T. and D.D.E. were found only in two samples. The authors concluded that the estimation of pesticides is essential for crude drugs used in the preparation of ayurvedic medicines. As the study also reports high residual buildup of a-H.C.H. and у-H.C.H., the authors suggest the judicious use of these pesticides and the choice of pesticides for use in agriculture (Rai et al. 2008). Considering the need to maintain the high quality of ayurvedic medicines, the Government of India has set limits for these contaminants (Table 4.1).
Adulteration and Substitution
With the depletion of medicinal plants in their natural habitat, many herbs used in Ayurveda are becoming rare. Plants like Coscinium fenestratum, Gymnema sylvestre and many others that were endemic to Indian forests have become endangered or threatened. This has given rise to widespread adulteration. Sometimes herbs are substituted with different parts of the same species. In the majority of cases, stems are used instead of roots. Thus, the roots of Sida species are substituted with their stems. The same is the case with Rubia cordifolia (Menon 2003). Adulterants of some threatened medicinal plants of Kerala are listed in Table 4.2.
Content of Bioactives
Ayurveda medicines are generally prepared using several crude drugs in combination. The celebrated Ayurveda tonic Cyavanaprasa contains 42 herbal ingredients (Anonymous 1978a). It is well known that the chemical constituents in these herbs vary due to genetic factors, chemical races, hybridization, ecological factors (light, temperature, altitude, latitude, water, soil chemistry), onto- genic stage of harvest, cultivation, post-harvest treatment and storage (Kumar 2016).
Herbs contain numerous phytocompounds. A common herb like turmeric contains around 200 distinct phytocompounds (Balaji and Chempakam 2010). Even though there are major compounds among them, the minor compounds are also essential to bring forth the biological activities attributed to the herb. While reporting the antibacterial activity of Daucus crinitus, Bendiabdellah et al. (2013) observed that there is some evidence that minor components in essential oils have a critical
Limits of Contaminants for Ayurveda, Siddha and Unani Products
Adapted from Lohar 2008.
Adulterants of Some Threatened Medicinal Plants of Kerala*
Questions on the quality, safety and efficacy (Q.S.E.) of ayurvedic medicines have been raised following their industrial manufacture. The Government of India has also recognized the medicinal use of ayurvedic products which conform to the three attributes of Q.S.E. However, assuring the Q.S.E. of an ayurvedic medicinal product at release does not ensure consistent therapeutic effects and or safety of the product during its shelf-life, as the therapeutic attributes of the product may be altered due to exposure to different environmental conditions during their storage. Therefore, systematic stability studies are to be carried out on all types of ayurvedic products to confirm their Q.S.E. during storage (Bansal et al. 2018).
Stability testing of ayurvedic products is more difficult and challenging when compared to that of a synthetic medicinal product. The active pharmaceutical ingredient of a synthetic product is well-defined qualitatively and quantitatively. Its content is directly related to the therapeutic effectiveness. Therefore, the actives in the formulation function as direct markers for stability testing of the product. Contrary to this, an ayurvedic product is a complex heterogeneous mixture of compounds like alkaloids, terpenoids, organic acids, saponins and so on. All these compounds are also prone to degradation under the influence of various environmental factors like temperature, light, air, moisture and pH. Therefore, it is possible that the contents of these phytocompounds change during its shelf-life, altering the Q.S.E. of the product (Bansal et al. 2018).
Several studies have been reported on the stability of herbal ingredients. For example, androgra- pholide present in the extract of Andrographis paniculata whole herb disintegrates on air oxidation (Garg et al. 2016). Similarly, lipid-soluble fractions like ar-turmerone, turmerone and curlone of dried rhizomes Curcuma longa are affected by light (Jain et al. 2007). Such evidence suggests that herbal materials can also undergo degradation. Moreover, the therapeutic actions of an herbal product are believed to be a function of the combined actions of chemically diverse bioactive compounds. Therefore, any change in the content of specific marker(s) during stability testing of an herbal product may not translate to a similar change in its therapeutic efficacy. Thus, monitoring of specific marker(s) during stability testing of herbal products may not form a sound basis for establishing their shelf-life (Bansal et al. 2018).
Stability studies of herbal products are often weakened by factors like the quality of the crude drug material used in the preparation of the product, use of different names of herbs, drying techniques, extraction methodologies, storage conditions, contamination of crude drugs, adulteration, substitution and improper agricultural practices (Bansal et al. 2018).
The selection of markers for assessment of the shelf-life of herbal products is the most challenging task during stability testing. A survey of available stability reports on herbal products reveals that different investigators have used different markers which are likely to disintegrate at higher temperatures for stability testing of herbal products (Livesey et al. 1999; Bernatoniene et al. 2011; Jiang et al. 2013). These reports suggest that there is great variability in susceptibility of different classes of markers to chemical change during shelf-life. Therefore, the phytocompound that is to be used as a marker in the stability study should be chosen judiciously, so as to obtain a reliable estimate of the stability of the product.
The United States’ F.D.A. has included biological assay as one of the quality control parameters (Anonymous 2016b). In view of this regulatory recommendation, it is necessary to evaluate the shelf-life of an herbal product vis-a-vis chemical stability and biological activity. But so far only a few studies have been conducted considering both marker compound and biological activity (Srivastava and Gupta 2009; Akowuah and Zhari 2010; Patil et al. 2010; Srivastava et al. 2010). Therefore, shelf-life studies of ayurvedic medicinal products should include the evaluation of physical and chemical stabilities, as well as the intended biological activity using suitable in vitro and in vivo methods (Bansal et al. 2018).
Considering the importance of stability testing in ensuring the quality of ayurvedic medicines, the Central Council for Research in Ayurvedic Sciences, Ministry of A.Y.U.S.H., Government of India has published General Guidelines for Drug Development of Ayurvedic Formulations (Anonymous 2018a). It discusses, among other subjects, stability testing and shelf-life determination of ayurvedic medicines. It provides clear guidelines on the selection of batches, container and closure systems, specifications, testing frequency, storage conditions and evaluation.
Knowing the biologically active constituent in an ayurvedic herb may not be sufficient to predict its efficacy, as ayurvedic formulations are composed of several herbs. In such a situation it is not possible to attribute a particular biological activity to a set of active markers. The W.H.O.’s supplementary guidelines on good manufacturing practices for the manufacture of herbal medicines state that it is often not feasible to determine the stability of each active ingredient. Additionally, as the herbal material in its entirety is regarded as the active ingredient, a mere determination of the stability of the constituents with known therapeutic activity will not usually be sufficient (Anonymous 2006b). Chromatographic fingerprints allow the detection of changes occurring during the storage of a complex mixture of biologically active substances like an ayurvedic medicine. By comparison of appropriate chromatographic fingerprints, the content of bioactives in an ayurvedic medicine can be shown to be within the defined limits (Anonymous 2006b).
Manufacture of ayurvedic medicines involves various processing methods like washing, drying, pulverizing, boiling in water, boiling together oils and plant juices or decoctions, fermentation and grinding. These processes can affect the phytochemical content of the herb(s). Zainol et al. (2009) studied the effect of different drying methods on the degradation of flavonoids in Centella asiatica. Leaves, roots and petioles of the herb were dried using hot air oven, vacuum oven and freeze-dryer. The study revealed the presence of a high concentration of flavonoids like naringin, rutin, quercetin, catechin, luteolin, kaempferol and apigenin in the plant parts of C. asiatica. Drying with a hot air oven resulted in the highest degradation of total flavonoids, followed by the vacuum oven and freeze-drying.
The medicinal quality of leaves of Azadirachta indica dried under shade, oven-dried at 45°C and at 70°C varied in final moisture content, color, crispness and in their phenolic content. Grinding was directly proportional to the crispness of the dried leaves. Finer particles were obtained from crisper leaves. The phenolics content was higher in powder obtained from shade-dried leaves compared to the oven-dried leaves at 45°C or at 70°C (Sejali and Anuar 2011).
Ayurvedic herbs are pulverized for preparing decoctions (kvdtha) and medicinal powders (ciirna). Different comminution processes are adopted for different herbs. Herbs with more stems and stalks need shredding or cutting mills, whereas hammer mills are suitable for hard and brittle materials such as resins. Leafy plants and rhizomes can be pulverized in a two- or three-stage process involving cutting, shredding and pulverization in hammer or pin mills. Pulverization should be carried out with care so that the herbal material is not damaged due to the generation of heat (Anonymous 2001 d).
Medicated oils (taila) and clarified butters (ghrta) are prepared by boiling oil or clarified butter with plant juices or decoctions. A small quantity of paste of herbs is also added. The mixture is boiled over a slow fire, with frequent stirring. As the water content of the mixture reduces slowly, the oil-insoluble portion of the herbal material starts settling down. It first resembles mud, then turns into a mass resembling soft or hard wax (see Chapter 3). The product is filtered at this stage. Different oils are filtered at different stages and at the hard wax stage, the medicated lipid has a temperature of 105°C. The stage of filtration and the intensity of heating the mixture can affect the content of bioactives in the finished product.
Preparation of arista and asava involves fermentation. The purity of raw materials and water, hygienic design of equipment used for production, physical separation of high care areas where critical operations are carried out and in which barriers are raised to prevent the entry of micro-organisms from raw materials, people, air or utensils and effective cleaning and disinfection of equipment and facilities are required to ensure product quality (Baxter and Hughes 2001).
Cooking in fat (frying) and grinding on granite stone are two processes usually employed in the production of avaleha (electuaries) and pills (gujika), respectively. For example, production of an avaliha like Cyavanaprasa involves cooking of a paste of steamed gooseberry pericarps in clarified butter and sesame oil (Anonymous 1978a). Grinding is invariably adopted in the production of ayurvedic pills (vide Section 4.7.1). The various processing methods are critical to the quality of ayurvedic medicines. Therefore, in-process control tests are to be conducted routinely to monitor and assure consistency in quality of ayurvedic products.