Quality concerns will differ depending on the particular plant or extract. The typical types of properties that are used to determine the quality or batch to batch consistency of a botanical ingredient would include: appearance, color, odor, botanical characteristics (for plant material), microbial count, pH, residue on evaporation or loss on drying, total ash, acid-insoluble ash, water soluble ash, heavy metal content, alcohol-soluble extractives, water-soluble extractives, foreign organic matter, solvent residue, moisture content, volatile oil content, pesticide residue, and of course the level of marker compound if the extract is standardized. In some cases, a fingerprint method may be developed to ensure that the plant or plant extract is what it claims to be and/or is consistent from batch to batch. This might be a DNA fingerprint, chromatography profile (e. g., TLC, HPLC or GC), or even an IR fingerprint. Generally, five to 10 characteristics are reviewed for a particular product and the assay results will be listed on the Certificate of Analysis which should be available for every batch of product that is purchased.
Microbial contamination is especially common in dried plant material where the microbial counts are generally very high. USP or CTFA plate count methods may be utilized to evaluate this. Irradiation is commonly used to sterilize herbaceous material. Extracts may have microbial issues depending on what solvent was used in the extraction process. Many organic solvents, such as ethanol and methanol, are antiseptics and so will effectively preserve an extract. Other extracts, especially water-based ones, are typically preserved or sterilized.
Pesticide levels can be a concern for some plant based products. The United States Pharmacopeia (8) is a good resource for acceptable levels. A table of 30 or more pesticides
and the maximum limit for each is shown under “General Method for Pesticide Residues Analysis” in the Chemical Tests section. Any pesticides not listed are considered unacceptable at any level. These limits were set for dietary supplements, but are a good guideline for cosmetics as well.
Some types of plants have a tendency to accumulate certain heavy metals (14). For instance, mugwort plants (Artemisia vulgaris L.) and coneflower roots (Echinacea spp.) are known to accumulate iron; black cherry stems (Prunus serotina E.) and buckbush stems (Symphoricarpos orbiculatus M.) accumulate lead; cassia plants (Cinnamomum aromaticum N.) and bladderwrack plants (Fucus vesiculosus L.) accumulate mercury (25). Thus, for certain plant materials or extracts heavy metal levels should be assayed and specified on the Certificate of Analysis.
Preservatives, antimicrobials, and/or antioxidants, may be added to extracts and should be identified by the extract manufacturer upon request. Analytical methods such as HPLC may also be applied to identify preservatives within an extract. Ash quantity is often used as a quality specification for extracts. Excessive quantities of ash may indicate the presence of buffers (sometimes used during extraction process to adjust the polarity of the solvent) or drying agents such as silica dioxide.