Phytochemical Profiling of Commercially Important South African Plants by Alvaro Viljoen, Weiyang Chen, Nduvho Mulaudzi, Guy Kamatou, and Maxleene Sandasi. London and Oxford, UK: Academic Press; 2022. Hardcover, 282 pages. ISBN: 9780128237793. $150.00.
South Africa has a rich history of traditional herbal medicine use, and many people in this country rely on botanical ingredients for their primary health care needs. According to the book’s introduction, an estimated 4,000 plant species are used for medicinal purposes in South Africa. While the South African Health Products Regulatory Authority established regulations in 2013 for herbal medicinal products packaged in pharmaceutical forms, such as tablets and capsules, traditional herbal medicines remain unregulated. However, the South African Department of Health is committed to evaluating the potential of African traditional medicine in health care. An important part of this effort is the development of quality-control standards for South African medicinal plants.
The book is written with this context in mind and provides quality control monographs for 25 commercially important South African medicinal plants. Each monograph includes a brief summary, followed by the plant’s taxonomy, common names in various local languages — one of my favorites is bobbejaandubbeltjie in Afrikaans, or devil’s claw (Harpagophytum procumbens and H. zeyheri, Pedaliaceae) — botanical description and geographical distribution of the plant, and phytochemical constituents (although concentration ranges are not provided). Though short, each monograph also provides a table with the therapeutic indications of the specific ingredient (e.g., aloe [Aloe ferox, Asphodelaceae] leaf exudate) based on traditional medicine, potential benefits based on in vitro and in vivo research, toxicity concerns, and the type of formulations that are found in commerce.
Most of each monograph is dedicated to detailed descriptions of the experimental conditions for chemical analysis and images of high-performance thin-layer chromatograms (HPTLC), traces obtained by ultra-high-performance liquid chromatography (UHPLC) with photodiode array (PDA) or mass spectrometric (MS) detection, or gas chromatography (GC) with MS or flame ionization detection (FID). Each monograph also contains mass spectra and UV-visible spectra of a few selected constituents.
The book is mainly geared toward quality control personnel in an industry setting but is also useful for analysts of regulatory agencies, researchers who study any of the 25 featured plant ingredients, and students of pharmacognosy, as it contains data on many economically important ingredients. The monographs provide useful information on identification and assessment of marker compounds in each of the medicinal plant ingredients. Since the chromatograms are based on the assessment of several samples that were collected in various places in South Africa, geographical variability was taken into consideration when developing the monographs. The availability of the UHPLC and GC profile images makes it easy to verify an ingredient if laboratory data correspond to the profile shown in the monograph. HPTLC images are in color and of high quality, and thus allow an easy comparison to in-house data from a quality control laboratory.
One suggestion for improvement is the quality of the UV-visible spectra. Some of these spectra are distorted, especially at lower wavelengths. One example is the absorption maximum of β-sitosterol in the monograph on Prunus africana (Rosaceae), which is given as 321.9 nm while the literature suggests that the maximum is below 200 nm. These spectral distortions can usually be corrected using the tools available in the instrument software. Additionally, it may be useful to indicate if the HPLC-UV profiles represent the absorption at a specific wavelength, or the total absorption over the 200-400 nm range.
Other than that, the book is written and presented without major flaws. I checked many of the structural drawings and found only one minor error in the umckaloabo (Pelargonium sidoides, Geraniaceae) monograph, where fraxidin is labeled as “fraxetin.” The compilation of monographs is a highly useful and welcome contribution to enhance the quality control of South African medicinal plants. Quality control methods are typically easy to implement since they use instruments that are commonly available in laboratory settings. I particularly liked the use of only two or three types of UHPLC columns to analyze the 25 plants for which monographs are presented. This permits analysis of those ingredients for which the same column is proposed in one UHPLC program.
It can be challenging to find a book that features quality-control methods for globally important plants such as baobab (Adansonia digitata, Malvaceae), rooibos (Aspalathus linearis, Fabaceae), devil’s claw, hoodia (Hoodia gordonii, Apocynaceae), rose-scented geranium (Pelargonium reniforme, Geraniaceae), and umckaloabo, which makes this text useful even to those outside of South Africa. While $150 may seem a bit of a hefty price tag, suitable quality control monographs for many of these plants are difficult to find elsewhere. I hope that the authors will continue their excellent work on developing methods for the chemical analysis of South African medicinal plants.
Stefan Gafner, PhD, is the chief science officer of the American Botanical Council and technical director of the ABC-AHP-NCNPR Botanical Adulterants Prevention Program.