Sid Talks Testing: Understanding Herbal Extracts
Recently while teaching a class on HPTLC Botanical Identification I realized that if I am going to talk about botanical identification with HPTLC, I needed to define some terms so that analysts had a better understanding of what they are actually analyzing. In conversations with clients, it has become evident that not everyone has a clear understanding of what all those numbers and terms actually mean or imply regarding the material they are buying, selling or putting into their products.
Primarily, I will be focusing on Powdered Extracts (PE’s), since that is where most of the terminology originates from that is somewhat confusing or misunderstood. PE’s start as Herbal Drug Preparations which are obtained by subjecting Herbal Drugs, otherwise known as crude raw materials, to treatments such as extraction, expression, fractionation, purification, concentration and/or fermentation. The end product, the extracts, are preparations that are frequently standardized, which means they are adjusted within an acceptable tolerance to a given content of constituents with apparently ‘known’ therapeutic activity; standardization is achieved by adjustment of the extract with inert material, or by blending batches of extracts, and quantified extracts are adjusted to a defined range of constituents.
Now that these terms are defined, it is important to understand how we get these materials to their finished form. It all starts with the Herbal Drug or the crude raw material. After extraction, the first step is called the ‘native’ or ‘genuine’ extract, which consists solely of genuine herbal extractable matter, but due to hygroscopocity (absorption of water), resulting in physical instability, native herbal drug preparations, in most cases, are intermediate products which must be further processed by the addition of excipients for adjustment (standardization), which is now called the not-native extract or herbal drug extract or preparation.
The ratio of starting Herbal Drug to the native herbal drug preparation or final native extract or Drug Extract Ratio, (DERnative), is the ratio of the mass of herbal drug (starting material) to the mass of resulting native herbal drug preparation (native extract). The mass of the native herbal drug preparation is always equal to ‘1’. A DERnative of 2:1 means that 2 parts herbal drug are needed to obtain one part of native herbal drug preparation. High values for the DERnative always stand for a low quantity of extractable matter and low values, for a high quantity of extractable matter. For example: DERnative = 20:1 à 5% extractable matter or DERnative = 2:1 à 50% extractable mater.
The next term that is important to understand is ‘Standardization’. The expression ‘standardization’ describes all measures which are taken during the manufacturing process and quality control leading to a reproducible quality. Standardization is the basic prerequisite for consistent efficacy of an herbal medicinal product, regardless of whether the ‘active’ constituents of an herbal drug are known or not. It is the adjusting of the herbal drug preparation to a defined content of a constituent or a group of constituents with known therapeutic activity, respectively by adding excipients or by blending with herbal drugs or herbal preparations. The range of content of therapeutically ‘active’ constituents must be chosen in a way that it can consistently be achieved, taking into account natural variability and technical processability without unnecessary dilution of other constituents.
With the above explanation of the nature and content of the Powdered Extract, I would hope that it will be a little easier to understand that while an extract that has a 20:1 ratio may be ‘more concentrated’ it is also of a narrow phytochemical constituent content since in order to get from 20 to 1, much of what is in the original herb is lost and what is left is a narrower spectrum of constituents than found in a 2:1 ratio. Whereas in an extract with a 2:1 ratio, where you have 50% extractable matter, there is more of what was in the original herb left in the extract thus making it a more phytochemically full spectrum extract.
In order to standardize the extract, measurements must be taken of a specific compound or group of related compounds in the native extract and then decide what quantity or level of compound one wants to consistently achieve or manufacture. Once that number or concentration is determined, it would have to be adjusted with each new extracted lot, either with added excipients and/or combined with other lots, to achieve the desired specification.
Each month Sidney Sudberg, Alkemist Founder & CSO, helps to demystify the science behind testing by discussing a testing-related topic.
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