This article focuses on authenticating the source of natural garlic oil and its value in the food and natural medicine industries. The paper highlights common types of fraud and adulteration in the food market and the primary methods available to authenticate natural garlic oil. In the case study described, garlic oil samples were analyzed using two methods: Gas Chromatography–Mass Spectrometry (GC-MS) and Carbon-14 (14C) testing by accelerator mass spectrometry (AMS). While GC-MS was used to identify the natural constituents of garlic oil, 14C analysis was able to detect the presence of petrochemical derivatives within sample ingredients.
1. The Source of Natural Garlic Oil
Within the nutrition industry, garlic is classified as both a vegetable and a seasoning, while in the health world, it is most often used for natural medicinal purposes. In recent years, the active components and physiological functions of garlic flavor has become a developing topic of research, with great interest in the active ingredient: garlic oil.
The extraction rate of garlic oil is only about 0.2% which means that only about two kilograms of garlic oil can be obtained by processing one ton of garlic.1 Therefore, natural garlic oil is known as "liquid gold" and its market price is generally high. As a natural flavor, garlic oil is widely used in the food industry for flavor modification and improvement.
2. Food Fraud Risks Faced by Natural Garlic Oil Products
With the rapid development of the global economy, the mainstream trends of "naturally sourced," and "returning to nature" have garnered more consumer interest. Because consumers are willing to accept high prices for naturally-sourced products, food fraud within the nutrition industry is often driven by economic interests. The economic benefits of food adulteration can entice businesses to add cheap false substances and remove or replace more expensive, authentic ingredients by fraudulent means.
According to a survey on food ingredient fraud by Moore et al., food authenticity problems mainly include replacement, addition and removal.2 Natural garlic oil commonly faces the following three food fraud and adulteration risks:
- The addition of material of inferior quality to replace the amount of high-quality material in the final product, such as adding poor-quality garlic oil.
- The addition of lower-cost ingredients in the form of cheaper food or raw materials, such as adding edible vegetable oil.
- The addition of synthetically-derived ingredients to natural garlic oil under the claim that they are natural.
The third kind of adulteration is particularly enticing to companies since synthetic alternatives to naturally occurring compounds are easily available to replace them and are more economical. For example, diallyl disulfide in natural garlic oil is one of its main sulfur compounds, the content of which is generally 20%-50%. This compound is available on the market as a monomer synthetic flavor at a more affordable price compared to the price of natural garlic oil. Therefore, natural garlic oil products are currently facing frequent instances of food fraud.
3. Identification Methods to Authenticate Natural Garlic Oil
Aroma Identification
In order to identify the first kind of adulteration mentioned above, garlic oil is often identified by its aroma. Garlic oil produced using high-quality raw material in the form of garlic heads and garlic cloves typically has a strong scent with no unpleasant odors. Inferior raw materials in garlic oil such as the production of frozen garlic rice waste material or the production of garlic yellow waste material exude a sour, soiled or mildewy aroma.3
Essential Oil Miscibility Discrimination
Another method used to determine ingredient falsification is a simple and rapid method called essential oil miscibility discrimination. The method dissolves one volume of garlic oil product in three volumes of 95% (volume fraction) ethanol at a certain temperature (such as 25℃). The presence of turbidity or oil droplets at the bottom of the resulting liquid indicates that other substances are mixed into the product, such as edible vegetable oil whose main components are fatty acids.
Gas Chromatograph
A gas chromatograph for chemical analysis is also utilized as a fast identification method in order to authenticate natural garlic oil. The typical gas chromatogram of natural garlic oil is filled with small molecular compounds containing sulfur. If macromolecular compounds are detected (such as octyl capric acid triglyceride, etc.) it can be deduced that the product may be mixed with other substances.
Furthermore, the addition of synthetic flavor ingredients to natural garlic oil with fraudulent claims of “100% natural ingredients” can be identified by the following two methods:
- Gas Chromatography-Mass Spectrometry (GC-MS)
- Carbon-14 Testing via Accelerator Mass Spectrometry (AMS)
Gas Chromatography-Mass Spectrometry (GC-MS)
Synthetic garlic oil is made using a compound called allyl chloride, which is not found in natural garlic oil. A 2012 study conducted by Zheng Ping et al. used gas chromatography-mass spectrometry to analyze 36 garlic oil samples and found that five samples contained allyl chloride.4 Accordingly, a rapid and sensitive detection method was proposed to determine whether the natural garlic oil contains synthetic flavor components.
F-1. Total Ion Current Chromatograms of Natural Garlic Oil
From the chromatogram of pure natural garlic oil, it can be seen that its composition is complex. In addition to the main components, there are many other sulfur compounds, more than 30 kinds in total.
Credit: Anhui Capa Bio-Tech Co., Ltd. (China)
F-2. Total Ion Current Chromatograms of Synthetic Flavor
The chromatogram of garlic essence samples from completely synthetic sources is much simpler and has fewer components, which is significantly different from the typical gas chromatogram of natural garlic oil.
Credit: Anhui Capa Bio-Tech Co., Ltd. (China)
Carbon-14 Testing via Accelerator Mass Spectrometry (AMS)
This method uses Accelerator Mass Spectrometry (AMS) to determine the content of carbon-14 (14C) in product ingredients.5 ASTM D6866 is a standardized method of carbon-14 testing that determines the percentage of natural-derived flavor ingredients in a product versus the percentage of material derived from petrochemical synthetic ingredients such as petroleum and coal. Carbon-14 is an isotope present in all living organisms. Although carbon-14 analysis cannot detect natural-sourced adulterants, the measurement of 14C in products and ingredients is an accurate method for identifying whether a material is composed of natural ingredients sourced from biomass. Ingredients and products that are made from synthetic materials will not contain any 14C. A product with completely natural ingredients will be reported as 100% biobased carbon. A product composed solely of petrochemical or synthetic materials will yield results of 0% biobased carbon whereas a mixture of natural and synthetic ingredients will have a result that falls within the range of 0% to 100% biobased carbon content.6
4. Case study: GC-MS vs. AMS measurement of garlic oil
Garlic oil samples from four sources were collected and analyzed using the gas chromatography-mass spectrometry (GC-MS) method. The results of fingerprint analysis were all satisfactory and all of them were identified as garlic oil components. However, further analysis using carbon-14 testing via AMS indicated that only one sample contained 100% biobased carbon content. The other three samples showed evidence of petrochemical derivatives, indicating adulteration. Table 1 summarizes the GC-MS and carbon-14 test results for each of the analyzed samples.
T-1. GC-MS and Carbon-14 test results of the samples
5. Conclusion
There is an evident consumer demand for natural-derived products and ingredients in the food and flavors industry. Due to its popularity in the food and health markets, natural garlic oil’s value will continue to grow. In order to ensure the authenticity of garlic oil ingredients, it is particularly important to implement quality control procedures to detect adulteration through the use of fraudulent ingredients. Therefore, it is key to utilize appropriate methods of authenticity identification such as GC-MS and carbon-14 analysis. These detection methods are valuable tools not only for the garlic oil industry but also for the development of the natural flavor industry as a whole.
References
1. Xianfeng Meng, Zhihong Zhang. Study on the extraction of garlic oil [J]. Journal of Changji University,2002,(1):97-98. (in Chinese)
2. MOORE J C, SPINK J, LIPP M. Development and application of a database of food ingredient fraud and economically motivated adulteration from 1980 to 2010 [J]. Journal of food science, 2012, 77(4):118-126.
3. Weiping Tao, Like Jian.Quality inspection method of litsea cubeba oil acquisition [J] Chinese and Foreign Technical Information,1996,(1):30-31.(in Chinese)
4. Ping Zheng, Xuan Shen, Xiang Zhang, Yanyun Hu. Analysis of natural garlic oil and synthetic allicin by gas chromatography-mass spectrometry [J]. Chinese journal of analytical chemistry,2005,33(9):1321-1323.(in Chinese)
5. Zhenjian Hou, Lijun Wang. Development of natural deep processed food and detection of food "naturalness" [J]. Food & machinery,2012,28(4):259-262. (in Chinese)
6. ASTM International. ASTM D6866-18, Standard Test Methods for Determining the Biobased Content of Solid, Liquid, and Gaseous Samples Using Radiocarbon Analysis; ASTM International: West Conshohocken, PA, 2018; https://www.astm.org/Standards/D6866.htm (accessed Dec 3, 2018).
