ELISA method to test adulterated cow milk in camel milk
Camel milk might be adulterated with cheaper cow's milk because of its high price. The establishment of a rapid and reliable method for detecting cow milk in camel milk is a matter of great concern. In the study, the chromatogram of camel milk with different adulteration ratios was analyzed by High Performance Liquid Chromatography (HPLC). The peak area of liquid chromatography was analyzed by Principal Component Analysis (PCA). β-lactoglobulin (β-Lg) was screened as a characteristic protein. Enzyme-Linked Immunosorbent Assay (ELISA) was established selected β-Lg as the antigenic indicator. This study was aimed at developing an ELISA method that enabled rapid and highly sensitive detection of the proportion of adulterated milk in camel milk. The minimum detection limit was 1% of cow milk in camel milk, and the results were highly reproducible with no significant difference between true and measured values (P > 0.05).
Camel milk has an important role in human nutrition in the arid and semi-arid regions of the world because it contains all the essential nutrients found in other milks (Devendra, 2016; Swelum et al., 2021). Camels are rich in nutrients such as bioactive peptides, lactoferrin, zinc, vitamins (Kaskous, 2016; Konuspayeva, Faye & Loiseau, 2009). The nutritional value of camel milk is better than cow milk, and its protein composition is quite close to breast milk. Therefore, camel milk is often used as a substitute for breastfeeding (Zou et al., 2022).
As is known to all, olive oil adulteration is the biggest adulteration problem in the world (Calvano, Ceglie, D Accolti, & Zambonin, 2012). The adulteration of dairy products has had a tendency to increase in recent years. Adulteration of camel milk not only occurs in the Chinese market, but also in the European Union and other countries were very common (Mabood et al., 2017).
Camel milk costs 2-10 times more than cow milk. Moreover, it is reported that camel milk was also used for other potential therapeutic purposes (DeshwalTiwari & Kadyan, 2021), such as anti-carcinogenic (Habib, Ibrahim, Schneider-Stock, & Hassan, 2013), anti-diabetic (Agrawal et al., 2007), anti-aging activities (HoZou & Bansal, 2022; Izadi, Khedmat & Mojtahedi, 2019), and anti-hypertensive (Quan, Tsuda & Miyamoto, 2008), Camel milk will not cause allergic issues for cow milk allergic children (Devendra, 2016). In this case, many merchants adulterate cow milk with camel milk to seek windfall profits (Merin et al., 2001). The effects of milk adulteration are not only economic but may even have serious health implications. (El-Sayed & El-Agamy, 2022). For this reason, it is very necessary to quickly detect whether there is cow milk in camel milk to ensure the quality and the legitimate rights and interests of consumers.
To date, a number of methods have been developed to detect adulteration in dairy products (El-Hatmi, 2015). A quantitative method was developed to detect the different kinds of milk by infrared spectroscopy (Nicolaou, Xu & Goodacre, 2010). Polypropylene gel electrophoresis was used to distinguish different source milk(Sharma et al., 2021). The adulteration of dairy products and camel milk was measured by the low-field NMR method and liquid chromatography (Ribeiro et al., 2014). Although these methods have become quite sophisticated, there is still disadvantage, such as the expensive and heavy experimental equipment and high testing costs. ELISA was chosen in this study, which is a sensitive, rapid, and highly specific method widely used in the food industry. For low concentrations of biomarkers, ELISA typically has higher sensitivity than HPLC because it takes advantage of the amplification effect of the enzyme. ELISA is generally more economical and higher throughput than HPLC. It’s necessary to screen for a signature protein to distinguish before developing an ELISA to detect camel milk adulterated with cow milk.