Monitoring product quality is of paramount importance in the dairy industry. Using sensors is an accurate, reliable, and cost-effective method for the quality analysis of dairy products. This article focuses on the application of sensors in the dairy industry, especially to ensure the quality and safety of milk.
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Importance of Quality and Safety Analysis of Milk
Testing milk quality is crucial for ensuring its safe production and consumption. Quality control helps to identify potential contaminants, adulterates, and pathogens in milk, thus contributing to good public health practices, especially in avoiding foodborne diseases.
Generally, milk quality is analyzed by determining a set of parameters related to hygiene, composition, and sanitary conditions. The failure to meet these standards affects both consumers and farmers.
High moisture content, rich nutrients, neutral pH, and milk all favor bacterial growth. Hence, contaminated milk can cause various foodborne infectious diseases, including brucellosis, listeriosis, and tuberculosis. The implementation of sound quality control measures in the dairy industry ensures the quality and safety of milk from farming to marketing.
Why Are Sensors Applied in the Milk Industry?
The latest automation tools help meet the quality standards at every stage of milk production. Compliance with sanitary and technical regulations and the accurate implementation of technological processes determine milk quality. Currently, sensor-based quality control systems are being used efficiently to meet the quality demand for milk production.
Conventional methods such as plate count and culture, flow cytometry, microscopy, and advanced immunological techniques are inexpensive, highly sensitive, and provide qualitative and quantitative information on the nature and count of microorganisms. However, these time-consuming and laborious processes limit their application to research laboratories.
To this end, fast and easy-to-use analytical methods with rapid feedback systems suitable for industrial set-up are required to guarantee milk quality and safety. Consequently, product loss is decreased by removing suspected batches at an early stage and helps producers predict product shelf life.
How Are Sensors Used in the Milk Industry?
Different types of sensors are used at different stages of milk production, as mentioned below.
- Heat Control: Controlling the heat of milk during pasteurization is crucial to ensure the production of high-quality products. Temperature sensors with a measurement range of up to 150 °C can help avoid overheating during the stage of pasteurization.
- Pressure Control: The pressure drop during the production of dairy products during the recognition phase ensures its safety and hygienic pressure sensors with a flat diaphragm and high resistance to shock, abrasives, and other harsh environments accurately measure the pressure variation.
- Level Control: Hydrostatic or ultrasonic level sensors are used to control the milk level in surge tanks. These sensors accurately detected the presence of foamy milk and other aggressive substances.
- Packaging Control: Optical sensors are extensively used to detect the presence of products during the packaging stage. Additionally, these sensors control the presence of caps and labels and detect the liquid level in transparent bottles.
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Chemical Sensors and Biosensors in Milk Industry
Chemical- and biosensors are intriguing alternatives to the conventional analytical methods used for quality control in the dairy industry. These sensors can transform chemical information into electrical signals.
Chemical and biosensors consist of two basic components: a system for recognizing chemical molecules and a physicochemical transducer. Different transducers that work on different principles, including electrochemical, acoustic, optical, thermal, piezoelectric, and others, are used in the dairy industry, offering various advantages, including sensitivity, minimal to no sample preparation, and quick response.
In general, the metabolic activities of bacteria in milk change physicochemical properties, including pH, conductivity, ionic content, viscosity, color, odor, and others. Furthermore, milk spoilage results in the formation of metabolic by-products, including hydrogen sulfide (H2S), ammonia (NH3), carbon dioxide (CO2), and hydrogen (H2).
The following are the commonly used sensors in the milk industry:
- pH sensors: Measuring the pH of milk is a preliminary technique for quality control in the milk industry. While the pH of fresh bovine milk is 6.7, that with bacterial metabolic by-products, like lactic acid, decreases the pH of the milk, indicating spoilage.
Commercially used pH sensors include pH-ion-sensitive field-effect transistors (ISFETs) and pH-glass electrodes manufactured by companies such as Hach, Hanna Instruments, Horiba, Mettler-Toledo, Orion, and BioControl.
- Impedimetric sensors: Changes in impedance in milk due to bacterial growth indicate the spoilage of milk. These sensors detect changes in electrical conductivity owing to the presence of charged ionic metabolites produced by bacterial growth and changes in interfacility impedance owing to the adhesion of bacteria to the electrode surface.
Commercially available impedimetric sensors include a bactometer, malthus systems, the rapid automated bacterial impedance technique (RABIT), and BacTrac.
- Enzymatic Biosensors: In this type of sensor, the enzyme is immobilized on an electrode by engulfment in a photocrosslinkable polymer to fabricate a flow-based biosensor that can detect organophosphate pesticides (OPs) in milk samples.
- Wireless Sensors: Remote query sensors that do not require a power source and without a physical connection to data-acquisition systems are currently in demand. These include a wireless passive, sterilizable potentiometric pH sensor, a three-dimensional (3D) printed “smart cap” to detect milk spoilage in cartons, and radio-frequency identification (RFID) sensors to analyze the freshness of the milk.
Recent Trends in the Milk Industry
An article published in Food Chemistry reported the fabrication of a new biosensor using tannic acid and polyethylene imine to modify screen-printed electrodes and adhere to the peptide sequence S-L-S-P-S-L-W-Q-V-S-M-L-G-G-G-G-G-E-P-L-Q-L-K-M.
The peptide-modified sensor facilitated the binding of beta-lactoglobulin, which triggers food allergy in most of the population. The new biosensor could detect the presence of beta-lactoglobulin in cow milk within a certain range.
Another article published in the Journal of Food Composition and Analysis reported the fabrication of titanium dioxide-based optical sensors to detect trace amounts of hydrogen peroxide and starch in milk.
Overall, utilizing sensors in the dairy industry substantially reduces detection time compared to conventional methods. Various sensors are used to detect different parameters to ensure the quality and safety of milk products. Although sensor-based quality control is well established at the industrial level, further investigation is needed to enhance its sensitivity.
Furthermore, the development of multifunctional and versatile biosensing systems has enabled the analysis of multiple analytes using a single device. Simultaneously, there is a need for portable devices with high specificity and sensitivity for multi-array analysis.
References and Further Reading
Sensors in the Dairy Industry. Accessed on 14 October 2023. Available at: www.azosensors.com/article.aspx?ArticleID=2587.
Poghossian, A., et al. (2019). Rapid methods and sensors for milk quality monitoring and spoilage detection. Biosensors and Bioelectronics, 140, p. 111272. doi.org/10.1016/j.bios.2019.04.040
Mishra, R. K., et al. (2012). A novel automated flow-based biosensor for the determination of organophosphate pesticides in milk. Biosensors and Bioelectronics, 32(1), pp. 56-61. Available at: https://pubmed.ncbi.nlm.nih.gov/22221795/
Venkatesan, M., et al. (2023). Designing Tannic Acid–Polyethyleneimine-Modified Electrode and Novel Affinity Peptide for β-Lactoglobulin Detection in Milk. Food Chemistry, p. 137714. doi.org/10.1016/j.foodchem.2023.137714
Gritsenko, M. M., et al. (2023). Titanium dioxide-based optical sensors for detecting milk adulteration. Journal of Food Composition and Analysis, 120, p. 105335. doi.org/10.1016/j.jfca.2023.105335