Ensuring the safety and quality of food products is critical to consumers and it is also one of the most important research topics in food science and technology of the past several decades. There are numerous factors that can affect food quality and safety. These factors are sometimes complicated, inter-correlated and difficult to track and control. For example, the pollutants in irrigation water, soil and the environment can be readily migrated and/or adsorbed into plant-based food products, such as fresh produce. As another example, the quality of harvested food products will be either positively or negatively impacted by post-harvest storage and delivery, such as the modified atmospheric packaging technique and cold chain delivery. That is also why food scientists have to pay attention to every single step “from the farm to the fork”.

Sometimes, food quality and food safety are two factors that need to be balanced. For example, a thermal processing technique needs to be applied for inactivation of the potential pathogenic bacteria in food products, but this will negatively impact the quality of the foods, such as the texture, colour and flavour. In this case, part of the quality of the food products has to be sacrificed to ensure the safety of the foods. As another example, pasteurized milk is a popular dairy product that can be produced by high temperature short time (HTST) processing. However, HTST is not able to fully inactivate spoilage bacteria, which is why pasteurized milk can only be stored in a refrigerator for about three weeks. Theoretically, sterilized milk has zero microbes due to a complete inactivation of the entire pathogenic and spoilage microorganisms. Although the shelf life of sterilized milk products is significantly extended, the taste and flavour has been significantly jeopardized. That is why consumers still prefer pasteurized milk products instead of sterilized milk products. In short, these two representative examples tell us that food safety and food quality are the two parameters we need to consider at all times. Food safety is the first priority. Once the safety of the food products is guaranteed, we should maximize the quality of the food products.

There are numerous ways to control the safety and quality of food products. Food law and regulation is the guideline for all food manufacturers to follow. For example, Hazard Analysis and Critical Control Points (HACCP) has been validated to be a very effective systematic preventive approach to food safety from biological, chemical and physical hazards in the production process. Unfortunately, HACCP may not be fully applied and followed for every single food processing event. In this case, detection will be a very important strategy to ensure food safety and quality by the following two approaches: (1) detection of food quality and safety during food processing and (2) detection of food quality and safety after food processing. By applying the first approach, the processing efficiency can be monitored. This will maximally ensure the processing techniques that can control the safety and quality of food products. The second approach is regarded as the “last defence” to ensure that only safe and high-quality food products will be delivered to the consumers.

During the past several decades, a variety of methods and techniques have been developed for the determination and control of food safety and quality. Instrumental analytical methods play a key role. Nowadays, chromatography-based instruments are widely available in every corner of the world. High performance liquid chromatography and liquid chromatography-mass spectrometry have been applied to determine various types of food chemical contaminations and food compositions. On the other side, conventional plating methods and various molecular techniques have been applied for accurate determination of pathogenic and spoilage bacteria in agri-food products. For all of the aforementioned determinations, there are three major limitations. First, food is a very complicated matrix. Therefore, an effective separation technique is extremely crucial to remove the interference of other food components that may impact on the determination by an instrumental detector, such as mass spectrometry. Second, the level of the target analyte (e.g., pesticide residue, Salmonella and norovirus) in the food products may be extremely low. Microbial enrichment is inevitable in most cases once the concentration of the targeted microorganism could not be directly detected by the current techniques. Third, sample preparation is time consuming and labour intensive. Essentially, this is due to the first two limitations (i.e., food sample matrix and low level of target analyte). Besides those aforementioned technical limitations, instrumental analysis is expensive and requires lab space and experienced personnel. Therefore, instrumental analysis could not achieve high-throughput screening of a large number of food product samples in a relatively short time period.

The concept of “sensing technique” or “sensor” is an object with the purpose to detect events and send the information to a PC that informs the output device for generation of the corresponding output. A sensing technique is a very general concept that includes chemical sensing techniques, biosensing techniques, electrochemical sensing techniques and others. Compared to instrumental analysis for food safety and quality control, sensing techniques have unique advantages. They are rapid, sensitive, portable and can provide high-throughput screening. In addition, some types of sensing techniques can partially reduce or even avoid sample preparation procedures as well as the enrichment of the target analyte(s). Therefore, we have drafted this book entitled “Sensing Techniques for Food Safety and Quality Control”. The most advanced sensing techniques and their applications in food safety and quality will be systematically introduced. Our major aim for this book is to let the readers become more familiar with the technical advancement of sensors in agri-food products.

In Chapter 1, the Raman spectroscopic sensing technique will be introduced. Raman spectroscopy has been recently applied in food analysis over the past two decades. A derivative of the Raman spectroscopic technique, called surface enhanced Raman spectroscopy (SERS), integrates nanotechnology and laser technology to create a new generation of sensing platform that can detect food contamination and quality parameters in an ultra-sensitive and high-throughput manner. The author, Dr Zhong Zhang at the University of Nebraska-Lincoln, is one of the leading experts in the United States in developing and applying Raman and SERS sensing techniques to study food chemical and microbiological hazards as well as food quality.

In Chapter 2, the quantum dot sensing technique will be introduced. Quantum dots are extremely small semiconductor particles with unique electronic and optical properties. Quantum dots are widely applied in solar cells, quantum computing, transistors and recently sensing techniques. As the authors of this chapter, Dr Russ Algar's group at the University of British Columbia is one of the leading teams in Canada applying quantum dots for biological and sensing applications.

Microfluidic “lab-on-a-chip” is a device that can integrate several laboratory functions onto a single device or chip of a few square millimetres to achieve a fully automated and high-throughput screening. The application of the “lab-on-a-chip” concept in food analysis has boomed during the past five years. The polymer-based microfluidic “lab-on-a-chip” device was created first, followed by the development of the paper-based microfluidic device, also known as “microfluidic v2.0”. Therefore, Chapter 3 and Chapter 4 are individually drafted to introduce the two generations of microfluidic techniques and their applications in food safety and quality control. Chapter 3 was written by Dr Xian Huang's group at Tianjin University. Dr Huang is one of the leading experts in China in developing microfluidic techniques for the study of biological systems. Chapter 4 was drafted by Dr Jie Xu's group at the University of Illinois, Chicago. Dr Xu has a great deal of experience in developing both polymer-based and paper-based “lab-on-a-chip” devices to study food safety and quality.

In Chapter 5, the colorimetric sensing technique will be introduced. This technique will facilitate a visual detection of food chemical and microbiological hazards by the naked eye. Therefore, a separate detector is not required, which will be suitable for in-field monitoring of food safety and quality. Dr Xiaonan Lu's group at the University of British Columbia drafted this chapter. His lab has a great deal of experience in applying colorimetric sensors to detect food chemical contaminants.

The next three chapters are related to developing very effective recognition elements that can separate and enrich the target analytes from the complicated food matrices. These recognition elements include antibody (Chapter 6), molecularly imprinted polymers (Chapter 7) and aptamer (Chapter 8) and all can be readily integrated into a sensing platform. In Chapter 9, the production of antibody and its application in immunoassay is systematically introduced by Dr Shuo Wang's group at Tianjin University of Science and Technology. Dr Wang is the authority in developing immunoassay in Asia. Currently, enzyme-linked immunosorbent assay (ELISA) is still the most successful knowledge translation for commercialization in food analysis. In Chapter 7, as the “artificial antibody”, the technique of molecularly imprinted polymers for sensing food safety and quality is introduced by Dr Yiwei Tang's group at Bohai University. Molecularly imprinted polymers are one of the most exciting techniques developed in analytical chemistry for food analysis during the past several decades. This type of “artificial antibody” has the potential to replace some natural antibodies in the future due to its easy synthesis and extreme stability in the environment. In Chapter 8, the aptamer-based sensing technique is introduced. Aptamers are oligonucleotides or peptides that can bind to a specific target molecule. Aptamers have been gradually applied to replace antibody that can recognize and capture target analyte in a complicated matrix, such as foods. As the authors of this chapter, Dr Maria DeRosa's group at Carleton University is one of the leading groups in Canada studying aptamer-based sensing technology and its bio-application.

In Chapter 9 and Chapter 10, two novel carbon materials (i.e., carbon nanotubes and graphene) are introduced. These two materials have many unusual properties. For example, graphene is about 200 times stronger than the strongest steel. In addition, the bonding between the atoms in carbon nanotubes is very strong and the tubes have extreme aspect ratios. These unusual properties have been smartly applied as the read-out components in a sensor. The application of carbon nanotubes as sensing materials is introduced in Chapter 9 by Dr Wei Xue's group at Rowan University while the application of graphene as a sensing material is introduced in Chapter 10 by Dr Xian Zhang at the University at Buffalo. Both Dr Xue and Dr Zhang have extensive research experience in developing and applying advanced carbon nanomaterials.

Finally, the smartphone-based sensing technique is introduced in Chapter 11 by Dr Jane Ru Choi at the University of Malaya. Rapid development of smartphones with various embedded sensors has enabled applications in biomedical diagnosis. Recently, their application in food analysis has started to emerge. Dr Choi is an experienced researcher of applying smartphones to detect target analyte in various matrices, including clinical samples and agri-food samples.

Taken together, this book will comprehensively introduce the advancement of sensing techniques for food safety and quality control. By applying various sensors for food analysis, a more rapid, high-throughput, convenient and reliable determination of agri-food products will be achieved.

I am grateful for the support from all members in Lu Food Safety Engineering Laboratory at UBC as well as the company of beloved Vivian and TUTU.

Xiaonan Lu

University of British Columbia, Vancouver, Canada