Food Process Monitoring Systems

The manufacture of foods and beverages is a highly competitive, interna­ tionalindustry, and the range ofproducts is becomingincreasingly diverse. Manufacturers are required to produce quality foods with the highest possible efficiency and lowest possible cost, and international legislation is imposingstrict controls on food safety. Process control is the essential link between quality, safety and cost. Radical changes in the technology of manufacturing bring with them new requirements for monitoring (and ultimately controlling) increasingly complex parameters. The aim of this book is to review the latest developments in monitoring systems, particu­ larly those suitable for the rapid sensing of composition, structure or microbial status. The emphasis is on 'up and coming' methods that have been proven in the laboratory or in other industrial environments, and offer potential in the food sector. As such, it is hoped that this book will increase the general awareness ofwhat new systems have to offer, and will act as a catalyst in the technology transfer process. The book features chapters on automated machine vision, fluorescence cytometry, infrared spectroscopy, light scattering spectroscopy, ultra­ sound, mass spectrometry, and chemical and biological sensors. In all cases, the basic approach is to describe the underlying principles, and then to consider the implementation of a particular technique. Examples are given of the practical application to specific problems in the food industry.

1 Introduction.- 2 Fluorescence cytometry for the rapid analysis of food microorganisms.- 2.1 Introduction.- 2.2 Optical analysis.- 2.2.1 Flow cytometry.- 2.2.2 Confocal scanning cytometry.- 2.3 Light sources for optical cytometry.- 2.4 Parameters measurable by optical techniques.- 2.4.1 Fluorescent labelling techniques.- 2.5 Research studies.- 2.5.1 Identification of bacteria by light scatter and nucleic acid staining.- 2.5.2 Identification of bacteria by immunofluorescent labelling.- 2.6 Routine use of flow cytometry in quality assurance.- 2.6.1 Analysis of fruit preparations.- 2.6.2 Analysis of milk products.- 2.6.3 Starter culture analysis.- 2.6.4 Shelf life prediction in salads and fruit juice manufacture.- 2.7 Conclusions.- References.- 3 Infrared spectroscopic methods.- 3.1 Introduction.- 3.2 Infrared spectroscopy.- 3.2.1 Infrared spectrometers.- 3.2.2 Approaches to sampling.- 3.2.3 Quantification.- 3.3 Instrumentation for process monitoring and control.- 3.3.1 Selective-wavelength instruments.- 3.3.2 FT-IR instruments.- 3.3.3 Dispersive instruments.- References.- 4 Machine vision for the food industry.- 4.1 Introduction.- 4.1.1 Customers judge food by its appearance.- 4.1.2 Human vision versus machine vision.- 4.2 Machine vision systems.- 4.2.1 Image formation.- 4.2.2 Non-visual sensing methods.- 4.2.3 Image acquisition.- 4.2.4 Image processing.- 4.2.5 Image analysis.- 4.2.6 Image interpretation and understanding.- 4.2.7 Current machine vision systems.- 4.3 Considerations for use of machine vision systems.- 4.3.1 Practical implications in using machine vision systems.- 4.3.2 Economic considerations in using machine vision.- 4.3.3 Environmental protection and safety.- 4.4 Machine vision applications for the food industry.- 4.4.1 Introduction.- 4.4.2 Shape and size.- 4.4.3 Region labelling and object segmentation.- 4.4.4 Appearance of product.- 4.4.5 Texture.- 4.4.6 Non-visual imaging techniques.- 4.4.7 Object segmentation using colour.- 4.4.8 Process monitoring and control.- 4.4.9 High level techniques for machine vision.- 4.4.10 Future applications of machine vision systems.- References.- 5 Particle sizing.- 5.1 Introduction.- 5.2 Particle sizing within the food processing industry.- 5.2.1 Sieving.- 5.2.2 Sedimentation.- 5.2.3 Optical microscopy.- 5.2.4 Electrozone sensing.- 5.2.5 Laser light scattering methods.- 5.3 Low angle laser light scattering (LALLS).- 5.3.1 Introduction.- 5.3.2 Theory.- 5.3.3 Material refractive indexes.- 5.3.4 Concentration range.- 5.3.5 Data analysis.- 5.3.6 Criteria for a minimum sample.- 5.3.7 Minimum sample volume assessment.- 5.3.8 Sample dilution.- 5.3.9 Results.- 5.4 Sub-micron particle sizing.- 5.4.1 Principle of operation.- 5.4.2 The analysis problem.- 5.4.3 Results.- 5.4.4 Required practice for PCS measurements.- 5.5 Measurement of mobility and zeta potential.- 5.5.1 Introduction.- 5.5.2 Measurement method.- 5.5.3 Applications.- References.- 6 Ultrasonic methods.- 6.1 Introduction.- 6.2 Principles of ultrasonic wave propagation.- 6.2.1 General principles.- 6.2.2 Pure materials.- 6.2.3 Multi-phase media.- 6.2.4 Summary.- 6.3 Measurement of ultrasonic properties.- 6.3.1 Introduction.- 6.3.2 Practical considerations.- 6.3.3 Technique to measure phase velocity and attenuation in liquids and dispersions.- 6.3.4 Double-liquid technique for measurement of velocity difference.- 6.3.5 Measurement of group velocity in liquids and dispersions.- 6.3.6 Summary of techniques available.- 6.4 Applications to food systems.- 6.4.1 Overview of methods used on foods and related materials.- 6.4.2 Velocity measurements.- 6.4.3 Attenuation measurements.- 6.4.4 Other ultrasonic applications.- 6.5 Future developments.- References.- 7 Mass spectrometry.- 7.1 Introduction: basic principles.- 7.2 Basic definitions.- 7.3 Ion analysis.- 7.3.1 Magnetic sector mass spectrometers.- 7.3.2 Quadrupole mass spectrometers.- 7.3.3 Time-of-flight mass spectrometers.- 7.3.4 Ion storage mass spectrometers.- 7.4 Detection and data acquisition.- 7.5 Tandem mass spectrometry.- 7.6 Ionization techniques.- 7.6.1 Electron impact ionization (EI).- 7.6.2 ‘Soft’ ionization techniques.- 7.7 Inlet systems: sample introduction.- 7.7.1 Gases and volatile compounds.- 7.7.2 Liquids.- 7.7.3 Solids.- 7.8 Applications in food science technology.- 7.8.1 Membrane inlet quadrupole mass spectrometry.- 7.8.2 Tandem mass spectrometry.- 7.8.3 GC-MS.- 7.9 Current and future developments.- References.- 8 Chemical sensors.- 8.1 Introduction.- 8.2 Sensor types.- 8.3 Microelectronic sensors for pH, acidity and ions.- 8.4 Sensor arrays for aroma and indicator volatiles.- 8.5 Biosensors based on amperometric, potentiometric and thermometric devices.- 8.6 Chemically sensitive optical and acoustic devices.- 8.7 Sensor applications employing the marker approach.- 8.8 Discussion.- References.