Fluorescence

References ............................................................................................................. 271 4.2 Blue, Green, Red, and Far-Red Fluorescence Signatures

of Plant Tissues, Their Multicolor Fluorescence Imaging, and Application for Agrofood Assessment................................................ 272 4.2.1 Native Fluorophores in Plants......................................................... 274

4.2.1.1 General Aspects of Plant Fluorescence ............................. 274 4.2.1.2 Blue-Green Fluorescence of Plants ................................... 275 4.2.1.3 Redþ Far-Red Chlorophyll Fluorescence of Plants.......... 276 4.2.1.4 Fluorescence Excitation Spectra........................................ 280 4.2.1.5 Fluorescence Characteristics of Plant Tissues................... 280

4.2.2 Fluorescence Emission Spectra of Plant Tissues ............................ 282 4.2.2.1 Shape of Emission Spectra in Different Plant Tissues...... 282 4.2.2.2 Dependence of Fluorescence Yield on the

Excitation Wavelength....................................................... 284

4.2.2.3 Contrasting Wavelength Behavior of Blue-Green and Redþ Far-Red Fluorescence ...................................... 285

4.2.2.4 Fluorescence Ratios as Assessment Criterion ................... 286 4.2.3 Basis for the Variation of Fluorescence Signatures

of Plant Tissues ............................................................................... 287 4.2.3.1 Dependence of Fluorescence on the Concentration

of Chlorophyll a and Ferulic Acid .................................... 287 4.2.3.2 Tissue Structure and Penetration of Excitation Light ....... 292 4.2.3.3 Tissue Structure: Penetration of Fluorescence

from Deeper Cell Layers ................................................... 294 4.2.3.4 Photosynthetic Activity ..................................................... 295

4.2.4 Examples for the Application of Multicolor Fluorescence Imaging in Studies of Plant Tissues ............................................... 296 4.2.4.1 Fluorescence Imaging and Fluorescence Ratio

Imaging of Plant Tissue and Fluorescence Agrofood ....... 297 4.2.4.2 Developmental Stage ......................................................... 304 4.2.4.3 Strain and Stress ................................................................ 306 4.2.4.4 Preventive Measures in Fluorescence Imaging ................. 308

4.2.5 Fluorescence Imaging Systems for Plant Tissues........................... 310 4.2.6 Conclusion....................................................................................... 314

References ............................................................................................................. 314 4.3 Monitoring Raw Material by Laser-Induced Fluorescence

Spectroscopy in the Production ................................................................. 319 4.3.1 Basics of Laser-Induced Fluorescence Spectroscopy ..................... 319

4.3.1.1 Fluorescence Mechanism................................................... 320 4.3.1.2 Instrumentation for Fluorescence Experiments ................. 322

4.3.2 Blue-Green LIF Spectra of Nutritional Valuable Compounds ....... 323 4.3.3 Application in Agricultural Product Monitoring ............................ 326

4.3.3.1 Examples of BG-LIF Spectra of Agricultural Products .... 326 4.3.3.2 What Information Can Be Extracted from LIF Spectra? .. 327

4.3.4 Future Prospects of Laser-Induced Fluorescence Spectroscopy in Field Measurements ............................................. 331

4.3.5 Conclusion....................................................................................... 332 Acknowledgments................................................................................................. 333 References ............................................................................................................. 333 4.4 Front-Face Fluorescence Analysis to Monitor Food Processing

and Neoformed Contamination.................................................................. 337 4.4.1 Introduction ..................................................................................... 337 4.4.2 Physical Approach of Process-Induced Food

Physicochemical Changes ............................................................... 338 4.4.2.1 Description of the Matrix-Induced Distortions ................. 338 4.4.2.2 Assessment of the Transfer Function ................................ 342 4.4.2.3 Extraction of Pure Fluorescence Related to Native

and Neoformed Compounds.............................................. 344 4.4.3 Chemometric Analysis of Front-Face Fluorescence Signal:

Assessment of Neoformed Contamination in Heat-Treated Oils and Starch-Based Products...................................................... 345

4.4.3.1 Introduction........................................................................ 345 4.4.3.2 Methodology...................................................................... 347 4.4.3.3 Results ............................................................................... 352

4.4.4 Conclusion....................................................................................... 355 References ............................................................................................................. 357 4.5 Integrated System Design .......................................................................... 359

4.5.1 Approaches in Multiband Spectroscopy ......................................... 359 4.5.1.1 X-Ray Fluorescence and Infrared Spectroscopy ............... 359 4.5.1.2 Infrared and Terahertz Spectroscopy................................. 362 4.5.1.3 Color Calibration for Image Analysis ............................... 364

4.5.2 Field Server Application ................................................................. 365 4.5.2.1 Concept of Field Server for Plant Monitoring .................. 365 4.5.2.2 Sensor Network ................................................................. 367 4.5.2.3 Optical Farming................................................................. 368

4.5.3 Tasting Robot .................................................................................. 369 4.5.3.1 Concept of Tasting Robot ................................................. 370 4.5.3.2 Spectroscopic Data of Foods............................................. 372 4.5.3.3 Sommelier Robot in the Future ......................................... 373

References ............................................................................................................. 374

Fluorescence spectroscopy is one of the most versatile analytical techniques available, which is also indicated by the enormous number of scientific papers published each year. In 2006, about 16,000 publications containing fluorescence can be found in the Web of Science, covering a broad spectrum from fundamental research to applied sciences, for example, in physics, life science, and geoscience. Compared with the other spectroscopic techniques, the sensitivity of fluorescence measurements is outstanding. With the latest generation of benchtop spectrophotometers, the detection of zeptomoles (typically few hundreds of molecules) is available; with the application of advanced high-end spectrophotometers, single-molecule detection is also achieved.