ABSTRACT
References ............................................................................................................. 387 5.2 Spectroscopic Technique for Measuring the Texture
of Horticultural Products: Spatially Resolved Approach .......................... 391 5.2.1 Introduction ..................................................................................... 391 5.2.2 Light Propagation in Scattering-Dominant Biological Materials ... 393
5.2.2.1 Scattering and Absorption ................................................. 393 5.2.2.2 Diffusion Theory Model.................................................... 395 5.2.2.3 Steady-State Solutions ....................................................... 396
5.2.3 Hyperspectral Imaging Technique for Measuring the Optical Properties of Horticultural Products............................. 398 5.2.3.1 Principle and Instrumentation............................................ 399 5.2.3.2 Procedures of Determining the Optical Properties............ 402
5.2.4 Applications .................................................................................... 405 5.2.4.1 Optical Properties of Fruits and Vegetables...................... 405 5.2.4.2 Evaluation of Apple Fruit Firmness .................................. 409
5.2.4.3 Estimation of Light Penetration Depths in Fruit ............... 409 5.2.4.4 Monte Carlo Simulation of Light Propagation
in Apple Fruit .................................................................... 411 5.2.5 Light-Scattering Technique Feasible for Assessing Fruit
Firmness in Practice ........................................................................ 413 5.2.5.1 Wavelengths Selection....................................................... 414 5.2.5.2 Instrumentation .................................................................. 414 5.2.5.3 Mathematical Description of Light-Scattering Profiles ..... 416 5.2.5.4 Fruit Firmness Assessment ................................................ 418
5.2.6 Conclusions and Needs for Future Research .................................. 419 Acknowledgment .................................................................................................. 420 References ............................................................................................................. 421 5.3 NMR for Internal Quality Evaluation
in Horticultural Products............................................................................ 423 5.3.1 Overview on Applications in Fruits and Vegetables ...................... 424 5.3.2 Basics of NMR Relaxometry and NMR Spectroscopy .................. 426
5.3.2.1 Magnetic Moment of Nucleus and Its Excitation ............. 426 5.3.2.2 Relaxation of Nucleus after Excitation ............................. 429 5.3.2.3 Signal Detection during Relaxation................................... 432 5.3.2.4 NMR Relaxometry and NMR Spectroscopy..................... 432
5.3.3 MRI Fundamentals.......................................................................... 435 5.3.3.1 Image Acquisition and Reconstruction ............................. 436 5.3.3.2 Effect of Movement on Image Quality ............................. 438 5.3.3.3 Sequence Parameters and Their Effects
on MR Image Quality........................................................ 440 5.3.3.4 Fast and Ultrafast MRI Sequences .................................... 441
5.3.4 Detailed View of Applications in Fruits ......................................... 445 5.3.4.1 Maturity in Avocados ........................................................ 445 5.3.4.2 Pit in Cherries and Olives ................................................. 447 5.3.4.3 Internal Browning in Apples ............................................. 448 5.3.4.4 Mealiness in Apples and Wooliness in Peaches ............... 452 5.3.4.5 Internal Breakdown in Pears ............................................. 453 5.3.4.6 Freeze Injury in Citrus....................................................... 458 5.3.4.7 Seed Identification in Citrus .............................................. 460
5.3.5 Concluding Remarks....................................................................... 462 References ............................................................................................................. 464
Food texture is an often underestimated quality trait that determines consumer satisfaction and the likelihood for the food product. One bad incidence of consumers
experiencing texture of foods that fail to meet their expectations can curtail future purchases of that food. Each type of food has specific textural attributes considered ideal, which frequently vary for consumers residing in different geographical locations. While the sensations experienced during mastication of food define the texture properties of food, visual cues and mechanical properties during handling provide the mind with information about the perceived texture before the food ever enters the mouth. Visually, the shape, size, color, and incidence of cell structure or air spaces preempt our expectation of food texture. Touching or cutting the food instantly provides information on the likely firmness, plus depending on response to this mechanical force, brittleness, adhesiveness, cohesiveness, elasticity, and springiness of food may be gauged. Slicing into food may also provide sounds providing further cues about the food texture such as crunchiness. Once food enters the mouth, initial touch attempts to deform food and provide some information about firmness. Slight shear from tongue movements provides stimuli reflecting the springiness, viscosity, and adhesiveness. The first few chews provide information on hardness and brittleness, and subsequent chews mix saliva with the food, forming a cohesive bolus that experiences higher shear allowing advanced detection of brittleness, moistness, crispness, graininess, smoothness, creaminess, and adhesiveness.
