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This paper presents porous polydimethylsiloxane (PDMS) optical phantoms with tunable microstructural and optical properties to mimic porous biological tissues (e.g., fruit) during the design and optimization of novel optical setups. A well connected salt network formed using salt particles of various size distributions was used to obtain porous PDMS phantoms of different porous features including porosity, pore size distribution, pore number density and pore connectivity. These microstructural features are strongly related to the light scattering from the phantom where a higher reduced scattering coefficient (μs′) was observed from the porous PDMS phantom with a higher number of small pores compared to the optical phantom with a lower number of larger pores. The prepared phantoms were used to validate GASMAS (gas in scattering media absorption spectroscopy) H2O and O2 sensors by quantifying the optical path length through the pores and the O2 concentration inside the pores. [ABSTRACT FROM AUTHOR]

Puffiness is one of the dominant postharvest disorders in easy-peeling citrus cultivars. In this study, the structural changes between healthy and puffy Satsuma mandarin were investigated and the potential of using optical methods for disorder detection was explored. To gain more insight in this disorder, the external appearance and internal quality attributes were first compared between healthy and puffy Iwasaki Satsuma mandarins at three harvest times. Although no consistent differences were observed in the appearance of fruits, the soluble solids content and Brix minus acid values in puffy mandarin were found to be higher compared to the corresponding healthy fruit. The structural properties of the flavedo and albedo tissue layer in the peel were quantified from X-ray CT scans. Whilst no differences were observed in the size of the oil glands in the flavedo, the pore size in the albedo of puffy mandarin was found to be larger with later harvest. The bulk optical properties of the intact fruit were estimated from laser scatter images with a metamodel calibrated on optical phantoms. The reduced scattering coefficient (μ s ') for the intact fruit was found to be lower in puffy mandarin relative to healthy fruit. The distinction between healthy and puffy mandarin based on μ s ' was further validated on Goku Wase Satsuma mandarin. The results obtained indicate that healthy and puffy mandarin can be separated well based on their μ s ' at all the selected wavelengths. This provides a basis for the non-destructive optical detection of puffing disorder at an early stage. [Display omitted] • External and internal attributes were compared between healthy and puffy mandarin. • Thickness of both flavedo and albedo tissue layers was lower in puffy mandarin. • Pore size in the albedo of puffy mandarin was larger at a later harvest time. • The μ s ' of the intact fruit was lower in the puffy than the healthy mandarin. [ABSTRACT FROM AUTHOR]

Insight in the transmission of light through intact fruit is important to optimize and interpret the signals acquired with spectroscopy methods such as tunable diode laser absorption spectroscopy (TDLAS). To this end, we quantified the bulk optical properties (BOP) of skin, outer cortex, inner cortex, and core tissue of three pear (Pyrus communis) cultivars (Thimo , Cepuna , and Conference) using double integrating spheres measurements in combination with the inverse adding doubling method. Similar trends and values were observed for the bulk optical properties of the three cultivars. A clear chlorophyll-a absorption feature was present in the bulk absorption coefficient (μ a) at 690 nm for the skin samples. At 761 nm, the bulk scattering coefficient (μ s) decreased from the skin towards the core region, for example from 256 ± 34 cm−1 to 146 ± 22 cm−1 for Conference pears. The observed anisotropy factor (g) of the skin was lower than these of the other tissue layers (0.87 ± 0.026 vs. 0.94 ± 0.08 for Conference). Next, Monte Carlo voxelized media (MCVM) simulations were performed based on these BOP values and validated against measurements with a TDLAS setup for gas in scattering media absorption spectroscopy (GASMAS) at 761 nm. In these experiments, the sample thickness was reduced by sequentially slicing the pear from the skin towards the center. Light transmittance through an intact pear at the height of the core region was found to be very low (1.9 × 10−4 ± 8.5 × 10−5%) and exponentially increased around 100-fold when the sample thickness decreased from 64 mm to 24 mm. The simulated transmittance profiles based on the measured BOP values at 761 nm followed the same trend as the measured GASMAS transmittance as a function of the fruit thickness. This shows that simulations based on these measured BOP values can be used to optimize the measurement configuration for O 2 monitoring in intact pear fruit with GASMAS. • The bulk optical properties of pear tissue layers: skin, outer cortex, inner cortex, and core. • 3D Monte Carlo simulation of diffuse transmittance through an intact pear. • Comparison of simulated and measured diffuse transmittance vs pear sample thicknesses. • Simulations provided a valuable tool for optimizing the amplification of GASMAS detectors in diffuse transmittance mode. [ABSTRACT FROM AUTHOR]

• Bulk optical properties of tissue layers were measured for Satsuma mandarin. • The pigment related μ a and the μ s in juice vesicles increased along harvest time. • Color change was presented in the μ a of flavedo along harvest time. • Influence from fruit size was related to the development stage. • The difference in the μ s of flavedo among cultivars enhanced during maturation. As Satsuma mandarin is a multi-layered fruit, the optical properties of the different tissue layers influence the performance of spectroscopy-based quality detection models. Therefore, the variation in the bulk optical properties (BOP) of the inner (juice vesicles) and outer (flavedo) tissue layer of Satsuma mandarin was investigated for different harvest times, fruit sizes and cultivars. Satsuma mandarin fruit from three different cultivars (Iwasaki, Okitsu and Goku Wase) were harvested at three different times around the recommended harvest date and the BOP of the inner and outer tissue layers were estimated from double integrating spheres measurements. Along the harvest time, the absorption peak related to carotenoids in the bulk absorption coefficient (μ a) spectrum increased in both tissue layers, while the values attributed to chlorophylls decreased in the flavedo. Moreover, a slightly increasing trend over the harvest time was observed in the bulk scattering coefficient (μ s) spectra of juice vesicles, especially at the early stage. The μ a values of both tissue layers and the μ s values of juice vesicles deviated among different fruit sizes, which can be related to the development stage. Smaller fruit presented a higher carotenoids concentration in juice vesicles, an advanced color change in flavedo throughout the maturation stages and higher μ s values in juice vesicles at earlier maturation stages. The μ a differences in pigment absorption among different cultivars were related to the maturation order. Earlier maturing cultivars possessed higher μ a values related to carotenoids absorption in juice vesicles and advanced color changes in flavedo. The μ s values of the flavedo differed among the cultivars and these differences were enhanced during maturation. These insights in the sources of variation in the bulk optical properties of Satsuma mandarin tissues can be used for simulation-based optimal design of an optical measurement configuration and interpretation of the acquired signals in spectroscopy-based quality detection and monitoring. [ABSTRACT FROM AUTHOR]

Optical measurement of fruit quality can provide the specific insights into the light absorption (μ a) of chemical compositions and the multiple scattering (μ s ′) by structured tissues, and contributes to their precise evaluation. This work comprehensively explored the bulk optical properties (BOPs) in the wavelength range of 600–1500 nm related to the soluble sugars, pectin constitution and microstructural features (area, perimeter, Feret's diameter, cell roundness, cell solidity and intercellular space) of 'Korla' pear cortex during post-harvest storage. The high correlation between μ a values around 980 nm and 1 485 nm and total sugars and sucrose contents were observed with the r values from 0.74 to 0.99. The μ s ′ of pear tissues were positively corelated to the firmness, cell microstructure parameters in cortex (area, perimeter, Feret's diameter and solidity), whereas negatively correlated to their cell roundness and intercellular properties. Besides, the partial least squares regression models based on the featured BOPs of pear cortex successfully predicted the total sugars and sucrose contents with the determination coefficients (R p 2) from 0.73 to 0.91. Further, the combined BOPs feature models based on the first component (PC1) scores of BOPs provide excellent prediction of firmness (R p 2 = 0.90) and acid soluble pectin (R p 2 = 0.93). Accordingly, this study indicated the optical properties have the possibility to present the sugar composition, firmness, pectin and microstructural characteristics of pear tissues. • Sugars and microstructure of pear tissues are reflected in optical properties (BOPs). • The total sugars and sucrose contribute to assess soluble solids in pears by BOPs. • The acid-soluble pectin and cell solidity are key to assess pear structure by BOPs. • The first component scores on BOPs improved the prediction of pear microstructure. [ABSTRACT FROM AUTHOR]

• Provides an overview of the principles and theory of light transfer in biological materials. • Presents instrumentation and data analysis procedures for emerging optical techniques. • Reviews applications of optical properties for fruit and vegetable quality evaluation. • Discusses issues, challenges and future research needs. This paper provides an overview of the principles and theory of measuring optical properties of biological materials. It then presents the instrumentation and data analysis procedures for implementing several emerging optical techniques, including spatially resolved, time-resolved, and spatial-frequency domain, along with the standard integrating sphere method. Applications of these techniques for optical property measurement, maturity and quality assessment, and defect detection of fruits and vegetables are then reviewed, followed with discussions on issues and challenges that still need to be addressed for these emerging optical techniques. While these optical techniques are overall more sophisticated in instrumentation and computation, they are based on radiative transfer theory or simplified diffusion approximation theory. Hence, measurement of optical absorption and scattering properties has the potential of providing more useful information for quality evaluation of horticultural products. At present, these techniques are still slow in measurement, and prone to errors due to modeling and instrumentation deficiencies. Further research is therefore needed in using a better mathematical modeling approach, improving data acquisition accuracy and speed, and developing more robust inverse algorithms for optical property estimations. [ABSTRACT FROM AUTHOR]

Hypoxia-related disorders in apple and pears such as browning have been associated with insufficient transport of respiratory gasses inside the fruit during controlled atmosphere (CA) storage. Tissue porosity affects gas exchange and, hence, fruit respiration. It might, therefore, be interesting to adapt the storage conditions to the porosity of the fruit, especially in the case of low-porosity fruit like pears, which are highly susceptible to browning disorders. To improve the current CA storage strategies in that direction, fast, non-destructive measurement of fruit porosity is required. To this end, X-ray CT-based porosity maps and spatially resolved spectroscopy (SRS) were used to characterize respectively the porosity and optical properties of intact pear cultivars (Pyrus communis L.), including 'Thimo', 'Cepuna', and 'Conference'. Thereafter, the link between the fruit porosity and light-scattering properties was investigated. The porosity of the tissue region from the fruit surface down to 3 mm deep as well as the spatially averaged porosity of intact pears from 3 cultivars were found to be linearly correlated to the reduced scattering coefficient (µ s') at 760 nm and 835 nm calculated from SRS measurements. Both 'Cepuna' and 'Conference' pears showed similar porosities and scattering levels, which were slightly higher than those observed for 'Thimo' pears. The presented results suggest the possible application of laser scatter imaging at 760 nm and 835 nm for fast, contactless and non-destructive assessment of pear porosity. • X-ray CT-based porosity mapping of intact pear. • Characterization of BOP of intact pear using SRS. • Relationship between scattering and microstructural properties of pear. • Porosity of intact pear linearly correlated to the µ s ' at 760 nm (R2 =0.66). [ABSTRACT FROM AUTHOR]

A global optimizer has been developed, capable of computing the optimal configuration in a probe for spatially resolved reflectance spectroscopy (SRS). The main objective is to minimize the number of detection fibers, while maintaining an accurate estimation of both absorption and scattering profiles. Multiple fibers are necessary to robustify the estimation of optical properties against noise, which is typically present in the measured signals and influences the accuracy of the inverse estimation. The optimizer is based on a robust metamodel-based inverse estimation of the absorption coefficient and a reduced scattering coefficient from the acquired SRS signals. A genetic algorithm is used to evaluate the effect of the fiber placement on the performance of the inverse estimator to find the bulk optical properties of raw milk. The algorithm to find the optimal fiber placement was repeatedly executed for cases with a different number of detection fibers, ranging from 3 to 30. Afterwards, the optimal designs for each considered number of fibers were compared based on their performance in separating the absorption and scattering properties, and the significance of the differences was tested. A sensor configuration with 13 detection fibers was found to be the combination with the lowest number of fibers which provided an estimation performance which was not significantly worse than the one obtained with the best design (30 detection fibers). This design resulted in the root mean squared error of prediction (RMSEP) of 1.411 cm −1 ( R 2 = 0.965) for the estimation of the bulk absorption coefficient values, and 0.382 cm −1 ( R 2 = 0.996) for the reduced scattering coefficient values. [ABSTRACT FROM AUTHOR]

The size of colloidal particles in food products has a considerable impact on the product's physicochemical, functional and sensory characteristics. Measurement techniques to monitor the size of suspended particles could, therefore, help to further reduce the variability in production processes and promote the development of new food products with improved properties. Visible and near-infrared (Vis/NIR) spectroscopy is already widely used to measure the composition of agricultural and food products. However, this technology can also be consulted to acquire microstructure-related scattering properties of food products. In this study, the effect of the fat globule size on the Vis/NIR bulk scattering properties of milk was investigated. Variability in fat globule size distribution was created using ultrasonic homogenization of raw milk. Reduction of the fat globule size resulted in a higher wavelength-dependency of both the Vis/NIR bulk scattering coefficient and the scattering anisotropy factor. Moreover, the anisotropy factor and the bulk scattering coefficients for wavelengths above 600 nm were reduced and were dominated by Rayleigh scattering. Additionally, the bulk scattering properties could be well ( R 2 ≥ 0.990) estimated from measured particle size distributions by consulting an algorithm based on the Mie solution. Future research could aim at the inversion of this model to estimate the particle size distributions from Vis/NIR spectroscopic measurements. [ABSTRACT FROM AUTHOR]

A hyperspectral scatter imaging system was developed for the contactless acquisition of spatially resolved diffuse reflectance profiles for the optical characterization of turbid food products in the wavelength range from 500 to 960 nm. To investigate the potential of this concept sugar foams with different microstructures, but with similar chemical compositions, have been prepared by applying different mixing times to the same mixtures of sugar and albumin. Hyperspectral scatter images have been acquired from these samples and the absorption and reduced scattering coefficients have been derived from spatially resolved reflectance profiles based on the diffusion approximation of the radiative transfer equation describing the light propagation in turbid media. The estimated reduced scattering coefficients μ=sub=s=/sub=′ spectra clearly reflected the effect of the different mixing times on the foam microstructure. On the other hand, similar absorption coefficient spectra were observed, confirming the identical chemical composition of the sugar-albumin matrix. These results indicate that the hyperspectral scatter imaging technique has potential as a non-contact and rapid method for online quality control and process monitoring of foamed food products. [ABSTRACT FROM AUTHOR]

Abstract: Non-invasive and non-destructive Near Infrared Reflectance Spectroscopy (NIRS) analysis of pork quality parameters is challenging due to the presence of a structured skin layer. The optical characterization (absorption coefficient, scattering coefficient and anisotropy factor) of porcine skin tissue can help in a better understanding of the light-tissue interaction, more efficient instrumental sensor designs and data modeling. For this purpose, double integrating spheres combined with an unscattered transmittance measurement system working in the range 1150–2250nm (interval step of 10nm) were used for optical characterization of pig epidermis and dermis. The estimated pig skin absorption coefficient spectra were dominated by water, while scattering coefficient spectra showed a steady decreasing tendency with increasing wavelength, except at strong absorption bands. The anisotropy factor spectra showed a stable value for each layer, although also some signatures were observed at strong absorption bands. Industrial relevance: A novel double integrating sphere system combined with an unscattered transmittance detector based both on a supercontinuum laser is used for optical characterization (absorption, scattering and angular scattering distribution) of pig skin tissues (epidermis and dermis) in the 1150–2250nm wavelength range. The estimated data reported are relevant to understand individual effects of absorption, scattering and angular scattering distribution of NIR light through the tissue. Moreover, it can be used for simulating non-destructive NIRS measurement what can have an impact in the advance of NIRS technology toward in vivo/intact analysis. [Copyright &y& Elsevier]

Abstract: Optical properties of pig subcutaneous adipose tissue were estimated using double integrating sphere (DIS) measurements in combination with an inverse adding doubling (IAD) light propagation model. Total reflectance, total transmittance and unscattered transmittance were measured for the wavelength range 1150–2250nm with 10nm resolution. These measurements were used to estimate the bulk optical properties (absorption coefficient, scattering coefficient and anisotropy factor) of 10 Iberian pig adipose tissue samples. The estimated absorption coefficient spectra were dominated by water and lipid absorption bands, the main chemical components of the adipose tissue. These values showed a suitable match with the theoretical values calculated based on the average composition of the tissue. The obtained scattering coefficient spectra showed a smooth decrease with increasing wavelength, which is typical for biological tissues. The anisotropy factor spectra of adipose tissue were obtained, which describe the angular scattering pattern, instead of using a fixed value for the estimation procedure. The optical characterization described in this paper is crucial for a better understanding of the impact of pure absorption and scattering on the NIR spectra collected by a single measurement in the laboratory, process line at the slaughterhouse or on the farm. Moreover, the estimated data reported in this study would promote a more efficient sensor design and data processing optimization. Industrial relevance: This paper provides an optical characterization (absorption, scattering and angular scattering distribution) of pig adipose tissues in a wide near-infrared wavelength range (1150–2250nm) based on a novel spectroscopic setup. The estimated data reported are relevant to promote the design of innovative NIRS sensors and the development of new modeling procedures in order to optimize the non-destructive analysis of intact adipose tissues. This can have an important impact on the implementation of NIRS quality control systems in the agro-industry. [Copyright &y& Elsevier]

Abstract: Proper control of the texture properties of aerated foods demands accurate measurement tools. Aerated sugar gels with identical composition but different microstructures were produced by applying different mixing times of 2, 4 and 8min. Compression test and acoustic emission measurements were carried out to characterize the mechanical properties of these foams. Significant differences in deformation properties and number of acoustic events were found depending on the foaming time, indicating differences in texture. Microstructural attributes such as bubble size and bubble number distributions of the different foams were measured based on micro- and nano-CT and were found to differ between the foams. Additionally, time and spatially resolved diffuse spectroscopy were used to evaluate their optical properties. While, as expected for foams with the same chemical composition, the absorption properties were not significantly different, a relationship between scattering and microstructural properties was found. The results show that microstructural properties affect the texture of aerated foams. Moreover, the latter can be measured nondestructively using time and spatially resolved diffuse spectroscopy. Industrial relevance: Food aeration is one of the fastest growing unit operations in the food industry (Zúñiga & Aguilera, 2008, 2009). Proper design and control of the texture properties of aerated foods demand accurate measurement tools of microstructural features. Food microstructure is defined as the spatial arrangement of structural components of food and their interactions. Structural elements include water and oil droplets, gas cells, fat crystals, strands, granules, micelles and interfaces. Changes in the microstructure during storage and processing can be significant and affect the macroscopic appearance, quality and perception of food. Due to the microscopic complexity, straightforward methodologies that link quality to food microstructure do not exist today, as opposed to many engineering materials with a well ordered microstructure, for which the relationship with macroscopic properties can be easily understood based on fundamental physics. The only way forward is to develop methods that measure directly the microstructural properties of foods. [Copyright &y& Elsevier]

The interaction of visible and near-infrared light with citrus tissues is of great importance for the design of new optical sensors for fruit quality inspection. In this study, the light propagation through citrus fruit was simulated using the Monte Carlo multi-layered (MCML) technique based on the bulk optical properties (BOP) of citrus tissues. Comparison of the diffuse reflectance profiles from MCML and from the laser scatter images confirmed the accuracy of the simulations. Simulation results indicated that most of the light was diffusely reflected or absorbed in the flavedo. Only a small fraction around 800 nm was transmitted through the three layers. Flavedo and albedo were found to contribute mostly to the diffuse reflectance spectra at 800 nm and their contributions respectively decreased and increased with source-detector distance. Although the contribution of juice vesicles increased with distance, the maximal diffuse reflectance intensity contributed by juice vesicles was located within 0.56 cm. Based on these results, the combination of the power intensity and the source-detector distance can be optimized to obtain more information about the layer of interest, which lays the foundations for designing new quality detection sensors for citrus fruit. • Light propagation in citrus fruit was simulated by Monte Carlo multi-layered model. • Good agreement of simulated and measured diffuse reflectance profiles. • Light was mainly absorbed by flavedo and diffusely reflected. • Flavedo and albedo contributed mostly to the diffuse reflectance spectra. [ABSTRACT FROM AUTHOR]

• TRS absorption coefficients are more related to pigment and water of the fruit flesh. • SRS absorption coefficients are strongly affected by pigments in the fruit skin. • Fruit softening was accompanied by increasing values of reduced scattering coefficient. • TRS and SRS capture valuable information on the changes in flesh texture. Bulk optical properties, in terms of absorption (μ a) and reduced scattering coefficients (μ ′ s), can be used for the non-destructive monitoring of fruit quality during ripening. In this study, the performance of time-resolved (TRS) and spatially-resolved (SRS) spectroscopy were compared by analyzing 'Braeburn' apples over a 21 d period of ripening. Nine batches of 20 apples each were measured on the blush side by TRS (540−1064 nm) and SRS (550−1000 nm). Every fruit was analyzed for skin color, texture characteristics, relative internal space volume (RISV), total solid soluble and titratable acidity contents. TRS absorption spectra showed two maxima, the highest at 980 nm (water) and the second at 670 nm (chlorophyll), while in SRS spectra the main peak was measured at 550 nm (anthocyanins) followed by that at 670 nm. The values of μ a 580 SRS and of μ a 670 SRS were much higher than those measured at the same wavelengths by TRS suggesting that TRS and SRS actually explore the apple tissue (skin and/or flesh) in a different way. The values of μ a 980 TRS were higher than those of μ a 980 SRS , probably due to the fact that water content was lower in the skin (mostly probed by SRS) than in the flesh (mostly probed by TRS). No significant correlations were found between μ a 580 SRS and μ a 580 TRS and between μ a 980 SRS and μ a 980 TRS but a low positive relationship was observed between μ a 670 TRS and μ a 670 SRS. On the contrary, high correlations were found between μ a 670 SRS and the spectral index I AD (index of absorbance difference) related to chlorophyll in the skin and between μ a 580 SRS and the spectral index ARI (anthocyanin reflectance index), related to anthocyanin content in the peel, suggesting that μ a 580 SRS is linked to the development of the red color in the peel. Both μ a 670 TRS and μ a 670 SRS decreased during fruit ripening, indicating a decline in chlorophyll in the flesh and skin, respectively. During the shelf life period, apples became soft and mealy, as mechanical and acoustic parameters decreased and RISV increased. Fruit softening was accompanied by increasing values of both μ ′ sTRS and μ ′ sSRS. The μ ′ sTRS and μ ′ sSRS were positively related to each other, were positively correlated to RISV and negatively related to mechanical and acoustic parameters. Both the TRS and SRS technique were able to follow ripening processes in 'Braeburn' apples during the shelf life period, as absorption phenomena were related to changes in pigments present in the fruit flesh and skin, while scattering events mirrored changes in the flesh texture. [ABSTRACT FROM AUTHOR]

• Bulk optical properties of citrus tissues were measured for different species. • Bulk optical properties were compared among tissue layers and fruit sizes. • Scattering coefficient was negatively correlated with the size of the oil glands. • Attenuation coefficient was most fit for the prediction of total soluble solids. • Absorption coefficient was most fit for the prediction of titratable acidity. Vis-NIR spectroscopy and hyperspectral imaging are useful tools for citrus quality evaluation in postharvest grading lines. The bulk optical properties (BOP) of citrus tissues determine the interaction of light with citrus fruit, and thereby influence the measured spectral signal. Therefore, knowledge about the BOP of citrus tissues is important for the improvement of spectral techniques and interpretation of spectral signals. In this study, the BOP of different citrus tissues (flavedo, albedo and juice vesicles) were measured for different fruit types (grapefruit, orange, lemon and lime) and the relationship between the BOP and different quality properties was explored. The bulk absorption coefficient (μ a) spectra in the NIR range were dominated by the absorption peaks of water around 980, 1200 and 1450 nm. For the flavedo tissues, absorption peaks around 480 nm were observed for all the species and an absorption peak around 680 nm was found for lime, which could respectively be attributed to carotenoids and chlorophyll. The differences in the bulk scattering coefficient (μ s) among different tissue layers were obvious: flavedo and albedo had high μ s values, ranging from 25 mm−1 to 35 mm−1, while the μ s values of the juice vesicles were below 3 mm−1 in the whole wavelength range (440 nm–1840 nm). The changes in anisotropy factor (g) with wavelength varied among different tissue layers. The g values for flavedo were relatively flat over the whole wavelength range, while an increasing and slightly decreasing trend could respectively be observed for albedo and juice vesicles. The absorption coefficient spectra for the flavedo tissues of the different species showed different absorption peaks related to the pigments which determine their skin color. The differences in μ s and g between the different species were smaller than the variation among different tissues. The bulk optical properties were then related to the quality properties. A negative correlation was found between the average value of μ s and the diameter of the oil glands in the flavedo. The best prediction models for total soluble solids (TSS) and titratable acidity (TA) were respectively achieved based on the attenuation coefficient (μ t) and μ a of juice vesicles. This study was the first attempt to measure the BOP of citrus tissues and gave a view on the correlation between BOP and quality properties, which made the foundation for further development and optimization of the optical design of quality sensors for citrus fruit. [ABSTRACT FROM AUTHOR]