Abstract 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 (μa) 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 (μs) among different tissue layers were obvious: flavedo and albedo had high μs values, ranging from 25 mm−1 to 35 mm−1, while the μs 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 μs 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 μs 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 (μt) and μa 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.

中文翻译：

---

柑橘组织的体积光学特性及其与品质特性的关系

摘要 Vis-NIR 光谱和高光谱成像是在采后分级线中评估柑橘品质的有用工具。柑橘组织的整体光学特性 (BOP) 决定了光与柑橘类水果的相互作用，从而影响测量的光谱信号。因此，有关柑橘组织 BOP 的知识对于改进光谱技术和解释光谱信号非常重要。在这项研究中，测量了不同水果类型（葡萄柚、橙子、柠檬和酸橙）的不同柑橘组织（果皮、反照率和汁泡）的 BOP，并探讨了 BOP 与不同品质特性之间的关系。NIR 范围内的体吸收系数 (μa) 光谱主要由 980、1200 和 1450 nm 附近的水吸收峰决定。对于 flavedo 组织，所有物种均在 480 nm 附近观察到吸收峰，石灰在 680 nm 附近发现吸收峰，这可能分别归因于类胡萝卜素和叶绿素。不同组织层的体散射系数（μs）差异明显：flavedo 和albedo 具有较高的μs 值，范围从25 mm-1 到35 mm-1，而汁囊泡的μs 值低于3 mm-在整个波长范围 (440 nm–1840 nm) 中为 1。各向异性因子 (g) 随波长的变化在不同组织层之间变化。flavedo 的 g 值在整个波长范围内相对平坦，而反照率和果汁囊泡的 g 值分别有增加和略微减少的趋势。不同物种的flavedo组织的吸收系数光谱显示出与决定其皮肤颜色的色素有关的不同吸收峰。不同物种间μs和g的差异小于不同组织间的差异。然后体光学特性与质量特性相关。发现 μs 的平均值与 flavedo 中油腺的直径呈负相关。总可溶性固形物（TSS）和可滴定酸度（TA）的最佳预测模型分别基于汁泡的衰减系数（μt）和μa实现。这项研究是首次尝试测量柑橘组织的 BOP，并给出了 BOP 与质量特性之间的相关性的观点，