Application of Time-of-flight Near-infrared Spectroscopy to Detect Sugar and Acid Content in Satsuma Mandarin
Application of Time-of-flight Near-infrared Spectroscopy to Detect Sugar and Acid Content in Satsuma Mandarin
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应用飞行时间近红外光谱法检测蜜柑糖酸含量
DOI：
10.21273/jashs.128.3.0391
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发表时间：
2003
影响因子：
1.9
通讯作者：
K. Miyamoto
中科院分区：
文献类型：
--
作者：
S. Tsuchikawa;Emiko Sakai;Kinuyo Inoue;K. Miyamoto
采用飞行时间近红外光谱仪(TOF-NIRS)对温州蜜柑中的糖酸含量进行了测定。详细研究了可溶性固形物、游离酸、激光波长、透射光探测位置等因素对时间分辨特性的影响。随着含糖量的增加，最大峰值的出现时间(At)和峰值延迟时间(∆t)也随之增大。然而，这些光学参数随着酸含量的增加而减小。对于浸泡在特定溶液中的聚氨酯嵌段的模型样品，添加蔗糖或柠檬酸可降低at和∆t。这些结果表明，时间分辨率不仅取决于可溶性固形物或游离酸的浓度，还受水果的其他内在因素的影响，如组织的光学特性或组织物质与液体的折射率差异。结果表明，糖分和酸含量测定的最佳光学参数分别为At和∆t。温州蜜柑(Citrus unshiu Marc.)是日本最受欢迎的园艺作物，年产≈114万吨。然而，由于面向消费者的食品多样化，水果产量本身正在逐年下降，迫使该行业将重点放在营销最高质量的水果上。选定的方法是开发用于质量检测和控制的非破坏性技术。无损检测系统能够以最少的时间和精力同时准确地测量内部质量，不仅对销售温州蜜柑，而且对其他农产品也是高度可靠的。由于可溶性固形物和游离酸的结合决定了温州蜜柑的口感，因此对两者进行评估尤为重要。在过去的几十年里，研究人员将重点放在了近红外光谱(NIR)的潜在用途上，这是一种检测有机物中有机化合物的实用光谱方法(Burns和Ciurczak，1992；Osborne，等人，1993)。透过率近红外法比漫反射光谱的光学信息更适合于探测样品的内部信息，而漫反射光谱是样品次表层的光学信息。我们已经证明了近红外光谱在园艺领域的重要性，并参考了其他研究人员的几份报告(Tuchikawa等人，2002a)。对于温州蜜柑，已经提出了几种使用透射率或反射率的近红外技术和装置(Kawano等人，1993；Miyamoto and Kitano，1995；Miyamoto，1998)。Miyamoto和Kitano(1995)研究了近红外透射率光谱作为一种非破坏性方法测定糖和酸含量的适用性。他们开发了一种在线装置，配备了卤素灯和线阵硅光电二极管来分级水果。用该装置可对含糖量进行预测，标准误差为0.6%，完全满足了供应商和消费者的需求。然而，由于≈含量较低，酸含量很难准确评价。此外，农产品的透射光行为直接受到组织的物理和化学性质的影响，因此详细检查组织的光学特性和透射光的输出来源非常重要。最近，我们开发了一种新的光学系统，可以精确地检测苹果的水核(Tuchikawa等人，2002a)。该系统由参数可调谐激光器和近红外光电倍增器组成，基于飞行时间近红外光谱(TOF-NIRS)的概念，其中传输输出功率的时间分辨概率是以纳秒灵敏度测量的(Tuchikawa和TsutSumi，2002b)。在先前的报告(Tsuhikawa等人，2002a)中，我们详细地研究了水核组织、激光波长和透射光的探测位置对时间分辨率的影响。还估算了苹果的光散射状态和实际光程长度，这是正确进行光学测量的关键因素。结果表明，检测水芯的光学参数为峰值出现的时间延迟。因此，输出信号的强度(例如吸光度)不一定是无损测定的最佳参数。这种复杂的光学技术应该也适用于其他水果。本研究将飞行时间-近红外光谱技术应用于温州蜜柑中糖酸含量的测定。充分研究了这些成分对传输输出功率的影响，并利用它们估计了更适合于检测内部质量的光学参数。我们还研究了一个模型样品(即浸泡在几种溶液中的聚氨酯块)的时间分辨特性，以模拟水果中的光散射状态。这些基础数据有助于在线测量系统的实现。
Time-of-fl ight near infrared spectroscopy (TOF-NIRS) was applied to the detection of sugar and acid con- tent in Satuma mandarin (Citrus unshiu Marc.). The combined effects on the time resolved profi les of soluble solids, free acids, laser beam wavelength, and detection position of transmitted light were investigated in detail. Attenuance of peak maxima (At) and time delay of peak maxima (∆t) increased as sugar content increased. However, these optical parameters decreased with increases in acid content. In the case of a model sample of a polyurethane block immersed in specifi ed solutions, At and ∆t decreased by adding sucrose or citric acid. These results suggested that time resolved profi le was governed not only by the concentration of soluble solid or free acid but also by other inherent factors of a fruit; for example, an optical characteristic of tissue or difference in refractive index between the tissue substance and the liquid. Results indicated the optimum optical parameters for detection of sugar and acid content were At and ∆t, respectively. Satsuma mandarin (Citrus unshiu Marc.) is the most popular horticultural crop in Japan with an annual production of ≈1.14 million tons. However, the production itself is decreasing an- nually due to diversifi cation of consumer-oriented food forcing the industry to focus on marketing the highest quality fruit. The selected approach has been to develop nondestructive technologies for quality determination and control. Nondestructive measure- ment systems that can accurately measure the internal quality simultaneously with minimal time and effort are highly desir- able for marketing not only Satsuma mandarin, but also other agricultural commodities. Because the combination of soluble solids and free acids determines the taste of Satsuma mandarin, it is especially important to evaluate both. In the past few decades, researchers have focused on the potential use of near infrared (NIR) spectroscopy, a practical spectroscopic procedure for the detection of organic compounds in organic matter (Burns and Ciurczak, 1992; Osborne, et al., 1993). The transmittance NIR method is more desirable for detecting internal information than the optical information from diffuse refl ectance spectra which are confi ned to the subsurface layer of samples. We have already demonstrated the importance of NIR spectroscopy in the horticultural fi eld and referred to several reports by other researchers (Tsuchikawa et al., 2002a). Also for Satsuma mandarin, several NIR techniques and devices using transmittance or refl ectance have been proposed (Kawano et al., 1993; Miyamoto and Kitano, 1995; Miyamoto, 1998). Miyamoto and Kitano (1995) examined the applicability of NIR transmittance spectra as a nondestructive method for determining sugar and acid contents. They developed an on-line device, equipped with a halogen lamp and a linear-array silicon photodiode for grading fruit. With this device, sugar content could be evaluated with a standard error of prediction of 0.6%, which fully satisfi ed both suppliers and consumers demands. However, acid content may be diffi cult to evaluate accurately because of its lower content of ≈1%. Furthermore, behavior of transmitted light through an agricultural product is directly affected by physical and chemical properties of the tissues, making it very important to examine in detail the optical characteristics of the tissue and the output origin of transmitted light. Recently, we have developed a new optical system which precisely detected water core in apple (Tsuchikawa et al., 2002a). The system, made up of a parametric tunable laser and a NIR photoelectric multiplier, was based on the concept of time-of- fl ight near infrared spectroscopy (TOF-NIRS), where a time resolved profi le of transmitted output power was measured with nanosecond sensitivity (Tsuchikawa and Tsutsumi, 2002b). In the previous report (Tsuchikawa et al., 2002a) we investigated in detail the variation of time resolved profi les resulting from water-core tissue, laser beam wavelength and detection position of transmitted light. Light scattering state and substantial optical path length in apple were also estimated, which were key factors for the correct optical measurements. Results indicated that the optical parameter for detection of water core was the time delay of the peak maxima. Therefore, the intensity of output signal (e.g., absorbance) was not necessarily the best parameter for nondestructive determination. Such a sophisticated optical technique should be available for other fruit. In this study, we applied TOF-NIRS to the detec- tion of sugar and acid contents in Satsuma mandarin. The effect of these constituents on the transmitted output power was fully examined and used to estimate the optical parameter preferable for detecting internal quality. We also investigated the behavior of time resolved profi le of a model sample (i.e., a polyurethane block immersed in several solutions) for simulation of the light scattering state in a fruit. These basic data can be helpful to real- ize an in-process measurement system.