IJET 2026 Vol.18(2): 78-83
DOI: 10.7763/IJET.2026.V18.1348
Non-Destructive Evaluation of the Physical Properties in Packed Tofu using Time-Domain Diffuse Optical Spectroscopy
Yoshito Saito1,*, Riku Miyakawa1, Takumi Murai1, Etsuko Ohmae2,3, Kentaro Okuyama4, Hiroko Wada2, Kenji Yoshimoto2, Hiroaki Suzuki2, and Yukio Ueda2
1. Graduate School of Science and Technology, Niigata University, Niigata, Japan
2. Hamamatsu Photonics K.K., Hamamatsu, Shizuoka, Japan
3. ScHAMAMATSU BioPhotonics Innovation Laboratory, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka, Japan
4. Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan
Email: ysaito@agr.niigata-u.ac.jp (Y.S.)
*Corresponding author
Manuscript received November 12, 2025; accepted December 1, 2025; published June 29, 2026
Abstract—The demand for packed tofu has been increasing globally in recent years. However, the manufacturing process lacks an established method for non-destructive evaluation of tofu coagulation and necessitating the disposal of a certain number of products for quality inspection. While Near-Infrared Spectroscopy (NIR) for estimating the reduced scattering coefficient (µs’) has been reported as a non-destructive method for predicting tofu viscosity, previous studies have only conducted contact measurements on tofu, with no reports of measurements through packages. Therefore, this study aimed to evaluate non-destructive methods for measuring the physical properties of packed tofu. A total of 10 packed tofu samples were prepared with different coagulant concentrations, and both physical and optical measurements were conducted. Physical property measurements included viscosity, Water Holding Capacity (WHC), and solid content. Optical measurements utilized Time-Domain Diffuse Optical Spectroscopy (TD-DOS) to calculate the µs’ and absorption coefficient (µa). Optical measurements were performed at three locations (direct, through-film, and bottom) with three source-detector distances (SD = 1 cm, 2 cm and 3 cm) at each location. Correlation analysis between viscosity and µs’ yielded correlation coefficient exceeding 0.90 for both direct and bottom measurements at SD = 2 and 3 cm. Additionally, the scanning electron microscopy (SEM) of the tofu microstructure revealed that homogeneity of the microstructure increased with viscosity increase, which might have increased µs’. These results demonstrate that measuring µs’ through the bottom of tofu’s pack enables non-destructive evaluation of tofu.
Keywords—near-infrared spectroscopy (NIRS), packed tofu, reduced scattering coefficient, Time-Domain Diffuse Optical Spectroscopy (TD-DOS), viscosity
Cite: Yoshito Saito, Riku Miyakawa, Takumi Murai, Etsuko Ohmae, Kentaro Okuyama, Hiroko Wada, Kenji Yoshimoto, Hiroaki Suzuki, and Yukio Ueda, "Non-Destructive Evaluation of the Physical Properties in Packed Tofu using Time-Domain Diffuse Optical Spectroscopy," International Journal of Engineering and Technology, vol. 18, no. 2, pp. 78-83, 2026.
Copyright © 2026 by the authors. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (
CC BY 4.0).
