Abstract-Monitoring the Progress of Lactic Acid Fermentation in Yogurt Manufacturing Using Terahertz Time-Domain–Attenuated Total-Reflection Spectroscopy

Koichiro Akiyama, Kazuki Horita, Tomoaki Sakamoto, Hiroshi Satozono, Hironori Takahashi, Yukihiro Goda,

https://link.springer.com/article/10.1007/s10762-019-00642-9

Lactic acid fermentation in yogurt manufacturing can be monitored using terahertz (THz)-attenuated total-reflection (ATR) spectroscopy. Yogurt manufacturing was performed on an ATR prism. The THz absorption coefficient and pH were measured for the entire 1000 min of the fermentation process. The absorption spectra were similar to the spectrum of water at the THz range. Temporal changes in the absorption coefficient at 0.4, 1.0, and 1.6 THz all decreased during the fermentation process, with two inflection points. The absolute value of the change in temporal absorption was greater at high frequencies than at low frequencies. However, the normalized absorption coefficient was larger at 0.4 THz. Because temporal changes in absorption corresponded with temporal changes in pH, the absorption changes appeared to be caused by the decomposition of the milk ingredients during the lactic acid fermentation. THz measurements can therefore be applied to the nondestructive monitoring of lactic acid fermentation in yogurt manufacturing.

Abstract-Evaluation of Drug Crystallinity in Aqueous Suspension Using Terahertz Time-Domain Attenuated Total Reflection Spectroscopy

1. Gen Takebe^*, 
2. Yoichi Kawada, 
3. Koichiro Akiyama, 
4. Hironori Takahashi, 
5. Hisayoshi Takamoto, 
6. Mitsuo Hiramatsu

http://onlinelibrary.wiley.com/doi/10.1002/jps.23716/abstract

Terahertz pulsed spectroscopy has recently been demonstrated to be a novel technique for the investigation of the solid-state properties of pharmaceutical materials. In this study, we directly measured the crystallinity of a drug suspended in water, using a terahertz pulsed attenuated total reflection (ATR) method. The dihydropyridine calcium channel blocker nifedipine is classified as a poorly soluble drug; its most stable crystalline form is known as form I. Transmission spectra, collected from 0.2 to 2.0 THz (6.6 to 66 cm⁻¹), of nifedipine crystals had a strong absorption peak at 1.2 THz (40 cm⁻¹) at room temperature. When the nifedipine crystals were mixed with poloxamer 188 and suspended in water, the resulting spectra measured using the ATR method had a peak at the same frequency as in the spectra obtained in transmission mode. Furthermore, the peak area was proportional to the amount of crystals. The upward sloping baseline in the spectra, corresponding to water absorption, decreased stepwise with increasing amounts of crystalline particles. We confirmed that the spectra gave excellent quantitative results, using partial least-squares regression analysis. The results suggest the possibility of using this method for qualitative and quantitative assessments of crystalline drugs in suspension. © 2013 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci