Prediction of water relaxation time using near infrared spectroscopy

Abstract

AbstractMolecular rotational relaxation time of water is believed to be an important parameter to evaluate the deterioration rate of biomaterial. In this work, we proposed and verified a method of using Fourier‐transform near infrared spectroscopy, which has advantages of non‐invasion, low‐cost, high spatial resolution as well as being time efficient, to predict the relaxation time of water in biomaterial. The Langevin equation of rotational Brownian motion of water dipole with double‐fold cosine potential barrier, solution of which gives the relaxation time as a function of potential barrier height, was applied to water–saccharide systems. We assumed that this potential barrier height is comparable to the increase of hydrogen bond strength of water in saccharide solution. The hydrogen bond strength values of pure water and saccharide solutions were calculated from the measured NIR absorbance band of water at 4500 –5500 cm−1. The relaxation times yielded by this method are in good agreement with those measured by dielectric spectroscopy.Practical ApplicationsWater plays important role in the investigation of long‐term preservation of biomaterials, since it is the medium of many chemical reactions which eventually lead to the deterioration. In principle, both cryopreservation and dry‐preservation involve the reduction of the mobility of water molecules to reduce chemical reaction rates. The rotational relaxation time as an indicator of molecular mobility of water was proved directly related to the protein deterioration rate. Compared with conventional methods of measuring water relaxation time such as dielectric spectroscopy or magnetic resonance, FT‐IR system has many advantages: low cost, non‐invasion, time efficient, and can provide spatial resolution up to μm level with infrared microscope. Therefore, our method may provide convenience to monitor crop growth and evaluate the quality of food in storage.